tag:theconversation.com,2011:/us/topics/particles-21527/articlesParticles – The Conversation2024-02-02T13:17:06Ztag:theconversation.com,2011:article/2208182024-02-02T13:17:06Z2024-02-02T13:17:06ZHow can I get ice off my car? An engineer who studies airborne particles shares some quick and easy techniques<figure><img src="https://images.theconversation.com/files/572255/original/file-20240130-29-7n5wna.jpeg?ixlib=rb-1.1.0&rect=0%2C3%2C1024%2C763&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Condensation and cold combine to create that layer of ice on car windshields in winter. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Oblodzone_szyby_samochodu,_zima_2009_%28ubt%29.jpeg">Tomasz Sienicki/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>If you live somewhere that gets cold in the winter, you’ve probably seen cars parked outdoors covered in a thin layer of ice on a chilly morning. But what causes this frost, and how can you get rid of it quickly?</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=xcpTqRYAAAAJ&hl=en">mechanical engineering professor</a> who studies how water vapor interacts with airborne particles under different atmospheric conditions. Frosty windshields are similar to some of the thermodynamic questions I study in the lab, and they’re also a pesky issue that I deal with every winter on my way to work. </p>
<h2>Windshield condensation</h2>
<p>The air in Earth’s atmosphere always contains a certain amount of water vapor, but there’s only so much water vapor the air can hold. Scientists call that limit 100% <a href="https://www.britannica.com/science/humidity">relative humidity</a>. <a href="https://www.weather.gov/arx/why_dewpoint_vs_humidity">The dew point</a> refers to the temperature at which relative humidity reaches 100%. </p>
<p>Wet air has high dew point temperature, while dry air has a low dew point temperature. With each degree drop in temperature, the air gets closer to its dew point temperature – or its water vapor carrying capacity. Any cooling after the dew point temperature has been reached causes <a href="https://sealevel.jpl.nasa.gov/ocean-observation/understanding-climate/air-and-water/">water to condense onto surfaces</a>, or form into fog.</p>
<p>Overnight, car windshields facing the cold dark sky are <a href="https://www.energy.gov/energysaver/principles-heating-and-cooling">radiatively cooled</a>, meaning they release heat out into their surrounding area in the form of visible and invisible light. As air comes in contact with the cold windshield, it can reach its dew point temperature. Then, the water vapor condenses onto the windshield.</p>
<p>When this radiative cooling drops the temperature on the windshield’s surface to <a href="https://www.britannica.com/science/freezing-point">below the freezing point</a>, 32 degrees Fahrenheit (zero degrees Celsius), the layer of condensed water on the windshield turns to frost. </p>
<h2>Defrosting your car</h2>
<p>To defrost an icy windshield, you can follow a few different approaches, some of which take longer and require more effort than others.</p>
<p>One option is to directly spray a small amount of warm liquid on the layer of frost to help melt it. For this approach to work, the spray liquid must be hot enough to raise the overall temperature of the frost layer to above <a href="https://pubchem.ncbi.nlm.nih.gov/ptable/melting-point/">the melting point</a>. But the temperature can’t be way hotter than the temperature of the glass or you’ll crack your windshield. </p>
<p>A better way to melt the ice without damaging your car is to spray your windows with a warm liquid that has a lower freezing point than water, like a mixture of rubbing alcohol and water. This warm mixture will melt the frost layer without heating up the glass, and the resulting liquid layer on the windshield will have a lower freezing point than water. It will remain liquid, and you can wipe it away with your windshield wipers. </p>
<p>Similar alcohol and water mixtures – <a href="https://www.britannica.com/science/glycol">glycol, for example</a> – are commonly used to maintain the <a href="https://mayekawa.es/images/pdf/ASHRAE_ENERGY_EFFICIENT_ICE_RINK_2015.pdf">icy surface of skating rinks</a>.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/A2Kl04dHm4k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A mix of water and rubbing alcohol can melt ice on your windshield.</span></figcaption>
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<p>This approach can melt the ice reasonably quickly and easily, without too much effort. You don’t even have to turn on your car. </p>
<p>If you have a little more time, you can start the car and run <a href="https://www.lifewire.com/how-do-car-defrosters-work-534663">the air defrost system</a> to blow hot air – aim for above 80 degrees Fahrenheit – onto the inside of the windshield. This warms the windshield and will eventually melt the frost layer. Once you see some melting, you can use the windshield wipers to wipe the rest of the ice away. </p>
<p>This option consumes more energy, as your car will have to heat up the windshield, but it doesn’t require you to do much. </p>
<p>Using the defrost system to blow warm air toward the windshield will also help to clear the inside of the windshield when it gets fogged up from condensation. Otherwise, if it’s dry outside, you can also clear up windshield fog by opening the car window and letting in outside air.</p>
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<a href="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person wearing a winter jacket uses a scraper on their frost-covered windshield." src="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.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"></a>
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<span class="caption">You can use an ice scraper to break the ice on your windshield into chunks, so your wiper blades can clean them off.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/ColoradoWeather/c8d71e03eb5144afad7c01e72eccf5c2/photo?Query=windshield%20wipers&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=296&digitizationType=Digitized&currentItemNo=17&vs=true&vs=true">AP Photo/David Zalubowski</a></span>
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<p>If you are in a hurry or need some exercise, you can use an ice scraper to break up frost on your windshield, creating smaller islands of ice. The windshield wiper can then mechanically dislodge the chunks by moving them around and melting them. This requires more energy on your part, but it doesn’t require much from your car.</p>
<p>If you have a relaxed start to your day, you can let the Sun warm the windshield and slowly melt the frost layer for you. This technique saves energy in every way imaginable.</p><img src="https://counter.theconversation.com/content/220818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suresh Dhaniyala 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>When you’re running late in the winter, you don’t want to have to spend time scraping frost off your windshield. Try some expert-recommended techniques instead.Suresh Dhaniyala, Bayard D. Clarkson Distinguished Professor of Mechanical and Aeronautical Engineering, Clarkson UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1972232023-01-17T06:07:50Z2023-01-17T06:07:50ZCurious Kids: is there such a thing as nothing?<figure><img src="https://images.theconversation.com/files/503647/original/file-20230109-5923-hy7ptu.jpg?ixlib=rb-1.1.0&rect=0%2C744%2C6989%2C3688&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/astronaut-leaving-earth-searching-new-home-1666242118">oneinchpunch/Shutterstock</a></span></figcaption></figure><p><strong>Is there such a thing as nothing? – Reggie, aged seven, Darlington</strong></p>
<p><strong>Could someone see nothing? What does nothing look like? – Maya, aged nine, Bristol</strong></p>
<p>Imagine you hear a noise outside your window. You think it might be a dog barking, or maybe a child shouting. But when you get up and have a look, there’s no dog or child. “Oh,” you say, “there’s nothing there.”</p>
<p>We often say we’ve “got nothing”, or that there’s “nothing there”. But what we mean is that we haven’t got a particular thing. When you looked outside, lots of things were there – trees, houses, cars and bicycles maybe – but the particular thing you were looking for wasn’t there. </p>
<p>Even if you were looking into a completely empty room, there would still be things there. There’s always air, and <a href="https://forces.si.edu/atmosphere/02_01_02.html">air is made up of molecules</a>, like the oxygen we need to breathe in to keep us alive. </p>
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<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">
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<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>
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<p>But what about space? There’s no air in space: that’s why astronauts need to wear a space suit that provides <a href="https://www.nasa.gov/audience/forstudents/nasaandyou/home/spacesuits_bkgd_en.html">oxygen to breathe</a> if they go on a “space walk”.</p>
<p>There are actually molecules in space, too, but they are so few and far between that it’s mostly empty space. This is called <a href="https://www.sciencefocus.com/space/is-space-a-perfect-vacuum/">a vacuum</a>. We might think that the emptiness we can see in between stars in the night sky, where there are very few molecules, will be where we find “nothing”.</p>
<p>It turns out, though, when you look into the dark night sky, you are not seeing “nothing”. This empty space is filled with energy, and that’s something even if you cannot hold it in your hand. Energy is what makes things happen.</p>
<figure class="align-center ">
<img alt="Mother and child looking up at Milky Way" src="https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503670/original/file-20230109-13-hyqjpv.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">
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<span class="caption">Looking at the universe.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/silhouette-mother-child-sitting-together-hold-1085451182">KIDSADA PHOTO/Shutterstock</a></span>
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<p>Energy never goes away and it is never made out of nothing. When you run, the energy in your motion comes from the energy you got out of the food you ate. When you stop, that energy goes into heat and making a minuscule impact on the motion of the Earth as your feet rub against it when you brake.</p>
<p>Einstein realised that energy and particles (tiny bits of stuff) are two sides of the same coin. The tiniest things we know of – such as particles, which are more than a million billion times smaller than we are – are made from energy. <a href="https://academickids.com/encyclopedia/index.php/Quantum_mechanics">About a century ago</a> scientists realised that these tiny things act differently to bigger things in the universe. Their behaviour cannot be predicted precisely, and it can only be described with something called “<a href="https://www.newscientist.com/definition/quantum-mechanics/">quantum mechanics</a>”.</p>
<h2>Particles and anti-particles</h2>
<p>This also means that the content of vacuum is not precisely zero. Tiny particles in it can meet their exact opposites, “<a href="https://www.bbc.co.uk/news/science-environment-13667475">anti-particles</a>”. When this happens they cancel each other out and vanish, but this leaves behind the energy that had made them in the first place.</p>
<p>The vacuum of space is a “soup” of energy and pairs of particles and anti-particles. The Dutch scientist <a href="https://www.scientificamerican.com/article/something-from-nothing-vacuum-can-yield-flashes-of-light/">Hendrik Casimir</a> suggested a way of proving this in 1948 – and half a century later, we have found out that he was right.</p>
<p>This energy in the vacuum also makes the universe <a href="https://www.space.com/42178-bringing-dark-energy-into-the-light.html">grow bigger</a> with time, like when you blow up a balloon.</p>
<p>There are other things in the vacuum of space, too. Space contains “fields”, which are a way to describe the influence something can have throughout a region of space. For instance, the Earth pulls at the Moon through space by way of a field called “gravity”. </p>
<p>When famous physicist Albert Einstein was figuring out how gravity works, he found that <a href="https://www.sciencenews.org/article/einsteins-genius-changed-sciences-perception-gravity">space actually has shape</a>. Something with a lot of mass, like a star or a planet, bends the space around it, like how a heavy ball held in the middle of an outstretched blanket makes the blanket change shape. If space has shape then surely space cannot be nothing.</p>
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<img alt="Earth and Moon shown with spacetime bending in green lines" src="https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504659/original/file-20230116-5823-nz2wpv.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">
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<span class="caption">Space bending around a planet.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/gravity-field-bend-spacetime-relativity-earth-1330914503">canbedone/Shutterstock</a></span>
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<p>It looks as if we won’t find “nothing” anywhere in our universe. Perhaps the place to look for nothing is beyond or outside the universe. This may be an impossible question, though. The universe is where space is, where stuff and energy are, and where time is. </p>
<h2>Outside the universe?</h2>
<p>Physicist <a href="https://www.newscientist.com/article/2053929-a-brief-history-of-stephen-hawking-a-legacy-of-paradox/">Stephen Hawking</a> explained the universe as having <a href="https://www.nextbigfuture.com/2018/03/hawking-talks-about-no-clear-big-bang-and-no-boundary-to-space-time.html">no boundary</a>, either in space or in time. When you are inside a house, the walls are the boundary and you could think about what’s outside, perhaps even see it through a window. But if the universe has no boundary, then there is no such thing as “outside” (or “before”). We could call it “nothing”, but it would be better to say it’s the absence of anything.</p>
<p>Nothing does exist as an idea. We can use “nothing” to count with: the idea of “zero” was being <a href="https://www.history.com/news/who-invented-the-zero">used 4,000 years ago</a>, and the oval symbol we use today was invented over 1,000 years ago.</p>
