tag:theconversation.com,2011:/au/topics/light-1930/articles
Light – The Conversation
2024-02-28T01:00:24Z
tag:theconversation.com,2011:article/224503
2024-02-28T01:00:24Z
2024-02-28T01:00:24Z
Leap of imagination: how February 29 reminds us of our mysterious relationship with time and space
<p>If you find it intriguing that February 28 will be followed this week by February 29, rather than March 1 as it usually is, spare a thought for those alive in 1582. Back then, Thursday October 4 was followed by Friday October 15.</p>
<p>Ten whole days were snatched from the present when Pope Gregory XIII issued a papal bull to “restore” the calendar from discrepancies that had crept into the Julian calendar, introduced by Julius Caesar in 45 BCE.</p>
<p>The new Gregorian calendar returned the northern hemisphere’s vernal equinox to its “proper” place, around March 21. (The equinox is when the Earth’s axis is tilted neither toward nor away from the sun, and is used to determine the date of Easter.) </p>
<p>The Julian calendar had observed a leap year every four years, but this meant time had drifted out of alignment with the dates of celestial events and astronomical seasons. </p>
<p>In the Gregorian calendar, leap days were added only to years that were a multiple of four – like 2024 – with an exception for years that were evenly divisible by 100, but not 400 – like 1700.</p>
<p>Simply put, leap days exist because it doesn’t take a neat 365 days for Earth to orbit the Sun. It takes 365.2422 days. Tracking the movement of celestial objects through space in an orderly pattern doesn’t quite work, which is why we have February – time’s great mop.</p>
<h2>Time and space</h2>
<p>This is just part of the history of how February – the shortest month, and originally the last month in the Roman calendar – came to have the job of absorbing those inconsistencies in the temporal calculations of the world’s most commonly used calendar.</p>
<p>There is plenty of <a href="https://theconversation.com/leap-day-fixing-the-faults-in-our-stars-54032">science</a>, <a href="https://theconversation.com/explainer-the-science-behind-leap-years-and-how-they-work-54788">maths</a> and <a href="https://theconversation.com/how-a-seasonal-snarl-up-in-the-mid-1500s-gave-us-our-strange-rules-for-leap-years-132659">astrophysics</a> explaining the relationship between time and the planet we live on. But I like to think leap years and days offer something even more interesting to consider: why do we have calendars anyway?</p>
<p>And what have they got to do with how we understand the wonder and strangeness of our existence in the universe? Because calendars tell a story, not just about time, but also about space.</p>
<p>Our reckoning of time on Earth is through our spatial relationship to the Sun, Moon and stars. Time, and its place in our lives, sits somewhere between the scientific, the celestial and the spiritual. </p>
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Read more:
<a href="https://theconversation.com/why-does-a-leap-year-have-366-days-218330">Why does a leap year have 366 days?</a>
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<p>It is <a href="https://shop.whitechapelgallery.org/products/time">notoriously slippery, subjective and experiential</a>. It is also marked, tracked and determined in myriad ways across different cultures, from tropical to solar to <a href="https://www.stuff.co.nz/pou-tiaki/300062097/matariki-and-the-maramataka-the-mori-lunar-calendar">lunar</a> calendars.</p>
<p>It is the Sun that measures a day and gives us our first reference point for understanding time. But it is the <a href="https://librarysearch.aut.ac.nz/vufind/Record/1145999?sid=25214690">Moon</a>, as a major celestial body, that extends our perception of time. By stretching a span of one day into something longer, it offers us a chance for philosophical reflection.</p>
<p>The Sun (or its effect at least) is either present or not present. The Moon, however, goes through phases of transformation. It appears and disappears, changing shape and hinting that one night is not exactly like the one before or after.</p>
<p>The Moon also has a distinct rhythm that can be tracked and understood as a pattern, giving us another sense of duration. Time is just that – overlapping durations: instants, seconds, minutes, hours, days, weeks, months, years, decades, lifetimes, centuries, ages.</p>
<h2>The elusive Moon</h2>
<p>It is almost impossible to imagine how time might feel in the absence of all the tools and gadgets we use to track, control and corral it. But it’s also hard to know what we might do in the absence of time as a unit of productivity – a measurable, dispensable resource.</p>
<p>The closest we might come is simply to imagine what life might feel like in the absence of the Moon. Each day would rise and fall, in a rhythm of its own, but without visible reference to anything else. Just endless shifts from light to dark.</p>
<p>Nights would be almost completely dark without the light of the Moon. Only stars at a much further distance would puncture the inky sky. The world around us would change – trees would grow, mammals would age and die, land masses would shift and change – but all would happen in an endless cycle of sunrise to sunset.</p>
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Read more:
<a href="https://theconversation.com/scientists-are-hoping-to-redefine-the-second-heres-why-157645">Scientists are hoping to redefine the second – here's why</a>
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<p>The light from the Sun takes <a href="https://www.skyatnightmagazine.com/space-science/how-take-light-from-sun-reach-earth">eight minutes</a> to reach Earth, so the sunlight we see is always eight minutes in the past. </p>
<p>I remember sitting outside when I first learned this, and wondering what the temporal delay might be between me and other objects: a plum tree, trees at the end of the street, hills in the distance, light on the horizon when looking out over the ocean, stars in the night sky.</p>
<p>Moonlight, for reference, takes about <a href="https://www.pbs.org/seeinginthedark/astronomy-topics/light-as-a-cosmic-time-machine.html">1.3 seconds</a> to get to Earth. Light always travels at the same speed, it is entirely constant. The differing duration between how long it takes for sunlight or moonlight to reach the Earth is determined by the space in between. </p>
<p>Time on the other hand, is anything but constant. There are countless ways we characterise it. The mere fact we have so many calendars and ways of describing perceptual time hints at our inability to pin it down. </p>
<p>Calendars give us the impression we can, and have, made time predictable and understandable. Leap years, days and seconds serve as a periodic reminder that we haven’t.</p><img src="https://counter.theconversation.com/content/224503/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily O'Hara does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
2024 is a leap year, when the shortest month mops up a bit of leftover time. But the extra day also tells us about space – and our place in it.
Emily O'Hara, Senior Lecturer, Spatial Design + Temporary Practices, Auckland University of Technology
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/221387
2024-01-30T16:01:27Z
2024-01-30T16:01:27Z
The surprising reason why insects circle lights at night: They lose track of the sky
<figure><img src="https://images.theconversation.com/files/571170/original/file-20240124-21-ynct7x.png?ixlib=rb-1.1.0&rect=30%2C20%2C6679%2C4446&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A multiple-exposure photograph of insects circling a light at night.</span> <span class="attribution"><span class="source">Samuel Fabian</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>It’s an observation as old as humans gathering around campfires: Light at night can draw an erratically circling crowd of insects. In art, music and literature, this spectacle is an enduring metaphor for <a href="https://roundglasssustain.com/wildvaults/moths">dangerous but irresistible attractions</a>. And watching their frenetic movements really gives the sense that something is wrong – that instead of finding food and evading predators, these nocturnal pilots are trapped by a light.</p>
<p>Sadly, centuries of witnessing what happens have produced little certainty about why it happens. How does a simple light change fast, precise navigators into helpless, flittering captives? We are researchers examining <a href="https://scholar.google.co.uk/citations?user=wG5HGs8AAAAJ&hl=en">flight</a>, <a href="https://scholar.google.com/citations?user=4i4wRGgAAAAJ&hl=en">vision</a> and <a href="https://scholar.google.co.in/citations?user=X-j5RnwAAAAJ&hl=en">evolution</a>, and we have used high-speed tracking techniques in <a href="https://www.nature.com/articles/s41467-024-44785-3">newly published research</a> to provide an answer.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/FxNRDxlVyxk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The reason insects fly around light will surprise you.</span></figcaption>
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<h2>Moths to a flame?</h2>
<p>Many old explanations for this hypnotic behavior have not fully panned out. An early notion was that the insects might be attracted to the heat of a flame. This was interesting, as some insects really <a href="https://doi.org/10.1016/j.foreco.2022.120629">are pyrophilic</a>: They are attracted to fire and have evolved to take advantage of conditions in recently burned areas. But most insects around a light are not in this category, and cool lights attract them quite well. </p>
<p>Another thought was that insects were just directly attracted to light, a <a href="https://doi.org/10.1007/s13355-013-0219-x">response called phototaxis</a>. Many insects move toward light, perhaps as a way to escape dark or entrapping surroundings. But if this were the explanation for the clusters around a light, you might expect them to bump straight into the source. This theory does little to explain the wild circling behavior.</p>
<p>Still another idea was that insects might mistake a nearby light for the Moon, as they attempted to use <a href="https://doi.org/10.1146/annurev.en.29.010184.001425">celestial navigation</a>. Many insects reference the Moon to keep their course at night.</p>
<p>This strategy relies on how objects at great distance seem to hover in place as you move along a straight path. A steady Moon indicates that you have not made any unintentional turns, as you might if you were buffeted by a gust of wind. Nearer objects, however, don’t appear to follow you in the sky but drift behind as you move past.</p>
<p>The celestial navigation theory held that insects worked to keep this light source steady, turning sharply in a failed attempt to fly straight. An elegant idea, but this model predicts that many flights will spiral inward to a collision, which doesn’t usually match the orbits we see. So what’s really going on?</p>
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<a href="https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Several cameras face a bright light on a stand in a forest setting at night." src="https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571761/original/file-20240128-21-f7q5vs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Scientists used high-speed stereo motion capture to document how the presence of artificial light at night affects insects’ flight behavior.</span>
<span class="attribution"><span class="source">Samuel Fabian</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Turning their backs to the light</h2>
<p>To examine this question in detail, we and our colleagues captured high-speed videos of insects around different light sources to precisely determine flight paths and body postures, both in the lab at <a href="https://www.imperial.ac.uk">Imperial College London</a> and at two field sites in Costa Rica, <a href="https://www.ciee.org/go-abroad/college-study-abroad/locations/costa-rica/monteverde">CIEE</a> and the <a href="https://www.estacionbiologica.com/">Estación Biológica</a>. We found that their flight patterns weren’t a close match for any existing model. </p>
<p>Rather, a broad swath of insects consistently pointed their backs toward the lights. This is a known behavior called the <a href="https://doi.org/10.1146/annurev.en.29.010184.001425">dorsal light response</a>. In nature, assuming that more light comes down from the sky than up from the ground, this response helps keep insects in the proper orientation to fly.</p>
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<figcaption><span class="caption">Artificial light at night interrupts the normal flight patterns of insects. This compilation video shows an orbiting behavioral motif in which insects circle the light.</span></figcaption>
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<p>But pointing their backs toward nearby artificial lights alters their flight paths. Just as airplanes bank to turn, sometimes rolling until the ground seems nearly straight out your window, banking insects turn as well. When their backs orient to a nearby light, the resulting bank loops them around the light, circling but rarely colliding. </p>
<p>These orbiting paths were only one of the behaviors we observed. When insects flew directly under a light, they often arched upward as it passed behind them, keeping their backs to the bulb until, eventually flying straight up, they stalled and fell out of the air. And even more compelling, when flying directly over a light, insects tended to flip upside down, again turning their backs to the light but then abruptly crashing.</p>
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<a href="https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagrams show insects rolling vertically or horizontally or inverting in the presence of artificial light." src="https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571763/original/file-20240128-21-1bjvpv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Three different observed turning behaviors in which flying insects turn their backs to artificial light.</span>
<span class="attribution"><span class="source">Jamie Theobald</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Why have a dorsal light response?</h2>
<p>Although light at night can harm <a href="https://www.jstor.org/stable/43597777">other animals</a> – for example, by <a href="https://doi.org/10.1073/pnas.1708574114">diverting migrating birds into urban areas</a> – larger animals don’t seem to lose their vertical orientation. So why do insects, the oldest and most species-rich group of flyers, rely on a response that leaves them so vulnerable?</p>
<p>It may have to do with their small size. Larger animals can sense gravity directly with sensory organs pulled by its acceleration, or any acceleration. Humans, for example, use the <a href="https://www.ncbi.nlm.nih.gov/books/NBK279394/">vestibular system of our inner ear</a>, which regulates our sense of balance and usually gives us a good sense of which way is down.</p>
<p>But insects have only small sensory structures. And especially as they perform rapid flight maneuvers, acceleration offers only a poor indication of which way is down. Instead, they seem to bet on the brightness of the sky. </p>
<p>Before modern lighting, the sky was usually brighter than the ground, day or night, so it provided a fairly reliable cue for a small active flyer hoping to keep a steady orientation. The artificial lights that sabotage this ability, by cueing insects to fly in circles, are relatively recent. </p>
<h2>The growing problem of nighttime lighting</h2>
<p>As new technology spreads, lights that pervade the night are <a href="https://doi.org/10.3390/rs13163311">proliferating faster then ever</a>. With the introduction of cheap, bright, <a href="https://www.energy.gov/eere/ssl/led-basics">broad-spectrum LEDs</a>, many areas, such as large cities, never see a dark night.</p>
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<a href="https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A view upward through treetops to a starry dark sky, with a bright light at the top of the screen from a light bulb near the ground." src="https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571762/original/file-20240128-31-eh9yyj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">This upward view at the authors’ field research site in Monteverde, Costa Rica, shows how artificial light competes with the night sky.</span>
<span class="attribution"><span class="source">Samuel Fabian</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Insects aren’t the only creatures affected. Light pollution disrupts circadian rhythms and physiological processes in other <a href="https://darksky.org/resources/what-is-light-pollution/effects/wildlife-ecosystems/">animals, plants</a> and <a href="https://darksky.org/resources/what-is-light-pollution/effects/human-health/">humans</a>, often with <a href="https://theconversation.com/new-atlas-shows-extent-of-light-pollution-what-does-it-mean-for-our-health-60836">serious health consequences</a></p>
<p>But insects trapped around a light seem to get the worst of it. Unable to secure food, easily spotted by predators and prone to exhaustion, many die before the morning comes.</p>
<p>In principle, light pollution is one of the easiest things to fix, often by just <a href="https://www.youtube.com/watch?v=EfhuU5Ceo_w">flipping a switch</a>. <a href="https://darksky.org/what-we-do/advancing-responsible-outdoor-lighting/">Restricting outdoor lighting</a> to useful, targeted warm light, no brighter than necessary, and for no longer than necessary, can greatly improve the health of nocturnal ecosystems. And the same practices that are good for insects help restore views of the night sky: Over one-third of the world population lives in areas where the <a href="http://dx.doi.org/10.1126/sciadv.1600377">Milky Way is never visible</a>. </p>
<p>Although insects circling around a light are a fascinating spectacle, it is certainly better for the insects and the <a href="https://www.si.edu/spotlight/buginfo/benefits">benefits they provide to humans</a> when we leave the night unlit and let them go about the activities they so masterfully perform under the night sky.</p><img src="https://counter.theconversation.com/content/221387/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samuel Fabian receives funding from the European Research Council and a National Geographic Explorer Grant.</span></em></p><p class="fine-print"><em><span>Jamie Theobald receives funding from the National Science Foundation and the U.S. Air Force Office of Scientific Research.</span></em></p><p class="fine-print"><em><span>Yash Sondhi receives funding from the Florida International University Graduate School, the Susan Levine Foundation, a National Geographic Explorer Grant, the American Philosophical Society, and the Kimberly-Green Latin-American and Caribbean Center.</span></em></p>
A new study shows how artificial light at night scrambles insects’ normal flight patterns, pulling them off course into orbit around the light.
Samuel Fabian, Postdoctoral Research Associate in Bioengineering, Imperial College London
Jamie Theobald, Associate Professor of Biological Sciences, Florida International University
Yash Sondhi, Postdoctoral Research Associate in Entomology, Mcguire Center for Lepidoptera & Biodiversity, Florida Museum of Natural History, University of Florida
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/217656
2023-12-13T20:53:51Z
2023-12-13T20:53:51Z
I’m your man: How Leonard Cohen’s life, poetry and song make him a prophet of love in a particularly dark midwinter
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<p>Leonard Cohen is hardly the first name that comes to mind as a spokesperson for “the true meaning of the holidays.” </p>
<p>As a religious studies scholar <a href="https://theconversation.com/life-of-brian-terry-joness-legacy-of-a-surprisingly-historical-jesus-130582">specializing in the history of earliest Christianity</a>, and a <a href="https://www.cbc.ca/player/play/2279666243993">Cohen fan from a Christian background</a>, I recognize that “festivity” is simply not a word that sits with Cohen — who was always more slyly depressing than holly jolly.</p>
<p>But <a href="https://podcasts.apple.com/ca/podcast/a-conversation-with-matthew-r-anderson/id1650272494?i=1000637487270">the beloved and late Jewish poet, novelist, and singer-songwriter from Montréal does talk about light, and profoundly so</a>. His words bring a certain bitter-sweetness to the shortest, darkest days of the year in the northern hemisphere, days which coincide with religious festivals involving light. </p>
<h2>Exterior, interior darkness</h2>
<p>Despite wide differences in their celebrations and what they commemorate, <a href="https://theconversation.com/hanukkahs-true-meaning-is-about-jewish-survival-88225">Hanukkah</a>, <a href="https://theconversation.com/apocalypse-booze-and-christmas-an-ancient-abc-172014">Christmas</a>, <a href="https://theconversation.com/yule-a-celebration-of-the-return-of-light-and-warmth-218779">Yule</a> and earlier in the year, <a href="https://theconversation.com/diwali-a-celebration-of-the-goddess-lakshmi-and-her-promise-of-prosperity-and-good-fortune-191992">Diwali</a> all feature candles and twinkling lights. </p>
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Read more:
<a href="https://theconversation.com/a-blaze-of-light-in-every-word-vale-leonard-cohen-68690">A blaze of light in every word: vale Leonard Cohen</a>
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<p>Whether or not these festivals were made for this purpose, they help people cope with short days, exterior darkness and even increased <em>interior</em> darkness accompanying <a href="https://www.cbc.ca/news/health/sad-science-why-winter-brings-us-down-but-won-t-for-long-1.2981920">seasonal affective disorder (SAD)</a> and other stresses as the nights get longer headed towards winter solstice.</p>
<h2>This year feels gloomier</h2>
<p>However, while violence never ceases, this year feels even gloomier, with a sharp rise in <a href="https://www.cbc.ca/news/canada/toronto/hate-crime-record-levels-toronto-1.7037413">hate crimes</a>, <a href="https://www.apa.org/monitor/2021/03/controlling-misinformation">polarizing disinformation</a> — some spread by <a href="https://www.routledge.com/American-Evangelicals-for-Trump-Dominion-Spiritual-Warfare-and-the-End/Gagn/p/book/9781032415680">“Christian” nationalists who deny democracy</a> while seeking to <a href="https://theconversation.com/the-christian-rights-efforts-to-transform-society-120878">remake North American society in their image</a> — <a href="https://theconversation.com/violent-and-disturbing-war-images-from-the-mideast-can-stir-deep-emotions-a-ptsd-expert-explains-how-to-protect-yourself-and-your-kids-from-overexposure-216405">and with war</a>. (Now we’re starting to sound more like Cohen.)</p>
<p>In reaction to the Israel-Hamas war and its global effects, instead of embracing festivals of light, some are choosing to downplay them. The city of Moncton, New Brunswick <a href="https://www.cbc.ca/news/canada/new-brunswick/moncton-city-hall-menorah-hanukkah-francis-weil-1.7046813#">decided not to display their traditional menorah and nativity scene</a>. But the decision provoked a strong negative response <a href="https://www.cbc.ca/news/canada/new-brunswick/moncton-menorah-mayor-dawn-arnold-statement-1.7048461">across Canada and globally, occasioning a speedy reversal</a>. </p>
<p>Cohen’s frequent mentions of failure, regret, suffering, violence and mortality make him far more <a href="https://www.youtube.com/watch?v=B6WnnZRSKYs">blue, than Christmas</a>. But I can identify at least four ways Cohen’s life and poetry make <a href="https://www.mqup.ca/prophets-of-love-products-9780228018643.php">him a prophet of love</a> who illuminates these dark times, based on my recent research on religious imagery in his poetry and music.</p>
<p><strong>1. Cohen wasn’t afraid to lean into the fact that, worldwide, people are religious, and religious symbols have power.</strong> Remove religious allusions from Cohen’s writing and you’d lose most of his work. His book titles, from the first <em>Let Us Compare Mythologies</em> (1956) to final <em>The Flame</em> (2018), show just how aware of <a href="https://www.firstthings.com/blogs/firstthoughts/2016/11/leonard-cohen-the-christ-haunted">the near universal symbolic currency of religion</a> Cohen was. </p>
<p>Religion was a handy way for Cohen to talk about sex. But equally true is that sex offered a device for him to talk about religion. For him, these insights were entwined with the sense that each person reflects the Divine. He observed, “I think that everybody leads a spiritual life… in touch… <a href="https://books.google.ca/books/about/Leonard_Cohen.html?id=s8RbAgAACAAJ&redir_esc=y">with their own deep pools of divine activity</a>.”</p>
<p><strong>2. Cohen never caricatured religious traditions. He pointed to the richness of many faiths while stating his own positionality.</strong> Cohen knew that understanding others starts with understanding oneself. “<a href="https://books.google.ca/books/about/Leonard_Cohen.html?id=s8RbAgAACAAJ&redir_esc=y">I would never say anything else but that I am a Jew</a>,” he repeatedly insisted. Cohen’s maternal grandfather was a noted scriptural scholar and his paternal <a href="https://globalnews.ca/news/9707000/shaar-hashomayim-celebrates-century-in-westmount/">great-grandfather helped found Montréal’s Congregation Shaar Hashomayim</a>. Yet as deeply rooted as he was in Judaism, Cohen’s knowledge of other faiths was both profound and wide-ranging. </p>
<p>In my research I show <a href="https://atlanticbooks.ca/stories/im-your-saint-cohen-and-st-paul-studied-in-prophets-of-love/">how important Jesus was to Cohen</a>, without making the mistake of claiming he was Christian. I explore the profound impact of Catholicism on his childhood. I also note how interwoven through Cohen’s corpus is his decades-long practice of Zen Buddhism, his readings in Sufi mysticism and his study of Hinduism. </p>
<p><a href="https://www.theguardian.com/music/2021/oct/17/how-leonard-cohen-mined-sacred-texts-for-lyrics-to-his-songs">Jewish tales from the Mishnah and Talmud</a>, <a href="https://www.heyalma.com/leonard-cohens-rabbi-reveals-the-jewish-theology-behind-the-music/">kabbalistic philosophy</a>, ancient Christian legends, poetry from Federico Garcia Lorca and Rumi, and <a href="https://www.npr.org/2016/10/21/498810429/leonard-cohen-on-poetry-music-and-why-he-left-the-zen-monastery">Zen reflections on longing</a>, attachment and nothingness all combine in his work. </p>
<p>As a poet, writer and thinker Cohen abhorred cliché, while leaning into religious complexity and diversity.</p>
<p><strong>3. Cohen respected faith and spirituality but called out religious hypocrisy.</strong> In 1984 he remarked: “<a href="https://books.google.ca/books/about/Leonard_Cohen.html?id=s8RbAgAACAAJ&redir_esc=y">There’s always the possibility of mystification and manipulation</a> …. There are evil forces in the world ready to imperialize religion but I’m confident the forces of good are stronger.” </p>
<p>These words seem optimistic for the man who also wrote:</p>
<blockquote>
<p>“Give me Stalin and St. Paul / I’ve seen the future, brother / It is murder” (“The Future,” from Stranger Music). </p>
</blockquote>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/LYzPVKg3wyo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Leonard Cohen’s ‘The Future.’</span></figcaption>
</figure>
<p>Cohen himself was not immune to abusing the power that comes with being revered. He was fortunate in successfully transforming his <a href="https://web.archive.org/web/20201211115215/https:/www.theglobeandmail.com/arts/article-leonard-cohens-tales-of-seduction-look-different-through-a-metoo/">seemingly misogynist relations with women</a> into lyrics rather than litigation, partly by the complicated and disarming ways he wrote about regret, apology and forgiveness, and partly <a href="https://sharpmagazine.com/2018/11/06/how-do-we-come-to-terms-with-leonard-cohens-legacy-in-the-metoo-era/">through age and death</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/marianne-and-leonard-a-new-film-tells-us-little-about-the-woman-fixed-in-the-role-of-musicians-muse-128112">Marianne & Leonard: a new film tells us little about the woman fixed in the role of musician's muse</a>
</strong>
</em>
</p>
<hr>
<p><strong>4. Most importantly, Cohen used religious stories and images to find common cause with and give courage to others in dark times.</strong> His most famous lines are perhaps from his song <em>Anthem</em>: </p>
<blockquote>
<p>“Ring the bells that still can ring / forget your perfect offering / There is a crack in everything / that’s how the light gets in.” </p>
</blockquote>
<p>Harry Freedman, in <em><a href="https://www.bloomsbury.com/ca/leonard-cohen-9781472987273/">Leonard Cohen: The Mystical Roots of Genius</a></em> finds multiple Jewish religious references behind <em>Anthem</em>. I’ve discovered even more. Cohen took on the mantle (importantly, for him a <em>biblical</em> mantle) of recognizing and lifting up the light that can be discovered in, despite, and through human suffering. As I have written elsewhere, “<a href="https://www.mqup.ca/prophets-of-love-products-9780228018643.php">A crack in everything means especially a crack in human beings</a>.”</p>
<p>In his last years Cohen lived into his name <a href="https://www.britannica.com/topic/cohen">of cohen (priest)</a>. Friends and colleagues of mine who attended his final concerts, some religious, but many <a href="https://theconversation.com/what-does-it-mean-to-be-spiritual-87236">“spiritual but not religious,”</a> described them as sacred spaces.</p>
<p>Cohen’s lyrics dwell on human failure, regret and violence. Yet according to his musical collaborator Sharon Robinson, <a href="https://www.rollingstone.com/music/music-features/sharon-robinson-reflects-on-touring-with-leonard-cohen-194281/">touring became “a type of meditation” for Cohen</a>, and his final concerts ended with him blessing the crowd. Typically for Cohen, who never let a line have only one meaning, the title of the album <em>You Want It Darker</em> refers to both his fans and his God. There is <a href="https://jewishreviewofbooks.com/articles/2315/darkness-and-light-leonard-cohen-and-the-new-cantors-a-playlist-for-the-high-holidays/">both a challenge to the Divine, and acceptance of an end</a>, in it.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/v0nmHymgM7Y?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Leonard Cohen’s ‘You Want it Darker.’</span></figcaption>
</figure>
<h2>Cohen’s ominous passing, ongoing relevance</h2>
<p>Cohen’s 2016 death on <a href="https://lithub.com/cohen-dies-trump-wins-and-we-will-sing-about-these-dark-times/">the eve of a sharp turn toward hate politics when Donald Trump was elected</a> seems doubly ominous seven years after the passing of the <a href="https://www.rollingstone.com/music/music-features/leonard-cohen-remembering-the-life-and-legacy-of-the-poet-of-brokenness-192994">poet of brokenness</a>. </p>
<p>Knowledgeable of many faiths, but observant above all of the human condition; daring the Divine to answer humanity’s sorrows: this is what makes Cohen an unlikely but fitting spokesperson for another dark midwinter season. </p>
<p>My own vote for a <a href="https://www.msn.com/en-ca/news/canada/douglas-todd-leonard-cohen-may-help-us-find-hope-in-today-s-holy-broken-world/ar-AA1izeLe">Cohen holiday favourite</a> might be <em>Come Healing</em>. It’s why Cohen, a man about whom surely no Hallmark festive movie will ever be made, just might be this year’s answer to the darkness: </p>
<blockquote>
<p>“And let the heavens falter / Let the earth proclaim / Come healing of the altar /
Come healing of the name.”</p>
</blockquote><img src="https://counter.theconversation.com/content/217656/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Robert Anderson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Leonard Cohen, a man about whom surely no Hallmark festive movie will ever be made, dared the Divine to answer humanity’s sorrows.
