tag:theconversation.com,2011:/es/topics/cosmology-410/articlesCosmology – The Conversation2024-02-28T19:15:08Ztag:theconversation.com,2011:article/2245252024-02-28T19:15:08Z2024-02-28T19:15:08ZWhat ended the ‘dark ages’ in the early universe? New Webb data just brought us closer to solving the mystery<figure><img src="https://images.theconversation.com/files/578478/original/file-20240228-16-jfjexw.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3000%2C2281&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2023/107/01GQQF4KP3GNVB12G6R0V8KSGM?news=true">NASA / ESA / CSA / Ivo Labbe (Swinburne) / Rachel Bezanson (University of Pittsburgh) / Alyssa Pagan (STScI)</a></span></figcaption></figure><p>About 400,000 years after the Big Bang, the cosmos was a very dark place. The glow of the universe’s explosive birth had cooled, and space was filled with dense gas – mostly hydrogen – with no sources of light.</p>
<p>Slowly, over hundreds of millions of years, the gas was drawn into clumps by gravity, and eventually the clumps grew big enough to ignite. These were the first stars.</p>
<p>At first their light didn’t travel far, as much of it was absorbed by a fog of hydrogen gas. However, as more and more stars formed, they produced enough light to burn away the fog by “reionising” the gas – creating the transparent universe dotted with brilliant points of light we see today.</p>
<p>But exactly which stars produced the light that ended the dark ages and triggered this so-called “epoch of reionisation”? In <a href="https://www.nature.com/articles/s41586-024-07043-6">research published in Nature</a>, we used a gigantic cluster of galaxies as a magnifying glass to gaze at faint relics of this time – and discovered that stars in small, faint dwarf galaxies were likely responsible for this cosmic-scale transformation.</p>
<h2>What ended the dark ages?</h2>
<p>Most astronomers already agreed that galaxies were the main force in reionising the universe, but it wasn’t clear how they did it. We know that stars in galaxies should make a lot of ionising photons, but these photons need to escape the dust and gas inside their own galaxy to ionise hydrogen out in the space between galaxies.</p>
<p>It hasn’t been clear what kind of galaxies would be able to produce and emit enough photons to get the job done. (And indeed, there are those who think more exotic objects like big black holes may have been responsible.)</p>
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Read more:
<a href="https://theconversation.com/looking-back-toward-cosmic-dawn-astronomers-confirm-the-faintest-galaxy-ever-seen-207602">Looking back toward cosmic dawn − astronomers confirm the faintest galaxy ever seen</a>
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<p>There are two camps among adherents of the galaxy theory. </p>
<p>The first thinks huge, massive galaxies produced the ionising photons. There were not many of these galaxies in the early universe, but each one produced a lot of light. So if a certain fraction of that light managed to escape, it might have been enough to reionise the universe.</p>
<p>The second camp thinks we are better off ignoring the giant galaxies and focussing on the huge number of much smaller galaxies in the early universe. Each one of these would have produced far less ionising light, but with the weight of their numbers they could have driven the epoch of reionisation.</p>
<h2>A magnifying glass 4 million lightyears wide</h2>
<p>Trying to look at anything in the early universe is very hard. The massive galaxies are rare, so they are hard to find. Smaller galaxies are more common but they are very faint, which makes it difficult (and expensive) to get high-quality data.</p>
<p>We wanted a look at some of the faintest galaxies around, so we used a huge group of galaxies called Pandora’s Cluster as a magnifying glass. The enormous mass of the cluster distorts space and time, amplifying the light from objects behind it.</p>
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<a href="https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo showing magnified galaxies." src="https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=247&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=247&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=247&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=310&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=310&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578484/original/file-20240228-24-wuvfsk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=310&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">Two of the most distant galaxies ever seen, as magnified by Pandora’s Cluster.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Abell_2744#/media/File:Webb_Finds_Distant_Galaxies_Seen_Behind_Pandora’s_Cluster_(weic2220a).jpeg">NASA / ESA/ CSA / T. Treu (UCLA)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>As part of the <a href="https://jwst-uncover.github.io">UNCOVER program</a>, we used the James Webb Space Telescope to look at magnified infrared images of faint galaxies behind Pandora’s Cluster.</p>
<p>We first looked at many different galaxies, then chose a few particularly distant (and therefore ancient) ones to examine more closely. (This kind of close examination is expensive, so we could only look at eight galaxies in greater detail.)</p>
<h2>The bright glow of hydrogen</h2>
<p>We selected some sources which were around 0.5% of the brightness of our Milky Way galaxy at that time, and checked them for the telltale glow of ionised hydrogen. These galaxies are so faint they were only visible at all thanks to the magnifying effect of Pandora’s Cluster.</p>
<p>Our observations confirmed that these small galaxies did exist in the very early universe. What’s more, we confirmed they produced around four times as much ionising light as we would consider “normal”. This is at the highest end of what we had predicted, based on our understanding of how early stars formed.</p>
<p>Because these galaxies produced so much ionising light, only a small fraction of it would have needed to escape to reionise the universe. </p>
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<a href="https://theconversation.com/unlocking-the-mystery-of-the-first-billion-years-of-the-universe-37368">Unlocking the mystery of the first billion years of the universe</a>
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<p>Previously, we had thought that around 20% of all ionising photons would need to escape from these smaller galaxies if they are to be the dominant contributor to reionisation. Our new data suggests even 5% would be sufficient – which is about the fraction of ionising photons we see escaping from modern galaxies.</p>
<p>So now we can confidently say these smaller galaxies could have played a very large role in the epoch of reionisation. However, our study was only based on eight galaxies, all close to a single line of sight. To confirm our results we will need to look at different parts of the sky. </p>
<p>We have new observations planned which will target other large galaxy clusters elsewhere in the universe, to find yet more magnified, faint galaxies to test. If all goes well, we will have some answers in a few years.</p><img src="https://counter.theconversation.com/content/224525/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Themiya Nanayakkara receives funding from Australian Research Council Laureate Fellowship FL180100060. </span></em></p>With the help of a magnifying glass 4 million lightyears wide, astronomers may have solved the riddle of what burned away the hydrogen fog that pervaded the early universe.Themiya Nanayakkara, Senior Scientist at the James Webb Australian Data Centre, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2198922024-02-05T13:30:46Z2024-02-05T13:30:46ZUS Moon landing marks new active phase of lunar science, with commercial launches of landers that will study solar wind and peer into the universe’s dark ages<figure><img src="https://images.theconversation.com/files/567940/original/file-20240104-21-s3p58r.jpg?ixlib=rb-1.1.0&rect=4%2C17%2C2991%2C1868&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dark, far side of the Moon is the perfect place to conduct radio astronomy. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/LunarEclipse/704e3da2df90473486270e23aa73419d/photo?Query=moon&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=399&digitizationType=Digitized&currentItemNo=12&vs=true&vs=true">AP Photo/Rick Bowmer</a></span></figcaption></figure><p>For the first time since 1972, NASA <a href="https://www.intuitivemachines.com/im-1">landed a craft on the surface of the Moon</a> in February 2024. But the agency didn’t do it alone – instead, it partnered with commercial companies. Thanks to new technologies and <a href="https://www.nasa.gov/commercial-lunar-payload-services/">public-private partnerships</a>, the scientific projects brought to the Moon on this craft and on future missions like it will open up new realms of scientific possibility. </p>