<p>Perhaps this is the only place where “nothing” exists: as an idea in our minds.</p><img src="https://counter.theconversation.com/content/197223/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jacco van Loon 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>Nothing is harder to find than you might think.Jacco van Loon, Astronomer, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1802312022-05-24T12:27:14Z2022-05-24T12:27:14ZNuclear isomers were discovered 100 years ago, and physicists are still unraveling their mysteries<figure><img src="https://images.theconversation.com/files/464572/original/file-20220520-20-x6afa8.jpg?ixlib=rb-1.1.0&rect=0%2C112%2C7367%2C5395&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Protons and neutrons in an atom's nucleus can be arranged in different configurations, creating nuclear isomers. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/atomic-structure-illustration-royalty-free-image/1339206072?adppopup=true">KTSdesign/SciencePhotoLibrary via Getty Images</a></span></figcaption></figure><p>Nobel laureate Otto Hahn is <a href="https://www.nobelprize.org/prizes/chemistry/1944/hahn/facts/">credited with the discovery of nuclear fission</a>. Fission is one of the most important discoveries of the 20th century, yet Hahn considered something else to be his <a href="https://doi.org/10.1007/978-1-4613-0101-1">best scientific work</a>.</p>
<p>In 1921, he was studying radioactivity at the Kaiser Wilhelm Institute for Chemistry in Berlin, Germany, when he noticed something he could not explain. One of the elements he was working with wasn’t behaving as it <a href="https://doi.org/10.1007/BF01491321">should have</a>. Hahn had unknowingly discovered the first nuclear isomer, an atomic nucleus whose protons and neutrons are arranged differently from the common form of the element, causing it to have unusual properties. It took another 15 years of discoveries in nuclear physics to be able to explain Hahn’s observations. </p>
<p><a href="https://scholar.google.com/citations?user=vlmJRrsAAAAJ&hl=en&oi=ao">We are</a> two <a href="https://www.physics.uoguelph.ca/people/dennis-mucher">professors of</a> nuclear physics who study rare nuclei including nuclear isomers.</p>
<p>The most common place to find isomers is inside stars, where they play a role in the <a href="https://theconversation.com/elements-from-the-stars-the-unexpected-discovery-that-upended-astrophysics-66-years-ago-93916">nuclear reactions that create new elements</a>. In recent years, researchers have begun to explore how isomers can be put to use for the benefit of humanity. They are already <a href="https://www.bnl.gov/newsroom/news.php?a=24796">used in medicine</a> and could one day offer powerful options for energy storage <a href="https://physicsworld.com/a/celebrating-a-century-of-nuclear-isomers">in the form of nuclear batteries</a>.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/yGHuZnfnUtI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This video shows radioactive uranium-238 in a chamber full of mist. The streaks are created as particles are emitted from the radioactive sample and pass through water vapor.</span></figcaption>
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<h2>On the hunt for radioactive isotopes</h2>
<p>In the early 1900s, scientists were on the hunt for new radioactive elements. An element is considered radioactive if it spontaneously releases particles in a process called <a href="https://www.youtube.com/watch?v=IDkNlU7zKYU">radioactive decay</a>. When this happens, the element is transformed over time into a different element.</p>
<p>At that time, scientists relied on three criteria to discover and describe a new radioactive element. One was to look at chemical properties – how the new element reacts with other substances. They also measured the type and energy of the particles released during the radioactive decay. Finally, they would measure how fast an element decayed. Decay speeds are described using the term half-life, which is the amount of time it takes for half of the initial radioactive element to decay into something else.</p>
<p>By the 1920s, physicists had discovered some radioactive substances with identical chemical properties but different half-lives. These are called isotopes. Isotopes are different versions of the same element that have the same number of protons in their nucleus, but different numbers of neutrons.</p>
<p>Uranium is a radioactive element with many isotopes, two of which occur naturally on Earth. These natural uranium isotopes decay into the element thorium, which in turn decays into protactinium, and each has its own isotopes. Hahn and his colleague <a href="https://theconversation.com/lise-meitner-the-forgotten-woman-of-nuclear-physics-who-deserved-a-nobel-prize-106220">Lise Meitner</a> were the first to discover and identify many different isotopes originating from the decay of the element uranium.</p>
<p>All the isotopes they studied behaved as expected, except for one. This isotope appeared to have the same properties as one of the others, but its half-life was longer. This made no sense, as Hahn and Meitner had placed all the known isotopes of uranium in a neat classification, and there were no empty spaces to accommodate a new isotope. They called this substance “uranium Z.” </p>
<p>The radioactive signal of uranium Z was about <a href="https://doi.org/10.1007/BF01491321">500 times weaker</a> than the radioactivity of the other isotopes in the sample, so Hahn decided to confirm his observations by using more material. He purchased and chemically separated uranium from 220 pounds (100 kilograms) of highly toxic and rare uranium salt. The surprising result of this second, more precise experiment suggested that the mysterious uranium Z, now known as protactinium-234, was an already known isotope, but with a very different half-life. This was the first case of an isotope with two different half-lives. Hahn published his discovery of the <a href="https://doi.org/10.1007/BF01491321">first nuclear isomer</a>, even though he could not fully explain it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the labeled parts of an atom." src="https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/464579/original/file-20220520-24-4pnisz.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">The discovery that the nucleus of an atom is made of both protons and neutrons allowed physicists to explain isotopes as well as uranium Z.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/bohr-atomic-model-of-a-nitrogen-atom-vector-royalty-free-illustration/1300855627?adppopup=true">PANGGABEAN/iStock via Getty Images</a></span>
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</figure>
<h2>Neutrons complete the story</h2>
<p>At the time of Hahn’s experiments in the 1920s, scientists still thought of atoms as a clump of protons surrounded by an equal number of electrons. It wasn’t until 1932 that James Chadwick suggested a third particle – neutrons – were also <a href="https://doi.org/10.1098/rspa.1932.0112">part of the nucleus</a>.</p>
<p>With this new information, physicists were immediately able to explain isotopes – they are nuclei with the same number of protons and different numbers of neutrons. With this knowledge, the scientific community finally had the tools to understand uranium Z. </p>
<p>In 1936 <a href="https://doi.org/10.1007/BF01497732">Carl Friedrich von Weizsäcker proposed</a> that two different substances could have the same number of protons and neutrons in their nuclei but in different arrangements and with different half-lives. The arrangement of protons and neutrons that results in the lowest energy is the most stable material and is called ground state. Arrangements resulting in less stable, higher energies of an isotope are called isomeric states.</p>
<p>At first nuclear isomers were useful in the scientific community only as a means to understand how nuclei behave. But once you understand the properties of an isomer, it’s possible to start asking how they can be used.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person getting an injection of a fluid." src="https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/464581/original/file-20220520-19-ubuap7.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>
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<span class="caption">Technetium-99m is an isomer that is commonly used for diagnosing many diseases, as doctors can easily track its movement through the human body. This photo shows a medical professional injecting technetium-99m into a patient.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Technetium-99m#/media/File:Tc99minjektion.jpg">Bionerd/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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</figure>
<h2>Isomers in medicine and astronomy</h2>
<p>Isomers have important applications in medicine and are used in tens of millions of diagnostic procedures annually. Since isomers undergo radioactive decay, special cameras can track them as they move through the body.</p>
<p>For example, technetium-99m is an isomer of technetium-99. As the isomer decays, it emits photons. Using photon detectors, doctors can track how technetium-99m <a href="https://doi.org/10.2967/jnumed.116.187807">moves throughout the body</a> and <a href="https://www.ncbi.nlm.nih.gov/books/NBK559013/">create images</a> of the heart, brain, lungs and other critical organs to help diagnose diseases including cancer. Radioactive elements and isotopes are normally dangerous because they emit charged particles that damage bodily tissues. Isomers like technetium are <a href="https://doi.org/10.4103/0971-6203.94740">safe for medical use</a> because they emit only a single, harmless photon at a time and nothing else as they decay.</p>
<p>Isomers are also important in astronomy and astrophysics. Stars are fueled by the energy released during nuclear reactions. Since isomers are <a href="https://iopscience.iop.org/article/10.3847/1538-4365/abc41d/pdf">present in stars</a>, nuclear reactions are different than if a material were in its ground state. This makes the study of isomers critical for understanding how stars produce all the elements in the universe.</p>
<h2>Isomers in the future</h2>
<p>A century after Hahn first discovered isomers, scientists are still <a href="https://doi.org/10.1038/d41586-022-00711-5">discovering new isomers using powerful research facilities</a> around the world, including the the <a href="https://frib.msu.edu/">Facility for Rare Isotope Beams</a> at Michigan State University. This facility came online in May 2022, and we hope it will unlock more than 1,000 new isotopes and isomers.</p>
<p>Scientists are also investigating whether nuclear isomers could be used to <a href="https://doi.org/10.1038/d41586-019-02664-8">build the world’s most accurate clock</a> or whether isomers may one day be the basis for the next generation of <a href="https://www.semanticscholar.org/paper/Controlled-Extraction-of-Energy-from-Nuclear-Litz-Merkel/7f0f5cb36908e0a890a21d33916f940735bd4152">batteries</a>. More than 100 years after the detection of a small anomaly in uranium salt, scientists are still on the hunt for new isomers and have just begun to reveal the full potential of these fascinating pieces of physics.</p><img src="https://counter.theconversation.com/content/180231/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Artemis Spyrou receives funding from the National Science Foundation in the US </span></em></p><p class="fine-print"><em><span>Dennis Mücher receives funding from the Natural Sciences and Engineering Research Council of Canada and the Social Sciences and Humanities Research Council of Canada.</span></em></p>Nuclear isomers are rare versions of elements with properties that mystified physicists when first discovered. Isomers are now used in medicine and astronomy, and researchers are set to discover thousands more of them.Artemis Spyrou, Professor of Nuclear Physics, Michigan State UniversityDennis Mücher, Associate Professor of Nuclear Physics, University of GuelphLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1815822022-04-20T19:36:25Z2022-04-20T19:36:25ZShould you wear a mask on a plane, bus or train when there’s no mandate? 4 essential reads to help you decide<figure><img src="https://images.theconversation.com/files/458911/original/file-20220420-25-qleeh8.jpg?ixlib=rb-1.1.0&rect=187%2C130%2C5120%2C3082&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It is now up to individuals whether to wear masks in airports and other mass transit areas.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/TravelMaskMandate/28ce57b3790b493190c8409bf0cd06d0/photo?Query=mask%20plane&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=469&currentItemNo=22">AP Photo/Evan Vucci</a></span></figcaption></figure><p>On April 18, 2022, a judge in Florida <a href="https://www.cnn.com/us/live-news/federal-mask-mandate-airlines-04-19-22/index.html">struck down the federal mandate requiring passengers on mass transit to wear masks</a>. While the U.S. Centers for Disease Control and Prevention still recommends that passengers mask up while on planes, trains or buses, it is no longer a requirement. When asked whether people should wear masks on planes, President Joe Biden replied: “<a href="https://www.cnn.com/us/live-news/federal-mask-mandate-airlines-04-19-22/index.html">That’s up to them</a>.”</p>
<p>The Conversation has been covering the science of masks since the beginning of the pandemic. Masking may no longer be required on mass transit, but you can always choose to still wear a mask. For those worried about being exposed to SARS-CoV-2 or developing COVID-19, below are highlights from four articles exploring the benefits of wearing a mask and how to get the most protection from wearing one. </p>
<h2>1. Masks can protect the person wearing them</h2>
<p>A lot of the reason for wearing a mask is to protect others. But early on in the pandemic, <a href="https://profiles.ucsf.edu/monica.gandhi">Monica Gandhi, a professor of medicine</a> at the University of California, San Francisco, explained how masks can protect the wearer, too.</p>
<p>“When you wear a mask – even a cloth mask – you typically are <a href="https://dx.doi.org/10.7326%2FM20-2567">exposed to a lower dose of the coronavirus</a> than if you didn’t,” Gandhi writes. “Both <a href="https://doi.org/10.1073/pnas.2009799117">recent experiments in animal models</a> using coronavirus and nearly a <a href="https://doi.org/10.1038/nri2802">hundred years of viral research</a> show that <a href="https://theconversation.com/cloth-masks-do-protect-the-wearer-breathing-in-less-coronavirus-means-you-get-less-sick-143726">lower viral doses usually mean less severe disease.</a>”</p>
<p>Though it’s only one of many factors, “the amount of virus that you’re exposed to – called the viral inoculum, or dose – has <a href="https://doi.org/10.1038/nri2802">a lot to do with how sick you get</a>. If the exposure dose is very high, the immune response can become overwhelmed,” explains Gandhi. “On the other hand, if the initial dose of the virus is small, the immune system is able to contain the virus.”</p>
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Read more:
<a href="https://theconversation.com/cloth-masks-do-protect-the-wearer-breathing-in-less-coronavirus-means-you-get-less-sick-143726">Cloth masks do protect the wearer – breathing in less coronavirus means you get less sick</a>
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<p>The better the mask, the lower the exposure dose. And in the many months since Gandhi wrote that story, a lot of work has been done to determine which kinds of masks are most effective. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An N95, surgical and cloth mask." src="https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458910/original/file-20220420-18-nanbe4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&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">Not all masks offer the same amount of filtration.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/protective-face-masks-commonly-used-during-2020-royalty-free-image/1248294245?adppopup=true">Gaelle Beller Studio/Moment via Getty Images</a></span>