Matthew Robert Anderson, Adjunct professor, Theological Studies, Concordia University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/216951
2023-11-21T16:54:17Z
2023-11-21T16:54:17Z
SAD lamps: do they work? Experts explain how they help the winter blues
<p>Have you ever noted that you sleep more in the winter months? Or eat more carbs or have low energy? If you do, then you might be one of the around <a href="https://www.theguardian.com/lifeandstyle/2017/oct/30/sad-winter-depression-seasonal-affective-disorder">6% of the</a> higher latitude populations with seasonal affective disorder (SAD). </p>
<p>If you’ve searched the internet for <a href="https://news.sky.com/story/seasonal-affective-disorder-or-sad-isnt-just-winter-blues-12983739">tips on how to fight the winter blues</a> you’ve probably been advised to buy a therapy lamp. So you may be wondering what research says about whether they are effective and how they work. </p>
<p>Before we examine the evidence for light therapy it’s important to understand why mood might be affected by sunlight. Vitamin D is produced <a href="https://www.tandfonline.com/doi/full/10.4161/derm.24494">when your skin is exposed to sunlight</a> and some scientists believe there is a link between <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10255717/">depression and low vitamin D levels</a>. </p>
<p>Studies have found about 10% of the population of <a href="https://www.tandfonline.com/doi/full/10.2147/PRBM.S114906">the far north</a>, for example in Alaska and Finland, experience SAD. Interestingly, Icelanders, who also live in these very northern latitudes, <a href="https://jamanetwork.com/journals/jamapsychiatry/article-abstract/496414">do not appear to suffer so much from SAD</a>. This might be <a href="https://www.ifis.org/blog/icelands-diet-health-problems-solutions-part-1#:%7E:text=Icelanders%20typically%20dine%20on%20a,%2C%20Arctic%20char%2C%20and%20monkfish.">because of their fish-packed diet</a>, which is rich in vitamin D. </p>
<p>Light also stimulates your visual system, regulating activity in the so-called circadian pacemaker. This is the <a href="https://www.sciencedirect.com/topics/neuroscience/suprachiasmatic-nucleus">suprachiasmatic nucleus</a> (SCN), a small region of the brain. The SCN gets direct input from the retina and is also packed with melatonin receptors. Melatonin supplements are now being touted as a <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060443/">treatment for depression</a>. So there are multiple reasons why <a href="https://pubmed.ncbi.nlm.nih.gov/37239299/">light might be important for mood</a>.</p>
<p>SAD was first described around 1980 in the US when a man, who experienced the symptoms outlined above, invented a light box to treat himself. </p>
<p>There have been many studies since examining light therapy in SAD with mixed and contradicting results. However, data from all these studies can be combined and examined using <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/meta-analysis">meta-analyses</a> to give a more accurate overall picture. A meta-analysis merges the findings of several independent studies. There have been several meta-analyses of this topic and most show that light therapy has a positive effect, not only on SAD, but also on major depression.</p>
<h2>Does light intensity matter</h2>
<p>Light intensity is <a href="https://www.britannica.com/science/lux">measured in lux</a>. A <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0447.1999.tb07236.x">1999 meta-analysis</a> of 39 scientific papers found that strong light intensity (6,000-10,000 lux) had a greater effect than medium light intensity (1,700-3,500 lux). Medium light intensity had a greater effect than dim lighting (less than 600 lux) on depressive symptoms in people with SAD. A <a href="https://pubmed.ncbi.nlm.nih.gov/31574513/">2019 meta-analysis</a> of 19 studies also found that brighter light (greater than than 1,000 lux) is needed to treat SAD.</p>
<figure class="align-center ">
<img alt="Young woman reading by a therapy lamp" src="https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558066/original/file-20231107-252894-tstzhi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Therapy lamp.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/woman-light-therapy-171525149">Image Point Fr/Shutterstock</a></span>
</figcaption>
</figure>
<p>You might be wondering whether light colour matters.</p>
<p>A <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0447.1997.tb09915.x">1997 meta-analysis</a> looked at 40 scientific papers examining different colours of light. It revealed that light of short to medium wavelengths (blue, green and yellow) were effective but that red or UV wavelengths did not seem to treat SAD. This study also reviewed the timing of the phototherapy. The data, although not significant (which means more studies are needed), suggested that phototherapy in both the morning and the evening was more effective than morning or evening alone.</p>
<h2>Does phototherapy work in non-seasonal depression?</h2>
<p>A <a href="https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.162.4.656?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed">2005 meta-analysis</a> of 23 studies found phototherapy worked for people with SAD and for people with non-seasonal depression. This paper reviewed six studies of combined treatment for non-seasonal depression. It found that phototherapy, although effective alone, did not produce a greater effect on depression symptoms when given together with antidepressant medication. </p>
<p>However, more recent studies agree that the combination treatment is more effective. A <a href="https://pubmed.ncbi.nlm.nih.gov/27835725/">2016 meta-analysis</a> of ten studies did find phototherapy augmented drug treatment of depression. A <a href="https://pubmed.ncbi.nlm.nih.gov/31600678/">2019 meta-analysis</a> of seven studies also found it increased the power of antidepressants.</p>
<p>So if you suffer from non-seasonal depression, then phototherapy may work as a first line treatment and will probably boost the effects of any antidepressant drug that you may be taking. </p>
<p>There is also a condition called <a href="https://www.sciencedirect.com/science/article/pii/S0165032707003515">sub-syndromal SAD</a> (SSAD or sub-SAD) affecting about <a href="https://www.theguardian.com/lifeandstyle/2017/oct/30/sad-winter-depression-seasonal-affective-disorder">10-15%</a> of higher latitude populations, where symptoms are milder or less frequent than SAD. Sub-SAD can also be treated with light therapy. </p>
<p>Vitamin D is <a href="https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/">essential for physical health</a> as well as mental health as it regulates calcium and phosphate levels, is critical for good bone density and for muscle and teeth health. It’s also essential for a healthy immune system. </p>
<p>There are other studies that look at <a href="https://pubmed.ncbi.nlm.nih.gov/29498416/">lighting in the workplace</a> and the effect on employees, for example certain types of light might improve alertness, while other lighting might increase headaches.</p>
<p>If you suffer from SAD, choose a higher intensity light for a faster effect, use the light for longer, for example, both morning and evening sessions. Avoid UV light which is ineffective for SAD and can lead to sunburn or skin cancer. And don’t forget to eat some fish to boost your vitamin D levels too.</p><img src="https://counter.theconversation.com/content/216951/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
SAD is a debilitating condition affecting many people, but there is light at the end of the tunnel.
Colin Davidson, Professor of Neuropharmacology, University of Central Lancashire
Claire Hutchinson, Professor of Experimental Psychology, University of the West of Scotland
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213836
2023-11-13T13:33:49Z
2023-11-13T13:33:49Z
Is time travel even possible? An astrophysicist explains the science behind the science fiction
<figure><img src="https://images.theconversation.com/files/554607/original/file-20231018-19-hyrxxn.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C960%2C540&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If traveling into the past is possible, one way to do it might be sending people through tunnels in space.</span> <span class="attribution"><a class="source" href="https://pixabay.com/photos/astronomy-desktop-space-galaxy-3217141/">by raggio5 via Pixabay</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York</strong></p>
</blockquote>
<hr>
<p>Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time. </p>
<p>But is this just a fun idea for movies, or could it really happen?</p>
<p>The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the <a href="https://www.grc.nasa.gov/www/k-12/airplane/thermo.html">laws of thermodynamics</a>, it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time. </p>
<p>It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.</p>
<h2>Time is relative</h2>
<p>However, physicist Albert Einstein’s <a href="https://www.space.com/36273-theory-special-relativity.html">theory of special relativity</a> suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the <a href="https://www.space.com/15830-light-speed.html">speed of light</a> – 671 million miles per hour! – will experience time slower than a person on Earth. </p>
<p>People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is <a href="https://www.space.com/33411-astronaut-scott-kelly-relativity-twin-brother-ages.html">6 minutes and 5 milliseconds younger</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/yuD34tEpRFw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Time isn’t the same everywhere.</span></figcaption>
</figure>
<p>Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves <a href="https://www.space.com/20881-wormholes.html">wormholes</a>, or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past. </p>
<p>However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be <a href="https://galileospendulum.org/2015/01/26/why-wormholes-probably-dont-exist/">incredibly challenging</a> to send humans through a wormhole space tunnel.</p>
<h2>Paradoxes and failed dinner parties</h2>
<p>There are also paradoxes associated with time travel. The famous “<a href="https://www.discovermagazine.com/the-sciences/what-is-the-grandfather-paradox-of-time-travel">grandfather paradox</a>” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.</p>
<p>Famously, physicist Stephen Hawking tested the possibility of time travel by <a href="https://www.euronews.com/culture/2023/06/28/culture-re-view-the-day-stephen-hawking-threw-a-time-traveller-party">throwing a dinner party</a> where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up. </p>
<p>As he <a href="https://www.penguinrandomhouse.com/books/77014/black-holes-and-baby-universes-by-stephen-hawking/">pointed out</a>: “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”</p>
<h2>Telescopes are time machines</h2>
<p>Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/QeRtcJi3V38?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Telescopes are a kind of time machine – they let you peer into the past.</span></figcaption>
</figure>
<p>NASA’s newest space telescope, the <a href="https://theconversation.com/a-cosmic-time-machine-how-the-james-webb-space-telescope-lets-us-see-the-first-galaxies-in-the-universe-187015">James Webb Space Telescope</a>, is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.</p>
<p>While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213836/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adi Foord does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Scientists are trying to figure out if time travel is even theoretically possible. If it is, it looks like it would take a whole lot more knowledge and resources than humans have now to do it.
Adi Foord, Assistant Professor of Astronomy and Astrophysics, University of Maryland, Baltimore County
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/205810
2023-10-16T12:30:12Z
2023-10-16T12:30:12Z
Why is space so dark even though the universe is filled with stars?
<figure><img src="https://images.theconversation.com/files/538108/original/file-20230718-17-5jcl17.jpg?ixlib=rb-1.1.0&rect=26%2C6%2C996%2C676&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This age old question has been dubbed Olbers' paradox.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-milky-way-appears-over-the-valle-de-la-luna-in-the-news-photo/1418507439?adppopup=true">John Moore via Getty Images News</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why is space so dark despite all of the stars in the universe? – Nikhil, age 15, New Delhi</strong></p>
</blockquote>
<hr>
<p>People have been asking why space is dark despite being filled with stars for so long that this question has a special name – <a href="https://lambda.gsfc.nasa.gov/product/suborbit/POLAR/cmb.physics.wisc.edu/tutorial/olbers.html">Olbers’ paradox</a>.</p>
<p>Astronomers estimate that there are about <a href="https://theconversation.com/how-many-stars-are-there-in-space-165370">200 billion trillion stars</a> in the observable universe. And many of those stars are as bright or even brighter than our sun. So, why isn’t space filled with dazzling light?</p>
<p><a href="http://www.astrojack.com/">I am an astronomer</a> who studies stars and planets – including those outside our solar system – and their motion in space. The study of distant stars and planets helps <a href="https://scholar.google.com/citations?user=pF3HbeQAAAAJ&hl=en&oi=ao">astronomers like me</a> understand why space is so dark.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/why-is-space-so-dark-even-though-the-universe-is-filled-with-stars-205810&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
<p><em>You can listen to more articles from The Conversation, narrated by Noa, <a href="https://theconversation.com/us/topics/audio-narrated-99682">here</a>.</em></p>
<hr>
<p>You might guess it’s because a lot of the stars in the universe are very far away from Earth. Of course, it is true that the farther away a star is, the less bright it looks – <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html">a star 10 times farther away looks 100 times dimmer</a>. But it turns out this isn’t the whole answer. </p>
<h2>Imagine a bubble</h2>
<p>Pretend, for a moment, that the universe is so old that the light from even the farthest stars has had time to reach Earth. In this imaginary scenario, all of the stars in the universe are not moving at all.</p>
<p>Picture a large bubble with Earth at the center. If the bubble were about 10 <a href="https://exoplanets.nasa.gov/faq/26/what-is-a-light-year/">light years</a> across, it would contain about <a href="https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs">a dozen stars</a>. Of course, at several light years away, many of those stars would look pretty dim from Earth. </p>
<p>If you keep enlarging the bubble to 1,000 light years across, then to 1 million light years, and then 1 billion light years, the farthest stars in the bubble will look even more faint. But there would also be more and more stars inside the bigger and bigger bubble, all of them contributing light. Even though the farthest stars look dimmer and dimmer, there would be a lot more of them, and the whole night sky should look very bright.</p>
<p>It seems I’m back where I started, but I’m actually a little closer to the answer.</p>
<h2>Age matters</h2>
<p>In the imaginary bubble illustration, I asked you to imagine that the stars are not moving and that the universe is very old. But the universe is only about <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html">13 billion years old</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of lightly colored galaxies and stars against dark background" src="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=770&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxies as they appeared approximately 13.1 billion years ago, taken by the James Webb Space Telescope.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/image-released-by-nasa-on-july-11-2022-shows-galaxy-cluster-news-photo/1241872380?adppopup=true">NASA/ESA/CSA/STScI/Handout from Xinhua News Agency via Getty Images</a></span>
</figcaption>
</figure>
<p>Even though that’s an amazingly long time in human terms, it’s short in astronomical terms. It’s short enough that the light from stars more distant than about 13 billion light years hasn’t actually reached Earth yet. And so the actual bubble around Earth that contains all the stars we can see only extends out to about <a href="https://science.nasa.gov/observable-universe">13 billion light years from Earth</a>.</p>
<p>There just are not enough stars in the bubble to fill every line of sight. Of course, if you look in some directions in the sky, you can see stars. If you look at other bits of the sky, you can’t see any stars. And that’s because, in those dark spots, the stars that could block your line of sight are so far away their light hasn’t reached Earth yet. As time passes, light from these more and more distant stars will have time to reach us. </p>
<h2>The Doppler shift</h2>
<p>You might ask whether the night sky will eventually light up completely. But that brings me back to the other thing I told you to imagine: that all of the stars are not moving. The universe is actually expanding, with the most distant galaxies <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">moving away from Earth at nearly the speed of light</a>. </p>
<p>Because the galaxies are moving away so fast, the light from their stars is pushed into colors the human eye can’t see. This effect is called the <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">Doppler shift</a>. So, even if it had enough time to reach you, <a href="https://svs.gsfc.nasa.gov/12856">you still couldn’t see</a> the light from the most distant stars with your eyes. And the night sky would not be completely lit up. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ikgRZt1BSyk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Doppler shift, also known as the redshift, is a phenomenon in which light from objects that are moving away from an observer appears more toward the red end of the spectrum.</span></figcaption>
</figure>
<p>If you wait even longer, eventually the stars will all burn out – <a href="https://astronomy.swin.edu.au/cosmos/m/main+sequence+lifetime">stars like the sun last only about 10 billion years</a>. Astronomers hypothesize that in the distant future – a thousand trillion years from now – the universe will go dark, <a href="https://en.wikipedia.org/wiki/The_Five_Ages_of_the_Universe">inhabited by only stellar remnants</a> like white dwarfs and black holes.</p>
<p>Even though our night sky isn’t completely filled with stars, we live in a very special time in the universe’s life, when we’re lucky enough to enjoy a rich and complex night sky, filled with light and dark.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205810/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Jackson receives federally funded research grants from NASA. </span></em></p>
An astronomer explains why space looks so dark despite containing 200 billion trillion stars.