<p>As parts of several projects launching this year, teams of scientists, including myself, will conduct radio astronomy from the south pole and the far side of the Moon.</p>
<p>NASA’s <a href="https://www.nasa.gov/commercial-lunar-payload-services/">commercial lunar payload services program</a>, or CLPS, will use uncrewed landers to conduct NASA’s first science experiments from the Moon in over 50 years. The CLPS program differs from past space programs. Rather than NASA building the landers and operating the program, commercial companies will do so in a public-private partnership. NASA identified <a href="https://www.nasa.gov/commercial-lunar-payload-services/clps-providers/">about a dozen companies</a> to serve as vendors for landers that will go to the Moon. </p>
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<figcaption><span class="caption">CLPS will send science payloads to the Moon in conjunction with the Artemis program’s crewed missions.</span></figcaption>
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<p>NASA buys space on these landers for <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">science payloads</a> to fly to the Moon, and the companies design, build and insure the landers, as well as contract with rocket companies for the launches. Unlike in the past, NASA is one of the customers and not the sole driver. </p>
<h2>Peregrine and Odysseus, the first CLPS landers</h2>
<p>The first two CLPS payloads are scheduled to launch during the first two months of 2024. There’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/to2-astrobotic/">Astrobotics payload</a>, which launched Jan. 8 before its lander, named Peregrine, <a href="https://www.space.com/astrobotic-peregrine-moon-lander-headed-to-earth">experienced a fuel issue</a> that cut its journey to the Moon short. </p>
<p>Next, there’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/op-to2-intuitive-machines/">Intuitive Machines payload</a>. Intuitive Machines’ lander, named Odysseus, <a href="https://www.intuitivemachines.com/im-1">landed near the south pole of the Moon</a> on Feb. 22, 2024. NASA has also planned a <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">few additional landings</a> – about two or three per year – for each of the next few years.</p>
<p>I’m a <a href="https://www.colorado.edu/faculty/burns/">radio astronomer</a> and co-investigator on NASA’s <a href="https://www.colorado.edu/ness/projects/radiowave-observations-lunar-surface-photoelectron-sheath-rolses">ROLSES program</a>, otherwise known as Radiowave Observations at the Lunar Surface of the photoElectron Sheath. ROLSES was built by the NASA Goddard Space Flight Center and is led by <a href="https://science.gsfc.nasa.gov/sci/bio/natchimuthuk.gopalswamy-1">Natchimuthuk Gopalswamy</a>. </p>
<p>The ROLSES instrument landed on the Moon as <a href="https://www.intuitivemachines.com/_files/ugd/7c27f7_51f84ee63ea744a9b7312d17fefa9606.pdf">one of six NASA payloads</a> on the Intuitive Machines lander in February. Between ROLSES and another mission scheduled for the lunar far side in two years, LuSEE-Night, our teams will land NASA’s first two radio telescopes on the Moon by 2026. </p>
<h2>Radio telescopes on the Moon</h2>
<p>The Moon – particularly the far side of the Moon – is an ideal place to do radio astronomy and study signals from extraterrestrial objects such as the Sun and the Milky Way galaxy. On Earth, the ionosphere, which <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">contains Earth’s magnetic field</a>, distorts and absorbs radio signals below the <a href="https://www.fcc.gov/general/fm-radio">FM band</a>. These signals might get scrambled or may not even make it to the surface of the Earth.</p>
<p>On Earth, there are also TV signals, satellite broadcasts and defense radar systems <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">making noise</a>. To do higher sensitivity observations, you have to go into space, away from Earth. </p>
<p>The Moon is what scientists call <a href="https://www.sciencefocus.com/space/what-is-tidal-locking">tidally locked</a>. One side of the Moon is always facing the Earth – the “<a href="https://www.rmg.co.uk/stories/topics/what-man-moon">man in the Moon</a>” side – and the other side, <a href="https://theconversation.com/whats-on-the-far-side-of-the-moon-111306">the far side</a>, always faces away from the Earth. The Moon has no ionosphere, and with about 2,000 miles of rock between the Earth and the far side of the Moon, there’s no interference. It’s radio quiet. </p>
<p>For our first mission with ROLSES, which launched in February 2024, we will collect data about environmental conditions on the Moon near its south pole. On the Moon’s surface, <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">solar wind</a> directly strikes the lunar surface and creates a charged gas, called <a href="https://www.psfc.mit.edu/vision/what_is_plasma">a plasma</a>. Electrons lift off the negatively charged surface to form a highly ionized gas. </p>
<p>This doesn’t happen on Earth because <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">the magnetic field deflects</a> the solar wind. But there’s no global magnetic field on the Moon. With a low frequency radio telescope like ROLSES, we’ll be able to measure that plasma for the first time, which could help scientists figure out how to keep astronauts safe on the Moon. </p>
<p>When astronauts walk around on the surface of the Moon, they’ll pick up different charges. It’s like walking across the carpet with your socks on – when you reach for a doorknob, a spark can come out of your finger. The same kind of discharge happens on the Moon from the charged gas, but it’s potentially more harmful to astronauts. </p>
<h2>Solar and exoplanet radio emissions</h2>
<p>Our team is also going to use ROLSES to look at the Sun. The Sun’s surface releases shock waves that send out highly energetic particles and low radio frequency emissions. We’ll use the radio telescopes to measure these emissions and to see bursts of low-frequency radio waves from shock waves within the solar wind.</p>
<p>We’re also going to examine the Earth from the surface of the Moon and use that process as a template for <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">looking at radio emissions from exoplanets</a> that may harbor life <a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">in other star systems</a>. </p>
<p>Magnetic fields are important for life because they shield the planet’s surface from the <a href="https://theconversation.com/the-scorching-winds-on-the-surface-of-the-sun-and-how-were-forecasting-them-44098">solar/stellar wind</a>. </p>
<p>In the future, our team hopes to use specialized arrays of antennas on the far side of the Moon to observe nearby stellar systems that are known to have exoplanets. If we detect the same kind of radio emissions that come from Earth, this will tell us that the planet has a magnetic field. And we can measure the strength of the magnetic field to figure out whether it’s strong enough to shield life.</p>
<h2>Cosmology on the Moon</h2>