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<h2>2. What makes for a good mask?</h2>
<p>The first thing to consider when wearing a mask is whether it’s a good one. <a href="https://scholar.google.com/citations?hl=en&user=MaEhNkQAAAAJ">Christian L'Orange is a professor of mechanical engineering</a> and has been testing different masks for the state of Colorado since the pandemic started. He explains that there are two things that make for a protective mask. “First, there’s the ability of the material to capture particles. The second factor is the fraction of inhaled or exhaled air leaking out from around the mask – essentially, how well a mask fits.”</p>
<p>When it comes to these two attributes, L'Orange says, “<a href="https://theconversation.com/what-is-the-best-mask-for-covid-19-a-mechanical-engineer-explains-the-science-after-2-years-of-testing-masks-in-his-lab-175481">the N95 and KN95 masks are the best option</a>.” This performance has a lot to do with the materials they are made from. “These fibers are very tightly packed together so the gaps a particle must navigate through are very small. This results in a high probability that particles will end up touching and sticking to a fiber as they pass through a mask. These polypropylene materials also often <a href="https://www.thomasnet.com/articles/machinery-tools-supplies/what-is-melt-blown-extrusion/">have a static charge</a> that can help attract and catch particles.”</p>
<p>Fit is the second important factor for a mask. As L'Orange writes, “a mask can offer protection only if it doesn’t leak.” N95s and KN95s are stiff and seal much better than other masks.</p>
<p>If you don’t have access to an N95 or KN95, surgical masks should be your second choice. They are made of densely woven material, but they don’t seal perfectly. Cloth masks should be your last choice because of their generally loose weave and bad fit. But there are ways to improve the performance of surgical and cloth masks. </p>
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<a href="https://theconversation.com/what-is-the-best-mask-for-covid-19-a-mechanical-engineer-explains-the-science-after-2-years-of-testing-masks-in-his-lab-175481">What is the best mask for COVID-19? A mechanical engineer explains the science after 2 years of testing masks in his lab</a>
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<h2>3. How to make a mask fit well</h2>
<p>“No matter how good a mask’s material is, it won’t work well if it doesn’t fit well,” writes <a href="https://scholar.google.com/citations?user=fZJWmF8AAAAJ&hl=en&oi=ao">Scott Schiffres, a mechanical engineer</a> at Binghamton University.</p>
<p>There are <a href="https://theconversation.com/cdc-says-masks-must-fit-tightly-and-two-are-better-than-one-153778">two ways to improve the fit and performance of surgical and cloth masks</a>. The first, explains Schiffres, is simply wearing two masks. “Double-masking is wearing a cotton mask over a medical-procedure mask.” This can greatly improve the fit and add a little bit more filtration. The second approach is to knot and tuck a surgical mask so that it fits better. </p>
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<figcaption><span class="caption">Knotting and tucking a surgical mask can make it fit much better.</span></figcaption>
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<p>As Schiffres explains in his article, “Knotting and tucking entails tying a knot in the elastic loops that go over your ears, close to where they attach to the mask. Then, you tuck the extra mask fabric into the gap that is often present where the ear loops attach to the mask, and flatten that part as much as possible. Both of these tricks make a better fit and <a href="https://www.cdc.gov/mmwr/volumes/70/wr/mm7007e1.htm?s_cid=mm7007e1_w">decrease the mask-wearers’ exposure to potentially infectious aerosols by 95%</a> as compared with wearing no mask at all. That’s a <a href="https://doi.org/10.1017/dmp.2013.43">15% improvement over the 80% efficiency found when using a single surgical mask</a>.</p>
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Read more:
<a href="https://theconversation.com/cdc-says-masks-must-fit-tightly-and-two-are-better-than-one-153778">CDC says masks must fit tightly – and two are better than one</a>
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<h2>4. Breakthrough cases and new variants</h2>
<p>The final consideration when deciding to wear a mask isn’t about you. Doing so can protect others. </p>
<p><a href="https://scholar.google.com/citations?user=XY7DNtgAAAAJ&hl=en&oi=ao">Sara Sawyer</a>, <a href="https://www.colorado.edu/pac/arturo-barbachano-guerrero">Arturo Barbachano-Guerrero</a> and <a href="https://scholar.google.com/citations?user=l2lpnYkAAAAJ&hl=en&oi=ao">Cody Warren</a> are virologists and biologists at the University of Colorado Boulder. In <a href="https://theconversation.com/alpha-then-delta-and-now-omicron-6-questions-answered-as-covid-19-cases-once-again-surge-across-the-globe-174703">a recent story</a>, they write that omicron "is often able <a href="https://doi.org/10.1038/s41586-021-04385-3">to evade existing immunity</a> long enough to start an infection, cause symptoms and transmit onward to the next person.” “This explains why reinfections and vaccine <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effectiveness/why-measure-effectiveness/breakthrough-cases.html">breakthrough infections</a> seem to be more common with omicron.”</p>
<p>Case numbers are low for now, and therefore so is the risk of catching or transmitting the coronavirus. But it is not zero; some places have higher risk than others, and new variants can come on quickly. As the team writes, all new variants that spread widely – so-called <a href="https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-classifications.html#anchor_1632154493691">variants of concern</a> – are likely to be highly transmissible.</p>
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Read more:
<a href="https://theconversation.com/alpha-then-delta-and-now-omicron-6-questions-answered-as-covid-19-cases-once-again-surge-across-the-globe-174703">Alpha then delta and now omicron – 6 questions answered as COVID-19 cases once again surge across the globe</a>
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<p>The person next to you on the plane might not be wearing a mask and, as it stands, that is their choice to make. If you want to lower your own chances of catching or spreading the coronavirus, there are still a number of reasons to wear a well-fitting, high-quality mask. </p>
<p><em>Editor’s note: This story is a roundup of articles from The Conversation’s archives.</em></p><img src="https://counter.theconversation.com/content/181582/count.gif" alt="The Conversation" width="1" height="1" />
Despite the halt to the federal mask mandate for mass transit, people may still choose to protect themselves. For those who do, the type of mask and how well it fits matter.Daniel Merino, Associate Breaking News Editor and Co-Host of The Conversation Weekly PodcastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1754812022-01-25T19:43:00Z2022-01-25T19:43:00ZWhat is the best mask for COVID-19? A mechanical engineer explains the science after 2 years of testing masks in his lab<figure><img src="https://images.theconversation.com/files/442356/original/file-20220124-13-tvy45q.jpg?ixlib=rb-1.1.0&rect=0%2C700%2C5592%2C2859&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Not all masks offer the same level of protection for you and those around you.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/high-angle-view-of-masks-on-white-background-royalty-free-image/1226906207?adppopup=true">Martin Barth/EyeEm via Getty Images</a></span></figcaption></figure><p><em>The Centers for Disease Control and Prevention has changed its guidelines about masks and respirators a number of times over the past two years and gave its most recent update on Jan. 14, 2022. The update states that cloth face coverings offer the least protection from the coronavirus compared with surgical masks or N95-style masks. <a href="https://scholar.google.com/citations?user=MaEhNkQAAAAJ&hl=en&oi=ao">Christian L'Orange is a mechanical engineer</a> who has been testing the performance of masks for the state of Colorado since the beginning of the pandemic. He explains the new CDC guidelines and the science of what makes for a good mask.</em></p>
<h2>1. What changed in the CDC guidelines?</h2>
<p>The CDC <a href="https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/types-of-masks.html">currently recommends</a> that you “wear the most protective mask you can that fits well and that you will wear consistently.” The question, then, is what type of mask offers the best protection for you – by filtering the air you breathe in – and for those around you – by filtering the air you breathe out?</p>
<p>The CDC’s updated guidelines clearly lay out the <a href="https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/types-of-masks.html">hierarchy of protection</a>: “Loosely woven cloth products provide the least protection, layered finely woven products offer more protection, well-fitting disposable surgical masks and KN95s offer even more protection, and well-fitting NIOSH-approved respirators (including N95s) offer the highest level of protection.”</p>
<p>From a performance standpoint, the <a href="https://doi.org/10.1093/annhyg/meq044">N95 and KN95 masks are the best option</a>. While <a href="https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover-guidance.html">supply chain limitations</a> led to the CDC recommending people not wear N95s early in the pandemic, today they are easily obtainable and should be your first choice if you want the most protection. </p>
<p>The biggest change in the new guidelines has to do with cloth masks. Previous guidance from the CDC had said that some cloth masks could offer <a href="https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/masking-science-sars-cov2.html">acceptable levels of protection</a>. The new guidance still acknowledges that cloth masks can offer a small amount of protection but places them at the very bottom of the bunch.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A tangled mass of fibers, as seen through a microscope." src="https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/442355/original/file-20220124-21-3h1min.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">N95 masks are made from a tangled web of tiny plastic fibers that are very effective at trapping particles.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:%D0%92%D0%BD%D0%B5%D1%88%D0%BD%D0%B8%D0%B9_%D1%81%D0%BB%D0%BE%D0%B9_%D0%BC%D0%B5%D0%B4%D0%B8%D1%86%D0%B8%D0%BD%D1%81%D0%BA%D0%BE%D0%B9_%D0%BC%D0%B0%D1%81%D0%BA%D0%B8_(%D0%BF%D0%BE%D0%BB%D1%8F%D1%80%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8F).jpg#/media/File:%D0%92%D0%BD%D0%B5%D1%88%D0%BD%D0%B8%D0%B9_%D1%81%D0%BB%D0%BE%D0%B9_%D0%BC%D0%B5%D0%B4%D0%B8%D1%86%D0%B8%D0%BD%D1%81%D0%BA%D0%BE%D0%B9_%D0%BC%D0%B0%D1%81%D0%BA%D0%B8_(%D0%BF%D0%BE%D0%BB%D1%8F%D1%80%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8F).jpg">Alexander Klepnev via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>2. What’s the difference between N95, surgical and cloth mask materials?</h2>
<p>The effectiveness of a mask – how much protection a mask provides the wearer – is a combination of two major elements. First, there’s the ability of the material to capture particles. The second factor is the fraction of inhaled or exhaled air leaking out from around the mask – essentially, how well a mask fits. </p>
<p>Most mask materials can be thought of as a tangled net of small fibers. Particles passing through a mask are stopped when they physically touch one of those fibers. N95s, KN95s and surgical masks are purpose-built to be effective at removing particles from air. Their fibers are typically made from melt-blown plastics, often polypropylene, and the strands are tiny – often less than <a href="https://doi.org/10.1016/B978-185617375-9/50004-3">four thousandths of an inch (10 micrometers) in diameter</a> – or approximately one third the width of a human hair. These small fibers create a large amount of surface area within the mask for filtering and collecting particles. Although the specific construction and thickness of the materials used in N95, KN95 and surgical masks can vary, the filter media used are often quite similar.</p>
<p>These fibers are very tightly packed together so the gaps a particle must navigate through are very small. This results in a high probability that particles will end up touching and sticking to a fiber as they pass through a mask. These polypropylene materials also often have a <a href="https://www.thomasnet.com/articles/machinery-tools-supplies/what-is-melt-blown-extrusion/">static charge</a> that can help attract and catch particles. </p>
<p>Cloth masks are typically made of common woven materials such as cotton or polyester. The fibers are often large and less densely packed together, meaning particles can <a href="https://doi.org/10.1021/acsnano.0c05025">easily pass through the material</a>. Adding more layers can help, but stacking layers has a <a href="https://doi.org/10.1080/02786826.2020.1817846">diminishing return</a> and the performance of a cloth mask, even <a href="https://jv.colostate.edu/masktesting/">with multiple layers</a>, will still typically not match that of surgical mask or N95.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A side view of man wearing a surgical mask" src="https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/442358/original/file-20220124-27-1ch5axg.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">Surgical masks are made of good materials but are hard to seal against the face and often allow air to escape past a person’s cheeks.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/men-wear-masks-to-prevent-pollution-pollution-royalty-free-image/1186031353?adppopup=true">Krisanapong Detraphiphat/Moment via Getty Images</a></span>
</figcaption>
</figure>
<h2>3. How much does fit matter for masks?</h2>
<p>Fit is the other major component in how effective a mask is. Even if the materials used in a mask were perfect and it removed all particles from the air that passed through it, a mask can offer protection only if it doesn’t leak.</p>
<p>When you breathe in and out, air will always take the path of least resistance. If there are any gaps between a mask and someone’s face, a substantial fraction of every breath will seep out through those gaps and the mask will <a href="https://doi.org/10.1021/acs.est.0c07291">provide relatively little protection</a>. </p>
<p>Many cloth mask designs simply do not seal well. They are not stiff enough to push against the face, there are gaps where the mask doesn’t even come in contact with the face and it is not possible to cinch them tightly enough against the skin to form a decent seal.</p>