Brian Jackson, Associate Professor of Astronomy, Boise State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/214907
2023-10-04T01:42:55Z
2023-10-04T01:42:55Z
What is an attosecond? A physical chemist explains the tiny time scale behind Nobel Prize-winning research
<figure><img src="https://images.theconversation.com/files/551866/original/file-20231003-27-fn9thz.jpg?ixlib=rb-1.1.0&rect=10%2C3%2C2295%2C1292&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Work in attosecond physics has led to a better understanding of how electrons move around. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/image-of-an-atomic-structure-consisting-of-protons-royalty-free-image/1337003441?phrase=electron">Oselote/iStock via Getty Images</a></span></figcaption></figure><p>A group of three researchers earned the <a href="https://www.nobelprize.org/uploads/2023/10/popular-physicsprize2023.pdf">2023 Nobel Prize in physics</a> for work that has revolutionized how scientists study the electron – by illuminating molecules with attosecond-long flashes of light. But how long is an attosecond, and what can these infinitesimally short pulses tell researchers about the nature of matter?</p>
<p><a href="https://www.austincollege.edu/aaron-harrison/">I first learned</a> of this area of research as a graduate student in physical chemistry. My doctoral adviser’s group had a project dedicated to studying <a href="http://bromine.cchem.berkeley.edu/atto.htm">chemical reactions with attosecond pulses</a>. Before understanding why attosecond research resulted in the most prestigious award in the sciences, it helps to understand what an attosecond pulse of light is.</p>
<h2>How long is an attosecond?</h2>
<p>“Atto” is the <a href="https://www.nrel.gov/comm-standards/editorial/scientific-notation.html">scientific notation prefix</a> that represents 10<sup>-18</sup>, which is a decimal point followed by 17 zeroes and a 1. So a flash of light lasting an attosecond, or 0.000000000000000001 of a second, is an extremely short pulse of light. </p>
<p>In fact, there are approximately as many attoseconds in one second as there are seconds in the <a href="https://81018.com/universeclock/">age of the universe</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing an attosecond, depicted as an orange collection of hexagons, on the left, with the age of the universe, depicted as a dark vacuum on the right, and a heartbeat, depicted as a human heart, in the middle." src="https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=256&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=256&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=256&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=322&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=322&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551859/original/file-20231003-21-rkpekw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=322&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An attosecond is incredibly small when compared to a second.</span>
<span class="attribution"><a class="source" href="https://www.nobelprize.org/prizes/physics/2023/press-release/">©Johan Jarnestad/The Royal Swedish Academy of Sciences</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Previously, scientists could study the motion of heavier and slower-moving atomic nuclei with <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/femtosecond-laser">femtosecond (10<sup>-15</sup>) light pulses</a>. One thousand attoseconds are in 1 femtosecond. But researchers couldn’t see movement on the electron scale until they could generate attosecond light pulses – electrons move too fast for scientists to parse exactly what they are up to at the femtosecond level.</p>
<h2>Attosecond pulses</h2>
<p>The rearrangement of electrons in atoms and molecules guides a lot of processes in physics, and it underlies practically every part of chemistry. Therefore, researchers have put a lot of effort into figuring out how electrons are moving and rearranging. </p>
<p>However, electrons move around very rapidly in physical and chemical processes, making them difficult to study. To investigate these processes, <a href="https://www.britannica.com/science/spectroscopy">scientists use spectroscopy</a>, a method of examining how matter absorbs or emits light. In order to <a href="https://doi.org/10.1146/annurev-physchem-040215-112025">follow the electrons in real time</a>, researchers need a pulse of light that is shorter than the time it takes for electrons to rearrange. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Vy71bJJ9EnU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Pump-probe spectroscopy is a common technique in physics and chemistry and can be performed with attosecond light pulses.</span></figcaption>
</figure>
<p>As an analogy, imagine a camera that could only take longer exposures, around 1 second long. Things in motion, like a person running toward the camera or a bird flying across the sky, would appear blurry in the photos taken, and it would be difficult to see exactly what was going on. </p>
<p>Then, imagine you use a camera with a 1 millisecond exposure. Now, motions that were previously smeared out would be nicely resolved into clear and precise snapshots. That’s how using the attosecond scale, rather than the femtosecond scale, can illuminate electron behavior. </p>
<h2>Attosecond research</h2>
<p>So what kind of research questions can attosecond pulses help answer?</p>
<p>For one, breaking a chemical bond is a fundamental process in nature where electrons that are shared between two atoms separate out into unbound atoms. The previously shared electrons undergo ultrafast changes during this process, and <a href="https://doi.org/10.1126/science.aax0076">attosecond pulses</a> made it possible for researchers to follow the real-time breaking of a chemical bond. </p>
<p>The <a href="https://doi.org/10.1038/nphys620">ability to generate attosecond pulses</a> – the research for which three researchers earned the <a href="https://www.nobelprize.org/prizes/physics/2023/press-release/">2023 Nobel Prize in physics</a> – first became possible in the early 2000s, and the field has <a href="https://phys.org/news/2010-04-electrons-science-attosecond-scale.html">continued to grow rapidly</a> since. By providing shorter snapshots of atoms and molecules, attosecond spectroscopy has helped researchers understand electron behavior in single molecules, such as how <a href="https://doi.org/10.1038/s41467-022-32313-0">electron charge migrates</a> and how <a href="https://doi.org/10.1063/5.0086775">chemical bonds</a> between atoms break. </p>
<p>On a larger scale, attosecond technology has also been applied to studying how electrons behave in <a href="https://doi.org/10.1126/science.abb0979">liquid water</a> as well as <a href="https://doi.org/10.1038/s42005-021-00635-y">electron transfer in solid-state semiconductors</a>. As researchers continue to improve their ability to produce attosecond light pulses, they’ll gain a deeper understanding of the basic particles that make up matter.</p><img src="https://counter.theconversation.com/content/214907/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aaron W. Harrison does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Three scientists won the 2023 Nobel Prize in physics for their work developing methods to shoot laser pulses that only last an attosecond, or a mind-bogglingly tiny fraction of a second.
Aaron W. Harrison, Assistant Professor of Chemistry, Austin College
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213145
2023-09-25T01:41:27Z
2023-09-25T01:41:27Z
Do blue-light glasses really work? Can they reduce eye strain or help me sleep?
<figure><img src="https://images.theconversation.com/files/549203/original/file-20230919-25-ucj5dq.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1000%2C666&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/asian-womans-eyes-stress-blue-blocking-1391138681">Shutterstock</a></span></figcaption></figure><p>Blue-light glasses are said to <a href="https://www.baxterblue.com.au/collections/blue-light-glasses">reduce eye strain</a> when using <a href="https://www.blockbluelight.com.au/collections/computer-glasses">computers</a>, improve your <a href="https://www.ocushield.com/products/anti-blue-light-glasses">sleep</a> and protect your eye health. You can buy them yourself or your optometrist can prescribe them.</p>
<p>But <a href="https://mivision.com.au/2019/03/debate-continues-over-blue-blocking-lenses/">do they work</a>? Or could they do you harm?</p>
<p>We <a href="https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013244.pub2/full">reviewed</a> the evidence. Here’s what we found.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/health-check-will-i-damage-my-eyes-if-i-dont-wear-sunglasses-68582">Health Check: will I damage my eyes if I don't wear sunglasses?</a>
</strong>
</em>
</p>
<hr>
<h2>What are they?</h2>
<p>Blue-light glasses, blue light-filtering lenses or blue-blocking lenses are different terms used to describe lenses that reduce the amount of short-wavelength visible (blue) light reaching the eyes. </p>
<p>Most of these lenses prescribed by an optometrist decrease blue light transmission by <a href="https://onlinelibrary.wiley.com/doi/10.1111/opo.12615">10-25%</a>. Standard (clear) lenses do not filter blue light.</p>
<p>A wide variety of lens products are available. A filter can be added to prescription or non-prescription lenses. They are widely marketed and are becoming <a href="https://onlinelibrary.wiley.com/doi/10.1111/opo.12615">increasingly popular</a>.</p>
<p>There’s often an added cost, which depends on the specific product. So, is the extra expense worth it?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-eye-disorders-may-have-influenced-the-work-of-famous-painters-92830">How eye disorders may have influenced the work of famous painters</a>
</strong>
</em>
</p>
<hr>
<h2>Blue light is all around us</h2>
<p>Outdoors, sunlight is the main source of blue light. Indoors, light sources – such as light-emitting diodes (LEDs) and the screens of digital devices – emit varying degrees of blue light. </p>
<p>The amount of blue light emitted from artificial light sources is much lower than from the Sun. Nevertheless, artificial light sources are all around us, at home and at work, and we can spend a lot of our time inside.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Blue light-filtering lenses block some blue light from screens from reaching the eye" src="https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/549210/original/file-20230920-16-tsb23b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Screens emit blue light. The lenses are designed to reduce the amount of blue light that reaches the eye.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/blue-light-blocking-ray-filter-lens-2286229107">Shutterstock</a></span>
</figcaption>
</figure>
<p>Our research team at the University of Melbourne, along with collaborators from Monash University and City, University London, sought to see if the best available evidence supports using blue light-filtering glasses, or if they could do you any harm. So we conducted a <a href="https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013244.pub2/full">systematic review</a> to bring together and evaluate all the relevant studies. </p>
<p>We included all randomised controlled trials (clinical studies designed to test the effects of interventions) that evaluated blue light-filtering lenses in adults. We identified 17 eligible trials from six countries, involving a total of 619 adults.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/does-my-treatment-work-how-major-medical-reviews-can-be-gold-standard-evidence-yet-flawed-205014">Does my treatment work? How major medical reviews can be 'gold standard' evidence, yet flawed</a>
</strong>
</em>
</p>
<hr>
<h2>Do they reduce eye strain?</h2>
<p>We found no benefit of using blue light-filtering lenses, over standard (clear) lenses, to reduce eye strain with computer use. </p>
<p>This conclusion was based on consistent findings from three studies that evaluated effects on eye strain over time periods ranging from two hours to five days.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/screentime-can-make-you-feel-sick-here-are-ways-to-manage-cybersickness-163851">Screentime can make you feel sick – here are ways to manage cybersickness</a>
</strong>
</em>
</p>
<hr>
<h2>Do they help you sleep?</h2>
<p>Possible effects on sleep were uncertain. Six studies evaluated whether wearing blue-light filtering lenses before bedtime could improve sleep quality, and the findings were mixed. </p>
<p>These studies involved people with a diverse range of medical conditions, including insomnia and bipolar disorder. Healthy adults were not included in the studies. So we do not yet know whether these lenses affect sleep quality in the general population.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1678293771539161089"}"></div></p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/booting-up-or-powering-down-how-e-readers-affect-your-sleep-36145">Booting up or powering down: how e-readers affect your sleep</a>
</strong>
</em>
</p>
<hr>
<h2>Do they boost your eye health?</h2>
<p>We did not find any clinical evidence to support using blue-light filtering lenses to protect the macula (the region of the retina that controls high-detailed, central vision). </p>
<p>None of the studies evaluated this.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/macular-diseases-cause-blindness-and-treatment-costs-millions-here-is-how-to-look-after-yours-196796">Macular diseases cause blindness and treatment costs millions. Here is how to look after yours</a>
</strong>
</em>
</p>
<hr>
<h2>Could they do harm? How about causing headaches?</h2>
<p>We could not draw clear conclusions on whether there might be harms from wearing blue light-filtering lenses, compared with standard (non blue-light filtering) lenses. </p>
<p>Some studies described how study participants had headaches, lowered mood and discomfort from wearing the glasses. However, people using glasses with standard lenses reported similar effects.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/health-check-what-causes-headaches-42254">Health Check: what causes headaches?</a>
</strong>
</em>
</p>
<hr>
<h2>What about other benefits or harms?</h2>
<p>There are some important general considerations when interpreting our findings. </p>
<p>First, most of the studies were for a relatively short period of time, which limited our ability to consider longer-term effects on vision, sleep quality and eye health. </p>
<p>Second, the review evaluated effects in adults. We don’t yet know if the effects are different for children.</p>
<p>Finally, we could not draw conclusions about the possible effects of blue light-filtering lenses on many vision and eye health measures, including colour vision, as the studies did not evaluate these.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-are-people-colour-blind-107599">Curious Kids: why are people colour blind?</a>
</strong>
</em>
</p>
<hr>
<h2>In a nutshell</h2>
<p>Overall, based on relatively limited published clinical data, our review does not support using blue-light filtering lenses to reduce eye strain with digital device use. It is unclear whether these lenses affect vision quality or sleep, and no conclusions can be drawn about any potential effects on the health of the retina. </p>
<p>High-quality research is needed to answer these questions, as well as whether the effectiveness and safety of these lenses varies in people of different ages and health status.</p>
<p>If you have eye strain, or other eye or vision concerns, discuss this with your optometrist. They can perform a thorough examination of your eye health and vision, and discuss any relevant treatment options.</p><img src="https://counter.theconversation.com/content/213145/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>In the past three years, Laura Downie's research laboratory at the University of Melbourne has received funding from Alcon Laboratories, Azura Ophthalmics, CooperVision and Novartis for clinical research studies unrelated to this article. She is affiliated with the Tear Film and Ocular Surface Society, as a global ambassador.</span></em></p>
They’re heavily promoted. Your optometrist may even prescribe them. But when we looked at the evidence, this is what we found.
Laura Downie, Associate Professor in Optometry and Vision Sciences, The University of Melbourne
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/212420
2023-09-04T17:37:53Z
2023-09-04T17:37:53Z
Dogs don’t see life through rose-coloured glasses, nor in black and white
<p>For a few months now, I’ve been treating six-year-old Samuel, who has the beginnings of myopia. He’s very quick for his age and often asks me questions about tests I give him, and about what I see inside his eyes. </p>
<p>But the last question surprised me. </p>
<p>Samuel knows that some people, like his father, don’t see colours well. But what about his little poodle, Scotch, he asked?</p>
<p>I’m not a veterinarian and don’t want to intrude on their domain of expertise. However, as an optometrist, I can offer some insights that might help answer Samuel’s question. </p>
<h2>Cones and rods</h2>
<p>Ambient light is composed of <a href="https://www.britannica.com/science/photon">particles (photons)</a>, which line up in rays. Light rays travel and strike objects. Some rays are absorbed, while others are reflected, depending on the characteristics of their surfaces and the composition of their materials. The wavelengths of the reflected rays determine the colour of the object as it is perceived by the eye. </p>
<p>Like everything about human vision, colour perception is complex. The retina, the sensitive part that lines the back of the eye, has two types of photon receptors: cones and rods. The cones, in the centre of the retina (fovea), perceive bright light and are <a href="https://askabiologist.asu.edu/rods-and-cones">responsible for colour perception</a>.</p>
<p>There are three types of cones. Each type contains a specific photo-pigment called opsin, which defines its nature. The opsin is produced under the influence of specific genes. The shortest opsin (“Cone S” for <em>short</em>) reacts mainly to blue light (420 nm). The longer one (“Cone L”) is more sensitive to orange-red light (560 nm) and the one in between (“Cone M” for <em>middle</em>) <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">is activated in the presence of green (530 nm)</a>.</p>
<p>However, each cone reacts to each of the rays entering the eye. For example, a red ball will produce a weak response from the S cone (3/10), a slightly stronger response from the M cone (5/10) and a <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">strong response from the L cone</a> (8/10). </p>
<p>The brain combines the signals emitted by each of these cones to form the colour it perceives. So, in the previous example, the perceived colour would be coded 3-5-8, corresponding to what we know as red. A pink colour might have the code 4-6-6, and blue, 8-6-3. Each combination of the 3-cone signals is unique, which allows us to appreciate different hues in all their variations. </p>
<p>That is, as long as the genetic code is intact. </p>
<p>The genes associated with colour vision can be mutated or defective, in which case the person will be partially or completely impaired. The best known of these anomalies is colour blindness (red-green deficiency or daltonism).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="perception of a plant according to a colour-blind person" src="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=331&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=331&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=331&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Colour blindness is associated with difficulty in perceiving red and green.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>And what about animals?</h2>
<p>Colour vision, in humans as in animals, <a href="https://www.discoverwildlife.com/animal-facts/animal-vision-how-do-animals-see/">has developed throughout evolution</a> and results from the needs of each species according to their environment, the prey they hunt and the threats they need to avoid.</p>
<p>For example, birds have a fourth opsin that allows them to see ultraviolet (UV) light. Humans cannot perceive this light because our crystalline (internal) lens <a href="https://www.nwf.org/Magazines/National-Wildlife/2012/AugSept/Animals/Bird-Vision">filters UV rays</a>. UV rays influence birds’ behavioural decisions, including foraging and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0065345408601059#:%7E:text=Publisher%20%20Summary,light%2C%20depending%20on%20the%20species.">their choice of a mate</a>.</p>
<p>So the colour vision of birds is more complex, with the result that the pigeon, which can perceive a myriad of colours, wins the <a href="https://nuscimagazine.com/the-world-through-the-eyes-of-a-pigeon/#:%7E:text=Though%20this%20range%20of%20vision,is%20one%20of%20these%20animal">award for best color vision among all species</a>.</p>
<p>Insects also perceive UV light. This function is essential for them to spot pollen, although their colour vision is very poor. Their eyes are made up of multiple lenses (ommatidia) that perceive <a href="https://www.mpg.de/14337047/how-flies-see-the-world">more movement than colour</a>. That’s much more practical while in fast flight.</p>
<p>Most forest-dwelling mammals have only two opsins. That’s because they lost the one associated with orange-red over the course of evolution. This explains why, unlike humans, these animals don’t perceive the orange bibs of hunters. </p>
<p>Snakes, on the other hand, are more sensitive to red and infrared light, thanks to their infrared receptors. This is an advantage when it comes to spotting prey, as <a href="https://phys.org/news/2006-08-snakes-vision-enables-accurate-prey.html">they can distinguish their heat even at night</a>. </p>
<p>Unsurprisingly, it’s the monkey that’s closest to the human, with its three opsins. It is said to be trichromatic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="close-up of a black dog's eyes" src="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dogs only perceive yellow-green and violet-blue. Colours are perceived as paler, like pastels.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Back to Scotch</h2>
<p>The vision of dogs — such as our friend Scotch — is <a href="https://ophtalmoveterinaire.com/maladies_oculaires/vision-comment-voit-mon-chien/#:%7E:text=For%20r%C3%A9sumer%2C%20the%20vision%20of,for%20his%20life%20of%20dog.">quite different</a>. </p>
<p>Unlike humans, dogs’ eyes are located on the side of the skull. As a result, dogs have a wider field of vision (250 to 280 degrees), but less simultaneous vision. </p>
<p>So Scotch’s vision of movement is well developed throughout his visual field. But his central vision is actually six times weaker than ours. This is equivalent to the vision of a very myopic person not wearing glasses. Why? Because the dog’s retina contains no fovea, and therefore fewer cones. </p>
<p>But while dogs eyes have fewer cones, they have more rods. And as an added bonus, they have an extra layer of the retina, called the tapetum lucidum — or carpet. When combined, these ingredients mean dogs see better in dim light and at night. This layer receives light and reflects it back onto the retina for a second exposure. This explains why your dog’s eyes seem to glow at night.</p>
<p>When it comes to colours, dogs are dichromats. They perceive only yellow-green and violet-blue. Colours are perceived paler, like pastels. And some colours don’t contrast: that’s why a red ball on green grass will appear to them as pale yellow on a grey background, with little contrast.</p>
<p>So it’s possible, depending on the colour of the ball, that Scotch will not see it, and as a result, will gaze up at Samuel with a lost look. As for the infrared, he perceives heat through his nose, not through his eyes.</p>
<p>Cats are also dichromats. Their vision is therefore similar to that of dogs, but their colour palette is different — more oriented towards violet and green. Having no perception of red-green, they are essentially colour-blind. They are also very short-sighted. Their clear vision is limited to a few meters in front of them.</p>
<p>Throughout cats’ evolution, other senses came to compensate for this. Among other things, although they only perceive certain contrasts, they are <a href="https://www.wired.com/2013/10/cats-eye-view/">formidable at perceiving movement</a>. Mice move quickly! </p>
<p>Every species adapts to its environment, and humans are no exception. Who knows what our colour vision will be like 500 years from now, after we’ve been exposed to more and more electronic devices and artificial colours? </p>
<p>But that’s a question for Samuel to answer when he’s older.</p><img src="https://counter.theconversation.com/content/212420/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>
Your faithful companion sees the world differently than you do, but it’s a mistake to assume dogs only see black, white and shades of grey.
Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de Montréal
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/207974
2023-07-05T12:23:21Z
2023-07-05T12:23:21Z
How splitting sound might lead to a new kind of quantum computer
<p>When you turn on a lamp to brighten a room, you are experiencing light energy transmitted as photons, which are small, discrete quantum packets of energy. These photons must obey the sometimes strange laws of quantum mechanics, which, for instance, dictate that photons are indivisible, but at the same time, allow a photon <a href="https://www.cambridge.org/highereducation/books/introduction-to-quantum-mechanics/990799CA07A83FC5312402AF6860311E#overview">to be in two places at once</a>. </p>
<p>Similar to the photons that make up beams of light, indivisible quantum particles <a href="https://news.mit.edu/2010/explained-phonons-0706">called phonons</a> make up a beam of sound. These particles emerge from the collective motion of quadrillions of atoms, much as a “stadium wave” in a sports arena is due to the motion of thousands of individual fans. When you listen to a song, you’re hearing a stream of these very small quantum particles.</p>
<p>Originally conceived to <a href="https://www.wiley.com/en-us/Introduction+to+Solid+State+Physics%2C+8th+Edition-p-9780471415268">explain the heat capacities of solids</a>, phonons are predicted to obey the same rules of quantum mechanics as photons. The technology to generate and detect individual phonons has, however, lagged behind that for photons. </p>
<p>That technology is only now being developed, in part by <a href="https://clelandlab.uchicago.edu/">my research group</a> at the Pritzker School of Molecular Engineering at the University of Chicago. <a href="https://scholar.google.com/citations?user=uE04v0gAAAAJ&hl=en&oi=ao">We are exploring</a> the fundamental quantum properties of sound by splitting phonons in half and entangling them together.</p>
<p>My group’s fundamental research on phonons may one day allow researchers to build a new type of quantum computer, called a mechanical quantum computer.</p>
<h2>Splitting sound with ‘bad’ mirrors</h2>
<p>To explore the quantum properties of phonons, our team uses acoustic mirrors, which can direct beams of sound. Our latest experiments, published in <a href="https://doi.org/10.1126/science.adg8715">a recent issue of Science</a>, however, involve “bad” mirrors, called beam splitters, that reflect about half the sound sent toward them and let the other half through. Our team decided to explore what happens when we direct a phonon at a beam splitter. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a line representing a beam splitter, which a phonon hits. Two dashed lines on either side of the beam splitter line demarcate that the phonon is both reflected off the beam splitter and transmitted to the other side, in superposition." src="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A beam splitter for phonons – the phonon enters a superposition state where it is both reflected and transmitted until it is detected.</span>
<span class="attribution"><span class="source">A.N. Cleland</span></span>
</figcaption>
</figure>
<p>As a phonon is indivisible; it cannot be split. Instead, after interacting with the beam splitter, the phonon ends up in what is called a “<a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">superposition state</a>.” In this state the phonon is, somewhat paradoxically, both reflected and transmitted, and you’re equally likely to detect the phonon in either state. If you intervene and detect the phonon, half the time you will measure that it was reflected and half the time that it was transmitted; in a sense, the state is <a href="https://doi.org/10.1119/1.3243279">selected at random</a> by the detector. Absent the detection process, the phonon will remain in the superposition state of being both transmitted and reflected. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UjaAxUO6-Uw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A brief Ted-Ed explainer on superposition, which happens when particles can exist in multiple places at once.</span></figcaption>
</figure>
<p>This superposition effect was observed many years ago with photons. Our results indicate that phonons have the same property. </p>
<h2>Entangled phonons</h2>
<p>After demonstrating that phonons can go into quantum superpositions just as photons do, my team asked <a href="https://doi.org/10.1126/science.adg8715">a more complex question</a>. We wanted to know what would happen if we sent two identical phonons into the beam splitter, one from each direction. </p>
<p>It turns out that each phonon will go into a similar superposition state of half-transmitted and half-reflected. But because of the physics of the beam splitter, if we time the phonons precisely, they will quantum-mechanically interfere with one another. What emerges is actually a superposition state of two phonons going one way and two phonons going the other – the two phonons are thus <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/entanglement">quantum-mechanically entangled</a>. </p>
<p>In quantum entanglement, each phonon is in a superposition of reflected and transmitted, but the two phonons are locked together. This means detecting one phonon as having been transmitted or reflected forces the other phonon to be in the same state.</p>
<p>So, if you detect, you’ll always detect two phonons, going one way or the other, never one phonon going each way. This same effect for light, the combination of superposition and interference of two photons, is called the <a href="https://doi.org/10.1103/PhysRevLett.59.2044">Hong-Ou-Mandel effect</a>, after the three physicists who first predicted and observed it in 1987. Now, my group has demonstrated this effect with sound. </p>
<h2>The future of quantum computing</h2>
<p>These results suggest that it may now be possible to build a mechanical quantum computer using phonons. There are continuing efforts to build <a href="https://news.mit.edu/2020/explained-quantum-engineering-1210">optical quantum computers</a> that require only the emission, detection and interference of single photons. These are in parallel with efforts to build electrical quantum computers, which through the use of large numbers of entangled particles promise an exponential speedup for certain problems, such as factoring large numbers or simulating quantum systems.</p>
<p>A quantum computer using phonons could be very compact and self-contained, built entirely on a chip similar to that of a laptop computer’s processor. Its small size could make it easier to implement and use, if researchers can further expand and improve phonon-based technologies.</p>
<p>My group’s <a href="https://doi.org/10.1126/science.adg8715">experiments with phonons</a> use qubits – the same technology that powers electronic quantum computers – which means that as the technology for phonons catches up, there’s the potential to integrate phonon-based computers with electronic quantum computers. Doing so could yield new, potentially unique computational abilities.</p><img src="https://counter.theconversation.com/content/207974/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew N. Cleland receives funding from various US federal funding agencies. He is a fellow of the American Physical Society (APS) and the American Association for the Advancement of Science. He is currently Past Chair of the Division of Quantum Information of the APS, and in 2023 held a Fulbright Distinguished Chair. He is a founder and a board member of Spectradyne LLC, a startup company based in Los Angeles that is commercializing electrical and optical detection of nanoparticles in fluids.</span></em></p>
Scientists show they can create quantum superpositions of sound particles, pointing to the potential for mechanical quantum computers.
Andrew N. Cleland, Professor of Molecular Engineering Innovation and Enterprise, University of Chicago Pritzker School of Molecular Engineering
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/203819
2023-05-03T12:11:10Z
2023-05-03T12:11:10Z
May 5, 2023, lunar eclipse will be a subtle show of astronomical wonder
<figure><img src="https://images.theconversation.com/files/523890/original/file-20230502-16-holf94.jpg?ixlib=rb-1.1.0&rect=7%2C32%2C2381%2C973&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Penumbral lunar eclipses slightly darken the Moon.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Penumbral_Lunar_Eclipse_2020-01-10.jpg#/media/File:Penumbral_Lunar_Eclipse_2020-01-10.jpg">H. Raab/Wikipedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>On May 5, 2023, people around the world will <a href="https://eclipse.gsfc.nasa.gov/LEdecade/LEdecade2021.html">witness a a lunar eclipse</a> when the Earth gets between the Sun and the Moon and casts part of its shadow on the Moon.</p>
<p>The eclipse will be visible in Africa, Asia, Australia and large portions of Europe, though not in the U.S. this time around. This eclipse is not what some call a “blood moon,” as it will not turn red. Instead, the Moon will dim slightly as it passes through a <a href="https://earthsky.org/astronomy-essentials/what-is-a-penumbral-eclipse-of-the-moon/">lighter part of the Earth’s shadow</a> – called the penumbra.</p>
<p>I am the <a href="https://www.abramsplanetarium.org/Staff/Index.html">director of the Abrams Planetarium</a> at Michigan State University and it is part of my job to get people outside and looking up, and eclipses are some of the easiest to see. While the upcoming event will not be the most stunning celestial display, it is just the first of a number of eclipses occurring over the next year, and they all work in similar ways.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the orientation of a lunar eclipse." src="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A lunar eclipse occurs when the Moon passes through the Earth’s shadow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Geometry_of_a_Lunar_Eclipse.svg#/media/File:Geometry_of_a_Lunar_Eclipse.svg">Sagredo/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>How do eclipses work?</h2>
<p>Both lunar and solar eclipses depend on particular orientations of the Earth, Sun and Moon. A lunar eclipse occurs when the Earth’s shadow covers all or part of the Moon. This can only happen when the Moon is directly on the opposite side of the Earth from Sun, which is also when full moons occur.</p>
<p>Like the Earth, half of the Moon is illuminated by the Sun at any one time. When the Moon and the Sun are perfectly opposite each other, people on Earth can see the entire lit-up side, which looks like a round disc in the night sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing how orientations of the Moon correspond to phases of the Moon." src="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=183&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=183&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=183&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=230&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=230&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=230&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lunar eclipses can only occur during a full moon when the Moon is opposite the Sun.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Fases_lunars.png#/media/File:Moon_phases_en.jpg">Orion 8/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>If the Moon had a totally flat orbit, every full moon would be a lunar eclipse. But the Moon’s orbit is tilted by about 5 degrees relative to Earth’s orbit of the Sun. Because of this small tilt, most of the time a full moon ends up a little above or below the shadow cast by the Earth.</p>
<p>But twice in each monthlong lunar orbit, the Moon crosses through the same horizontal plane as the Earth and the Sun. If this happens during a full moon, the Sun, Earth and Moon will form a straight line and the Moon will pass through the Earth’s shadow, resulting in a lunar eclipse.</p>
<h2>The Earth’s shadow</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A circular shadow on a wall with a dark center and lighter ring around it." src="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The shadow on the wall has a darker center surrounded by a lighter, but still shadowed, outer ring, just like the shadow cast by Earth.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Shadow_Blister_Effect.png#/media/File:Shadow_Blister_Effect.png">User4288/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>As the Sun shines light on Earth, Earth casts a shadow behind itself. But the darkness of shadows are not always uniform, and the shadow cast by the Earth is no exception. </p>
<p>The rays of light coming from a wide, or extended, light source – such as the Sun or a flashlight – don’t all come from the exact same location. Since the Sun is large, there can be quite a distance between the origin of rays of light heading toward Earth. </p>
<p>This difference in location means that when Earth blocks the light coming from one part of the Sun, it might not block out light coming from another location on the Sun. This results in <a href="http://www.differencebetween.net/science/difference-between-penumbra-and-umbra/">parts of Earth’s shadow that are darker</a> – the darkest part is where all light is blocked, while the lighter parts are because some light still makes it past the Earth.</p>
<p>A total lunar eclipse is when the Moon passes entirely through the darkest part, or umbra, of the Earth’s shadow. A partial lunar eclipse is when the umbra covers part of the Moon. The eclipse on May 5, 2023, is the last kind of eclipse where only the lighter part of the shadow will cover the Moon, which is why it is known as a penumbral lunar eclipse.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map showing regions of Earth where people can see the lunar eclipse." src="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The lunar eclipse on May 5, 2023, will be visible for most of Africa, Asia, Europe and Australia.</span>
<span class="attribution"><a class="source" href="https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2023May05N.pdf">NASA</a></span>
</figcaption>
</figure>
<h2>How can you see the lunar eclipse?</h2>
<p>As long as you are on the night side of the Earth when a lunar eclipse happens, you can see it. The May 5 penumbral eclipse will be visible in most of Europe and Africa at moonrise, Asia and Australia will be able to see the entirety of the event in the middle of the night, and locations throughout the Pacific Ocean will be able to see it at moonset. </p>
<p>Lunar eclipses are relatively short, only lasting a few hours from start to finish. Totality, the part of the eclipse that is darkest, lasts about 30 to 60 minutes depending on how close to the center of the shadow you are. </p>
<p>For people in North and South America where the eclipse won’t be visible, there will be <a href="https://eclipse.gsfc.nasa.gov/LEdecade/LEdecade2021.html">plenty more in the next few years</a>. The next lunar eclipse will be Oct. 28, 2023, and will be a partial eclipse visible primarily in Africa, Europe and Asia. But the Americas will have their own penumbral eclipse on March 25, 2024, followed by a partial lunar eclipse on Sep. 18, 2024. </p>
<p>For those hoping to catch the next total lunar eclipse, they will have to wait until March 14, 2025, when a total lunar eclipse will be visible from the Americas, western Europe and western Africa.</p><img src="https://counter.theconversation.com/content/203819/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Not all lunar eclipses are alike. An astronomer explains the science behind the slight dimming of the Moon on May 5, 2023.
Shannon Schmoll, Director of the Abrams Planetarium, Michigan State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/204618
2023-04-27T05:14:11Z
2023-04-27T05:14:11Z
New nanoparticle source generates high-frequency light
<figure><img src="https://images.theconversation.com/files/523123/original/file-20230427-26-fls8hc.jpeg?ixlib=rb-1.1.0&rect=8%2C0%2C5982%2C3997&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>High-frequency light is useful. The higher the frequency of light, the shorter its wavelength – and the shorter the wavelength, the smaller the objects and details the light can be used to see.</p>
<p>So violet light can show you smaller details than red light, for example, because it has a shorter wavelength. But to see really, really small things – down to the scale of billionths of a metre, thousands of times less than the width of a human hair – to see those things, you need <em>extreme ultraviolet light</em> (and a good microscope).</p>
<p>Extreme ultraviolet light, with wavelengths between 10 and 120 nanometres, has many applications in medical imaging, studying biological objects, and deciphering the fine details of computer chips during their manufacture. However, producing small and affordable sources of this light has been very challenging.</p>
<p>We have found a way to make nanoparticles of a common semiconductor material emit light with a frequency up to seven times higher than the frequency of light sent to it. We generated blue-violet light from infrared light, and it will be possible to generate extreme ultraviolet light from red light with the same principles. Our research, carried out with colleagues from the University of Brescia, the University of Arizona and Korea University, is <a href="https://www.science.org/doi/10.1126/sciadv.adg2655">published in Science Advances</a>.</p>
<h2>The power of harmonics</h2>
<p>Our system starts out with an ordinary laser that produces long-wavelength infrared light. This is called the pump laser, and there’s nothing special about it – such lasers are commercially available, and they can be compact and affordable.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram illustrating the setup of the light-emitting system" src="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=637&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=637&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=637&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Incoming laser light hitting a nanoparticle which then emits higher frequency light.</span>
<span class="attribution"><span class="source">Zalogina et al. / Science Advances</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But next we fire short pulses of light from this laser at a specially engineered nanoparticle of a material called aluminium gallium arsenide, and that’s where things get interesting.</p>
<p>The nanoparticle absorbs energy from the laser pulses, and then emits its own burst of light. By carefully engineering the size and shape of the nanoparticle, we can create powerful resonances to amplify certain harmonics of the emitted light.</p>
<p>What does that mean, exactly? Well, we can make a useful analogy with sound.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the first seven harmonics of a guitar string." src="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=666&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=666&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=666&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=837&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=837&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=837&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Harmonics in a guitar string: in the fundamental frequency, the wavelength is the length of the whole string, but in the higher harmonics multiple shorter wavelengths fit within the length of the string.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Harmonic">Wikimedia / Y Landman</a></span>
</figcaption>
</figure>
<p>When you pluck a string on a guitar, it vibrates with what’s called its <em>fundamental frequency</em> – which makes the main note you hear – plus small amounts of higher frequencies called harmonics, which are multiples of the fundamental frequency. The body of the guitar is designed to produce resonances that amplify some of these harmonics and dampen others, creating the overall sound you hear.</p>
<p>Both light and sound share similarities in their physics – these are both propagating waves (acoustic waves in the case of sound, and electromagnetic waves in the case of light).</p>
<figure class="align-center ">
<img alt="A close up of a hand strumming an acoustic guitar" src="https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Just as the body of a guitar dampens some frequencies and amplifies others, carefully designed nanoparticles can boost high-frequency harmonics of laser light.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>In our light source, the pump laser is like the main note of the string, and the nanoparticles are like the guitar body. Except what’s special about the nanoparticles is that they massively amplify those higher harmonics of the pump laser, producing light with a higher frequency (up to seven times higher in our case, and a wavelength correspondingly seven times shorter).</p>
<h2>What it’s good for</h2>
<p>This technology allows us to create new sources of light in parts of the electromagnetic spectrum such as the extreme ultraviolet, where there are no natural sources of light and where current engineered sources are too large or too expensive.</p>
<p>Conventional microscopes using visible light can only study objects down to a size of about a ten-millionth of a metre. The resolution is limited by the wavelength of light: violet light has the wavelength of about 400 nanometres (one nanometre is one billionth of a metre). </p>
<p>But there are plenty of applications, such as biological imaging and electronics manufacturing, where being able to see down to a billionth of a metre or so would be a huge help.</p>
<p>At present, to see at those scales you need “super-resolution” microscopy, which lets you see details smaller than the wavelength of the light you are using, or electron microscopes, which do not use light at all and create image using a flux of electrons. However, such methods are quite slow and expensive.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-quantum-hack-for-microscopes-can-reveal-the-undiscovered-details-of-life-161182">A quantum hack for microscopes can reveal the undiscovered details of life</a>
</strong>
</em>
</p>
<hr>
<p>To understand the advantages of a light source like ours, consider computer chips: they are made of very tiny components with feature sizes almost as small as a billionth of a metre. During the production process, it would be useful for manufacturers to use extreme ultraviolet light to monitor the process in real time.</p>
<p>This would save resources and time on bad batches of chips. The scale of the industry is such that even a 1% increase in chip yields could save billions of dollars each year. </p>
<p>In future, nanoparticles like ours could be used to produce tiny, inexpensive sources of extreme ultraviolet light, illuminating the world of extremely small things.</p><img src="https://counter.theconversation.com/content/204618/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sergey Kruk receives funding from the Australian Research Council (DE210100679). </span></em></p><p class="fine-print"><em><span>Anastasiia Zalogina does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
A new way to make high-frequency light could make it easier to look at things 10 times smaller than conventional microscopes can see.
Anastasiia Zalogina, Postdoctoral researcher, Australian National University
Sergey Kruk, ARC DECRA Fellow, Research School of Physics, Australian National University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/202952
2023-04-24T12:24:51Z
2023-04-24T12:24:51Z
Can rainbows form in a circle? Fun facts on the physics of rainbows
<figure><img src="https://images.theconversation.com/files/521644/original/file-20230418-20-88ojk7.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C8959%2C5547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The higher your vantage point, the more likely you’ll see more of the rainbow’s circle. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/double-rainbow-hangs-in-the-sky-above-buildings-and-the-news-photo/1405823752">Chen Hui/VCG via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Can rainbows form in a circle? – Henry D., age 7, Cambridge, Massachusetts</strong></p>
</blockquote>
<hr>
<p>The legend goes that there is a pot of gold hidden at the end of every rainbow. But is there really an “end” to a rainbow, and can we ever get to it?</p>
<p>Most us go through life seeing rainbows only as arches of color in the sky, but that’s only half of what is really a circle of color.</p>
<p>Normally, when you look at a rainbow, the Earth’s horizon in front of you hides the bottom half of the circle. But if you are standing on a mountain where you can see both above and below you, and the sun is behind you and it is misty or has just rained, chances are good that you will see more of the rainbow’s circle.</p>
<figure class="align-center ">
<img alt="A rainbow in the mist below a waterfall in Iceland." src="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&rect=0%2C52%2C5000%2C3270&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How full this rainbow looks depends in part on how high up you’re standing while watching sunlight hit the waterfall’s mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/iceland-south-coast-skogarfoss-waterfall-rainbow-news-photo/452271798">Wolfgang Kaehler/LightRocket via Getty Images</a></span>
</figcaption>
</figure>
<p>To see the full circle, however, you will have to be in an airplane, literally above the clouds. Or you could create your own rainbow. I am <a href="https://www.uml.edu/Honors/People/chowdhury-partha.aspx">a physicist</a>, and I’ll explain how to do that in a minute.</p>
<h2>How a rainbow forms</h2>
<p><a href="https://scijinks.gov/rainbow/">Rainbows form</a> when sunlight from behind you hits millions of tiny round water droplets in front of you and bounces back to your eyes.</p>
<p>As a sunbeam hits a droplet at an angle, it bends into the water and separates out into a spectrum of colors. Scientists <a href="https://global.canon/en/technology/s_labo/light/001/02.html">call the bending of light “refracting</a>.” The colors separate because each “color” of light <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/rainbows/colours-of-the-rainbow">travels with a different speed</a> in water, or, for that matter, any transparent material that light can travel through, like glass in a prism.</p>
<p>When the colors hit the back wall of the water droplet, the angle is now too shallow for them to bend out into the air, so they reflect back into the water droplet and return to its entrance wall. From there, the colors can bend out again into air and reach your eye.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/q73VNpFA-0Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The United Kingdom’s Meteorology Office explains how light refracts, or bends, in a water droplet or a prism.</span></figcaption>
</figure>
<p>As you look at these droplets, the different colors happen to bunch up at a slightly different angle, and each color forms the <a href="https://atoptics.co.uk/rainbows/primcone.htm">circular rim of a cone</a> with your eye at the tip of the cone. And, voila, you have your own personal rainbow.</p>
<p>The droplets that send the colors to your eye cannot send them to anyone else, so even though everyone near you sees the same rainbow at a distance, each person really sees their own slightly different rainbow. It’s all in the eye of the beholder.</p>
<p>For rainbows to form, the shape of the water droplets has to be very close to a sphere for all of them to bend and reflect the colors in harmony. This happens for very small droplets, such as a fine mist, or just after a rain shower when the air is just moist. As the droplets get larger, gravity distorts their shape and the rainbow vanishes.</p>
<figure class="align-center ">
<img alt="An elephant in water closes its eyes while the photographer captures a rainbow across its trunk and forehead." src="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Even though it looks like this elephant is bathing in a rainbow, the elephant wouldn’t see it in the same way.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/an-elephant-is-pictured-under-a-rainbow-of-water-sprayed-to-news-photo/1242012110">Mads Claus Rasmussen / Ritzau Scanpix / AFP</a></span>
</figcaption>
</figure>
<p>A rainbow is not physically present where it appears to be, similar to your image in a mirror. So, I’m sorry to say that you can never actually reach your rainbow. And, alas, nobody can ever find that pot of gold.</p>
<p>But you can <a href="https://www.youtube.com/watch?v=dIdE-pqYqbs">create your own rainbow</a>. </p>
<h2>How to create and see a circular rainbow</h2>
<p>One experiment you can try in summer is to turn on a sprinkler hose using the “mist” setting. Remember to have the sun behind you. If you create a fine mist screen in front of you and look at your shadow, you might see a rainbow. </p>
<figure class="align-center ">
<img alt="A young boy plays in a fountain, with a rainbow overhead." src="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It might take some work, but you can see your own full-circle rainbows in the mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/young-boy-cools-off-under-a-rainbow-in-a-fountain-on-a-warm-news-photo/1266045824">Gary Hershorn/Getty Images</a></span>
</figcaption>
</figure>
<p>It is not difficult to see colors, but to see a full circle, you will need some patience and practice, just like scientists.</p>
<p>So next time you are on an airplane, grab the window seat. If you are flying a little above the cloud cover, keep a lookout for the small shadow of your plane on the clouds. That means the sun is behind you. </p>
<p>The clouds are tiny water droplets, so chances are you may see a small circle of color around the shadow of the airplane. This phenomenon is <a href="https://science.howstuffworks.com/nature/climate-weather/atmospheric/pilots-glory-rainbow-airplane-shadow.htm">nicknamed “pilot’s glory</a>,” because pilots who fly all the time and have a good view from the cockpit have a better chance of seeing it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An airplane's shadow has a circular rainbow around it as it flies over mountains." src="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The circular rainbow you see around an airplane’s shadow is called ‘pilot’s glory.’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/imatty35/6708114761/">Matthew Straubmuller/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>And if you really can’t wait to see what it looks like, there’s <a href="https://education.nationalgeographic.org/resource/rainbow/">always the internet</a>.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/202952/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Partha Chowdhury does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Each rainbow is personal – the rainbow you see isn’t exactly the same rainbow the next person sees. It’s all in the eye of the beholder.
Partha Chowdhury, Professor of Physics, UMass Lowell
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/203382
2023-04-07T15:56:02Z
2023-04-07T15:56:02Z
On April 8, 2024, parts of Ontario, Québec, the Maritimes and Newfoundland will see a total eclipse of the sun. Here’s how to get ready for it.