<p>The Lunar Surface Electromagnetic Experiment at Night, or <a href="https://www.colorado.edu/ness/projects/lunar-surface-electromagnetics-experiment-night-lusee-night">LuSEE-Night</a>, will fly in early 2026 to the far side of the Moon. LuSEE-Night marks scientists’ first attempt to do cosmology on the Moon.</p>
<p>LuSEE-Night is a novel collaboration between NASA and the Department of Energy. Data will be sent back to Earth using a communications satellite in lunar orbit, <a href="https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/A_pathway_for_communicating_at_the_Moon">Lunar Pathfinder</a>, which is funded by the European Space Agency.</p>
<p>Since the far side of the Moon is <a href="https://cosmicdawn.astro.ucla.edu/lunar_telescopes.html">uniquely radio quiet</a>, it’s the best place to do cosmological observations. During the two weeks of lunar night that happen every 14 days, there’s no emission coming from the Sun, and there’s no ionosphere. </p>
<p>We hope to study an unexplored part of the early universe called the <a href="https://www.astronomy.com/science/the-beginning-to-the-end-of-the-universe-the-cosmic-dark-ages/">dark ages</a>. The dark ages refer to before and just after the formation of the very first stars and galaxies in the universe, which is beyond what the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> can study.</p>
<p>During the dark ages, the universe was less than 100 million years old – today the universe is 13.7 billion years old. The universe was full of hydrogen <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">during the dark ages</a>. That hydrogen radiates through the universe at low radio frequencies, and when new stars turn on, they ionize the hydrogen, producing a radio signature in the spectrum. Our team hopes to measure that signal and learn about how the earliest stars and galaxies in the universe formed.</p>
<p>There’s also a lot of potential new physics that we can study in this last unexplored cosmological epoch in the universe. We will investigate the nature of <a href="https://theconversation.com/dark-matter-the-mystery-substance-physics-still-cant-identify-that-makes-up-the-majority-of-our-universe-85808">dark matter</a> and early <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">dark energy</a> and test our fundamental models of physics and cosmology in an unexplored age.</p>
<p>That process is going to start in 2026 with the LuSEE-Night mission, which is both a fundamental physics experiment and a cosmology experiment.</p>
<p><em>This is an updated version of an article originally published on Feb. 5, 2024.</em></p><img src="https://counter.theconversation.com/content/219892/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jack Burns receives funding from NASA.</span></em></p>Projects under NASA’s CLPS program – including the Odysseus lander that made it to the lunar surface – will probe unexplored questions about the universe’s formation.Jack Burns, Professor of Astrophysical and Planetary Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2204232024-01-08T21:23:31Z2024-01-08T21:23:31ZWhy is the universe ripping itself apart? A new study of exploding stars shows dark energy may be more complicated than we thought<figure><img src="https://images.theconversation.com/files/568137/original/file-20240107-25-i5il3j.jpg?ixlib=rb-1.1.0&rect=5%2C14%2C938%2C930&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The remains of a Type Ia supernova – a kind of exploding star used to measure distances in the universe.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-article/exploded-star-blooms-like-cosmic-flower/">NASA / CXC / U.Texas</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>What is the universe made of? This question has driven astronomers for hundreds of years. </p>
<p>For the past quarter of a century, scientists have believed “normal” stuff like atoms and molecules that make up you, me, Earth, and nearly everything we can see only accounts for 5% of the universe. Another 25% is “dark matter”, an unknown substance we can’t see but which we can detect through how it affects normal matter via gravity. </p>
<p>The remaining 70% of the cosmos is made of “dark energy”. Discovered in 1998, this is an unknown form of energy believed to be making the universe expand at an ever-increasing rate. </p>
<p>In <a href="https://arxiv.org/abs/2401.02929">a new study</a> soon to be published in the Astronomical Journal, we have measured the properties of dark energy in more detail than ever before. Our results show it may be a hypothetical vacuum energy first proposed by Einstein – or it may be something stranger and more complicated that changes over time. </p>
<h2>What is dark energy?</h2>
<p>When Einstein developed the General Theory of Relativity over a century ago, he realised his equations showed the universe should either be expanding or shrinking. This seemed wrong to him, so he added a “cosmological constant” – a kind of energy inherent in empty space – to balance out the force of gravity and keep the universe static. </p>
<p>Later, when the work of Henrietta Swan Leavitt and Edwin Hubble showed the universe was indeed expanding, Einstein did away with the cosmological constant, calling it his “greatest mistake”.</p>
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<a href="https://theconversation.com/more-than-70-of-the-universe-is-made-of-dark-energy-the-mysterious-stuff-even-stranger-than-dark-matter-131569">More than 70% of the Universe is made of 'dark energy', the mysterious stuff even stranger than dark matter</a>
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<p>However, in 1998, two teams of researchers found the expansion of the universe was actually accelerating. This implies that something quite similar to Einstein’s cosmological constant may exist after all – something we now call dark energy.</p>
<p>Since those initial measurements, we’ve been using supernovae and other probes to measure the nature of dark energy. Until now, these results have shown the density of dark energy in the universe appears to be constant.</p>
<p>This means the strength of dark energy remains the same, even as the universe grows – it doesn’t seem to be spread more thinly as the universe gets bigger. We measure this with a number called <em>w</em>. Einstein’s cosmological constant in effect set <em>w</em> to –1, and earlier observations have suggested this was about right.</p>
<h2>Exploding stars as cosmic measuring sticks</h2>
<p>How do we measure what is in the universe and how fast it is growing? We don’t have enormous tape measures or giant scales, so instead we use “standard candles”: objects in space whose brightness we know. </p>
<p>Imagine it is night and you are standing on a long road with a few light poles. These poles all have the same light bulb, but the poles further away are fainter than the nearby ones. </p>
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<span class="caption">In a Type Ia supernova, a white dwarf slowly pulls mass from a neighboring star before exploding.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/resources/2172/type-ia-supernova/">NASA / JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>This is because light fades proportionately to distance. If we know the power of the bulb, and can measure how bright the bulb appears to be, we can calculate the distance to the light pole. </p>
<p>For astronomers, a common cosmic light bulb is a kind of exploding star called a Type Ia supernova. These are white dwarf stars which often suck in matter from a neighbouring star and grow until they reach 1.44 times the mass of our Sun, at which point they explode. By measuring how quickly the explosion fades, we can determine how bright it was and hence how far away from us.</p>
<h2>The Dark Energy Survey</h2>
<p>The <a href="https://www.darkenergysurvey.org/">Dark Energy Survey</a> is the largest effort yet to measure dark energy. More than 400 scientists across multiple continents work together for nearly a decade to repeatedly observe parts of the southern sky. </p>