<p>But leaking is a concern for all masks. Although the materials used in surgical masks are quite effective, they often bunch and fold on the sides. These gaps provide an easy route for air and particles to leak out. Knotting and tucking surgical masks or wearing a cloth mask over a surgical mask can both <a href="https://www.nytimes.com/article/double-masking-tips-coronavirus.html">significantly reduce leakage</a>.</p>
<p>N95 masks aren’t immune to this problem either; if the nose clip isn’t securely pushed against your face, the mask is leaking. What makes N95s unique is that a <a href="https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/n95-respirators-surgical-masks-face-masks-and-barrier-face-coverings">specific requirement</a> of the N95 certification process is making sure the masks can form a good seal.</p>
<h2>4. What is different about omicron?</h2>
<p>The mechanics of how masks function is likely no different for omicron than any other variant. The difference is that the omicron variant <a href="https://www.cdc.gov/coronavirus/2019-ncov/variants/omicron-variant.html">is more easily transmitted</a> than previous variants. This high level of infectiousness makes wearing good-quality masks and wearing them correctly to limit the chances of catching or spreading the coronavirus that much more critical.</p>
<p>[<em>Over 140,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-140ksignup">Sign up today</a>.]</p>
<p>Unfortunately, the attributes that make for a good mask are the very things that make masks uncomfortable and not very stylish. If your cloth mask is comfy and light and feels like you are wearing nothing at all, it probably isn’t doing much to keep you and others safe from the coronavirus. The protection offered by a high-quality, well-fitting N95 or KN95 is the best. Surgical masks can be very effective at filtering out particles, but getting them to fit correctly can be tricky and makes the overall protection they will provide you questionable. If you have other options, cloth masks should be a last choice.</p><img src="https://counter.theconversation.com/content/175481/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian L'Orange receives funding associated with the testing and evaluation of testing masks including fee-for-service testing and funding from the World Health Organization.</span></em></p>The CDC’s updated mask guidelines say that cloth masks offer the least protection from COVID-19. Differences in the materials masks are made from and the ways they fit are the reason.Christian L'Orange, Assistant Research Professor of Mechanical Engineering, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1731322021-12-22T13:12:07Z2021-12-22T13:12:07Z2021: a year physicists asked, ‘What lies beyond the Standard Model?’<figure><img src="https://images.theconversation.com/files/438717/original/file-20211221-48250-esf86c.jpg?ixlib=rb-1.1.0&rect=45%2C21%2C1566%2C1027&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Experiments at the Large Hadron Collider in Europe, like the ATLAS calorimeter seen here, are providing more accurate measurements of fundamental particles.</span> <span class="attribution"><a class="source" href="https://cds.cern.ch/record/910381">Maximilien Brice</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>If you ask a physicist like me to explain how the world works, my lazy answer might be: “It follows the Standard Model.”</p>
<p><a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">The Standard Model</a> explains the fundamental physics of how the universe works. It has endured over 50 trips around the Sun despite experimental physicists constantly probing for cracks in the model’s foundations. </p>
<p>With few exceptions, it has stood up to this scrutiny, passing experimental test after experimental test with flying colors. But this wildly successful model has conceptual gaps that suggest there is a bit more to be learned about how the universe works.</p>
<p>I am a <a href="https://scholar.google.com/citations?user=N_cqAjYAAAAJ&hl=en&oi=sra">neutrino physicist</a>. <a href="https://neutrinos.fnal.gov/whats-a-neutrino/">Neutrinos</a> represent three of the <a href="https://www.iop.org/explore-physics/physics-stepping-stones/standard-model">17 fundamental particles in the Standard Model</a>. They zip through every person on Earth at all times of day. I study the properties of interactions between <a href="https://neutrinos.fnal.gov/whats-a-neutrino/">neutrinos</a> and normal matter particles.</p>
<p>In 2021, physicists around the world ran a number of experiments that probed the Standard Model. Teams measured basic parameters of the model more precisely than ever before. Others investigated the fringes of knowledge where the best experimental measurements don’t quite match the predictions made by the Standard Model. And finally, groups built more powerful technologies designed to push the model to its limits and potentially discover new particles and fields. If these efforts pan out, they could lead to a more complete theory of the universe in the future.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing the particles of the Standard Model." src="https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438763/original/file-20211222-17-y5l097.png?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">The Standard Model of physics allows scientists to make incredibly accurate predictions about how the world works, but it doesn’t explain everything.</span>
<span class="attribution"><a class="source" href="https://cds.cern.ch/images/OPEN-PHO-CHART-2015-001-1/">CERN</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Filling holes in Standard Model</h2>
<p>In 1897, J.J. Thomson discovered the first fundamental particle, the electron, using nothing more than <a href="https://www.britannica.com/science/atom/Discovery-of-electrons">glass vacuum tubes and wires</a>. More than 100 years later, physicists are still discovering new pieces of the Standard Model.</p>
<p><a href="https://www.energy.gov/science/doe-explainsthe-standard-model-particle-physics">The Standard Model</a> is a <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">predictive framework</a> that does two things. First, it explains what the basic particles of matter are. These are things like electrons and the quarks that make up protons and neutrons. Second, it predicts how these matter particles interact with each other using “messenger particles.” These are called bosons – they include photons and the famous Higgs boson – and they communicate the basic forces of nature. The Higgs boson wasn’t <a href="https://atlas.cern/updates/feature/higgs-boson">discovered until 2012</a> after decades of work at CERN, the huge particle collider in Europe.</p>
<p>The Standard Model is incredibly good at predicting many aspects of how the world works, but it does have some holes.</p>
<p>Notably, it does not include any description of gravity. While Einstein’s theory of <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">General Relativity describes how gravity works</a>, physicists have not yet discovered a particle that conveys the force of gravity. A proper “Theory of Everything” would do everything the Standard Model can, but also include the messenger particles that communicate how gravity interacts with other particles.</p>
<p>Another thing the Standard Model can’t do is explain why any particle has a certain mass – physicists must measure the mass of particles directly using experiments. Only after experiments give physicists these exact masses can they be used for predictions. The better the measurements, the better the predictions that can be made.</p>
<p>Recently, physicists on a team at CERN measured <a href="https://atlas.cern/updates/briefing/twice-higgs-twice-challenge">how strongly the Higgs boson feels itself</a>. Another CERN team also measured the Higgs boson’s mass <a href="https://cms.cern/news/cms-precisely-measures-mass-higgs-boson">more precisely than ever before</a>. And finally, there was also progress on measuring the mass of neutrinos. Physicists know neutrinos have more than zero mass but less than the amount currently detectable. A team in Germany has continued to refine the techniques that could allow them to <a href="https://www.katrin.kit.edu/index.php">directly measure the mass of neutrinos</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blue circular particle acellerator." src="https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438712/original/file-20211221-15-17289qh.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">Projects like the Muon g-2 experiment highlight discrepancies between experimental measurements and predictions of the Standard Model that point to problems somewhere in the physics.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Fermilab_g-2_(E989)_ring.jpg#/media/File:Fermilab_g-2_(E989)_ring.jpg">Reidar Hahn/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Hints of new forces or particles</h2>
<p>In April 2021, members of the <a href="https://news.fnal.gov/2021/04/first-results-from-fermilabs-muon-g-2-experiment-strengthen-evidence-of-new-physics/">Muon g-2 experiment at Fermilab announced</a> their first <a href="https://theconversation.com/how-we-found-hints-of-new-particles-or-forces-of-nature-and-why-it-could-change-physics-158564">measurement of the magnetic moment of the muon</a>. The muon is one of the fundamental particles in the Standard Model, and this measurement of one of its properties is the most accurate to date. The reason this experiment was important was because the measurement didn’t perfectly match the Standard Model prediction of the magnetic moment. Basically, muons don’t behave as they should. This finding could point to <a href="https://news.uchicago.edu/story/what-muon-g-2-results-mean-how-we-understand-universe">undiscovered particles that interact with muons</a>.</p>
<p>But simultaneously, in April 2021, physicist Zoltan Fodor and his colleagues showed how they used a mathematical method called Lattice QCD to <a href="https://theconversation.com/proof-of-new-physics-from-the-muons-magnetic-moment-maybe-not-according-to-a-new-theoretical-calculation-157829">precisely calculate the muon’s magnetic moment</a>. Their theoretical prediction is different from old predictions, still works within the Standard Model and, importantly, matches experimental measurements of the muon.</p>
<p>The disagreement between the previously accepted predictions, this new result and the new prediction must be reconciled before physicists will know if the experimental result is truly beyond the Standard Model.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A spinning galaxy in space." src="https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=436&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=436&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=436&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=548&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=548&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438713/original/file-20211221-129369-zkmpnf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=548&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">New tools will help physicists search for dark matter and other things that could help explain mysteries of the universe.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/dark-matter-halo-surrounding-galaxy-royalty-free-illustration/932730112?adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span>
</figcaption>
</figure>
<h2>Upgrading the tools of physics</h2>
<p>Physicists must swing between crafting the mind-bending ideas about reality that make up theories and advancing technologies to the point where new experiments can test those theories. 2021 was a big year for advancing the experimental tools of physics. </p>
<p>First, the world’s largest particle accelerator, the <a href="https://theconversation.com/ten-years-of-large-hadron-collider-discoveries-are-just-the-start-of-decoding-the-universe-102331">Large Hadron Collider at CERN</a>, was shut down and underwent some substantial upgrades. Physicists just restarted the facility in October, and they plan to begin the <a href="https://cerncourier.com/a/protons-back-with-a-splash/">next data collection run in May 2022</a>. The upgrades have boosted the power of the collider so that it can <a href="https://www.universetoday.com/140769/the-large-hadron-collider-has-been-shut-down-and-will-stay-down-for-two-years-while-they-perform-major-upgrades/">produce collisions at 14 TeV</a>, up from the previous limit of 13 TeV. This means the batches of tiny protons that travel in beams around the circular accelerator together carry the same amount of energy as an 800,000-pound (360,000-kilogram) passenger train traveling at 100 mph (160 kph). At these incredible energies, physicists may discover new particles that were too heavy to see at lower energies.</p>
<p>Some other technological advancements were made to help the search for dark matter. Many astrophysicists believe that dark matter particles, which don’t currently fit into the Standard Model, could answer some outstanding questions regarding the way gravity bends around stars – called <a href="https://www.nasa.gov/content/discoveries-highlights-shining-a-light-on-dark-matter">gravitational lensing</a> – as well as the <a href="https://phys.org/news/2019-10-dark-massive-spiral-galaxies-breakneck.html">speed at which stars rotate in spiral galaxies</a>. Projects like the Cryogenic Dark Matter Search have yet to find dark matter particles, but the teams are <a href="https://supercdms.slac.stanford.edu/overview">developing larger and more sensitive detectors</a> to be deployed in the near future. </p>
<p>[<em>Over 140,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-140ksignup">Sign up today</a>.]</p>
<p>Particularly relevant to my work with neutrinos is the development of immense new detectors like <a href="http://www.hyper-k.org/en/">Hyper-Kamiokande</a> and <a href="https://lbnf-dune.fnal.gov/">DUNE</a>. Using these detectors, scientists will hopefully be able to answer questions about a <a href="https://cerncourier.com/a/why-does-cp-violation-matter-to-the-universe/">fundamental asymmetry in how neutrinos oscillate</a>. They will also be used to watch for proton decay, a proposed phenomenon that certain theories predict should occur. </p>
<p>2021 highlighted some of the ways the Standard Model fails to explain every mystery of the universe. But new measurements and new technology are helping physicists move forward in the search for the Theory of Everything.</p><img src="https://counter.theconversation.com/content/173132/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aaron McGowan has received funding in the past from the U.S. Department of Energy. </span></em></p>Physicists know a lot about the most fundamental properties of the universe, but they certainly don’t know everything. 2021 was a big year for physics – what was learned and what’s coming next?Aaron McGowan, Principal Lecturer in Physics and Astronomy, Rochester Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1175382019-05-28T11:10:42Z2019-05-28T11:10:42ZCurious Kids: how long has gravity existed?<figure><img src="https://images.theconversation.com/files/276775/original/file-20190528-42600-gdbw65.jpg?ixlib=rb-1.1.0&rect=23%2C0%2C2346%2C1476&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Gravity helps stars to form. </span> <span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2017/02/Star_formation_on_filaments_in_RCW106">UNIMAP / L. Piazzo, La Sapienza – Università di Roma; E. Schisano / G. Li Causi, IAPS/INAF, Italy</a>, <a class="license" href="http://artlibre.org/licence/lal/en">FAL</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<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>, which gives children of all ages the chance to have their questions about the world answered by experts. All questions are welcome: you or an adult can send them – along with your name, age and town or city where you live – to curiouskids@theconversation.com. We won’t be able to answer every question, but we’ll do our best.</em></p>