<figure><img src="https://images.theconversation.com/files/519687/original/file-20230405-22-8wx57z.jpg?ixlib=rb-1.1.0&rect=25%2C11%2C1862%2C1212&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Watching a solar eclipse is always fascinating. During the phase when the moon completely obstructs the sun, daylight gives way to a deep twilight sky.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>You might not know exactly what you will be doing a year from now, on April 8, 2024. It’s pretty hard to predict a year in advance. However, on that date, <a href="https://solarsystem.nasa.gov/eclipses/2024/apr-8-total/where-when/">a total solar eclipse will occur in parts of Mexico, the United States and Canada — including parts of southern Ontario and Québec, New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland</a> — a rare phenomenon. </p>
<p>The total solar eclipse will be visible in locations including: Niagara Falls and Hamilton, Ont.; Montréal; Fredericton, N.B.; western P.E.I.; the northern tip of Cape Breton, N.S.; and Gander, Nfld.</p>
<p>Cities like Toronto and Ottawa will be just beyond the path of the total solar eclipse. </p>
<p>While partial solar eclipses happen quite frequently, the total disappearance of the sun behind the moon only occurs <a href="https://espacepourlavie.ca/en/total-or-annular-solar-eclipse">when the moon is closer to our planet or the sun is at its furthest point from it</a>. It is a question of the size of the moon compared to the sun. When the two are perfectly aligned, it creates a shadow cone that allows people on Earth who are within this narrow band to enjoy the unique spectacle of a total eclipse. </p>
<p>On average, this alignment only occurs <a href="https://espacepourlavie.ca/en/frequency-solar-eclipses">once every 375 years</a>, but it can vary. For example, the last total eclipse visible in Montréal occurred on Aug. 31, 1932. Other regions in Canada have not been as lucky. In St. John’s, Nfld., the last total eclipse was on Feb. 3, 1440, and locals will have to wait a total of 765 years for the next one, which will happen on July 17, 2205! The record belongs to Regina, Sask., which had a total eclipse in 54 BC, but will not see another one until Oct. 17, 2153 — or a total of 2207 years! </p>
<p>So try not to miss the total eclipse in places like Montréal in 2024. If you do, you’ll have to go to a location like <a href="https://espacepourlavie.ca/en/frequency-solar-eclipses">Calgary for the next one, in 20 years</a>. </p>
<p>Yet the phenomenon does pose significant risks to eye health. As an optometrist, I am very concerned about eye health issues. I certainly wouldn’t want anyone to go blind after watching a solar eclipse without properly protecting their eyes.</p>
<h2>Watch it, but protect yourself</h2>
<p>Watching a total solar eclipse is always fascinating. During the phase when the moon completely obstructs the sun, daylight is transformed into a deep twilight sky. The sun’s outer atmosphere (known as the sun’s corona) gradually appears, <a href="https://solarsystem.nasa.gov/eclipses/2024/apr-8-total/overview/">shining like a halo around the moon</a>. The bright stars and planets become more visible in the sky.</p>
<p>In daylight, the sun usually emits visible light that is so intense we cannot look directly at it for very long. If our eye ever looks directly at the sun, we have the reflex of turning away from it immediately, after <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging">an average of only 0.25 seconds</a>. This reflex provides natural protection for eyes against the harmful rays of the sun, some of which — notably ultraviolet and infrared radiation — are not visible. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="total solar eclipse" src="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During a total solar eclipse, the sun’s outer atmosphere (called the solar corona) gradually appears, shining like a halo around the moon that faces it.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Ultraviolet radiation (UV)</h2>
<p>UVs accounts for <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging.">seven per cent of solar radiation</a>. They are partly absorbed by the cornea (the clear part at the front of the eye) and the crystalline lens (the natural lens inside the eye), without causing any damage, unless the exposure is too great. </p>
<p>In such cases, depending on the amount of UV radiation it absorbs, the cornea may develop inflammation, known as keratitis. The lens, in turn, loses its transparency — this is called a cataract. Other impacts can be expected, such as the development of <a href="https://www.nei.nih.gov/about/news-and-events/news/protecting-your-eyes-suns-uv-light#:%7E:text=Prolonged%20exposure%20to%20UV%20rays,are%20linked%20to%20UV%20exposure">small cysts (pinguecula) on the conjunctiva (white of the eye) or a membrane invading the cornea (pterygium)</a>.</p>
<p>Eyelids can also develop skin cancers. The upper eyelid, which is usually not exposed on the outside when our eyes are open, is particularly at risk when we lie on the beach with our eyes closed without protection. Finally, UV light predisposes us to <a href="https://theconversation.com/macular-degeneration-is-a-leading-cause-of-blindness-heres-how-to-prevent-it-160683">macular degeneration</a>, which is a damage to our best retinal cells and can result in varying degrees of vision loss.</p>
<p>These <a href="https://www.aao.org/eye-health/tips-prevention/sun">diseases</a> all develop as a result of direct radiation, but can also come about when the sun’s rays are strongly reflected by surfaces such as snow (snow ophthalmia), sand or water. It is therefore recommended to wear protective eyewear that cuts out all UV rays (UV400 protection) when you plan to spend more than a few minutes in the sun. For both <a href="https://theconversation.com/summer-is-here-why-you-need-to-protect-your-childrens-eyes-116498">children</a> and adults, the frame should wrap around the eyes, so that no rays pass through the side or top.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="child wears sunglasses at the beach" src="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">For both children and adults, the frame of sunglasses should wrap around the eyes, so that no rays pass through from the side or top.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Infrared radiation (IR)</h2>
<p>IRs make up the majority of the radiation emitted by the sun — <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging">54 per cent</a>. We feel the effects because it is thermal radiation, which is accompanied by heat. </p>
<p>While the cornea (burning) and lens (cataract) can also be affected by IR, it is more the retina that can suffer from inappropriate exposure to IR. Again, it is a question of intensity and duration. As with UV radiation, the more intense the radiation, the more permanent damage will occur in a short period of time.</p>
<p>IR damage to the retina destroys the cells that allow us to see and ultimately creates a scotoma, a permanent black spot in our field of vision. This is a cause of blindness. </p>
<h2>Eclipse and radiation</h2>
<p>When the Sun is only partially hidden (partial eclipse), the UV and IR radiation is as important as in full sunlight. However, because of the reduced luminosity, we no longer have the natural reflex of turning our eyes away. So it may seem more comfortable to observe the sun for several seconds or even minutes. Without protection, this type of exposure can lead to the pathologies described above and contribute to blindness if the central retina is affected. <a href="https://www.theguardian.com/us-news/video/2017/aug/21/donald-trump-look-directly-sun-eclipse-video">U.S. President Donald Trump was reminded of this in 2017</a>, when he watched a partial eclipse without protection, putting his vision at risk. </p>
<p>During a total eclipse, however, it is possible, during the short duration of the total obstruction of the sun (one minute 37 seconds), to <a href="https://www.nasa.gov/content/eye-safety-during-a-total-solar-eclipse/#:%7E:text=During%20the%20short%20time%20when,put%20back%20on%20your%20glasses.">look at the solar corona without protection</a>. But you must be very vigilant and remember to put protection back in place as soon as the Moon starts to move and the radiation becomes present again, even though the ambient luminosity is still reduced. </p>
<p>The same precautions should be taken when viewing the eclipse directly through binoculars, a telescope, a camera or other optical means. For example, do not look at your phone screen with the naked eye when trying to take pictures of the eclipse. The rays are not blocked by these instruments and can cause significant eye damage. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Trump points at the sun" src="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">President Donald Trump points at the sun without protective glasses during the partial solar eclipse on Aug. 21, 2017, at the White House in Washington, D.C.</span>
<span class="attribution"><span class="source">(AP Photo/Andrew Harnik)</span></span>
</figcaption>
</figure>
<h2>A question of protection</h2>
<p>So, what kind of eye protection are we talking about exactly? Sunscreens that can be mounted in glasses or in temporary glasses, made of cardboard, but that cover the entire surface of the eye perfectly. Once again, it is important to avoid leaving a gap between the eye and the protective screen through which harmful radiation can enter. Permitted filters <a href="https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety">must meet ISO-12312-2</a>.</p>
<p>Before wearing such filters, be sure to follow the instructions provided with the equipment. It is very important for parents to ensure that children wear the filters properly and do not play with them. When the observation is over, do not remove the filters while you are still looking at the sun: look away, turn your back to the sun and remove the filters. Then don’t look at the sky anymore. </p>
<h2>If ever…</h2>
<p>Damage to the cornea and retina can occur within hours of exposure, but not always immediately. If you have ever been inadvertently or recklessly exposed, monitor your vision in the hours after the eclipse. If you notice any blurring or changes in your vision, you should consult an optometrist or ophthalmologist as soon as possible. </p>
<p>Many activities will be organized for the arrival of the total eclipse. To make the most of this unique event, watch for announcements from organizations such as <a href="https://espacepourlavie.ca/en">Space for Life</a>, institutions such as the Université de Montréal, or your local astronomy clubs. These organizations will provide information, may provide protective glasses/filters and, most importantly, will help you to better understand the phenomenon. </p>
<p>See you in a year’s time! But in the meantime, whether young and old, let’s all protect our eyes properly.</p><img src="https://counter.theconversation.com/content/203382/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>
Some parts of North America will witness a total solar eclipse in April 2024. This may seem far away, but you should think about preparing for this rare and fascinating phenomenon.
Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de Montréal
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/203060
2023-04-04T00:57:42Z
2023-04-04T00:57:42Z
Famous double-slit experiment recreated in fourth dimension by physicists
<figure><img src="https://images.theconversation.com/files/519143/original/file-20230403-14-9ynrlj.jpeg?ixlib=rb-1.1.0&rect=897%2C997%2C3569%2C2123&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Tobias Carlsson / Unsplash</span></span></figcaption></figure><p>More than 200 years ago, the English scientist Thomas Young carried out a famous test known as the “<a href="https://royalsocietypublishing.org/doi/10.1098/rstl.1804.0001">double-slit experiment</a>”. He shone a beam of light at a screen with two slits in it, and observed the light that passed through the apertures formed a pattern of dark and bright bands.</p>
<p>At the time, the experiment was understood to demonstrate that light was a wave. The “interference pattern” is caused by light waves passing through both slits and interfering with each other on the other side, producing bright bands where the peaks of the two waves line up and dark bands where a peak meets a trough and the two cancel out.</p>
<p>In the 20th century, physicists realised the experiment could be adapted to demonstrate that light not only behaves like a wave, but also like a particle (called a photon). In quantum mechanical theory, this particle still has wave properties – so the wave associated with even a single photon passes through both slits, and creates interference.</p>
<p>In a new twist on the classic experiment, we replaced the slits in the screen with “slits” in time – and discovered a new kind of interference pattern. Our results are <a href="https://www.nature.com/articles/s41567-023-01993-w">published today</a> in Nature Physics.</p>
<h2>Slits in time</h2>
<p>Our team, led by Riccardo Sapienza at Imperial College London, fired light through a material that changes its properties in femtoseconds (quadrillionths of a second), only allowing light to pass through at specific times in quick succession. </p>
<p>We still saw interference patterns – but instead of showing up as bands of bright and dark, they showed up as changes in the frequency or colour of the beams of light.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-light-a-wave-or-a-particle-162514">Curious Kids: is light a wave or a particle?</a>
</strong>
</em>
</p>
<hr>
<p>To carry out our experiment, we devised a way to switch on and off the reflectivity of a screen incredibly quickly. We had a transparent screen that became a mirror for two brief instants, creating the equivalent of two slits in time. </p>
<h2>Colour interference</h2>
<p>So what do these slits in time do to light? If we think of light as a particle, a photon sent at this screen might be reflected by the first increase of reflectivity or by the second, and reach a detector.</p>
<p>However, the wave nature of the process means the photon is in a sense reflected by both temporal slits. This creates interference, and a varying pattern of colour in the light that reaches the detector. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-wave-particle-duality-7414">Explainer: what is wave-particle duality</a>
</strong>
</em>
</p>
<hr>
<p>The amount of change in colour is related to how fast the mirror changes its reflectivity. These changes must be on timescales comparable with the length of a single cycle of a light-wave, which is measured in femtoseconds.</p>
<p>Electronic devices cannot function quickly enough for this. So we had to use light to switch on and off the reflectivity of our screen. </p>
<p>We took a screen of indium tin oxide, a transparent material used in mobile phone screens, and made it reflective with a brief pulse of laser light.</p>
<h2>From space to time</h2>
<p>Our experiment is a beautiful demonstration of wave physics, and also shows how we can transfer concepts such as interference from the domain of space to the domain of time.</p>
<p>The experiment has also helped us in understanding materials that can minutely control the behaviour of light in space and time. This will have applications in signal processing and perhaps even light-powered computers.</p><img src="https://counter.theconversation.com/content/203060/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stefan Maier does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
In an update of one of the most famous experiments in physics, scientists have used ‘slits in time’ to explore the properties of light and ultrafast optical materials.
Stefan Maier, Head of School of Physics and Astronomy, Monash University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/199013
2023-02-01T16:07:35Z
2023-02-01T16:07:35Z
The true relationship between screens, books and nearsightedness
<figure><img src="https://images.theconversation.com/files/507539/original/file-20230201-11-q2h3vk.jpg?ixlib=rb-1.1.0&rect=22%2C0%2C2474%2C1666&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/es/image-photo/kids-reading-book-under-blanket-elder-1071593237">Shutterstock / EvgeniiAnd</a></span></figcaption></figure><p>At one time or another we have surely heard or read that the excessive use of screens is causing an increase in cases of nearsightedness. Moreover, it is said that this relationship is direct, meaning that screens are responsible for the fact that more and more people around the world are nearsighted. Not surprisingly, there are also studies that conclude that <a href="https://www.nature.com/articles/519276a">children who spend more time in front of books or screens develop more nearsightedness than those who do not</a>.</p>
<p>And not only that. We have always assumed that nearsightedness and the use of glasses is directly related to performing tasks that require a special visual effort. Or to very studious people, or to avid life-long book readers.</p>
<p>Since we have recently replaced many of these tasks that involved reading paper with electronic screens, we have shifted the responsibility from one culprit to another.</p>
<p>However, this long-assumed direct relationship has not been scientifically proven. Although it is considered to be true because of the correlation/causation hypothesis, it is important to be careful with these parallels, since correlation does not always imply causation.</p>
<p>Tyler Vigen, a Harvard lawyer, does an excellent job of explaining this. On his website <a href="https://www.tylervigen.com/spurious-correlations">Spurious Correlations</a>, he has been carrying out a statistical experiment with arbitrary data obtained from different sources for years – data that when overlapped on graphs generates some of the most far-fetched correlations. For example, it can be deduced from the data that between 2000 and 2009 there was a correlation between the increase in per capita cheese consumption and deaths caused by becoming entangled in bedsheets. Sounds absurd, right?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=237&fit=crop&dpr=1 600w, https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=237&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=237&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=297&fit=crop&dpr=1 754w, https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=297&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/437541/original/file-20211214-13-sf4m87.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=297&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Correlation between per capita cheese consumption and deaths by becoming entangled in bedsheets.</span>
<span class="attribution"><a class="source" href="https://www.tylervigen.com/spurious-correlations">Tyler Vigen / Spurious Correlations</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>What is certain is that the increase in cases of nearsightedness is real and cannot be entirely explained by genetic factors. Therefore, it is necessary to look at environmental factors.</p>
<h2>Accomplices – but not the main culprit</h2>
<p>Are screens – or rather their excessive use – the cause of nearsightedness? The latest studies suggest that they are not directly responsible.</p>
<p>Nearsightedness, which is the difficulty focusing on distant objects, occurs when the eyeball is too long relative to the focusing power of the eye’s cornea and lens. This causes light rays to be directed to a point before the retina.</p>
<p>We are also nearsighted when the cornea, the lens or both are too curved for the length of our eyeball. In some cases, <a href="https://www.mayoclinic.org/diseases-conditions/nearsightedness/symptoms-causes/syc-20375556">all of these factors occur simultaneously</a>.</p>
<p>These anomalies are corrected with lenses that transmit light information to the back of our eye.</p>
<p>The process by which an eye develops nearsightedness is not entirely known, but we do know that for our vision to develop correctly we need to promote and <a href="https://iovs.arvojournals.org/article.aspx?articleid=2772538">practice both near and distance vision</a>.</p>
<p>In this sense, it seems logical to suspect that ongoing exposure to screens from an early age at a time when the eye is still maturing may favour the development of vision of near objects, to the detriment of distance vision. However, there is not enough data to conclude that this causes nearsightedness to occur.</p>
<h2>Eye fatigue</h2>
<p>No one disputes that <a href="https://pubmed.ncbi.nlm.nih.gov/30663136/">excessive use of screens</a> causes “eye fatigue”, also known as “computer syndrome”, which causes redness, stinging and itchy eyes, dry eyes (or conversely, constant tearing), headache, etc. This occurs because when we look at a screen, we blink less (unconsciously), we stare at a specific point for a long time or from an inappropriate angle and we expose ourselves to the excessive brightness of these devices.</p>
<p>What can we do to fight it? Don’t bother <a href="https://onlinelibrary.wiley.com/doi/10.1111/opo.12738">with blue light filters</a> – which are unfairly blamed. The best recommendation to reduce the signs of eye fatigue is to blink frequently and take breaks <a href="https://www.optometrytimes.com/view/deconstructing-20-20-20-rule-digital-eye-strain">following the 20/20/20 rule</a>. In other words, every 20 minutes, take a 20-second break and look at (and try to focus on) an object 20 feet (6 metres) away.</p>
<p>If you look through a window and with light, even better. Why with light? Because it is suspected that one of the possible culprits for the development of nearsightedness is a lack of light.</p>
<h2>Lack of light</h2>
<p>Indeed, it has been proven that children who read a lot, whether on paper or on a digital screen are generally <a href="https://pubmed.ncbi.nlm.nih.gov/26497977/">less exposed to sunlight during the day</a>. And, it has recently been <a href="https://iovs.arvojournals.org/article.aspx?articleid=246623">demonstrated</a> that there is a relationship between nearsightedness and a lack of sunlight.</p>
<p>It seems that solar radiation (especially high-energy radiation, such as blue and <a href="https://pubmed.ncbi.nlm.nih.gov/28063778/">violet light</a>) would stimulate <a href="https://www.pnas.org/content/118/22/e2018840118">dopamine release by retinal amacrine cells</a> (another type of cell other than photoreceptors). This would inhibit the growth of the eye, avoiding the typical elongation that leads to nearsightedness.</p>
<p>There is also experimental evidence that shows that in different animal species, including monkeys, exposure to high-energy violet light could <a href="https://pubmed.ncbi.nlm.nih.gov/22169102/">protect against nearsightedness</a>.</p>
<p>In short, all signs point to the fact that neither books nor electronic devices are directly to blame for the increase in nearsightedness around the world. They have only become accomplices in this phenomenon by keeping children away from sunlight.</p>
<hr>
<p><em>500,000+ people get our newsletters. Join them, <a href="https://memberservices.theconversation.com/newsletters/?region=europe&nl=europe">subscribe now</a>.</em></p>
<hr><img src="https://counter.theconversation.com/content/199013/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Conchi Lillo no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.</span></em></p>
Evidence suggests that neither books nor electronic devices are directly to blame for the increase in myopia worldwide. Rather, they enhance this phenomenon by keeping children out of the sunlight.
Conchi Lillo, Profesora titular de la Facultad de Biología, investigadora de patologías visuales, Universidad de Salamanca
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/195470
2022-12-23T07:42:07Z
2022-12-23T07:42:07Z
Curious Kids: why doesn’t the rainbow have black, brown and grey in it?
<figure><img src="https://images.theconversation.com/files/500707/original/file-20221213-16072-576dx.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C5393%2C3595&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/asian-little-girl-painting-colorful-rainbow-1901905942">SUKJAI PHOTO/Shutterstock</a></span></figcaption></figure><p><strong>Why doesn’t the rainbow have colours like black, brown and grey in it? – Ivy, aged four, Kent, UK</strong></p>
<p>Many of us have seen rainbows in the sky once the sun starts shining again after a spell of rain. For us to see a rainbow, the conditions need to be just right. </p>
<p>We need some water droplets in the air – like rain or even fog – and we need the Sun to be behind us and quite low to the ground. This is because a <a href="https://www.bbc.co.uk/bitesize/topics/z6hv9j6/articles/zxh9cmn">rainbow is created</a> by light passing through water droplets. </p>
<hr>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series by <a href="https://theconversation.com/uk">The Conversation</a> that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskids@theconversation.com">curiouskids@theconversation.com</a> and make sure you include the asker’s first name, age and town or city. We won’t be able to answer every question, but we’ll do our very best.</em></p>
<hr>
<p>The light that comes from the sun seems white to us. But the white light we see in everyday life is actually made up of a mix of different colours. When the light goes through a raindrop, these colours can separate out. </p>
<h2>Waves of light</h2>
<p>You wouldn’t know it to look at it, but light travels in waves, like waves moving across the ocean. Each of the colours in the rainbow have what we call a different “wavelength”. </p>
<p>This means that the distance between the tops of the wave is a different length for each colour. The colours, from violet with the shortest wavelength to red with the longest, are called the “<a href="https://www.sciencelearn.org.nz/resources/47-colours-of-light">visible spectrum</a>”.</p>
<p>Raindrops look more like little balls than the teardrop shapes we often draw. When light hits one one of these little balls of water, the light can change direction. We call this “refraction”. </p>
<p>Each of the different wavelengths is refracted by a slightly different amount. If the light hits the raindrop at the right angle, the refraction separates the wavelengths out into their different colours. As lots of light is refracted through lots of raindrops, we see these colours as a rainbow in the sky. The order the colours come in is set by how long their wavelength is.</p>
<figure class="align-center ">
<img alt="Diagram of light refracting when it travels through a raindrop." src="https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=453&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=453&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=453&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=570&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=570&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499002/original/file-20221205-17-muyp18.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=570&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Light travelling through a raindrop.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/rainbow-raindrop-refracts-reflects-light-440189362">Fouad A. Saad/Shutterstock</a></span>
</figcaption>
</figure>
<p>When we learn about the rainbow, we are taught that there are seven colours: red, orange, yellow, green, blue, indigo and violet. But this isn’t strictly true. </p>
<h2>Colours in the rainbow</h2>
<p>The different colours blend into each other, and it is difficult to tell where one colour ends and another begins. There are other colours in between them, where they mix – like turquoise between blue and green.</p>
<figure class="align-center ">
<img alt="Diagram of the colours in the visible spectrum." src="https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499009/original/file-20221205-15-c3qq36.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The visible spectrum.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/spectrum-portion-electromagnetic-that-visible-human-1154529739">Belozersky/Shutterstock</a></span>
</figcaption>
</figure>
<p>Blue and green are next to each other in the colour spectrum, which is why we can see turquoise where they blend into each other. Some colours, though, are mixes of colours that aren’t next to each other in the spectrum. </p>
<p>Brown, for instance, is a mix of red and green. But the red and green bands in the rainbow aren’t next to each other, so we don’t see them mix to make brown. The same is the case for many other colours that are mixtures - if the colour bands in the rainbow don’t overlap then they can’t mix.</p>
<figure class="align-center ">
<img alt="Landscape photo with rainbow" src="https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500708/original/file-20221213-16682-u7oobq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A rainbow over fields.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/rainbow-rural-area-switzerland-beautiful-intense-1246431082">Peter Maerky/Shutterstock</a></span>
</figcaption>
</figure>
<p>But there are two colours we would never see in a rainbow - black and white. Black is the <a href="https://www.adobe.com/uk/creativecloud/design/discover/is-black-a-color.html">absence of colour</a> – it’s what’s we see when there’s no light at all. </p>
<p>On the other hand, white is a combination of all the colours together. When light is refracted by raindrops it separates the white light out into the visible spectrum, meaning it is no longer white. Grey is a mix of black and white, and as we can’t ever see black and white in a rainbow, we also can’t see colours made by mixing them. </p>
<p>Next time you see a rainbow, look out for how many colours you can spot in it – and the colours that you can’t see.</p><img src="https://counter.theconversation.com/content/195470/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Rawlings does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Rainbows are made when water droplets split light up into colours.