<p>Repeated observations let us look for changes, like new exploding stars. The more often you observe, the better you can measure these changes, and the larger the area you search, the more supernovae you can find.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of a red-lit observatory building with the starry sky in the background." src="https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568132/original/file-20240107-15-yxxsh1.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"></a>
<figcaption>
<span class="caption">The Cerro Tololo Inter-American Observatory 4-metre telescope which was used by and the Dark Energy Survey.</span>
<span class="attribution"><a class="source" href="https://vms.fnal.gov/asset/detail?recid=1814576">Reidar Hahn / Fermilab</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The first results indicating the existence of dark energy used only a couple of dozen supernovae. The latest results from the Dark Energy Survey use around 1,500 exploding stars, giving much greater precision.</p>
<p>Using a specially built camera installed on the 4-metre Blanco Telescope at the Cerro-Tololo Inter-American Observatory in Chile, the survey found thousands of supernovae of different types. To work out which ones were Type Ia (the kind we need for measuring distances), we used the 4-metre Anglo Australian Telescope at Siding Spring Observatory in New South Wales. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/relax-the-expansion-of-the-universe-is-still-accelerating-67691">Relax, the expansion of the universe is still accelerating</a>
</strong>
</em>
</p>
<hr>
<p>The Anglo Australian Telescope took measurements which broke up the colours of light from the supernovae. This lets us see a “fingerprint” of the individual elements in the explosion. </p>
<p>Type Ia supernovae have some unique features, like containing no hydrogen and silicon. And with enough supernovae, machine learning allowed us to classify thousands of supernovae efficiently. </p>
<h2>More complicated than the cosmological constant</h2>
<p>Finally, after more than a decade of work and studying around 1,500 Type Ia supernovae, the Dark Energy Survey has produced a new best measurement of <em>w</em>. We found <em>w</em> = –0.80 ± 0.18, so it’s somewhere between –0.62 and –0.98.</p>
<p>This is a very interesting result. It is close to –1, but not quite exactly there. To be the cosmological constant, or the energy of empty space, it would need to be exactly –1. </p>
<p>Where does this leave us? With the idea that a more complex model of dark energy may be needed, perhaps one in which this mysterious energy has changed over the life of the universe.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/from-dark-gravity-to-phantom-energy-whats-driving-the-expansion-of-the-universe-60433">From dark gravity to phantom energy: what's driving the expansion of the universe?</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/220423/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brad E Tucker receives funding from the Australian Research Council and ACT Government. </span></em></p>After a decade studying thousands of supernovae, astronomers are still perplexed by the enigma that led Einstein to his ‘greatest mistake’.Brad E Tucker, Astrophysicist/Cosmologist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2182352023-12-04T19:13:34Z2023-12-04T19:13:34ZWas going to space a good idea?<figure><img src="https://images.theconversation.com/files/562901/original/file-20231201-29-6zecp3.jpeg?ixlib=rb-1.1.0&rect=412%2C0%2C1078%2C1092&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-article/astronaut-bruce-mccandless-first-ever-untethered-spacewalk/">NASA</a></span></figcaption></figure><p>In 1963, six years after the first satellite was launched, editors from the Encyclopaedia Britannica posed a question to five eminent thinkers of the day: “Has man’s conquest of space increased or diminished his stature?” The respondents were philosopher <a href="https://plato.stanford.edu/entries/arendt/">Hannah Arendt</a>, writer <a href="https://www.neh.gov/humanities/2015/novemberdecember/feature/the-talented-mr-huxley">Aldous Huxley</a>, theologian <a href="https://www.britannica.com/biography/Paul-Tillich">Paul Tillich</a>, nuclear scientist <a href="https://en.wikipedia.org/wiki/Harrison_Brown">Harrison Brown</a> and historian <a href="https://en.wikipedia.org/wiki/Herbert_J._Muller">Herbert J. Muller</a>.</p>
<p>Sixty years later, as the rush to space accelerates, what can we learn from these 20th-century luminaries writing at the dawn of the space age?</p>
<h2>The state of space 60 years on</h2>
<p>Much has happened since. Spacecraft have landed on planets, moons, comets and asteroids across the Solar System. The two <a href="https://theconversation.com/after-45-years-the-5-billion-year-legacy-of-the-voyager-2-interstellar-probe-is-just-beginning-188077">Voyager</a> deep space probes, launched in 1977, are in interstellar space.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-live-in-space-what-weve-learned-from-20-years-of-the-international-space-station-144851">How to live in space: what we've learned from 20 years of the International Space Station</a>
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<hr>
<p>A handful of people are living in two Earth-orbiting space stations. Humans are getting ready to return to the Moon after more than 50 years, this time to establish a permanent base and mine the deep ice lakes at the south pole. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map of the lunar south pole showing the terrain in grey and green circles representing the crater ice deposits." src="https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/561651/original/file-20231126-15-8m249t.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">Water ice in the permanently shadowed craters of the lunar south pole.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/3577">NASA/Goddard Space Flight Center Scientific Visualization Studio. Data from JAXA/Selene</a></span>
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</figure>
<p>There were only 57 satellites in Earth orbit in 1963. Now there are around <a href="https://www.pixalytics.com/satellites-orbiting-earth-2023/">10,000</a>, with tens of thousands more planned. </p>
<p>Satellite services are part of everyday life. Weather prediction, farming, transport, banking, disaster management, and much more, all rely on satellite data.</p>
<p>Despite these tremendous changes, Arendt, Huxley and Tillich, in particular, have some illuminating insights. </p>
<h2>A brave new world</h2>
<p>Huxley is famous for his 1932 dystopian science fiction novel <a href="https://en.wikipedia.org/wiki/Brave_New_World">Brave New World</a>, and his experimental use of psychedelic drugs.</p>
<p>In <a href="https://www.britannica.com/topic/Aldous-Huxley-on-the-conquest-of-space-1980710">his essay</a>, he questioned who this “man” who had conquered space was, noting it was not humans as a species but Western urban-industrial society that had sent emissaries into space.</p>
<p>This has not changed. The 1967 <a href="https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/outerspacetreaty.html">Outer Space Treaty</a> says space is the province of all humanity, but in reality it’s dominated by a few wealthy nations and individuals. </p>
<p>Huxley said the notion of “stature” assumed humans had a special and different status to other living beings. Given the immensity of space, talking of conquest was, in his opinion, “a trifle silly”.</p>
<p>Tillich was a theologian who fled Nazi Germany before the second world war. In his essay he wrote about how seeing Earth from outside allowed us to “demythologise” our planet. </p>
<p>In contrast to the much-discussed “<a href="https://en.wikipedia.org/wiki/Overview_effect">overview effect</a>” which inspires astronauts with a feeling of almost mystical awe, Tillich argued that the view from space made Earth a “large material body to be looked at and considered as totally calculable”. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Grey and white craters on the lunar surface." src="https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=590&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=590&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=590&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=742&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=742&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562269/original/file-20231128-24-y80m5i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=742&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An image of the lunar surface taken by the US Ranger 7 spacecraft in 1964.</span>