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<p><em><strong>How long has gravity existed? - Aine, aged 13, Edinburgh, UK.</strong></em></p>
<p>Gravity is <a href="https://www.esa.int/kids/en/learn/Earth/Natural_disasters/What_Is_Gravity">a force</a> between two masses, so gravity exists wherever there is mass. To discover when gravity started to exist, we need to understand what mass is, and when it started to exist. </p>
<p>Let’s dive right in: “mass” is what we use to measure how much “matter” there is. Scientists use <a href="http://www.chem4kids.com/files/matter_intro.html">the term “matter”</a> to describe stuff like stars, planets, oceans, rocks, molecules, atoms, particles like electrons and protons that make up atoms, and even the particles that make up electrons and protons.</p>
<p>Very nearly everything you encounter in everyday life counts as “matter”: a book, a glass of water, a bird – anything you might also call “stuff”. </p>
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Read more:
<a href="https://theconversation.com/curious-kids-is-everything-really-made-of-molecules-109145">Curious Kids: is everything really made of molecules?</a>
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<p>There are <a href="https://theconversation.com/curious-kids-is-everything-really-made-of-molecules-109145">some exceptions</a>: for example, neither light nor sound is matter, nor are feelings. Light can even travel through completely empty space, where there’s no matter at all. </p>
<p>If a feather and a football are both made of matter, you might wonder why they’re so different. Well, a football has much more matter than a feather, so we’d say its “mass” is higher. </p>
<p>On the other hand, a kilogram of feathers and a kilogram of iron have the same mass because they weigh the same – even though the feathers take up a lot more space. </p>
<p>If you could count every particle in your body, then you could add up all of their masses and you would have a measure of your own mass. </p>
<h2>Mass, weight and gravity</h2>
<p>Of course, that isn’t how we actually measure masses in real life. Here on Earth, we measure mass via weight. Mass and weight are not quite the same thing, but they are related. </p>
<p>If you took a scale to the moon and weighed yourself on it, the number it showed would be smaller than when you weighed yourself on the Earth – even though your mass is still the same, your weight would change. This is because the scale you use is actually not measuring your mass directly, but rather the gravitational force your mass is feeling from the Earth, or the moon.</p>
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<img alt="" src="https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=576&fit=crop&dpr=1 600w, https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=576&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=576&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=724&fit=crop&dpr=1 754w, https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=724&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/276778/original/file-20190528-42556-4yguri.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=724&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">You weigh less on the moon.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/apollo08_earthrise.jpg">NASA.</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>How strong gravity is <a href="https://www.esa.int/kids/en/learn/Earth/Natural_disasters/What_Is_Gravity">depends on</a> the mass of both objects, as well as the distance between them. Because the Earth has a lot more mass than the moon, the force of gravity you experience on Earth is stronger. That’s why you weigh more on Earth than on the moon. </p>
<h2>A cosmic creation</h2>
<p>So, when did mass first appear? Based on our best understanding of the physics of the universe, the first mass was created in the form of tiny particles (a LOT of them) right after the beginning of the universe itself, about <a href="https://www.esa.int/kids/en/learn/Our_Universe/Story_of_the_Universe/The_Big_Bang">13.7 billion years ago</a>.</p>
<p>The creation of matter happened so fast after the creation of the universe that you could fit more than a million of those instants in the time it takes to blink an eye. And from that moment, gravity was at work, pulling matter together, gathering atoms and molecules into dense clouds that eventually formed stars and galaxies and planets.</p>
<p>Of course, there are <a href="https://physics.info/newton-first/">many forces</a> in nature, and gravity is only one of them. The other forces work on matter too, so there has always been a cosmic dance between the different forces in the universe, which makes it look how it does. </p>
<p>Gravity might be the force that we’re all most familiar with because we all have felt it since the moment we were born, but actually compared to many of the other forces it’s not especially strong. </p>
<p>But since gravity is found anywhere there is mass, it’s basically everywhere, at all times. </p>
<p>The same gravity that keeps you on the ground here on Earth also holds the Earth together, holds the Earth in orbit around the sun, and holds the sun in orbit around the rest of the galaxy. </p>
<p>Gravity has existed for as long as the universe has, and it will keep existing, for as long as we do, and beyond. </p>
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<p><em>More <a href="https://theconversation.com/topics/curious-kids-36782?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Curious Kids</a> articles, written by academic experts:</em></p>
<ul>
<li><p><em><a href="https://theconversation.com/curious-kids-why-do-we-lose-our-baby-teeth-111911?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Why do we lose our baby teeth? - Jack, age 8.</a></em></p></li>
<li><p><em><a href="https://theconversation.com/curious-kids-why-do-pets-have-dark-eyes-while-humans-have-mostly-white-eyes-115391?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Our guinea pigs have dark eyes. Why do we have white eyes? - Rhoswen, aged three, Bristol, UK.</a></em></p></li>
<li><p><em><a href="https://theconversation.com/curious-kids-how-was-the-earth-made-112067?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">How was the Earth made? - Audrey, age 5.</a></em></p></li>
</ul><img src="https://counter.theconversation.com/content/117538/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brooke Simmons has previously received funding from the National Aeronautics and Space Administration (NASA) to research galaxies, which are mentioned in this article. </span></em></p>Gravity exists because the universe is full of ‘stuff’ – here’s how it came to be.Brooke Simmons, Lecturer in Astrophysics, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1137612019-03-19T08:12:42Z2019-03-19T08:12:42ZWe did a breakthrough ‘speed test’ in quantum tunnelling, and here’s why that’s exciting<figure><img src="https://images.theconversation.com/files/264571/original/file-20190319-28468-3c5vq6.jpg?ixlib=rb-1.1.0&rect=44%2C0%2C5000%2C3125&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Future technologies will exploit today's advances in our understanding of the quantum world.</span> <span class="attribution"><span class="source">Shutterstock/PopTika </span></span></figcaption></figure><p>When you deal with things at the quantum scale, where things are very small, the world is quite fuzzy and bizarre in comparison to our everyday experiences.</p>
<p>For example, we can’t ordinarily walk through solid walls. But at the quantum scale, when a particle encounters a seemingly insurmountable barrier, it can sometimes pass through to the other side – a process known as quantum tunnelling.</p>
<p>But how fast a particle could tunnel through a barrier was always a puzzle.</p>
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Read more:
<a href="https://theconversation.com/what-do-we-mean-by-meaning-science-can-help-with-that-113269">What do we mean by meaning? Science can help with that</a>
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<p>In work <a href="https://www.nature.com/articles/s41586-019-1028-3" title="Attosecond angular streaking and tunnelling time in atomic hydrogen">published today in Nature</a> we’ve solved part of the problem.</p>
<p>Why is that important? It’s a breakthrough that could have an impact on future technologies we see in our homes, at work or elsewhere.</p>
<p><a href="https://www.forbes.com/sites/chadorzel/2015/08/13/what-has-quantum-mechanics-ever-done-for-us/" title="What Has Quantum Mechanics Ever Done For Us?">Many of today’s technologies</a> – such as semiconductors, the LED screen on your smart phone, or lasers – are based on our understanding of how things work in the quantum world. </p>
<p>So the more we can learn, the more we can develop.</p>
<h2>Back to the tunnelling</h2>
<p>For quantum particles, such as electrons, when we say they can tunnel through barriers, we don’t refer to a physical obstacles, but barriers of energy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264561/original/file-20190319-28471-zsqubt.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">
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<span class="caption">Things behave differently in the quantum world.</span>
<span class="attribution"><span class="source">Shutterstock/VectorMine</span></span>
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<p>Tunnelling is possible due to the <a href="https://theconversation.com/explainer-what-is-wave-particle-duality-7414" title="Explainer: what is wave-particle duality">wave nature of the electron</a>. Quantum mechanics assigns wave nature to every particle, and hence there is always a finite probability for the wave to propagate through barriers, just as sound travels through walls. </p>
<p>It may sound counterintuitive, but this is what is exploited in technologies such as <a href="https://www.britannica.com/technology/scanning-tunneling-microscope">scanning tunnelling microscopes</a>, which allow scientists to create images with atomic resolution. This is also naturally observed in nuclear fusion, and in biological processes such as photosynthesis.</p>
<p>Although the phenomenon of quantum tunnelling is well studied and utilised, physicists still lacked a complete understanding of it, especially with regards to its dynamics. </p>
<p>If we could exploit the dynamics of tunnelling – for example, use it to carry more information – it could possibly give us a new handle on future quantum technologies. </p>
<h2>A tunnel speed test</h2>
<p>The first step towards this goal is to measure the speed of the tunnelling process. This is no simple feat, as the time scales involved in the measurement are extremely small. </p>
<p>For energy barriers the size of few billionths of a metre, as in our experiment, some physicists had calculated the tunnelling process would take around a hundred attoseconds (1 attosecond is a billionth of a billionth of a second). </p>
<p>To put things in perspective, if an attosecond is stretched to a second, then a second equals the age of the universe.</p>
<p>The estimated times are so extremely small that they were previously treated as practically instantaneous. Hence for our experiment we needed a clock that can time these events with enormous accuracy and precision. </p>
<p>The technological advancements in <a href="https://www.griffith.edu.au/centre-quantum-dynamics/our-research-groups/ultrafast-attosecond-science">ultrafast laser systems</a> enabled us to implement such a clock at the Australian Attosecond Science Facility, Centre for Quantum Dynamics, at Griffith University.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264582/original/file-20190319-60969-1blumxs.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>
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<span class="caption">Part of the experiment set up at the Griffith University lab.</span>
<span class="attribution"><span class="source">U. Satya Sainadh</span>, <span class="license">Author provided</span></span>
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<p>The clock in the experiment is not mechanical or electrical – rather it is the rotating electric field vector of an ultrafast laser pulse.</p>
<p>Light is just electromagnetic radiation made of electric and magnetic fields varying at a rapid rate. We used this rapidly changing field to induce tunnelling in atomic hydrogen and also as a stopwatch to measure when it ends. </p>
<h2>How fast?</h2>
<p>The choice of using atomic hydrogen (which is simply a bound pair of one electron and one proton) avoids the complications that arise from other atoms, making it easier to compare and interpret the results unambiguously. </p>
<p>The tunnelling time we measured was found to be no more than 1.8 attoseconds, much smaller than some theories had predicted. This measurement calls for a serious reconsideration of our understanding of tunnelling dynamics.</p>
<p>Various theories estimated a range of tunnelling times – from zero to hundreds of attoseconds – and there was no consensus among physicists on which single theoretical estimate was correct. </p>
<p>A basic reason for the disagreements lies in the very concept of time in quantum mechanics. Because of quantum uncertainties, there can be no absolute certainty in the time at which a particle enters into or emerges from the barrier.</p>
<p>But experiments like ours, using precise measurements on simple systems, could guide us in refining our understanding of such times </p>
<h2>The next technologies</h2>
<p>Quantum leaps in the technological world are often rooted in the quest for fundamental science.</p>
<p>Future quantum technologies that incorporates many of the quantum features – such as superposition and entanglement – will lead to what technologists call the “second quantum revolution”.</p>
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Read more:
<a href="https://theconversation.com/weve-designed-a-flux-capacitor-but-it-wont-take-us-back-to-the-future-92841">We've designed a 'flux capacitor', but it won't take us Back to the Future</a>
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<p>By fully understanding the quantum dynamics of the simplest possible atomic tunnelling event – with a single proton and a single electron – we have shown that certain types of theories can be relied on to give the right answer, where other types of theories fail. </p>
<p>This gives us confidence about what theories to apply to other, more complicated systems. </p>