James Rawlings, Hourly Paid Lecturer in Physics, Nottingham Trent University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/192885
2022-10-24T09:09:46Z
2022-10-24T09:09:46Z
Manipulating light can induce psychedelic experiences – and scientists aren’t quite sure why
<figure><img src="https://images.theconversation.com/files/491042/original/file-20221021-19-9xwbq2.jpg?ixlib=rb-1.1.0&rect=3%2C14%2C1224%2C782&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Brion Gysin and William Burroughs with the Dreamachine, 1972.</span> <span class="attribution"><span class="source">Charles Gatewood</span>, <span class="license">Author provided</span></span></figcaption></figure><p>For millennia, people have used mind-altering techniques to achieve different states of consciousness, envision spiritual figures, connect with nature, or simply for the fun of it. Psychedelic substances, in particular, have a long and controversial <a href="https://theconversation.com/psychedelic-drugs-can-be-almost-as-life-altering-as-near-death-experiences-189325">history</a>. But for just as long, people have been having these experiences without drugs too, using <a href="https://www.mdpi.com/2076-3425/11/1/101">rhythmic techniques such as rocking, chanting or drumming</a>.</p>
<p>Perhaps the most powerful technique of this kind is flickering light, called “ganzflicker”. Ganzflicker effects can be achieved by turning a light on and off, or by alternating colours in a rapid, rhythmic pattern (like a strobe). This can create an instant psychedelic experience. </p>
<p>Ganzflicker elicits striking visual phenomena. People can see geometric shapes and illusory colours but sometimes also complex objects, such as animals and faces – all without any chemical stimulants. Sometimes ganzflicker can even lead to altered states of consciousness (such as losing a sense of time or space) and emotions (ranging from fear to euphoria).</p>
<p>Although its effects are little known today, ganzflicker has influenced and inspired many people through the ages, including the two of us. We are an art historian and brain scientist working together on an interactive showcase of ganzflicker techniques used in science and art. Our collaboration has culminated in the museum exhibition <a href="https://reshannereeder.com/ganzflicker-exhibit">“Ganzflicker: art, science, and psychedelic experience”</a>, which is part of the 2022 <a href="https://www.beinghumanfestival.org/">Being Human festival</a>. </p>
<p>Ganzflicker’s effects were first documented in 1819 by the physiologist <a href="https://www.karger.com/Article/FullText/235945">Jan E. Purkinje</a>. Purkinje discovered that illusory patterns could appear if he faced the sun and waved his hand in front of his closed eyelids.</p>
<figure class="align-center ">
<img alt="a series of geometric pattern drawings." src="https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=516&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=516&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=516&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=648&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=648&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491040/original/file-20221021-19-ovckhv.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=648&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">From Jan E. Purkinje’s documentation of the subjective visual phenomena he saw when he waved his hand in front of his closed eyes.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Near the end of the 19th century, an English toymaker and amateur scientist, <a href="https://www.nature.com/articles/051200c0">Charles Benham</a>, produced the first commercially available flicker device: a top with a monochrome pattern that, when spun, produced illusory colours that swirled around the disc. </p>
<p>Modified versions of Benham’s “artificial spectrum top” were used in experiments well into the 20th century. William Grey Walter, a pioneering neurophysiologist and cybernetician, <a href="https://link.springer.com/chapter/10.1007/978-3-642-70911-1_17">pushed flicker effects further</a> by using electric strobe lights, synchronised with the brain’s rhythms.</p>
<p>Fascinated by the mind-altering potential of Walter’s machinery, the artist Brion Gysin, in collaboration with writer William S. Burroughs and mathematician Ian Sommerville, invented the <a href="http://mindcontrol-research.net/wp-content/uploads/2016/12/14_2_dream-machine-plans.pdf">Dreamachine</a> (1962).</p>
<h2>The swinging 60s of drug-free psychedelics</h2>
<p>A Dreamachine consists of an upright cylinder with patterns cut into it and a lightbulb suspended at its centre. When spun on a turntable at 78rpm, the flickering patterns (viewed through closed eyelids) can cause trance-like hallucinations.</p>
<p>Gysin thought of the Dreamachine as a new kind of artwork – “the first art object to be seen with the eyes closed” – and a form of entertainment, which he believed could replace the television. Others saw the Dreamachine’s potential to be a source of spiritual inspiration.</p>
<p>Burroughs thought it could be <a href="https://faroutmagazine.co.uk/brion-gysin-the-pioneering-artist-who-invented-the-dreamachine/">used to</a> “storm the citadels of enlightenment”. The poet Alan Ginsberg said: “It sets up optical fields as religious and mandalic as hallucinogenic drugs – it’s like being able to have jewelled biblical designs and landscapes without taking chemicals.”</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ZWuQKAggegU?wmode=transparent&start=1" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Flicker experiments in art did not stop with the Dreamachine. Others included Tony Conrad’s groundbreaking structuralist film <a href="https://fourthree.boilerroom.tv/film/flicker-tony-conrad">The Flicker</a> (1966), which was the first artwork to include the warning “may induce epileptic seizures or produce mild symptoms of shock treatment in certain persons”. </p>
<p>The conceptual artist James Turrell’s <a href="https://jamesturrell.com/work/bindu-shards/">Bindu Shards</a> (2010) was an enclosed globe that bombards the observer with strobe light. And, more recently, Collective Act created its own <a href="https://dreamachine.world">Dreamachine</a> (2022) , a public planetarium-style artwork inspired by Gysin’s which toured the UK.</p>
<h2>The science of ganzflicker</h2>
<p>Two hundred years after Jan Purkinje documented the physiological properties of ganzflicker, scientists still do not have a definitive explanation for how it works. </p>
<p>A recent theory proposes that visual phenomena may be the result of interactions between external flicker and the brain’s natural rhythmic electrical pulses, with more intense images manifesting <a href="https://theconversation.com/pseudo-hallucinations-why-some-people-see-more-vivid-mental-images-than-others-test-yourself-here-163025">when the frequencies of flicker and the brain are closest</a>.</p>
<p>It is also likely that a strong visual flicker influences brain states. Meaningful visions, altered conscious states and heightened emotions may be the result of <a href="https://www.nature.com/articles/s41467-020-18591-6">imaginative suggestion</a>, which is amplified by the trance-inducing properties of <a href="https://www.mdpi.com/2076-3425/11/1/101">rhythmic stimulation</a>.</p>
<p>What is perhaps most powerful about ganzflicker is its universality. Engineers, mathematicians, artists, historians and scientists have all been united by this modest, drug-free means of eliciting dramatic changes in consciousness. The new wave of popularity on this topic will undoubtedly lead to illuminating discoveries in the coming years.</p><img src="https://counter.theconversation.com/content/192885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew MacKisack received funding for this exhibition from the Being Human festival, the UK’s national festival of the humanities, taking place 10–19 November 2022. Led by the School of Advanced Study, University of London, in partnership with the Arts and Humanities Research Council and the British Academy. For further information please see beinghumanfestival.org.</span></em></p><p class="fine-print"><em><span>Reshanne Reeder received funding for this exhibition from the Being Human festival, the UK’s national festival of the humanities, taking place 10–19 November 2022. Led by the School of Advanced Study, University of London, in partnership with the Arts and Humanities Research Council and the British Academy. For further information please see beinghumanfestival.org.</span></em></p>
Flickering light can make people see different colours and shapes or feel altered emotions or sense of time.
Matthew MacKisack, Associate Research Fellow, University of Exeter
Reshanne Reeder, Senior Lecturer in Psychology, Edge Hill University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/187051
2022-08-17T12:38:53Z
2022-08-17T12:38:53Z
Flies evade your swatting thanks to sophisticated vision and neural shortcuts
<figure><img src="https://images.theconversation.com/files/478807/original/file-20220811-20-9x44dv.jpg?ixlib=rb-1.1.0&rect=22%2C29%2C4966%2C3485&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fly brains can process images very quickly.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/house-fly-royalty-free-image/535501923">www.shutterexperiments.com/Moment via GettyImages</a></span></figcaption></figure><p>Sitting outside on a summer evening always sounds relaxing until flies and mosquitoes arrive – then the swatting begins. Despite their minuscule eyes and a <a href="https://www.fruitflybrain.org/#/">brain</a> roughly <a href="https://www.hhmi.org/news/complete-fly-brain-imaged-at-nanoscale-resolution">1 million times</a> smaller than yours, flies can evade almost every swat. </p>
<p>Flies can thank their fast, sophisticated eyesight and some neural quirks for their ability to escape swats with such speed and agility.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=4i4wRGgAAAAJ">Our lab</a> <a href="https://scholar.google.com/citations?user=WBxN0p4AAAAJ&hl=en&oi=ao">investigates insect flight and vision</a>, with the goal of finding out how such tiny creatures can process visual information to perform challenging behaviors, such as escaping your swatter so quickly.</p>
<h2>Faster vision</h2>
<p>Flies have compound eyes. Rather than collecting light through a single lens that makes the whole image – the strategy of human eyes – flies form images built from multiple <a href="https://doi.org/10.1007/978-3-642-74082-4_3">facets</a>, lots of individual lenses that focus incoming light onto clusters of photoreceptors, the light-sensing cells in their eyes. Essentially, each facet produces an individual pixel of the fly’s vision. </p>
<p>A fly’s world is fairly low resolution, because small heads can house only a limited number of facets – usually <a href="https://www.jstor.org/stable/24954051">hundreds to thousands</a> – and there is no easy way to sharpen their blurry vision up to the millions of pixels people effectively see. But despite this coarse resolution, flies see and process fast movements very quickly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of a fly eye, showing tiny hexagonal facets and the photoreceptor layer under these facets." src="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tiny hexagonal ‘facets’ take in light, and the photoreceptors beneath them process it in quick flashes.</span>
<span class="attribution"><a class="source" href="https://www.epfl.ch/labs/lis/research/completed/curvace/">Ecole Polytechnique Fédérale de Lausanne, Switzerland</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We can infer how animals perceive fast movement from how quickly their photoreceptors can process light. Humans discern a maximum of <a href="https://www.mdpi.com/1648-9144/57/10/1096/htm">about 60 discrete flashes</a> of light per second. Any faster usually appears as steady light. The ability to see discrete flashes depends on the lighting conditions and which part of the retina you use. </p>
<p>Some LED lights, for example, emit discrete flashes of light quickly enough that they appear as steady light to humans – unless you turn your head. In your peripheral vision you may notice a flicker. That’s because your peripheral vision processes light more quickly, but at a lower resolution, like fly vision. </p>
<p>Remarkably, some flies can see as many as <a href="https://doi.org/10.2307/1539540">250 flashes per second</a>, around four times more flashes per second than people can perceive. </p>
<p>If you took one of these flies to the cineplex, the smooth movie you watched made up of 24 frames per second would, to the fly, appear as a series of static images, like a slide show. But this fast vision allows it to react quickly to prey, obstacles, competitors and your attempts at swatting.</p>
<p><a href="https://faculty.fiu.edu/%7Etheobald/">Our research</a> shows that flies <a href="https://doi.org/10.1016/j.visres.2020.02.007">in dim light lose some ability to see fast movements</a>. This might sound like a good opportunity to swat them, but humans also lose their ability to see quick, sharp features in the dark. So you may be just as handicapped your target. </p>
<p>When they do fly in the dark, flies and mosquitoes <a href="https://doi.org/10.1016/j.cub.2022.01.078">fly erratically</a>, with twisty flight paths to escape swats. They can also rely on <a href="https://doi.org/10.1016/bs.aiip.2016.04.007">nonvisual cues</a>, such as information from small hairs on their body that sense changes in the air currents when you move to strike.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/9wqZ7Jt3thg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Flight of a mosquito. Source: Intellectual Ventures.</span></figcaption>
</figure>
<h2>Neural tricks</h2>
<p>But why do flies see more slowly in the dark? You may have noticed your own vision becoming sluggish and blurry in the dark, and much less colorful. The process is similar for insects. Low light means <a href="https://doi.org/10.1098/rstb.2016.0062">fewer photons</a>, and just like cameras and telescopes, eyes depend on photons to make images. </p>
<p>But unlike a nice camera, which allows you to switch to a larger lens and gather more photons in dark settings, animals can’t swap out the optics of their eyes. Instead, they rely on <a href="https://doi.org/10.1016/S0042-6989(98)00262-4">summation</a>, a neural strategy that adds together the inputs of neighboring pixels, or increases the time they sample photons, to form an image.</p>
<p>Big pixels and longer exposures capture more photons, <a href="https://faculty.fiu.edu/%7Etheobald/visual-pooling/">but at the cost of sharp images</a>. Summation is equivalent to taking photographs with grainy film (higher ISO) or slow shutter speeds, which produce blurrier images, but avoid <a href="https://www.youtube.com/watch?v=eAhEatlueXA">underexposing</a> your subjects. Flies, <a href="https://doi.org/10.1016/j.visres.2018.05.007">especially small ones</a>, can’t see quickly in the dark because, in a sense, they are waiting for enough photons to arrive until they are sure of what they are seeing.</p>
<h2>Flight maneuverability</h2>
<p>In addition to rapidly perceiving looming threats, flies need to be able to fly away in a split second. This requires preparation for takeoff and <a href="https://doi.org/10.1126/science.1248955">quick flight maneuvers</a>. After visually detecting a looming threat, fruit flies, for example, adjust their posture in <a href="https://doi.org/10.1016/j.cub.2008.07.094">one-fifth of a second</a> before takeoff. Predatory flies, such as <a href="https://doi.org/10.1159/000435944">killer flies</a>, coordinate their legs, wings and halteres – dumbbell-shaped remnants of wings used for sensing in-air rotations – to quickly catch their prey midflight. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tkK63pHFML0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Flight of a fly. Notice how they adjust their posture before takeoff. Source: The New York Times.</span></figcaption>
</figure>
<h2>How best to swat a fly</h2>
<p>To outmaneuver a fly, you must strike faster than it can detect your approaching hand. With practice, you may improve at this, but flies have honed their escapes over hundreds of millions of years. So instead of swatting, using other ways to manage flies, such as installing fly traps and cleaning backyards, is a better bet. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/OEIk_68miZc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Escape behavior of a fly in slow motion. Source: Florian Muijres et al, 2014 Science.</span></figcaption>
</figure>
<p>You can lure certain flies into a narrow neck bottle filled with apple cider vinegar and beer. Placing a funnel in the bottle neck makes it easy for them to enter, but difficult to escape. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A simple home-made fruit fly trap" src="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=854&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=854&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=854&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1074&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1074&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1074&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Apple cider vinegar and beer trap to control fruit flies in your kitchen or backyard.</span>
<span class="attribution"><span class="source">Ravindra Palavalli-Nettimi</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As for mosquitoes, some commercial repellents may work, but removing stagnant water around the house – in some plants, pots or any open containers – will help <a href="https://www.cdc.gov/mosquitoes/mosquito-control/athome/outside-your-home/index.html">eliminate their egg-laying sites</a> and reduce the number of mosquitoes around from the start. Avoid insecticides, as they also <a href="https://environment-review.yale.edu/deadlier-intended-pesticides-might-be-killing-beneficial-insects-beyond-their-targets-0">harm useful insects</a> such as bees and butterflies.</p><img src="https://counter.theconversation.com/content/187051/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Theobald receives funding from the National Science Foundation (IOS-1750833). </span></em></p><p class="fine-print"><em><span>Ravindra Palavalli-Nettimi does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Why is it so difficult to swat a fly? A team of insect experts explains how a fly’s sophisticated vision allows it to quickly react to visual cues.