<span class="attribution"><a class="source" href="https://science.nasa.gov/mission/ranger-7/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>When spacecraft began imaging the lunar surface in the 1960s, the process of calculation started for the Moon. Now, its minerals are being evaluated as commodities for human use.</p>
<h2>Have humans changed, or is it how we view Earth?</h2>
<p>Like Tillich, Arendt left Germany under the shadow of Nazism in 1933. She’s best remembered for her studies of totalitarian states and for coining the term “<a href="https://theconversation.com/is-it-time-to-reconsider-the-idea-of-the-banality-of-evil-216737">the banality of evil</a>”. </p>
<p><a href="https://www.thenewatlantis.com/publications/the-conquest-of-space-and-the-stature-of-man">Her essay</a> explored the relationship between science and the human senses. It’s a dense and complex piece; almost every time I read it, I come away with something different.</p>
<p>In the early 20th century, Einstein’s <a href="https://www.space.com/36273-theory-special-relativity.html">theory of special relativity</a> and <a href="https://www.newscientist.com/definition/quantum-physics/">quantum mechanics</a> showed us a reality far beyond the ability of our senses to comprehend. Arendt said it was absurd to think such a cosmos could be “conquered”. Instead, “we have come to our present capacity to ‘conquer space’ through our new ability to handle nature from a point in the universe outside the earth”. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-it-time-to-reconsider-the-idea-of-the-banality-of-evil-216737">Is it time to reconsider the idea of 'the banality of evil'?</a>
</strong>
</em>
</p>
<hr>
<h2>The new geocentrism</h2>
<p>The short human lifespan and the impossibility of moving faster than the speed of light mean humans are unlikely to travel beyond the Solar System. There is a limit to our current expansion into space.</p>
<p>When that limit is reached, said Arendt, “the new world view that may conceivably grow out of it is likely to be once more geocentric and anthropomorphic, although not in the old sense of the earth being the center of the universe and of man being the highest being there is”. Humans would turn back to Earth to make meaning of their existence, and cease to dream of the stars.</p>
<p>This new geocentrism may be exacerbated by an environmental problem already emerging from the rapid growth of satellite megaconstellations. The light they reflect is obscuring the <a href="https://www.discovermagazine.com/environment/light-pollution-threatens-millennia-old-indigenous-navigation-methods">view of the night sky</a>, cutting our senses off from the larger cosmos.</p>
<h2>The far future</h2>
<p>But what if it were technologically possible for humans to expand into the galaxy? </p>
<p>Arendt said assessing humanity from a position outside Earth would reduce the scale of human culture to the point at which humans would become like laboratory rats, studied as statistical patterns. From far enough away, all human culture would appear as nothing more than a “large scale biological process”. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/longtermism-why-the-million-year-philosophy-cant-be-ignored-193538">Longtermism – why the million-year philosophy can't be ignored</a>
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</em>
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<p>Arendt did not see this as an increase in stature: </p>
<blockquote>
<p>The conquest of space and the science that made it possible have come perilously close to this point [of seeing human culture as a biological process]. If they ever should reach it in earnest, the stature of man would not simply be lowered by all standards we know of, but have been destroyed.</p>
</blockquote>
<p>Sixty years on, nations are competing to exploit lunar and asteroid mineral resources. Private corporations and space billionaires are increasingly being touted as the way forward. After the Moon, Mars is the next world in line for “conquest”. The contemporary movement known as <a href="https://aeon.co/essays/why-longtermism-is-the-worlds-most-dangerous-secular-credo">longtermism</a> promotes living on other planets as insurance against <a href="https://en.wikipedia.org/wiki/Global_catastrophic_risk">existential risk</a>, in a far future where humans (or some form of them) spread to fill the galaxies.</p>
<p>But the question remains. Is space travel enhancing what we value about humanity? Arendt and her fellow essayists were not convinced. For me, the answer will depend on what values we choose to prioritise in this new era of interplanetary expansion. </p>
<hr>
<p><em>This article developed from a panel discussion at the Wheeler Centre. You can <a href="https://www.abc.net.au/listen/programs/bigideas/space-race-travel-humanity-ethics-hannah-arrendt-science/102961384">listen to it here</a>.</em></p><img src="https://counter.theconversation.com/content/218235/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alice Gorman is a Vice-Chair of the Global Expert Group for Sustainable Lunar Activities and a Fellow of the Outer Space Institute.</span></em></p>Sixty years ago, philosopher Hannah Arendt argued an interplanetary perspective may be bad news for humanity as we know it.Alice Gorman, Associate Professor in Archaeology and Space Studies, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2166872023-11-30T17:23:41Z2023-11-30T17:23:41ZDo we live in a giant void? It could solve the puzzle of the universe’s expansion<figure><img src="https://images.theconversation.com/files/561941/original/file-20231127-17-nls0xj.png?ixlib=rb-1.1.0&rect=73%2C217%2C1207%2C840&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Pablo Carlos Budassi/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>One of the biggest mysteries in cosmology is the rate at which the universe is expanding. This can be predicted using the standard model of cosmology, also known as <a href="https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.html">Lambda-cold dark matter (ΛCDM)</a>. This model is based on detailed observations of the light left over from the Big Bang – the so-called cosmic microwave background (<a href="https://theconversation.com/the-cmb-how-an-accidental-discovery-became-the-key-to-understanding-the-universe-45126">CMB</a>).</p>
<p>The universe’s expansion makes galaxies move away from each other. The further away they are from us, the more quickly they move. The relationship between a galaxy’s speed and distance is governed by “Hubble’s constant”, which is about 43 miles (70 km) per second per Megaparsec (a unit of length in astronomy). This means that a galaxy <a href="https://theconversation.com/the-universes-rate-of-expansion-is-in-dispute-and-we-may-need-new-physics-to-solve-it-100154">gains about 50,000 miles per hour</a> for every million light years it is away from us.</p>
<p>But unfortunately for the standard model, this value has recently been disputed, leading to what scientists call the <a href="https://doi.org/10.1093/mnras/stab187">“Hubble tension”</a>. When we measure the expansion rate using nearby galaxies and supernovas (exploding stars), it is 10% larger than when we predict it based on the CMB.</p>
<p>In our <a href="https://dx.doi.org/10.1093/mnras/stad3357">new paper</a>, we present one possible explanation: that we live in a giant void in space (an area with below average density). We show that this could inflate local measurements through outflows of matter from the void. Outflows would arise when denser regions surrounding a void pull it apart – they’d exert a bigger gravitational pull than the lower density matter inside the void.</p>