<p>Measurements at the attosecond scale not only add an extra dimension for the future quantum technologies but also can fundamentally help in understanding the elephant of the quantum room: what is <em>time</em>? </p>
<hr>
<p><em><strong>You might also like</strong></em>: In <a href="https://theconversation.com/trust-me-im-an-expert-the-explainer-episode-96286">Trust Me, I’m An Expert: The explainer episode</a>, Andrew White, a professor in physics at the University of Queensland, tells us how far quantum mechanics has come, why the research hit a wall, and what exciting breakthroughs might be just around the corner.</p><img src="https://counter.theconversation.com/content/113761/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>U. Satya Sainadh receives funding from Technion for his research. </span></em></p>Things get weird at the quantum level and now we know they can happen really fast when a particle pushes through an almost insurmountable barrier.U. Satya Sainadh, Postdoctoral researcher, Technion - Israel Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1115732019-02-12T12:33:10Z2019-02-12T12:33:10ZCurious Kids: what causes the northern lights?<figure><img src="https://images.theconversation.com/files/258503/original/file-20190212-174887-2wfoul.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4851%2C3224&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A magical sight. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/ronel_reyes/8479833336/sizes/l">Ronel Reyes/Flickr.</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></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>, which gives children of all ages the chance to have their questions about the world answered by experts. All questions are welcome: find out how to enter at the bottom of this article.</em> </p>
<hr>
<blockquote>
<p><strong>What causes the northern lights? – Ffion, age 6.75, Pembrokeshire, UK.</strong></p>
</blockquote>
<p>I first saw the <a href="https://theconversation.com/uk/topics/northern-lights-14791">northern lights</a> three years ago, while driving home one night. They were so beautiful, I had to stop the car and get out to have a proper look, even though it was cold. Although the northern lights might look like magic, they can actually be explained by science – with a bit of help from the Sun, birds and fizzy drinks. </p>
<p>The energy for making the northern lights comes from the Sun. The Sun creates something called the “solar wind”. This is different to the light that we get from the Sun, which keeps us warm and helps us to see during the day.</p>
<p>This solar wind drifts away from the Sun through space, carrying tiny particles called protons and electrons. Protons and electrons are some of the tiny building blocks that make up most of the stuff in the universe, like plants and chocolate and me and you.</p>
<p>Think of the smallest Lego bricks you have in your toy box, which can be stuck together to make bigger things - these are what protons and electrons (and neutrons too) are to the universe. These particles carry lots of energy from the Sun, on their journey through space.</p>
<h2>The solar wind</h2>
<p>Sometimes the solar wind is strong, and sometimes it’s weak. We can only see the northern lights at times when the solar wind is strong enough. </p>
<p>When the solar wind reaches planet Earth, something very interesting happens: it runs into the Earth’s magnetic field. The magnetic field forces the solar wind away, and makes it travel around the Earth instead.</p>
<p>The magnetic field is what makes the needle on a compass point north, and is how birds know where to go when they migrate – it’s also why we have the north and south poles at all. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fVsONlc3OUY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The magnetic field interacts with the solar wind and guides the protons and electrons down towards Earth along the magnetic field, away from the middle of the planet and toward the north and south poles.</p>
<p>Because of this, we get both northern and <a href="https://theconversation.com/uk/topics/southern-lights-15736">southern lights</a> – also known as the <a href="https://theconversation.com/uk/topics/aurora-borealis-14790">aurora borealis</a> and the <a href="https://theconversation.com/uk/topics/aurora-australis-15735">aurora australis</a>. </p>
<h2>Shake it up</h2>
<p>When the solar wind gets past the magnetic field and travels towards the Earth, it runs into the atmosphere. The atmosphere is like a big blanket of gas surrounding our planet, which contains lots of different particles that make up the air that we breathe and help to protect us from harmful radiation from the Sun. </p>
<p>As the protons and electrons from the solar wind hit the particles in the Earth’s atmosphere, they release energy – and this is what causes the northern lights. </p>
<p>Here’s how it happens: imagine you have a bottle of fizzy drink, and you give it a good shake. This puts lots of energy into the bottle, and when you open it, this energy will be released in a big stream of fizzy bubbles. </p>
<p>In the same way, the protons and electrons from the Sun “shake up” the particles in the atmosphere. Then, the particles let out all that energy in the form of light (instead of bubbles). </p>
<p>Different types of particles in the atmosphere make different colours after they’re shaken up – oxygen makes red and green light, and nitrogen makes blue light. Our eyes see green best out of all the colours, so we see green the brightest when we look at the northern lights.</p>
<p>It is easiest to see the northern lights in winter when is it very dark at night, and also outside of cities and away from street lights. You are more likely to see them the further north you are too. Check out this great website <a href="https://aurorawatch.lancs.ac.uk/">Aurora Watch</a> from Lancaster University – it might just help you find them!</p>
<p><em>This article has been corrected: the Earth’s magnetic field is not weaker at the poles, as the article originally stated.</em></p>
<hr>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question – along with your name, age and town or city where you live – to curiouskids@theconversation.com. Send as many questions as you want! We won’t be able to answer every question, but we’ll do our best.</em></p>
<hr>
<p><em>More <a href="https://theconversation.com/topics/curious-kids-36782?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Curious Kids</a> articles, written by academic experts:</em></p>
<ul>
<li><p><em><a href="https://theconversation.com/curious-kids-why-do-spiders-have-hairy-legs-108602?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Why do spiders have hairy legs? - Audrey, age five, Melbourne, Australia</a></em></p></li>
<li><p><em><a href="https://theconversation.com/curious-kids-why-are-there-different-seasons-at-specific-times-of-the-year-109380?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">Why do we have different seasons at specific times of the year? – Shrey, age nine, Mumbai, India</a></em></p></li>
<li><p><em><a href="https://theconversation.com/curious-kids-how-is-water-made-109434?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=CuriousKidsUK">How is water made? – Clara, age eight, Canberra, Australia</a></em></p></li>
</ul><img src="https://counter.theconversation.com/content/111573/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul O'Mahoney 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>The northern lights might look like magic, but they can actually be explained by science – here’s how.Paul O'Mahoney, Post-Doctoral Research Assistant in Photobiology, University of DundeeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811882017-09-03T20:01:57Z2017-09-03T20:01:57ZCurious Kids: Why do stars twinkle?<figure><img src="https://images.theconversation.com/files/180452/original/file-20170801-22169-m3uof.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C2663&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lasers being shone from the European Southern Observatory's Very Large Telescope in Chile.
These lasers help remove the twinkles in the night sky and help astronomers see stars clearer on Earth than ever before.</span> <span class="attribution"><a class="source" href="http://eso.org/public/images/16fkc16776-cc/">F. Kamphues/ESO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
<blockquote>
<p><strong>Why do stars twinkle? – Max, 3, Earlwood.</strong> </p>
</blockquote>
<p>Max, that’s a fantastic question! And the answer, it turns out, is all around us.</p>
<p>Have you ever been out on a really hot day? Like ice-cream-melting-through-your-hands hot? Well, if you have, you may have noticed trees near the horizon being a bit wobbly or blurry. It looks strange, and something very similar is happening when we see stars twinkle in the night sky. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.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">The light from the setting Sun bends through the atmosphere creating a mirage. This mirage behaves the same way as a star’s twinkling light.</span>
<span class="attribution"><span class="source">Brocken Inaglory</span></span>
</figcaption>
</figure>
<p>When we look up, we don’t just look into space. We’re actually looking at space through all of the air above us, called <a href="https://theconversation.com/curious-kids-why-is-the-sky-blue-and-where-does-it-start-81165">the atmosphere</a>. </p>
<p>The Earth’s atmosphere is a layer of air. A whopping 120 kilometres tall, or more. This air, around and above us, moves and swirls around the Earth at different speeds. </p>
<p>How fast this air travels, depends on its temperature. When the air is hot, it has loads of energy and loves to move around. But when the air is cold, it doesn’t move as much.</p>
<p>Hot air is also lighter than cold air, so it rises past, and mixes with, the cold air around it. This mixing creates swirls in the atmosphere known as “turbulence”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=479&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=479&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=479&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=602&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=602&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=602&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">van Gogh’s painting ‘The Starry Night’ artistically shows the stars light being swirled by turbulence in our atmosphere.</span>
<span class="attribution"><span class="source">Vincent van Gogh, Wikimedia</span></span>
</figcaption>
</figure>
<p>Air can also be bumped around as it passes up and down hills and mountains on the Earth’s surface, creating waves that reach into the upper atmosphere. These waves disturb the air above, also causing turbulence.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.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">Air can be pushed up as it passes above mountains and hills, creating waves in the atmosphere. These waves can create really cool cloud patterns like this near the Moul n'ga Cirque in Southeast Algeria.</span>
<span class="attribution"><span class="source">Pir6mon/wikimedia</span></span>
</figcaption>
</figure>
<p>As light from a star races through our atmosphere, it bounces and bumps through the different layers, bending the light before you see it. Since the hot and cold layers of air keep moving, the bending of the light changes too, which causes the star’s appearance to wobble or twinkle.</p>
<p>Indigenous Australians and Torres Strait Islanders have been observing the twinkling of stars for thousands of years. The stars’ twinkling shows how the winds are moving, which can really help when <a href="https://theconversation.com/stories-from-the-sky-astronomy-in-indigenous-knowledge-33140">predicting weather</a> - like really hot days.</p>
<h2>Correcting the twinkle</h2>
<p>While twinkling looks pretty, astronomers find it very annoying. This is because it blurs the things we want to see, like distant galaxies.</p>
<p>What can we do about this?</p>
<p>Well, space is the best place to see a star without a twinkle. However, getting big telescopes into space is very hard. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=433&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=433&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=433&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=544&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=544&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=544&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">NASA’s Spitzer Space Telescope snapped this photo of hundreds of thousands of stars lurking in the Milky Way Galaxy, thanks to its infrared photography equipment.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/#/details-PIA03654.html">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We can build big telescopes on the ground that use <a href="https://www.youtube.com/watch?v=gDGvNyVApgg">lasers and bendable mirrors</a> - bending the mirrors to match the twinkling starlight. This then shows us the whole universe, as if the atmosphere vanished above us!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronomers use lasers to work out how the atmosphere moves, so that they can remove the twinkle from stars they observe. This whole process is called ‘adaptive optics’.</span>
<span class="attribution"><span class="source">G. Hüdepohl/ESO</span></span>
</figcaption>
</figure>
<h2>But what about the planets?</h2>
<p>So that’s the story of why stars appear to twinkle in the sky. If you look really carefully, you might have noticed that planets, like Venus and Jupiter, don’t seem to twinkle like the stars around them.</p>
<p>Why is that? </p>
<p>Well, if you look at a star through even the biggest telescope, you still just see a tiny point of light. This light comes through the atmosphere in a tiny beam - that can be easily knocked around.</p>
<p>If you look at the planets through a telescope, you see their disks - they are close enough to us that we can “zoom in”, and see a planet, rather than a point of light. That means that the light from those planets comes through the atmosphere in a much thicker beam than that from a star - and that thicker beam is much harder to knock around. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Only stars twinkle in the night sky. Planets in our solar system are too close and big for them to twinkle. Venus is the brightest light nearer to the centre. Jupiter is just north-west of Venus.</span>
<span class="attribution"><span class="source">Brocken Inaglory/Wikimedia</span></span>
</figcaption>
</figure>
<p>As a result, the planets barely flicker, while the stars twinkle like crazy.</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:</em></p>
<p><em>* Email your question to curiouskids@theconversation.edu.au
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* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a> by tagging <a href="https://twitter.com/ConversationEDU">@ConversationEDU</a> with the hashtag #curiouskids, or
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/81188/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p><p class="fine-print"><em><span>Belinda Nicholson is supported by an Australian Government Research Training Program (RTP) Scholarship.