Jamie Theobald, Associate Professor of Biological Sciences, Florida International University
Ravindra Palavalli-Nettimi, Postdoctoral Research Associate, Florida International University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/184828
2022-07-14T12:34:04Z
2022-07-14T12:34:04Z
To search for alien life, astronomers will look for clues in the atmospheres of distant planets – and the James Webb Space Telescope just proved it’s possible to do so
<figure><img src="https://images.theconversation.com/files/473980/original/file-20220713-20-g1f04j.png?ixlib=rb-1.1.0&rect=34%2C116%2C691%2C572&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">TRAPPIST-1e is a rocky exoplanet in the habitable zone of a star 40 light-years from Earth and may have water and clouds, as depicted in this artist's impression.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:TRAPPIST-1e_artist_impression_2018.png#/media/File:TRAPPIST-1e_artist_impression_2018.png">NASA/JPL-Caltech/Wikimedia Commons</a></span></figcaption></figure><p>The ingredients for life are <a href="https://doi.org/10.1073/pnas.98.3.805">spread throughout the universe</a>. While Earth is the only known place in the universe with life, detecting life beyond Earth is a <a href="https://www.planetary.org/articles/the-2020-astrophysics-decadal-survey-guide">major goal</a> of <a href="https://www.planetary.org/space-policy/what-is-the-decadal-survey">modern astronomy</a> and <a href="https://www.planetary.org/space-policy/what-is-the-decadal-survey">planetary science</a>.</p>
<p>We are two scientists who study <a href="https://scholar.google.com/citations?user=2SCIYjIAAAAJ&hl=en&oi=ao">exoplanets</a> and <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en&oi=ao">astrobiology</a>. Thanks in large part to next-generation telescopes like James Webb, researchers like us will soon be able to measure the chemical makeup of atmospheres of planets around other stars. The hope is that one or more of these planets will have a chemical signature of life.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing green bands around stars." src="https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473981/original/file-20220713-24-ei1562.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">There are many known exoplanets in habitable zones – orbits not too close to a star that the water boils off but not so far that the planet is frozen solid – as marked in green for both the solar system and Kepler-186 star system with its planets labeled b, c, d, e and f.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Kepler186f-ComparisonGraphic-20140417_improved.jpg#/media/File:Kepler186f-ComparisonGraphic-20140417_improved.jpg">NASA Ames/SETI Institute/JPL-Caltech/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>Habitable exoplanets</h2>
<p>Life <a href="https://doi.org/10.1073/pnas.1816535115">might exist in the solar system</a> where there is liquid water – like the subsurface aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, searching for life in these places is incredibly difficult, as they are hard to reach and detecting life would require sending a probe to return physical samples.</p>
<p>Many astronomers believe there’s a <a href="https://exoplanets.nasa.gov/news/1675/life-in-the-universe-what-are-the-odds/">good chance that life exists on planets orbiting other stars</a>, and it’s possible that’s where <a href="https://doi.org/10.1016/j.actaastro.2022.03.019">life will first be found</a>.</p>
<p>Theoretical calculations suggest that there are around <a href="https://www.technologyreview.com/2020/11/06/1011784/half-milky-way-sun-like-stars-home-earth-like-planets-kepler-gaia-habitable-life/">300 million potentially habitable planets</a> in the Milky Way galaxy alone and <a href="https://doi.org/10.3847/1538-3881/abc418">several habitable Earth-sized planets</a> within only 30 light-years of Earth – essentially humanity’s galactic neighbors. So far, astronomers have <a href="https://exoplanets.nasa.gov/">discovered over 5,000 exoplanets</a>, including hundreds of potentially habitable ones, using <a href="https://sci.esa.int/web/exoplanets/-/60655-detection-methods">indirect methods</a> that measure how a planet affects its nearby star. These measurements can give astronomers information on the mass and size of an exoplanet, but not much else.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing two lines each with two peaks in the blue and red wavelengths." src="https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473983/original/file-20220713-17654-sd7qoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Every material absorbs certain wavelengths of light, as shown in this diagram depicting the wavelengths of light absorbed most easily by different types of chlorophyll.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Chlorophyll_ab_spectra-en.svg#/media/File:Chlorophyll_ab_spectra-en.svg">Daniele Pugliesi/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Looking for biosignatures</h2>
<p>To detect life on a distant planet, astrobiologists will study starlight that has <a href="https://doi.org/10.1089/ast.2017.1729">interacted with a planet’s surface or atmosphere</a>. If the atmosphere or surface was transformed by life, the light may carry a clue, called a “biosignature.”</p>
<p>For the first half of its existence, Earth sported an atmosphere without oxygen, even though it hosted simple, single-celled life. Earth’s biosignature was very faint during this early era. That changed abruptly <a href="https://asm.org/Articles/2022/February/The-Great-Oxidation-Event-How-Cyanobacteria-Change">2.4 billion years ago</a> when a new family of algae evolved. The algae used a process of photosynthesis that produces free oxygen – oxygen that isn’t chemically bonded to any other element. From that time on, Earth’s oxygen-filled atmosphere has left a strong and easily detectable biosignature on light that passes through it.</p>
<p>When light bounces off the surface of a material or passes through a gas, certain wavelengths of the light are more likely to remain trapped in the gas or material’s surface than others. This selective trapping of wavelengths of light is why objects are different colors. Leaves are green because chlorophyll is particularly good at absorbing light in the red and blue wavelengths. As light hits a leaf, the red and blue wavelengths are absorbed, leaving mostly green light to bounce back into your eyes.</p>
<p>The pattern of missing light is determined by the specific composition of the material the light interacts with. Because of this, astronomers can learn something about the composition of an exoplanet’s atmosphere or surface by, in essence, measuring the specific color of light that comes from a planet. </p>
<p>This method can be used to recognize the presence of certain atmospheric gases that are associated with life – such as oxygen or methane – because these gasses leave very specific signatures in light. It could also be used to detect peculiar colors on the surface of a planet. On Earth, for example, the chlorophyll and other pigments plants and algae use for photosynthesis capture specific wavelengths of light. These pigments <a href="https://doi.org/10.1073/pnas.1304213111">produce characteristic colors</a> that can be detected by using a sensitive infrared camera. If you were to see this color reflecting off the surface of a distant planet, it would potentially signify the presence of chlorophyll.</p>
<h2>Telescopes in space and on Earth</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A giant gold mirror in a lab." src="https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=899&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=899&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=899&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473985/original/file-20220713-17654-d5rtyi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The James Webb Space Telescope is the first telescope able to detect chemical signatures from exoplanets, but it is limited in its capabilities.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:JWST_Full_Mirror.jpg#/media/File:JWST_Full_Mirror.jpg">NASA/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>It takes an incredibly powerful telescope to detect these subtle changes to the light coming from a potentially habitable exoplanet. For now, the only telescope capable of such a feat is the new <a href="http://jwst.nasa.gov/">James Webb Space Telescope</a>. As it <a href="https://blogs.nasa.gov/webb/2022/07/11/nasas-webb-telescope-is-now-fully-ready-for-science/">began science operations</a> in July 2022, James Webb took a reading of the spectrum of the <a href="https://www.nytimes.com/2022/07/12/science/wasp-96b-exoplanet-webb-telescope.html">gas giant exoplanet WASP-96b</a>. The spectrum showed the presence of water and clouds, but a planet as large and hot as WASP-96b is unlikely to host life.</p>
<p>However, this early data shows that James Webb is capable of detecting faint chemical signatures in light coming from exoplanets. In the coming months, Webb is set to turn its mirrors toward <a href="https://www.space.com/42512-trappist-1-planet-could-host-life.html">TRAPPIST-1e</a>, a potentially habitable Earth-sized planet a mere 39 light-years from Earth.</p>
<p>Webb can look for biosignatures by studying planets as they pass in front of their host stars and capturing <a href="https://www.physics.uu.se/research/astronomy-and-space-physics/research/planets/exoplanet-atmospheres/">starlight that filters through the planet’s atmosphere</a>. But Webb was not designed to search for life, so the telescope is only able to scrutinize a few of the nearest potentially habitable worlds. It also can only detect changes to <a href="https://doi.org/10.3847/1538-3881/ab21e0">atmospheric levels of carbon dioxide, methane and water vapor</a>. While certain combinations of these gasses <a href="https://doi.org/10.1038/s41550-021-01579-7">may suggest life</a>, Webb is not able to detect the presence of unbonded oxygen, which is the strongest signal for life.</p>
<p>Leading concepts for future, even more powerful, space telescopes include plans to block the bright light of a planet’s host star to reveal starlight reflected back from the planet. This idea is similar to using your hand to block sunlight to better see something in the distance. Future space telescopes could use small, internal masks or large, external, umbrella-like spacecraft to do this. Once the starlight is blocked, it becomes much easier to study light bouncing off a planet.</p>
<p>There are also three enormous, ground-based telescopes currently under construction that will be able to search for biosignatures: the <a href="http://gmto.org/">Giant Magellen Telescope</a>, the <a href="https://www.tmt.org/">Thirty Meter Telescope</a> and the <a href="https://www.eso.org/sci/facilities/eelt/">European Extremely Large Telescope</a>. Each is far more powerful than existing telescopes on Earth, and despite the handicap of Earth’s atmosphere distorting starlight, these telescopes might be able to probe the atmospheres of the closest worlds for oxygen.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cow and its calf standing in a field." src="https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=511&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=511&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473982/original/file-20220713-12-4xssot.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=511&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Animals, including cows, produce methane, but so do many geologic processes.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cows_eating_grass_(42882305160).jpg#/media/File:Cows_eating_grass_(42882305160).jpg">Jernej Furman/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Is it biology or geology?</h2>
<p>Even using the most powerful telescopes of the coming decades, astrobiologists will only be able to detect strong biosignatures produced by worlds that have been completely transformed by life.</p>
<p>Unfortunately, most gases released by terrestrial life can also be produced by nonbiological processes – cows and volcanoes both release methane. Photosynthesis produces oxygen, but sunlight does, too, when it splits water molecules into oxygen and hydrogen. There is a <a href="https://doi.org/10.1089/ast.2017.1727">good chance astronomers will detect some false positives</a> when looking for distant life. To help rule out false positives, astronomers will need to understand a planet of interest well enough to understand whether its <a href="https://doi.org/10.1089/ast.2017.1737">geologic or atmospheric processes could mimic a biosignature</a>. </p>
<p>The next generation of exoplanet studies has the potential to pass the bar of the <a href="https://quoteinvestigator.com/2021/12/05/extraordinary/">extraordinary evidence</a> needed to prove the existence of life. The first data release from the James Webb Space Telescope gives us a sense of the exciting progress that’s coming soon.</p><img src="https://counter.theconversation.com/content/184828/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation.</span></em></p><p class="fine-print"><em><span>Daniel Apai receives funding from NASA and the Gordon and Betty Moore Foundation.</span></em></p>
Life on Earth has dramatically changed the chemistry of the planet. Astronomers will measure light that bounces off distant planets to look for similar clues that they host life.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
Daniel Apai, Professor of Astronomy and Planetary Sciences, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/182311
2022-05-05T18:01:15Z
2022-05-05T18:01:15Z
Corals and sea anemones turn sunscreen into toxins – understanding how could help save coral reefs
<figure><img src="https://images.theconversation.com/files/461387/original/file-20220504-16-dvzlw6.jpg?ixlib=rb-1.1.0&rect=172%2C181%2C4820%2C3423&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Many places have banned sunscreens with certain chemicals in an attempt to help protect coral reefs.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/egypt-red-sea-hurghada-teenage-girl-snorkeling-at-royalty-free-image/932631960?adppopup=true">Westend61 via Getty Images</a></span></figcaption></figure><p>Sunscreen bottles are frequently labeled as “reef-friendly” and “coral-safe.” These claims generally mean that the lotions replaced oxybenzone – a chemical that can harm corals – with something else. But are these other chemicals really safer for reefs than oxybenzone?</p>
<p>This question led <a href="https://mitchlab.sites.stanford.edu/djordje-vuckovic">us</a>, two <a href="https://scholar.google.com/citations?hl=en&user=RQcNZ6QAAAAJ">environmental chemists</a>, to team up with <a href="https://med.stanford.edu/pringlelab/people/john-pringle.html">biologists</a> who study <a href="https://med.stanford.edu/pringlelab.html">sea anemones as a model for corals</a>. Our goal was to uncover how sunscreen harms reefs so that we could better understand which components in sunscreens are really “coral-safe.” </p>
<p>In <a href="https://www.science.org/doi/10.1126/science.abo4627">our new study</a>, published in Science, we found that when corals and sea anemones absorb oxybenzone, <a href="https://doi.org/10.1126/science.abn2600">their cells turn it into phototoxins</a>, molecules that are harmless in the dark but become toxic under sunlight.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dead coral reef." src="https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461392/original/file-20220504-19-dpmjpk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Reefs around the world – like the Great Barrier Reef seen here – are bleaching and dying because of stressors like increased water temperatures, and sunscreens may be exacerbating the issues.</span>
<span class="attribution"><span class="source">Amanda Tinoco</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Protecting people, harming reefs</h2>
<p>Sunlight is made of many different wavelengths of light. Longer wavelengths – like visible light – are typically harmless. But light at shorter wavelengths – like ultraviolet light – can pass through the surface of skin and damage DNA and cells. Sunscreens, including oxybenzone, work by absorbing most of the UV light and converting it into heat.</p>
<p>Coral reefs around the world have suffered in recent decades from <a href="https://oceanservice.noaa.gov/facts/coralreef-climate.html">warming oceans and other stressors</a>. Some scientists thought that sunscreens coming off of swimmers or from wastewater discharges could also be harming corals. They conducted lab experiments that showed that oxybenzone concentrations as low as 0.14 mg per liter of seawater can <a href="https://doi.org/10.1007/s00244-015-0227-7">kill 50% of coral larvae in less than 24 hours</a>. While most field samples typically have lower sunscreen concentrations, one popular snorkeling reef in the U.S. Virgin Islands <a href="https://doi.org/10.1007/s00244-015-0227-7">had up to 1.4 mg oxybenzone per liter of seawater</a> – more than 10 times the lethal dose for coral larvae. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chemical diagram of oxybenzone." src="https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=320&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=320&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=320&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=403&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=403&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461389/original/file-20220504-21-dognyj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=403&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Oxybenzone is a common ingredient in many sunscreens.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Oxybenzone.svg#/media/File:Oxybenzone.svg">Fvasconcellos via WikimediaCommons</a></span>
</figcaption>
</figure>
<p>Likely inspired by this research and a number of <a href="https://dx.doi.org/10.1289%2Fehp.10966">other studies</a> <a href="https://doi.org/10.1080/10934529.2011.602936">showing damage</a> to <a href="https://doi.org/10.1016/j.aquatox.2008.08.018">marine life</a>, Hawaii’s legislators <a href="https://www.washingtonpost.com/news/energy-environment/wp/2018/05/02/hawaii-might-be-about-to-ban-your-favorite-sunscreen-to-protect-its-coral-reefs/">voted</a> in 2018 to ban oxybenzone and another ingredient in sunscreens. Soon after, lawmakers in other places with coral reefs, like the <a href="https://psmag.com/news/the-us-virgin-islands-bans-potentially-dangerous-sunscreen-chemicals">Virgin Islands</a>, <a href="https://www.nytimes.com/2018/11/02/world/asia/palau-sunscreen-ban-coral.html">Palau</a> and <a href="https://www.visitaruba.com/news/general/aruba-officially-bans-plastics-and-oxybenzone/">Aruba</a>, implemented their own bans.</p>
<p>There is still an <a href="https://theconversation.com/theres-insufficient-evidence-your-sunscreen-harms-coral-reefs-109567">open debate</a> whether the concentrations of oxybenzone in the environment are high enough to damage reefs. But everyone agrees that these chemicals can cause harm under certain conditions, so understanding their mechanism is important. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A number of small test tubes with little sea anemones growing inside of them." src="https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461396/original/file-20220504-15-7bssds.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">By putting sea anemones into test tubes with oxybenzone and controlling what kinds of light they were exposed to, we could see whether the sunscreen was reacting to light.</span>
<span class="attribution"><span class="source">Djordje Vuckovic</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Sunscreen or toxin</h2>
<p>While laboratory evidence had shown that sunscreen can harm corals, very little research had been done to understand how. Some studies suggested that oxybenzone <a href="https://doi.org/10.1016/j.envint.2014.05.015">mimics hormones</a>, disrupting reproduction and development. But another theory that our team found particularly intriguing was the possibility that the sunscreen behaved as a <a href="https://doi.org/10.1007/s00244-015-0227-7">light-activated toxin in corals</a>. </p>
<p>To test this, we used the sea anemones our colleagues breed as a model for corals. Sea anemones and corals are closely related and share a lot of biological processes, including a symbiotic relationship with algae that live within them. It is <a href="https://doi.org/10.1016/j.tree.2008.03.004">extremely difficult to perform experiments with corals under lab conditions</a>, so anemones are typically much better for lab-based studies like ours.</p>
<p>We put 21 anemones in test tubes full of seawater under a lightbulb that emits the full spectrum of sunlight. We covered five of the anemones with a box made of acrylic that blocks the exact wavelengths of UV light that oxybenzone normally absorbs and interacts with. Then we exposed all the anemones to 2 mg of oxybenzone per liter of seawater.</p>
<p>The anemones under the acrylic box were our “dark” samples and the ones outside of it our control “light” samples. Anemones, like corals, have a translucent surface, so if oxybenzone were acting as a phototoxin, the UV rays hitting the light group would trigger a chemical reaction and kill the animals – while the dark group would survive.</p>
<p>We ran the experiment for 21 days. On Day Six, the first anemone in the light group died. By Day 17, <a href="https://doi.org/10.1126/science.abn2600">all of them had died</a>. By comparison, none of the five anemones in the dark group died during the entire three weeks. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close-up of a blue coral." src="https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461391/original/file-20220504-18-8tlovg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Corals – like the mushroom coral seen here – and sea anemones absorb oxybenzone and metabolize it, but in doing so, they turn it into a toxin.</span>
<span class="attribution"><span class="source">Christian Renicke</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Metabolism converts oxybenzone to phototoxins</h2>
<p>We were surprised that a sunscreen was behaving as a phototoxin inside the anemones. We ran a chemical experiment on oxybenzone and confirmed that, on its own, it behaves as a sunscreen and not as a phototoxin. It’s only when the chemical was absorbed by anemones that it became dangerous under light. </p>
<p>Any time an organism absorbs a foreign substance, its cells try to get rid of the substance using various metabolic processes. Our experiments suggested that one of these processes was turning oxybenzone into a phototoxin.</p>
<p>To test this, we analyzed the chemicals that formed inside anemones after we exposed them to oxybenzone. We learned that our anemones had replaced part of oxybenzone’s chemical structure – a specific hydrogen atom on an alcohol group – with a sugar. Replacing hydrogen atoms on alcohol groups with sugars is something that <a href="https://passel2.unl.edu/view/lesson/2aee31ac6c74/7#:%7E:text=Phase%20II%20-%20Introduction,-Phase%20II%20reactions&text=reactions%20are%20anabolic%20processes%20which,solubility%20and%20usually%20reduced%20mobility.">plants</a> and <a href="https://doi.org/10.1007/1-4020-4142-X_3">animals</a> commonly do to make chemicals less toxic and more water soluble so they are easier to excrete.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chemical chart showing two different molecular structures." src="https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=155&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=155&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=155&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=195&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=195&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461602/original/file-20220505-21-skvp4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=195&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When cells try to process oxybenzone, they replace part of an alcohol group (highlighted in red on the left) with a sugar (in red on the right) and in doing so turn the sunscreen into a phototoxin.</span>
<span class="attribution"><span class="source">Djordje Vuckovic</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>But when you remove this alcohol group from oxybenzone, oxybenzone ceases to function as a sunscreen. Instead, it holds on to the energy it absorbs from UV light and kicks off a series of <a href="https://doi.org/10.1111/php.12716">rapid chemical reactions</a> that <a href="https://doi.org/10.1021/acsomega.9b03244">damage cells</a>. Rather than turning the sunscreen into a harmless, easy-to-excrete molecule, the anemones <a href="https://doi.org/10.1126/science.abn2600">convert oxybenzone into a potent, sunlight-activated toxin</a>.</p>
<p>When we ran similar experiments with mushroom corals, we found something surprising. Even though <a href="https://doi.org/10.1016/j.tree.2008.03.004">corals are much more vulnerable to stressors than sea anemones</a>, they did not die from oxybenzone and light exposure during our entire eight-day experiment. The coral made the same phototoxins from oxybenzone, but all of the toxins were stored in the symbiotic algae living in the coral. The algae seemed to absorb the phototoxic byproducts and, in doing so, likely protected their coral hosts. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two rows of photos of sea anemones, with the top row showing a slower death." src="https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=128&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=128&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=128&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=161&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=161&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461603/original/file-20220505-22-e336i2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=161&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This photo series shows how darker-colored anemones on top with algae in them lived longer than the lighter-colored anemones on the bottom that did not have algae living in them.</span>
<span class="attribution"><span class="source">Djordje Vuckovic and Christian Renicke</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We suspect that the corals would have died from the phototoxins if they did not have their algae. It is not possible to keep corals without algae alive in the lab, so we did some experiments on anemones without algae instead. These anemones died about two times faster and had almost three times as many phototoxins in their cells compared than the same anemones with algae.</p>
<h2>Coral bleaching, ‘reef-safe’ sunscreens and human safety</h2>
<p>We believe there are a few important takeaways from our effort to better understand how oxybenzone harms corals. </p>
<p>First, <a href="https://doi.org/10.1126/science.aan8048">coral bleaching events</a> – in which the corals expel their algal symbionts because of high seawater temperatures or other stressors – likely leave corals particularly vulnerable to the toxic effects of sunscreens. </p>
<p>Second, it’s possible that oxybenzone could also be dangerous to other species. In our study, we found that human cells can also turn oxybenzone into a potential phototoxin. If this happens inside the body, where no light can reach, it’s not an issue. But if this occurs in the skin, where light can create toxins, it could be a problem. Previous studies have suggested that oxybenzone <a href="https://doi.org/10.1097/PSN.0000000000000244">could pose health risks to people</a>, and some researchers have recently <a href="https://doi.org/10.1016/j.jaad.2021.12.011">called for more research into its safety</a>.</p>
<p>Finally, the chemicals used in many alternative “reef-safe” sunscreens contain the same alcohol group as oxybenzone – so could potentially also be converted to phototoxins.</p>
<p>We hope that, taken together, our results will lead to safer sunscreens and help inform efforts to protect reefs. </p>
<p>[<em>Understand new developments in science, health and technology, each week.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-understand">Subscribe to The Conversation’s science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/182311/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Djordje Vuckovic has spoken with Soliome, a company involved in the production of novel sunscreen components. He received funding from the National Science Foundation. </span></em></p><p class="fine-print"><em><span>Bill Mitch has spoken with Soliome, a company involved in the production of novel sunscreen components. He receives funding from the U.S. National Science Foundation and the Stanford Woods Institute of the Environment.</span></em></p>
Researchers have long suspected that an ingredient in sunscreen called oxybenzone was harming corals, but no one knew how. A new study shows how corals turn oxybenzone into a sunlight-activated toxin.
Djordje Vuckovic, PhD candidate in Civil and Environmental Engineering, Stanford University
Bill Mitch, Professor of Civil and Environmental Engineering, Stanford University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/170849
2021-11-15T13:11:18Z
2021-11-15T13:11:18Z
Have we made an object that could travel 1% the speed of light?
<figure><img src="https://images.theconversation.com/files/429624/original/file-20211101-21-hweqmz.jpg?ixlib=rb-1.1.0&rect=389%2C463%2C8635%2C3891&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It only takes light about eight minutes to go from the Sun to Earth.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/sunrise-in-space-royalty-free-image/174578300?adppopup=true"> loops7/E+ via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Have we made an object that could travel at at least 1% the speed of light? – Anadi, age 14, Jammu and Kashmir, India</strong></p>
</blockquote>
<hr>
<p><a href="https://www.universetoday.com/38040/speed-of-light-2/">Light is fast</a>. In fact, it is the fastest thing that exists, and a law of the universe is that nothing can move faster than light. Light travels at 186,000 miles per second (300,000 kilometers per second) and can go from the Earth to the Moon in just over a second. Light can streak from Los Angeles to New York in less than the blink of an eye.</p>
<p>While 1% of anything doesn’t sound like much, with light, that’s still really fast – close to 7 million miles per hour! At 1% the speed of light, it would take a little over a second to get from Los Angeles to New York. This is more than 10,000 times faster than a commercial jet.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A spacecraft with the sun in the background." src="https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=522&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=522&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429627/original/file-20211101-25-c3f9c9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=522&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Parker Solar Probe, seen here in an artist’s rendition, is the fastest object ever made by humans and used the gravity of the Sun to get going 0.05% the speed of light.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Parker_Solar_Probe.jpg">NASA/Johns Hopkins APL/Steve Gribben</a></span>
</figcaption>
</figure>
<h2>The fastest things ever made</h2>
<p><a href="https://hypertextbook.com/facts/1999/MariaPereyra.shtml">Bullets</a> can go 2,600 mph (4,200 kmh), more than three times the speed of sound. The fastest aircraft is NASA’s <a href="https://www.wearethemighty.com/tech/the-8-fastest-man-made-objects-ever/">X3 jet plane</a>, with a top speed of 7,000 mph (11,200 kph). That sounds impressive, but it’s still only 0.001% the speed of light.</p>
<p>The fastest human-made objects are spacecraft. They use rockets to break free of the Earth’s gravity, which takes a speed of 25,000 mph (40,000 kmh). The spacecraft that is traveling the fastest is NASA’s <a href="https://www.cnet.com/home/energy-and-utilities/nasa-solar-probe-becomes-fastest-object-ever-built-as-it-touches-the-sun/">Parker Solar Probe</a>. After it launched from Earth in 2018, it skimmed the Sun’s scorching atmosphere and used the Sun’s gravity to reach 330,000 mph (535,000 kmh). That’s blindingly fast – yet only 0.05% of the speed of light.</p>
<h2>Why even 1% of light speed is hard</h2>
<p>What’s holding humanity back from reaching 1% of the speed of light? In a word, energy. Any object that’s moving has energy due to its motion. Physicists call this kinetic energy. To go faster, you need to increase kinetic energy. The problem is that it takes a lot of <a href="https://www.omnicalculator.com/physics/relativistic-ke">kinetic energy</a> to increase speed. To make something go twice as fast takes four times the energy. Making something go three times as fast requires nine times the energy, and so on. </p>
<p>For example, to get a teenager who weighs 110 pounds (50 kilograms) to 1% of the speed of light would cost 200 trillion Joules (a measurement of energy). That’s roughly the same amount of energy that 2 million people in the U.S. use in a day.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A shiny golden-hued square with a small spacecraft attached in space with a planet in the background." src="https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429630/original/file-20211101-21-5bh2wr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Solar sails, the thin shiny square seen in this artist’s rendition of the Japanese IKAROS spacecraft, could propel a spacecraft to 10% the speed of light.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:IKAROS_solar_sail.jpg#/media/File:IKAROS_solar_sail.jpg">Andrzej Mirecki via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>How fast can we go?</h2>
<p>It’s possible to get something to 1% the speed of light, but it would just take an enormous amount of energy. Could humans make something go even faster?</p>
<p>Yes! But engineers need to figure out new ways to make things move in space. All rockets, even the sleek new rockets used by SpaceX and Blue Origins, <a href="https://www.sciencelearn.org.nz/resources/393-types-of-chemical-rocket-engines">burn rocket fuel</a> that isn’t very different from gasoline in a car. The problem is that burning fuel is very inefficient. </p>
<p>Other methods for pushing a spacecraft involve using <a href="https://www.nasa.gov/feature/glenn/2020/the-propulsion-we-re-supplying-it-s-electrifying">electric or magnetic forces</a>. <a href="https://www.nasa.gov/directorates/spacetech/niac/2012_Phase_II_fusion_driven_rocket/">Nuclear fusion</a>, the process that powers the Sun, is also much more efficient than chemical fuel. </p>
<p>Scientists are researching many other ways to go fast – even <a href="https://theconversation.com/warp-drives-physicists-give-chances-of-faster-than-light-space-travel-a-boost-157391">warp drives</a>, the faster-than-light travel popularized by Star Trek. </p>
<p>One promising way to get something moving very fast is to use a solar sail. These are large, thin sheets of plastic attached to a spacecraft and designed so that sunlight can push on them, like wind in a normal sail. A few spacecraft have used solar sails to show that they work, and scientists think that a solar sail could <a href="http://ffden-2.phys.uaf.edu/webproj/212_spring_2015/Robert_Miller/physics.html#:%7E:text=Solar%20sails%20have%20a%20maximum,the%20sail%20propelling%20it%20forward">propel spacecraft to 10% of the speed of light</a>. </p>
<p>One day, when humanity is not limited to a tiny fraction of the speed of light, we might <a href="https://tauzero.aero/">travel to the stars</a>.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/170849/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation and the Hearst Foundation.</span></em></p>
The fastest things ever made by humans are spacecraft, and the fastest spacecraft reached 330,000 mph – only 0.05% the speed of light. But there are ways to go faster.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/169940
2021-11-05T03:02:21Z
2021-11-05T03:02:21Z
Curious Kids: what is energy made of?