<p>In this scenario, we would need to be near the centre of a void about a billion light years in radius and with density about 20% below the average for the universe as a whole – so not completely empty. </p>
<p>Such a large and deep void is unexpected in the standard model – and therefore controversial. The CMB gives a snapshot of structure in the infant universe, suggesting that matter today should be rather uniformly spread out. However, directly counting the number of galaxies in different regions <a href="https://dx.doi.org/10.1088/0004-637X/775/1/62">does indeed suggest</a> we are in a local void.</p>
<h2>Tweaking the laws of gravity</h2>
<p>We wanted to test this idea further by matching many different cosmological observations by assuming that we live in a large void that grew from a small density fluctuation at early times. </p>
<p>To do this, our <a href="https://doi.org/10.1093/mnras/staa2348">model</a> didn’t incorporate ΛCDM but an alternative theory called Modified Newtonian Dynamics (<a href="https://theconversation.com/dark-matter-may-not-actually-exist-and-our-alternative-theory-can-be-put-to-the-test-110238">MOND</a>).</p>
<p>MOND was originally proposed to explain anomalies in the rotation speeds of galaxies, which is what led to the suggestion of an invisible substance called “dark matter”. MOND instead suggests that the anomalies can be explained by Newton’s law of gravity <a href="https://theconversation.com/dark-matter-our-review-suggests-its-time-to-ditch-it-in-favour-of-a-new-theory-of-gravity-186344">breaking down</a> when the gravitational pull is very weak – as is the case in the outer regions of galaxies.</p>
<p>The overall cosmic expansion history in MOND would be similar to the standard model, but structure (such as galaxy clusters) would grow faster in MOND. Our model captures what the local universe might look like in a MOND universe. And we found it would allow local measurements of the expansion rate today to fluctuate depending on our location.</p>
<p>Recent galaxy observations have allowed a crucial new test of our model based on the velocity it predicts at different locations. This can be done by measuring something called the bulk flow, which is the average velocity of matter in a given sphere, dense or not. This varies with the radius of the sphere, with <a href="https://doi.org/10.1093/mnras/stad1984">recent observations</a> showing <a href="https://doi.org/10.1093/mnras/stad2764">it continues</a> out to a billion light years.</p>
<p>Interestingly, the bulk flow of galaxies on this scale has quadruple the speed expected in the standard model. It also seems to increase with the size of the region considered – opposite to what the standard model predicts. The likelihood of this being consistent with the standard model is below one in a million. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="CMB temperature fluctuations (colour differences)." src="https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562170/original/file-20231128-29-ixfi7y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">CMB temperature fluctuations (colour differences).</span>
<span class="attribution"><a class="source" href="https://wmap.gsfc.nasa.gov/media/121238/index.html">NASA</a></span>
</figcaption>
</figure>
<p>This prompted us to see what our study predicted for the bulk flow. We found it yields a quite good <a href="https://doi.org/10.1093/mnras/stad3357">match</a> to the observations. That requires that we are fairly close to the void centre, and the void being most empty at its centre.</p>
<h2>Case closed?</h2>
<p>Our results come at a time when popular solutions to the Hubble tension are in trouble. Some believe we just need <a href="https://theconversation.com/the-universes-rate-of-expansion-is-in-dispute-and-we-may-need-new-physics-to-solve-it-100154">more precise measurements</a>. Others think it can be solved by assuming the high expansion rate we measure locally is <a href="https://doi.org/10.1146/annurev-nucl-111422-024107">actually the correct one</a>. But that requires a slight tweak to the expansion history in the early universe so the CMB still looks right.</p>
<p>Unfortunately, an influential review highlights seven <a href="https://www.mdpi.com/2218-1997/9/9/393">problems</a> with this approach. If the universe expanded 10% faster over the vast majority of cosmic history, it would also be about 10% younger – contradicting the <a href="https://dx.doi.org/10.3847/1538-4357/ace439">ages</a> of the oldest stars.</p>
<p>The existence of a deep and extended local void in the galaxy number counts and the fast observed bulk flows strongly suggest that structure grows faster than expected in ΛCDM on scales of tens to hundreds of millions of light years. </p>
<p>Interestingly, we know that the massive galaxy cluster <a href="https://hubblesite.org/contents/media/images/2014/22/3361-Image.html">El Gordo</a> formed <a href="https://physicsworld.com/a/are-giant-galaxy-clusters-defying-standard-cosmology/">too early</a> in cosmic history and has too high a mass and collision speed to be compatible with the standard model. This is yet more evidence that structure forms too slowly in this model.</p>
<p>Since gravity is the dominant force on such large scales, we most likely need to extend Einstein’s theory of gravity, General Relativity – but only on scales <a href="https://iai.tv/articles/the-challenge-to-dark-matter-mond-is-wrong-auid-2676?_auid=2020">larger than a million light years</a>.</p>
<p>However, we have no good way to measure how gravity behaves on much larger scales – there are no gravitationally bound objects that huge. We can assume General Relativity remains valid and compare with observations, but it is precisely this approach which leads to the very severe tensions currently faced by our best model of cosmology.</p>
<p>Einstein is thought to have said that we cannot solve problems with the same thinking that led to the problems in the first place. Even if the required changes are not drastic, we could well be witnessing the first reliable evidence for more than a century that we need to change our theory of gravity.</p><img src="https://counter.theconversation.com/content/216687/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Indranil Banik receives funding from the Science and Technology Facilities Council to conduct tests of modified gravity theories.</span></em></p>If we lived in a cosmic area with below average density, it would explain recent contradictory measurements of the universe’s expansion.Indranil Banik, Postdoctoral Research Fellow in Astrophysics, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2154142023-11-15T13:21:33Z2023-11-15T13:21:33ZThe universe is expanding faster than theory predicts – physicists are searching for new ideas that might explain the mismatch<figure><img src="https://images.theconversation.com/files/559383/original/file-20231114-23-g88npv.png?ixlib=rb-1.1.0&rect=8%2C7%2C1189%2C1210&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The James Webb Space Telescope's deep field image shows a universe full of sparkling galaxies.</span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1?news=true">NASA/STScI</a></span></figcaption></figure><p>Astronomers have known for decades that the universe is expanding. When they use telescopes to observe faraway galaxies, they see that these <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">galaxies are moving away</a> from Earth.</p>
<p>To astronomers, the wavelength of light a galaxy emits is longer the faster the galaxy is moving away from us. The farther away the galaxy is, the more its light has shifted toward the longer wavelengths on the red side of the spectrum – so the higher the “redshift.”</p>
<p>Because the speed of light is finite, fast, but not infinitely fast, seeing something far away means we’re looking at the thing how it looked in the past. With distant, high-redshift galaxies, we’re <a href="https://theconversation.com/looking-back-toward-cosmic-dawn-astronomers-confirm-the-faintest-galaxy-ever-seen-207602">seeing the galaxy</a> when the universe was in a younger state. So “high redshift” corresponds to the early times in the universe, and “low redshift” corresponds to the late times in the universe. </p>