</span></em></p><p class="fine-print"><em><span>Brad Carter and Jonti Horner 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>How exactly do the stars twinkle in the night sky? As it turns out, the answer is full of hot air… and cold air.Jake Clark, PhD Student, University of Southern QueenslandBelinda Nicholson, PhD Candidate, University of Southern QueenslandBrad Carter, Professor (Physics), University of Southern QueenslandJonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811872017-08-29T20:09:48Z2017-08-29T20:09:48ZCurious Kids: Why are rainbows round?<figure><img src="https://images.theconversation.com/files/182892/original/file-20170822-5133-1ks4kxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rainbows get their round shape from a process called reflection.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/luigimengato/7685561868/in/photolist-cH9vMo-ai7BRp-4mTrjK-ncjZuK-6Uf6sR-9UKsz4-5KWErK-bbpTaZ-dy3DRv-29rHy9-6qHyyJ-oe6PUh-ejjoa2-63PuMi-5iknHp-7KaCkZ-ehX39G-64EoZz-6s8DDE-28FCJE-4V4NM5-6s4KJc-r9Avy-nHunPx-XrEitn-9WkAkX-4UZy9x-4V4PgQ-ar15xi-PZEhf-pzLgZ6-5cHmP9-a3LXEu-4HyKk1-a1SpTa-6m7Qzo-5cH6ys-bo4Fpb-8ajowg-6s4wfT-gN2o5s-bAYwH6-cTz8FJ-4vra25-pZngQ5-9fbtq9-7DiqMV-gPpA8s-Q1cRF-4UZwuM">Flickr/Luigi Mengato</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
<hr>
<blockquote>
<p><strong>Why are rainbows round? – Georgina, age 5.</strong> </p>
</blockquote>
<p>This is a really complicated question. It’s a hard thing even for many adults to understand. To answer your question, I have to explain two things – refraction and reflection. </p>
<p>Refraction gives you the colours of the rainbow, and reflection gives you its round shape.</p>
<h2>Refraction and colour</h2>
<p>When you are out on a bright sunny day, it may look like sunlight is all one colour. But in fact, the white sunlight you see is made up of many different colours of light mixed together. </p>
<p>But what are different colours of light? In fact, light is a wave. Light waves come in different sizes called “wavelengths”. Every colour has a different wavelength. For example, violet light has a much shorter wavelength than red light.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=173&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=173&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=173&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=218&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=218&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182896/original/file-20170822-5162-a2gi5e.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=218&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 colour of the rainbow has a different wavelength.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>The next thing to know is that when light enters water at an angle, it changes direction. This is called “refraction”. You can see this every time you look into a pond. Ripples on the water make everything under the water look wonky. This is because the light bends as it goes between the air and the water. The amount the light bends depends on its colour. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179150/original/file-20170721-14739-1mji504.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sunlight is refracted and reflected by a water drop.</span>
</figcaption>
</figure>
<p>The shorter the wavelength of the colour, the more it changes direction. So violet light changes direction more than green light. And yellow light changes direction more than red light. </p>
<p>Refraction is why all the colours in the sunlight end up separating when it hits the water drop, and we are then able to see all the colours of the rainbow. </p>
<h2>Reflection and shape</h2>
<p>Now we can move onto why rainbows have a round shape. The final thing that happens when sunlight hits a raindrop is that some of that light bounces back, or is “reflected”. </p>
<p>So when you see a rainbow, you’re actually seeing light that has hit a raindrop and bounced back onto your eye.</p>
<p>Here’s where we need to get stuck into some maths. In raindrops, sunlight bounces back, or reflects, most strongly at a certain angle - 42 degrees. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=332&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=332&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=332&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179356/original/file-20170724-21223-1upwvls.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">As long as the angle is right, then the light will be reflected and you see a rainbow.</span>
</figcaption>
</figure>
<p>If we draw rays of sunlight that reflect at 42 degrees into your eyes then those rays start to look like they form a circular arc in the sky. So the <em>reflection</em> gives you the shape of the rainbow, while the <em>refraction</em> gives you the colours of the rainbow.</p>
<p>If you are standing on the ground, then the rainbow stops when it hits the ground. If you are lucky enough to look out on some rain from a plane, then instead of seeing just a part of the circle, you may be able to see a complete circular rainbow, like this: </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1067&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1067&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1067&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179359/original/file-20170724-29742-1mbkhj9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">From the air you can see circular rainbows.</span>
</figcaption>
</figure>
<p>If you like rainbows – and who doesn’t – then there is a whole website full of them <a href="http://www.atoptics.co.uk">here</a>. This site shows many examples of different types of rainbows and other natural light shows that happen as sunlight is refracted and reflected by the Earth’s atmosphere.</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:</em></p>
<p><em>* Email your question to curiouskids@theconversation.edu.au
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* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a> by tagging <a href="https://twitter.com/ConversationEDU">@ConversationEDU</a> with the hashtag #curiouskids, or
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/81187/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Buchler 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>Georgina, age 5, wants to know why rainbows are round.Ben Buchler, Associate professor, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811652017-07-25T20:08:52Z2017-07-25T20:08:52ZCurious Kids: Why is the sky blue and where does it start?<figure><img src="https://images.theconversation.com/files/178566/original/file-20170718-21742-rh5ong.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Earth, shot from space, as it absorbs and reflects rays of light coming from the Sun - the same white-looking rays that give our sky its colour.</span> <span class="attribution"><a class="source" href="https://images-assets.nasa.gov/image/iss040e080833/iss040e080833~orig.jpg">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
<hr>
<blockquote>
<p><strong>Why is the sky blue and where does it start? – Oliver Scott, age 7, Wombarra.</strong> </p>
</blockquote>
<p>This is something that parents get asked every day. And it’s a great question, Oliver! </p>
<p>Some people think the sky is blue because of sunlight reflected off the ocean and back into the sky. But the sky is blue even in the middle of the countryside, nowhere near the sea!</p>
<p>Others think it’s because of the water in our atmosphere. But the sky is blue in places that are extremely dry, like the desert.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=307&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=307&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=307&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=386&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=386&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178606/original/file-20170718-22034-1gz1pjc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=386&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 blue sky over the Sahara desert in Libya.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>So what’s the real reason?</p>
<p>The sky is blue because of the way sunlight interacts with our atmosphere.</p>
<p>If you’ve ever played with a prism or seen a rainbow, then you know light is made up of different colours. The name “ROY G. BIV” helps us remember these colours: red, orange, yellow, green, blue, indigo, and violet. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178593/original/file-20170718-22028-1kksypu.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">A rainbow over my house in suburban Melbourne, 2017.</span>
<span class="attribution"><span class="source">Duane Hamacher</span></span>
</figcaption>
</figure>
<p>These colours make up just a tiny portion of the electromagnetic spectrum, which includes ultraviolet waves, microwaves, and radio waves. This means the invisible waves that cause sunburns, allow us to heat-up our leftovers, and let us listen to the radio are all forms of light.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=142&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=142&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=142&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=179&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=179&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178591/original/file-20170718-22049-1nm2axq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=179&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 spectrum of light, showing the wavelength with objects of comparable size.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Light moves as waves of different lengths: some are short, making bluer light, and some are long, making redder light. As sunlight reaches our atmosphere, molecules in the air scatter the bluer light but let the red light pass through. Scientists call this <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html">Rayleigh scattering</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=274&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=274&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=274&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=344&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=344&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178582/original/file-20170718-22017-2tq1fd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=344&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 spectrum of light we can see. Each colour from red to blue looks has a shorter distance between the waves.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>When the Sun is high in the sky, it appears its <a href="http://solar-center.stanford.edu/SID/activities/GreenSun.html">true colour</a>: white. At sunrise and sunset, we see a much redder sun. This is because the sunlight is passing through a thicker layer of our atmosphere. This scatters the blue and green light along the way, allowing the redder light to pass through and illuminate the clouds in a beautiful array of red, orange, and pink. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178580/original/file-20170718-22049-ayt454.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">Red sunlight illuminating the clouds at sunset outside Melbourne during the 2017 winter solstice.</span>
<span class="attribution"><span class="source">Duane Hamacher</span></span>
</figcaption>
</figure>
<p>Rayleigh scattering can affect how we see the Moon. When the Moon passes through the shadow of the Earth during a total lunar eclipse, blue and green light is scattered in the Earth’s atmosphere, letting red light pass through. Our atmosphere acts a like a magnifying glass, refracting (bending) the red sunlight onto the Moon. This can give it an eerie dark red hue.</p>
<p>For this reason, many cultures - including some <a href="http://www.abc.net.au/science/articles/2011/06/15/3244593.htm">Australian Aboriginal groups</a> - associate lunar eclipses with blood.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179570/original/file-20170725-24759-1vqrztk.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">The dark red colour of the Moon during a total lunar eclipse on 15 May 2003.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/frank_schulenburg/21589241520/in/photolist-yTLvm5-4tEwJW-93wuZt-CrAvMc-pCbPKG-9UhV2x-4tAy7v-4tEw9W-4tEBvL-4tF2Mf-pkHYqU-pkHXTb-pkJtPx-4tEtno-4tEFVs-n9tLaY-4tApEz-4tELhj-yUeUey-pzpHJe-4tAQtR-yVsU9n-n9tKsf-piG5JR-4tAxTn-pkGNDT-4tArD2-4tDZPS-4tERrQ-pAbj8a-4tF3Em-yUe6j3-yTH1vK-pinDkT-4tEUzJ-4tEFFb-n8QD1S-93wrDv-piF7WQ-pkHHj3-naUet9-pBWzmt-4tECkm-yUjNpP-4tEzDj-4tAAUD-4tF2vq-4tDZhS-4tAWT6-zdLyD4">Frank Schulenburg/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Rayleigh scattering works on other planets, too. Did you know that the sky on Mars is also blue? (When there are no big storms kicking red dust into the air, that is!)</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=313&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=313&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=313&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=394&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=394&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178575/original/file-20170718-22011-96v430.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=394&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 photo of the Martian sky from the Viking spacecraft on August 29, 1976.</span>
<span class="attribution"><span class="source">NASA/JPL.</span></span>
</figcaption>
</figure>
<p>And finally, where does the sky start? </p>
<p>This is a tricky question. A bird flying 50 meters above us looks like it’s in the sky. But so do aeroplanes, and they fly more than 10,000 metres overhead. </p>
<p>“The sky” is just our atmosphere as we see it from underneath. A majority of our atmosphere extends about 16 km upward, and this is where most of the Rayleigh scattering happens. </p>