<figure><img src="https://images.theconversation.com/files/430400/original/file-20211104-19-1eby6ie.jpg?ixlib=rb-1.1.0&rect=14%2C8%2C1982%2C1320&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-rendering-abstract-energy-ball-fire-755829682">Jivacore / Shutterstock</a></span></figcaption></figure><blockquote>
<p>What is energy made of? — Ela, age 8, Melbourne </p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Hi Ela! What a great question! </p>
<p>For scientists, energy is not really a <em>thing</em> and so it isn’t made of something else, in the way a house is made of bricks.</p>
<p>Energy is more like a <em>capacity</em>. A capacity is an ability to <em>do</em> something. </p>
<h2>Energy and work</h2>
<p>Think of a musician: they have the capacity to play an instrument. A painter has the capacity to paint. </p>
<p>Energy is the capacity for something to <em>do work</em>.</p>
<p>Something does work when it exerts a force on another object, pushing the object to move in a particular direction. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430401/original/file-20211104-14-8v9jk8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When you hit a ball with a bat, the bat transfers some of its kinetic energy to the ball to change its speed and direction.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>What does that mean? Well, imagine someone throws a ball to you and you hit it with a bat. When the bat hits the ball, it changes the ball’s speed and direction. </p>
<p>Energy is the capacity the bat has to change the direction of the ball. When the bat is swinging, it can change the direction of any ball it hits. </p>
<p>When you swing the bat, you put energy stored in your muscles into it. The harder you swing, the more work the bat can do, so the more energy it carries.</p>
<h2>Types of energy</h2>
<p>There are many ways for something to do work, so there are different kinds of energy. </p>
<p>We have already encountered one: the swinging of the bat. This is called <em>kinetic energy</em>. It is the energy something has because it is moving. </p>
<p>Another kind of energy is <em>potential energy</em>. Potential energy is the capacity something has to do work because of its position in relation to other objects. </p>
<p>This means putting things in certain places gives them energy. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=899&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=899&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=899&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430402/original/file-20211104-15-1vgzy1f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If you balance a bucket of water on top of a door, you give it potential energy. When the door is opened, the bucket starts to move downwards, drenching the unlucky person who opened it.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Here’s a fun example: imagine putting a bucket of water on top of a door that is half open. When someone walks through the door, the bucket will fall on their head. </p>
<p>Because the bucket is on top of the door, it can fall. And when it falls, it can do some work. Not only will it soak whoever walks through the door, but it will also hit them on the head. </p>
<p>So the bucket has the capacity to do work just because it is put on top of the door, and not because it is moving. That capacity is the bucket’s potential energy. </p>
<h2>Einstein’s famous equation</h2>
<p>The famous physicist Albert Einstein made an equation about energy, which you may have seen before: <em>E</em> = <em>m</em> <em>c</em> ². </p>
<p>In this equation, the <em>E</em> is for energy, the <em>m</em> is for mass (which is roughly how much matter, or physical stuff, is in something), and <em>c</em> means the speed of light. </p>
<p>What the equation seems to say is that energy equals mass times some number. So then, isn’t energy made of something after all?</p>
<p>Not quite, because some things with no mass can still have energy. For example, light. We know it has energy because we catch light’s energy in solar panels, and turn it into electricity. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-solar-panels-work-123515">Curious Kids: how do solar panels work?</a>
</strong>
</em>
</p>
<hr>
<p>But light is <a href="https://theconversation.com/curious-kids-is-light-a-wave-or-a-particle-162514">made of tiny particles called photons</a>, and photons have no mass.</p>
<p>So, if energy were made of mass, then light would have no energy at all! That would make a mystery out of solar power. </p>
<p>As it turns out, even though light has no mass it does have something called <em>momentum</em>, which gives it a capacity to do work. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-light-a-wave-or-a-particle-162514">Curious Kids: is light a wave or a particle?</a>
</strong>
</em>
</p>
<hr>
<h2>Mass, energy and momentum</h2>
<p>There’s a more complicated version of Einstein’s equation that shows how energy is related to mass and momentum. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=250&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=250&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=250&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=314&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=314&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430403/original/file-20211104-25-1muuzcb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=314&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Light is so fast it travels all the way from the Sun to Earth in just over 8 minutes.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>One important thing to know is that light moves very fast. Because the amount of energy in something depends on how much mass it has multiplied by the square of the speed of light, that means a little bit of matter carries a lot of energy!</p>
<p>Light travels almost 300 million metres in a single second, which means one kilogram of mass is equivalent to almost nine quintillion joules of energy! That’s a 9 with 18 zeroes after it: 9,000,000,000,000,000,000.</p>
<p>The trick is unleashing that capacity. That’s actually how nuclear bombs (and nuclear power) work: they unlock the energy captured in matter to produce an enormous effect.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/testing-the-theory-taking-einstein-to-primary-schools-9710">Testing the theory: taking Einstein to primary schools</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/169940/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sam Baron receives funding from the Australian Research Council. </span></em></p>
Energy isn’t really made of anything else. It’s a kind of capacity to do things
Sam Baron, Associate professor, Australian Catholic University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/170108
2021-11-01T02:27:07Z
2021-11-01T02:27:07Z
LED face masks are popular on social media for glowing skin – but they could disrupt your sleep
<figure><img src="https://images.theconversation.com/files/429513/original/file-20211101-23-k9xukq.jpg?ixlib=rb-1.1.0&rect=42%2C42%2C4681%2C3109&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/woman-led-light-therapy-facial-beauty-1506384749">Shutterstock</a></span></figcaption></figure><p>LED face masks are the latest device promoted on social media as a marriage of technology and beauty. </p>
<p>A range of celebrities have endorsed portable versions of the product that was previously offered in beauty salons. Actress Olivia Munn <a href="https://www.usmagazine.com/stylish/pictures/celebrities-who-use-led-light-therapy-at-home-treatment-benefits/olivia-munn-19/">carries hers with her at all times</a>. Julia Roberts, Victoria Beckham and Chrissy Tiegen are also <a href="https://www.harpersbazaar.com/uk/beauty/skincare/a31908990/celebrity-led-mask/">reportedly</a> fans. The trend has even achieved the social media holy grail – a Kardashian Instagram <a href="https://www.instagram.com/p/BCemzbnk1qQ/?taken-by=kourtneykardash&hl=en%22">post</a>. </p>
<p>But regardless of whether they’ll help make your skin glow, our understanding of circadian rhythms suggests they have the potential to disrupt users’ sleep-wake cycles.</p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://twitter.com/TheCut/status/1445116733170278403","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/6-ways-to-stop-daylight-saving-derailing-your-childs-sleep-123871">6 ways to stop daylight saving derailing your child’s sleep</a>
</strong>
</em>
</p>
<hr>
<h2>Daily rhythms</h2>
<p>The human body has its own internal clock which, among other things, helps to control our sleep-wake patterns. This internal clock is influenced by several factors, the most potent being light exposure directly into the eyes. More specifically, short-wavelength “blue light” <a href="https://journals.sagepub.com/doi/10.1177/0748730415585413">influences this system the most</a>. </p>
<p>Exposure to this type of light at night has been shown <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/jpi.12562">interrupt the production of melatonin</a> – also known as “the sleep hormone”. <a href="https://www.psychiatrictimes.com/view/role-melatonin-circadian-rhythm-sleep-wake-cycle">Melatonin</a> is produced by the pineal gland in the brain and released within 2 hours of your habitual bedtime – preparing the body for sleep. But bright blue light exposure may interrupt this process. </p>
<p>There are a range of sources for blue light – including our beloved phones, electronic devices and also the room lighting in our homes. While it has become a common recommendation to avoid using electronic devices close to bedtime, in the context of blue light exposure, our phones and tablets <a href="https://winksleep.online/blog/65-blue-screenlight-making-it-harder-to-fall-asleep-is-the-number-1-sleep-myth-of-our-time">do not seem to be bright enough to impact sleep</a>. In fact, home lighting appears to have a greater influence – likely due to the <a href="https://sleepjunkies.com/home-lighting-circadian-rhythms/">transition to energy-efficient LED, “blue light” wavelength light</a>.</p>
<p>Last year, Monash University researchers examined sleep and light exposure in 57 participants, finding that <a href="https://www.nature.com/articles/s41598-020-75622-4#Sec7">nearly half of them had LED lighting that suppressed melatonin by 50%</a>. The study also found those with greater evening light exposure had increased wakefulness after bedtime. </p>
<p>Insufficient sleep has been shown to increase the likelihood of poor health outcomes, including <a href="https://academic.oup.com/eurheartj/article/32/12/1484/502022">cardiovascular disease</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="woman with phone in bed" src="https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427973/original/file-20211022-23-1twj2py.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Room LED lighting may be a bigger issue than phones and devices when it comes to sleep disruption.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/closeup-asian-women-using-smartphone-late-1746438284">Shutterstock</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/poor-sleep-is-really-bad-for-your-health-but-we-found-exercise-can-offset-some-of-these-harms-163270">Poor sleep is really bad for your health. But we found exercise can offset some of these harms</a>
</strong>
</em>
</p>
<hr>
<h2>How face masks compare to other LED sources</h2>
<p>LED mask manufacturers say they are <a href="https://www.marieclaire.com/beauty/g32894063/led-light-therapy-masks/">the “future of skin care”</a>, with masks emitting light at different wavelengths to target particular skin-related outcomes. </p>
<p>Several devices are FDA-approved in the United States, and claim to <a href="https://www.violetgrey.com/product/led-mask/DG-BA568110?utm_source=pepperjam&utm_medium=affiliate&utm_campaign=21181&clickId=3730626806">target acne with “blue light” modes</a> – the precise wavelength range that may impact melatonin production. </p>
<p>To date, no experimental research studies have examined the impact of these devices, and their blue light settings, on sleep or the human body clock. But given the device’s proximity to users’ eyes and the intensity of LED light bulbs, it is reasonable to flag concerns about their possible impact on our body clock. </p>
<p><a href="https://lens.monash.edu/@sean-cain">Sean Cain</a>, a leading scientist on the impact of light exposure on human health, coined an analogy to provide perspective to the sources of artificial light. The light we receive from electronic devices can be thought of as like a glass of water being poured over your head, while home LED lighting is more like a bucket of water. In keeping with this analogy, could LED masks be something on the scale of a bathtub or swimming pool? Further research could quantify their effect. </p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://www.instagram.com/p/BCemzbnk1qQ/?taken-by=kourtneykardash\u0026hl=en","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/snooze-blues-how-using-your-favourite-song-as-an-alarm-can-help-you-wake-up-more-alert-158233">Snooze blues? How using your favourite song as an alarm can help you wake up more alert</a>
</strong>
</em>
</p>
<hr>
<h2>You can still make like a Kardashian … in the daytime</h2>
<p>These concerns, based on well-established circadian principles, do not rule out the use of these devices entirely. However, it is important for people who use them to avoid doing so at night – especially on the blue light settings. </p>
<p>Ideally, use of the masks should be during daylight hours, to avoid potential sleep disturbances and/or shifts in the human body clock. Future research could clarify any negative outcomes associated with these devices and potentially prompt manufacturers to provide recommendations on the timing of their use.</p><img src="https://counter.theconversation.com/content/170108/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dean J. Miller's position at CQUniversity is funded by WHOOP inc . </span></em></p>
LED face masks are popular with celebrities and promise a glowing complexion. But should they come with ‘daytime use’ recommendation?
Dean J. Miller, Research Officer, CQUniversity Australia
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/169602
2021-10-26T12:19:57Z
2021-10-26T12:19:57Z
Type of ultraviolet light most effective at killing coronavirus is also the safest to use around people
<figure><img src="https://images.theconversation.com/files/428067/original/file-20211022-9818-i87045.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5779%2C3752&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">UV light at most wavelengths can kill COVID–19. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/lamp-for-sterilization-covid-19-prevention-concept-royalty-free-image/1296016011?adppopup=true">andriano_cz/iStock via Getty Images</a></span></figcaption></figure><p>Scientists have long known that ultraviolet light can <a href="https://theconversation.com/ultraviolet-light-can-make-indoor-spaces-safer-during-the-pandemic-if-its-used-the-right-way-141512">kill pathogens on surfaces and in air and water</a>. <a href="https://www.nytimes.com/2020/03/28/travel/coronavirus-hotels-private-jets-virtual-spas.html">UV robots are used to disinfect</a> empty hospital rooms, buses and trains; UV bulbs in HVAC systems eliminate pathogens in building air; and <a href="https://www.nytimes.com/2008/03/02/business/02novel.html">UV lamps kill bugs in drinking water</a>.</p>
<p>Perhaps you have seen UV wands, UV LEDs and UV air purifiers advertised as silver bullets to protect against the coronavirus. While decades of research have looked at the ability of UV light to kill many pathogens, there are no set standards for UV disinfection products with regard to the coronavirus. These products may work to kill SARS-CoV-2, the virus that causes COVID-19, but they also may not. </p>
<p>I am an <a href="https://scholar.google.com/citations?user=uAS7KNUAAAAJ&hl=en&oi=ao">environmental engineer and expert in UV disinfection</a>. In May 2021, my colleagues and I set out to accurately test various UV systems and see <a href="https://doi.org/10.1128/AEM.01532-21">which was the most effective</a> at killing off – or inactivating – SARS-CoV-2.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing UV light breaking down a strand of DNA." src="https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/428307/original/file-20211025-27-12cylg0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When UV light enters a cell, it breaks the bonds that hold DNA or RNA together.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:DNA_UV_mutation.svg#/media/File:DNA_UV_mutation.svg">NASA/David Herring via WikimediaCommons</a></span>
</figcaption>
</figure>
<h2>How does UV light kill a virus?</h2>
<p>Light is categorized by wavelength – the distance between peaks of a wave of light – and is measured in nanometers. UV wavelengths range from 100 to 400 nanometers – shorter in wavelength than the violet hues in visible light – and are invisible to the human eye. As wavelength shortens, photons of light contain higher amounts of energy.</p>
<p>Different wavelengths of UV light work better than others for inactivating viruses, and this depends on how well the wavelengths are absorbed by the virus’s DNA or RNA. When UV light gets absorbed, the photons of light transfer their energy to and <a href="https://doi.org/10.1038/s41598-021-93231-7">damage the chemical bonds of the genetic material</a>. The virus is then unable to replicate or cause an infection. Researchers have also shown the proteins that viruses use to attach to a host cell and initiate infection – like the spike proteins on a coronavirus – are also <a href="https://doi.org/10.1021/acs.est.7b04602">vulnerable to UV light</a>.</p>
<p>The dose of light matters too. Light can vary in intensity – bright light is more intense, and there is more energy in it than in dim light. Being exposed to a bright light for a short time can produce the same UV dose as being exposed to a dim light for a longer period. You need to know the right dose that can kill coronavirus particles at each UV wavelength.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A man with sunburned shoulders sitting on a beach." src="https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/428069/original/file-20211022-17-63e9kd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sunburns are caused by UV light damaging skin cells.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/man-with-sun-burnt-shoulders-sitting-on-beach-rear-royalty-free-image/85775471?adppopup=true">Ian Hooton/Science Photo Library via Getty Images</a></span>
</figcaption>
</figure>
<h2>Making ultraviolet lights safe for people</h2>
<p>Traditional UV systems use wavelengths at or around 254 nanometers. At these wavelengths the light is dangerous to human skin and eyes, <a href="https://doi.org/10.1111/php.13402">even at low doses</a>. Sunlight includes UV light near these wavelengths; anyone who has ever gotten a bad sunburn knows just how dangerous UV light can be. </p>
<p>However, recent research has shown that at certain UV wavelengths – specifically below 230 nanometers – the high-energy photons <a href="https://iuva.org/resources/covid-19/Far%20UV-C%20Radiation-%20Current%20State-of%20Knowledge.pdf">are absorbed by the top layers of dead skin cells</a> and don’t penetrate into the active skin layers where damage can occur. Similarly, the <a href="https://doi.org/10.1111/php.13402">tear layer around eyes also blocks out these germicidal UV rays</a>.</p>
<p>This means that at wavelengths of UV light below 230 nanometers, people can move around more freely while the air around them is being disinfected in real time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a lamp above a sample of water containing the coronavirus." src="https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=317&fit=crop&dpr=1 600w, https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=317&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=317&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/428310/original/file-20211025-19717-bfs99z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers used this setup to test multiple different UV lights at various doses to see what it took to kill SARS-CoV-2.</span>
<span class="attribution"><span class="source">Karl Linden</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Testing different wavelengths</h2>
<p>My colleagues and I tested five commonly used UV wavelengths to see which work best to inactivate SARS-CoV-2. Specifically, we tested how large a dose is needed to <a href="https://doi.org/10.1128/AEM.01532-21">kill 90% to 99.9% of the viral particles present</a>.</p>
<p>We ran these tests in a biosafety level three facility at the <a href="https://environmentalscience.cals.arizona.edu/person/charles-chuck-gerba">University of Arizona</a> that is built to handle lethal pathogens. There we tested numerous lights across the UV spectrum, including UV LEDs that emit light at 270 and 282 nanometers, traditional UV tube lamps at 254 nanometers and a newer technology called an <a href="https://www.ushio.eu/excimer-explained/">excited dimer, or excimer, UV source</a> at 222 nanometers. </p>
<p>To test each device we spiked a sample of water with millions of SARS-CoV-2 viruses and coated a petri dish with a thin layer of this mixture. We then shined UV light on the petri dish until we achieved a specific dose. Finally we examined the viral particles to see if they could still infect human cells in culture. If the viruses could infect the cells, the dose was not high enough. If the viruses did not cause an infection, the UV source at that dose had successfully killed the pathogen. We carefully repeated this process for a range of UV doses using the five different UV devices.</p>
<p>While all of the wavelengths we tested can inactivate SARS-CoV-2 at very low doses, the ones that required the lowest dose were the <a href="https://doi.org/10.1128/AEM.01532-21">systems that emit UV light at a wavelength of 222 nanometers</a>. In our experiment, it took a dose of less than 2 millijoules of energy per square centimeter to kill 99.9% of viral particles. This translates to needing about 20 seconds to disinfect a space receiving a low intensity of short wavelength UV light, similar to that used in our test.</p>
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<p>These 222-nanometer systems are almost twice as effective as conventional UV tube lamps, which are often used in ultraviolet disinfecting systems. But importantly, the winning lamp also happens to be the safest for humans, too. At the same UV light intensity it takes to kill 99.9% of SARS-CoV-2 in 20 seconds, a person could be safely exposed to 222-nanometer light for <a href="https://doi.org/10.1111/php.13402">up to one hour and 20 minutes</a>.</p>
<p>What this means is that <a href="https://edenpark.com/">widely available</a> types of <a href="https://www.ushio.com/product/care222-filtered-far-uv-c-excimer-lamp-module/">UV lamp</a> lights can be used to safely knock down levels of the coronavirus with people present.</p>
<h2>Better use of existing tech</h2>
<p>Many places or organizations – ranging from the <a href="https://www.defense.gov/News/Feature-Stories/Story/Article/2309289/air-guard-wing-receives-dods-first-uv-light-disinfectant-system/">U.S. Air Force</a> to the <a href="https://www.spaceneedle.com/elevatingclean">Space Needle in Seattle</a> to <a href="https://www.boeing.com/confident-travel/research/CAP-3_Disinfection_with_Far-UV.html">Boeing</a> – are already using or investigating ways to use UV light in the 222 nanometer range to protect public health. </p>
<p>I believe that our findings are important because they quantify the exact doses needed to achieve various levels of SARS-CoV-2 control, whether that be killing 90% or 99.9% of viral particles. </p>
<p>Imagine coffee shops, grocery stores, school classrooms, restaurants and concert venues now made safe by this technology. And this is not a solution for just SARS-CoV-2. These technologies could help protect human health in public spaces in future times of crisis, but also during times of relative normalcy, by reducing exposure to everyday viral and bacterial threats.</p><img src="https://counter.theconversation.com/content/169602/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Karl Linden advises various companies promoting the use of UV light for disinfection. He receives funding from federal agencies and industry to conduct research in his role as a professor at the University of Colorado Boulder. He is affiliated with the International Ultraviolet Association. </span></em></p>
UV lights come in a variety of different wavelengths, but not all are equally effective at disinfection. Researchers tested a number of commercially available lights to find the best.
Karl Linden, Professor of Environmental Engineering and the Mortenson Professor in Sustainable Development, University of Colorado Boulder
Licensed as Creative Commons – attribution, no derivatives.