<p>But as astronomers have studied these distances, they’ve learned that the universe is not just expanding – its rate of expansion is accelerating. And that expansion rate is even faster than the leading theory predicts it should be, leaving <a href="https://rekeeley.github.io/">cosmologists like me</a> puzzled and looking for new explanations. </p>
<h2>Dark energy and a cosmological constant</h2>
<p>Scientists call the source of this acceleration <a href="https://theconversation.com/dark-energy-map-gives-clue-about-what-it-is-but-deepens-dispute-about-the-cosmic-expansion-rate-143200">dark energy</a>. We’re not quite sure what drives dark energy or how it works, but we think its behavior could be explained by <a href="https://doi.org/10.1086/300499">a cosmological constant</a>, which is a <a href="https://doi.org/10.1038/d41586-018-05095-z">property of spacetime</a> that contributes to the expansion of the universe. </p>
<p>Albert Einstein originally came up with this constant – he marked it with a lambda in his theory of <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">general relativity</a>. With a <a href="https://www.livescience.com/cosmological-constant.html">cosmological constant</a>, as the universe expands, the energy density of the cosmological constant stays the same.</p>
<p>Imagine a box full of particles. If the volume of the box increases, the density of particles would decrease as they spread out to take up all the space in the box. Now imagine the same box, but as the volume increases, the density of the particles stays the same. </p>
<p>It doesn’t seem intuitive, right? That the energy density of the cosmological constant does not decrease as the universe expands is, of course, very weird, but this property helps explain the accelerating universe.</p>
<h2>A standard model of cosmology</h2>
<p>Right now, the leading theory, or standard model, of cosmology is <a href="https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.html">called “Lambda CDM</a>.” Lambda denotes the cosmological constant describing dark energy, and CDM stands for cold dark matter. This model describes both the acceleration of the universe in its late stages as well as the expansion rate in its early days.</p>
<p>Specifically, the Lambda CDM explains observations of the cosmic microwave background, which is the afterglow of microwave radiation from when the universe <a href="https://doi.org/10.1051/0004-6361/201833910">was in a “hot, dense state</a>” about 300,000 years after the Big Bang. Observations using the <a href="https://www.esa.int/Enabling_Support/Operations/Planck">Planck satellite</a>, which measures the <a href="https://www.esa.int/Science_Exploration/Space_Science/Herschel/Cosmic_Microwave_Background_CMB_radiation">cosmic microwave background</a>, led scientists to create the Lambda CDM model. </p>
<p>Fitting the Lambda CDM model to the cosmic microwave background allows physicists to predict the value of the <a href="https://news.uchicago.edu/explainer/hubble-constant-explained">Hubble constant</a>, which isn’t actually a constant but a measurement describing the universe’s current expansion rate. </p>
<p>But the Lambda CDM model isn’t perfect. The expansion rate scientists have calculated by measuring distances to galaxies, and the expansion rate as described in Lambda CDM using <a href="https://doi.org/10.3847/2041-8213/ac5c5b">observations of the cosmic microwave background</a>, don’t line up. Astrophysicists call that disagreement the Hubble tension.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration showing the progression of the Universe's expansion after the Big Bang. The Universe is depicted as a cylindrical funnel with labels along the bottom showing the first stars, the development of planets, and now the dark energy acceleration" src="https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553089/original/file-20231010-21-bzoffm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The universe is expanding faster than predicted by popular models in cosmology.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/infographics/the-big-bang-and-expansion-of-the-universe">NASA</a></span>
</figcaption>
</figure>
<h2>The Hubble tension</h2>
<p>Over the past few years, I’ve been <a href="https://doi.org/10.1103/PhysRevLett.131.111002">researching ways</a> to explain this Hubble tension. The tension may be indicating that the Lambda CDM model is incomplete and physicists should modify their model, or it could indicate that it’s time for researchers to come up with new ideas about how the universe works. And new ideas are always the most exciting things for a physicist.</p>
<p>One way to explain the Hubble tension is to modify the Lambda CDM model by changing the expansion rate at low redshift, at late times in the universe. Modifying the model like this can help physicists predict what sort of physical phenomena might be causing the Hubble tension. </p>
<p>For instance, maybe dark energy is not a cosmological constant but instead the result of gravity working in new ways. If this is the case, dark energy would evolve as the universe expands – and the cosmic microwave background, which shows what the universe looked like only a few years after its creation, would have a different prediction for the Hubble constant. </p>
<p>But, <a href="https://doi.org/10.1103/PhysRevLett.131.111002">my team’s latest research</a> has found that physicists can’t explain the Hubble tension just by changing the expansion rate in the late universe – this whole class of solutions falls short.</p>
<h2>Developing new models</h2>
<p>To study what types of solutions could explain the Hubble tension, we <a href="https://doi.org/10.1103/PhysRevLett.131.111002">developed statistical tools</a> that enabled us to test the viability of the entire class of models that change the expansion rate in the late universe. These statistical tools are very flexible, and we used them to match or mimic different models that could potentially fit observations of the universe’s expansion rate and might offer a solution to the Hubble tension.</p>
<p>The models we tested include evolving dark energy models, where dark energy acts differently at different times in the universe. We also tested interacting dark energy-dark matter models, where dark energy interacts with dark matter, and modified gravity models, where gravity acts differently at different times in the universe. </p>
<p>But none of these could fully explain the Hubble tension. These results suggest that physicists should study the early universe to understand the source of the tension.</p><img src="https://counter.theconversation.com/content/215414/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ryan Keeley 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>The universe is expanding faster than physicists would expect. To figure out what processes underlie this fast expansion rate, some researchers are first trying to rule out what processes can’t.Ryan Keeley, Postdoctoral Scholar in Physics, University of California, MercedLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2116042023-08-31T14:09:55Z2023-08-31T14:09:55ZHow our ancestors viewed the sky: new film explores both indigenous and modern cosmology<p>Something remarkable is happening in a remote part of South Africa’s Northern Cape province, in a semi-desert area called the Karoo. In the past 15 years 64 radio receiving dishes have appeared on the landscape. These constitute the <a href="https://www.sarao.ac.za/gallery/meerkat/">MeerKAT telescope</a>, a precursor to the <a href="https://www.skao.int/en/about-us/skao">Square Kilometre Array Observatory</a> (SKAO), which will – when it is completed and fully functional in 2030 – be the world’s largest radio telescope.</p>
<p>The SKAO will receive signals emanating from the dark regions between the stars and galaxies. This data, studied by <a href="https://www.skao.int/en/resources/what-radio-astronomy">radio astronomers</a>, has the capacity to inform us about dark matter and could change our conception of the universe irrevocably.</p>