<p>If you’ve ever seen video of a rocket going into space, you can see the blue sky fade away to a black background as it climbs above the atmosphere.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zsJpUCWfyPE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch a space shuttle launch. You can see the skies turn from blue to black as the shuttle moves above the Earth’s atmosphere.</span></figcaption>
</figure>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/81165/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duane W. Hamacher receives funding from the Australian Research Council.</span></em></p>Some people think the sky is blue because of sunlight reflected off the ocean and back into the sky. But that’s not the real reason.Duane Hamacher, Senior ARC Discovery Early Career Research Fellow, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/643812016-10-18T14:32:51Z2016-10-18T14:32:51ZRadio galaxies: the mysterious, secretive “beasts” of the Universe<figure><img src="https://images.theconversation.com/files/141448/original/image-20161012-13485-ao5jja.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Jets generated by supermassive black holes at the centers of galaxies can transport huge amounts of energy across great distances.</span> <span class="attribution"><span class="source">REUTERS/X-ray: NASA/CXC/Tokyo Institute of Technology/J.Kataoka et al</span></span></figcaption></figure><p>Most pictures of galaxies that you see, such as the <a href="http://hubblesite.org/gallery/album/">beautiful images</a> from the <a href="http://hubblesite.org/">Hubble Space Telescope</a>, are optical images. These are made using telescopes which detect light in the same wavelength range that our eyes see. However, scientists can design telescopes which use different parts of the electromagnetic spectrum, such as shorter-wavelength ultraviolet light or longer-wavelength infrared and radio emission. </p>
<p>When we use a <a href="http://www.ska.ac.za/about/faqs/#toggle-id-3">radio telescope</a> to look at galaxies, we find that some have pairs of giant jets extending from their centre out into space.</p>
<p>Jets – powerful, lightning fast particles – are the beasts of the universe, far larger than anything visible in optical image. They often stretch to many millions of times the size of the galaxy itself. There is often no evidence of these jets in the optical images.</p>
<p>They also don’t give up their secrets easily. We have a good idea what jets are and how they’re formed. But, for example, we don’t understand yet what causes these jets to start in the first place. That’s where the powerful <a href="https://www.skatelescope.org/">Square Kilometre Array</a> (SKA) radio telescope that’s currently being built in South Africa enters the picture. Its size and scope can help scientists probe more deeply than ever before.</p>
<h2>The making of a jet</h2>
<p>So how are jets formed? </p>
<p>Galaxies come in many different shapes and sizes, and all galaxies of any reasonable size have a supermassive black hole at their centre. The larger the galaxy, the larger the black hole at its centre. These black holes are many millions of times the mass of the sun. In most galaxies they simply sit passively at the heart of the galaxy. </p>
<p>In some galaxies, however, gas and dust is falling into this supermassive black hole causing vast quantities of energy to be released. This sometimes results in hugely energetic streams of particles – channelled by twisted magnetic fields – being ejected from the galaxy centre. </p>
<p>These powerful fountains of particles are spewed out into space at nearly the speed of light. They form the impressive jets visible in radio images. These particles travel through space for many millions of kilometres until they are eventually slowed down and stopped when they interact with old clouds of gas left over from when the galaxy formed. These jets are immensely powerful and can be thousands of light years across. </p>
<p>Although we understand the processes forming the jets, we don’t know what causes these jets to start in the first place. </p>
<p>Some observations suggest they may be triggered when two galaxies collide, thrusting large quantities of gas and dust into the path of the supermassive black hole at the galactic centre. But this certainly does not seem to be the case for all radio galaxies. There is evidence that some radio galaxies stop ejecting the streams of energetic particles, then start again many thousands of years later. However we don’t know if all radio galaxies go through several active phases like this, or if this is unusual. </p>
<h2>Still so much to learn</h2>
<p>It takes a long time for radio galaxies to grow so large – sometimes up to tens to hundreds of millions of years. This means scientists can’t study radio jets by watching one grow. Instead we have to look at lots of different radio galaxies at different stages in their life cycles. </p>
<p>And understanding radio galaxy jets is important. Because they’re so powerful, these jets have a strong influence on both the galaxy they come from and its surroundings. </p>
<p>From building models of how galaxies evolve with time and comparing them to observations, scientists know that something must be dramatically slowing down the rate at which stars form in the most massive galaxies. Scientists believe that radio jets may be responsible. They heat the gas within the galaxy, preventing it from forming into stars. </p>
<p>However, this process is not well understood. For example, there is also evidence that radio jets may increase the rate of star formation in some galaxies, by compressing gas into dense clouds. Understanding how radio jets interact with their host galaxies and wider environment is key to understanding how galaxies form and evolve with time. This is one of astronomy’s key unanswered questions.</p>
<p>The completion of the SKA, which is being built in South Africa and Australia, will help answer these questions.</p>
<h2>Solving mysteries</h2>
<p>When the SKA is fully operational – sometime after 2020 – it will observe up to a billion galaxies. That includes some of the very first galaxies to form. Using these observations, astronomers should be able to unlock the secrets of radio galaxies. </p>
<p>The <a href="https://www.ska.ac.za/science-engineering/meerkat/">MeerKAT telescope</a>, a precursor to the SKA, is already taking data at the South African site, in the remote Karoo, and will allow us to start answering some of these questions next year. </p>
<p>Perhaps these mysterious beasts of the Universe won’t remain a mystery much longer.</p><img src="https://counter.theconversation.com/content/64381/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Imogen Whittam works for SKA South Africa. She receives funding from SKA South Africa. She is affiliated with SKA South Africa and the University of the Western Cape. </span></em></p>It’s difficult to get jets - powerful, lightning fast particles - to give up their secrets. The new Square Kilometre Array radio telescope could hold the key to solving jets’ mysteries.Imogen Whittam, Post-doctoral researcher in Astrophysics, University of the Western CapeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/490252015-10-15T04:13:25Z2015-10-15T04:13:25ZBenefits of knowing more about neutrinos which pass through our bodies unnoticed<figure><img src="https://images.theconversation.com/files/98365/original/image-20151014-12654-1q4usks.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Neutrinos, we're looking for you! Japan's Super-Kamiokande detector.</span> <span class="attribution"><span class="source">Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo</span></span></figcaption></figure><p>The observation that <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/">neutrinos</a> have mass, which led to the 2015 Nobel Prize for Physics being awarded jointly to Japan’s Takaaki Kajita Japan and Canada’s Arthur McDonald, is important for two key reasons. First, it provides a deeper knowledge of the fundamental tenets of nature. Second, as with any discovery, it comes with innovation in science and technology. </p>
<p>While we know of the existence of neutrinos, not much is known about them. Neutrinos exist in huge numbers in the universe. That is why understanding neutrinos is directly relevant to our knowledge of the universe. </p>
<p>Now that it has been established that neutrinos have <a href="http://www.sciencedaily.com/releases/2015/10/151006083633.htm">mass</a>, we have a key to better understanding how mass is distributed in the universe. Neutrinos may also contribute to understanding why the universe is continuously expanding. </p>
<p>It sits on the similar scale as the discovery of the <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/">Higgs boson</a> at the <a href="http://home.web.cern.ch/topics/large-hadron-collider">Large Hadron Collider</a> at European Organisation for Nuclear Research (<a href="http://home.web.cern.ch/about">CERN</a>), and the future discoveries expected from the <a href="http://www.ska.ac.za/about/project.php">Square Kilometre Array</a> (SKA) project. </p>
<p>Any discovery in experimental science is the result of titanic efforts to overcome technological difficulties and challenges. When the neutrino was first <a href="http://www.pbs.org/wnet/hawking/strange/html/neutrinos.html">postulated</a> in 1930, many thought that it would be mission impossible to detect them, let alone to study its properties – such as its mass.</p>
<p>The relentless need to understand nature better forces scientists to innovate with which to push the boundaries of science and technology. The efforts exerted to demonstrate that neutrinos contain mass have bolstered science and technology in <a href="http://www.cbc.ca/news/technology/canadian-s-nobel-prize-in-physics-highlights-why-basic-science-matters-1.3262835">Canada</a> and <a href="http://www.gmanetwork.com/news/lite/story/539768">Japan</a>. South Africa’s <a href="http://mg.co.za/article/2013-11-27-sa-will-feel-economic-benefits-of-ska-says-director-general">support</a> of projects at CERN, the SKA and other efforts already have a similar effect.</p>
<p>Boosting science and technology via large scientific projects brings the added value of human capacity development in high technology that South Africa is in so much need of.</p>
<h2>What are neutrinos?</h2>
<p>Before answering this question we need to backtrack a bit. Matter is made of <a href="http://education.jlab.org/atomtour/">atoms</a>. Atoms are made of positively charged <a href="http://dictionary.reference.com/browse/nuclei">nuclei</a> and negatively charged <a href="http://dictionary.reference.com/browse/electron">electrons</a> travelling very fast around the nuclei. </p>
<p>The electro-magnetic force holds the electrons in orbit around the nuclei because opposite electric charges attract each other. Nuclei are very heavy compared to electrons and are composed of protons and neutrons. </p>
<p>Neutrinos can be thought of cousins of the electrons, only neutral. Neutrinos share some of the properties of the electrons – for instance, the spin. There is one type of neutrino coupled to the electron, which is called electron neutrino. The electron has an anti-particle, the positron, which has positive electric charge. There is also an electron anti-neutrino.</p>
<p>In nature there are other charged particles that are similar to the electron, which are called muons and taus. These are heavier than the electron. The muons and taus also have two other types of neutrinos respectively. In total we are aware of three types of neutrinos (electron, muon, and tau) and their anti-particles.</p>
<h2>Why are neutrinos elusive?</h2>
<p>Neutrinos do not have electric charge. Therefore, they do not get repelled or attracted to other charged particles in nature. They interact very weakly with matter so they very rarely leave a trace. </p>
<p>Vast amounts of neutrinos <a href="http://timeblimp.com/?page_id=1033">pass through us</a> every day, but we do not feel them because neutrinos hardly ever interact with the atoms that make up our bodies.</p>
<p>Most of the neutrinos that pass through earth come from the sun and are produced by nuclear fusion. These are called solar neutrinos. The other neutrinos are produced as a result of the collision of cosmic particles with the Earth’s atmosphere. These are called atmospheric neutrinos.</p>
<h2>How can we tell that neutrinos have mass?</h2>
<p>There are three types of neutrinos. If neutrinos were massless then they would travel forever unencumbered. If neutrinos have mass then, as they travel, they gradually “disappear” to become a different type of neutrino. </p>
<p>This is referred to as neutrino oscillation and it is a quantum mechanical effect. </p>
<p>For instance, the Sun creates electron neutrinos. By the time neutrinos reach Earth we only observe about one-third of the emitted neutrinos. The remaining two-thirds of the electron neutrinos becomes muon and tau neutrinos. Through this process, it is directly demonstrated that neutrinos have mass.</p>
<h2>Decades of research pay off</h2>
<p>Neutrinos were put forward in 1930 as a means to explain missing energy from a certain type of nuclear reactions. It was not until 1956 that neutrinos were detected unequivocally in laboratory conditions, for which a <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1995/press.html">Nobel Prize in Physics</a> was awarded in 1995. </p>
<p>Scientists from all over the world have not stopped investigating the nature of these elusive particles. Neutrinos were known to be neutral and assumed to be massless. It was not until the late 1990s and early 2000s that experimental techniques became available in order to elucidate if neutrinos have mass. </p>
<p>The latter signifies a major discovery in physics, leading to a Nobel Prize in Physics in 2015. The fact of the matter is that to date we do not really know how neutrinos acquire mass. Unravelling this mystery may lead to other groundbreaking discoveries.</p><img src="https://counter.theconversation.com/content/49025/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bruce Mellado receives funding from the DST, the NRF, Wits research office.</span></em></p>The Nobel Prize-winning research on neutrinos is expected to push the boundaries of science and technology.Bruce Mellado, Professor of Physics, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.