<p>In his new, award-winning documentary, <a href="https://www.youtube.com/watch?v=z2g7eGjWGCk">!Aitsa</a>, filmmaker Dane Dodds explores the intellectual background and science of the SKAO alongside indigenous conceptions of the cosmos held by ancient <a href="http://lloydbleekcollection.cs.uct.ac.za/">ǀXam San people</a> and their Afrikaans-speaking descendants living in the Karoo today. As the film’s advisor I saw my task as bringing into focus the hidden assumptions that must be recognised in any encounter between knowledge, traditions and cosmology.</p>
<p>!Aitsa (a South African exclamation of praise or surprise) explores the SKAO’s approach to understanding the universe through big data made comprehensible by the techniques of empirical science, machine learning, artificial intelligence and instrumentation. The film also examines <a href="https://www.tandfonline.com/doi/abs/10.1080/08949468.2023.2168962?journalCode=gvan20">Karoo star-lore</a> as it is shared and spread by an interwoven tapestry of oral traditions. Conventional ideas about the <a href="https://www.tandfonline.com/doi/abs/10.1080/01436597.2018.1447374">nature of science</a> are challenged and the dominant structures of <a href="https://www.tandfonline.com/doi/abs/10.1080/02533952.2020.1850626">knowledge creation</a> are questioned as a result.</p>
<p>To the ǀXam and San people, being in the world as a person includes “the sky’s things” – an understanding of and deep connection with the cosmos. In an age progressively dominated by digital and automated knowledge it was important that the film hold space for this notion.</p>
<h2>Inflected with star-lore</h2>
<p>Through <a href="https://scholar.google.com/citations?user=dBUudaAAAAAJ&hl=en">my own research</a> in the fields of archaeoacoustics, rock art and oral tradition I have come to understand that there is a profound multiplicity of connections within the ǀXam knowledge tradition. In a ǀXam conception of the universe there is no alienating distance between inner and outer, person, stars and space. That’s because their cultural understanding of reciprocities encourages ecological and cosmic connection. </p>
<p>!Aitsa strives to express astronomy as a lived-body experience. One person interviewed in the film says:</p>
<blockquote>
<p>When I look up into the sky and look at how my star is positioned, and look up at the star’s direction, I know which way to walk.</p>
</blockquote>
<p>Another describes the Milky Way as being “right at the centre of a person’s spirituality.”</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/z2g7eGjWGCk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The trailer for !Aitsa.</span></figcaption>
</figure>
<h2>Animism and animation</h2>
<p>The instruments of modern science deliver facts, innovation and technical advancement. But all this comes with societal entanglements and colonial dynamics, a part of the <a href="https://archive.unu.edu/unupress/unupbooks/uu05se/uu05se00.htm">intellectual history</a> of scientific endeavour that assumes authority and stands aloof from the kinds of sensory perceptions and lived experience that are central to ǀXam San cosmology.</p>
<p>!Aitsa investigates a modern pre-disposition that considers <a href="https://www.journals.uchicago.edu/doi/pdf/10.1086/200061">animistic knowledge</a> and reasoning as inherently flawed. Animism is the notion that any living thing has a distinct spiritual essence. It’s a mistake to dismiss ǀXam cultural expression as a mythology that is intrinsically animistic and therefore quaint.</p>
<p>The ǀXam and San people are known as “<a href="https://books.google.co.za/books/about/People_of_the_Eland.html?id=D_wwAQAAIAAJ&redir_esc=y">the people of the eland</a>” and so, to illustrate the way their beliefs animate “things”, an eland antelope is a key character in !Aitsa. The animal’s presence compels the viewer to consider the importance of relationship and relatedness. </p>
<h2>Soundscapes</h2>
<p>Sound plays a crucial role in the film, and was another opportunity to showcase an element of |Xam San culture. The soundtrack (you can hear a preview <a href="https://soundcloud.com/s_i_l_v_a_n/aitsa-film-ost-preview">here</a>) draws on composer Simon Kohler’s musical creativity and the archaeoacoustic research I have done on lithophones, otherwise known as gong rocks, which produce sounds not dissimilar to that of a bell when it is struck.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/how-the-music-of-an-ancient-rock-painting-was-brought-to-life-185475">How the music of an ancient rock painting was brought to life</a>
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<p>Sound is the most ephemeral and transitory of presences but in the film the gong rock sound is a thread linking voices and images, past and present. Collecting the sound required two trips into the Karoo. There we recorded a variety of rock sounds – deep bass-vibrations through to light metallic tinkles. We brought these recordings back into the Cape Town sound studio where the sound was “composed” to create the soundtrack that viewers will hear throughout the film.</p>
<h2>What next?</h2>
<p><a href="https://www.aitsafilm.com/">!Aitsa</a> had its world premiere at <a href="https://cphdox.dk/film/aitsa/">CPH:DOX</a> in Denmark in 2023, with sold out screenings and <a href="https://mubi.com/en/lists/cph-dox-2023-best-to-worst">rave reviews</a>. The film won the Grand Prize at Estonia’s <a href="https://www.chaplin.ee/">Pärnu International Film Festival</a> and was voted Best of the Fest at the Encounters Film Festival in Cape Town. !Aitsa is selected to screen in Canada at <a href="https://planetinfocus.org/">planetinfocus</a> and in October 2023 at the <a href="https://psff.cz/">Prague Science Film Fest</a> and is up for selection at the <a href="https://www.idfa.nl/en">idfa Festival</a> in the Netherlands in November.</p>
<p>In 2024 !Aitsa will go on a road trip, visiting remote places in the Karoo where the film will be screened to audiences who do not have the means for or access to cinemas. </p>
<p>We also hope to take the film to Australia so that the Wajarri Yamaji Aboriginal people can see, listen and connect with their counterparts in the Karoo. This is an important connection because the Wajarri Yamaji live in the Murchison region in Western Australia where the low-frequency component of the SKAO is <a href="https://www.skao.int/en/partners/skao-members/133/australia">currently under construction</a>.</p><img src="https://counter.theconversation.com/content/211604/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Neil Rusch 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>To the ǀXam and San people, being in the world as a person includes “the sky’s things” - an understanding of and deep connection with the cosmos.Neil Rusch, Research Associate, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2086212023-07-03T20:07:29Z2023-07-03T20:07:29ZAstronomers see ancient galaxies flickering in slow motion due to expanding space<figure><img src="https://images.theconversation.com/files/535172/original/file-20230702-177413-sljzpk.png?ixlib=rb-1.1.0&rect=0%2C22%2C3840%2C2132&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA / ESA / J. Olmsted (STScI)</span></span></figcaption></figure><p>According to our best understanding of physics, the fact space is expanding should influence the apparent flow of time, with the distant Universe appearing to run in slow motion.</p>
<p>But observations of highly luminous and variable galaxies, known as quasars, have failed to reveal this cosmic time dilation – until now. </p>
<p>In a <a href="https://doi.org/10.1038/s41550-023-02029-2">new study</a> published in Nature Astronomy, we use two decades of observation to untangle the complex flickering of almost 200 quasars. Buried within this flickering is the imprint of expanding space, with the Universe appearing to be ticking five times slower when it was only a billion years old. </p>
<p>This shows quasars obey the rules of the cosmos, putting to bed the idea they represented a <a href="https://phys.org/news/2010-04-discovery-quasars-dont-dilation-mystifies.html">challenge to modern cosmology</a>. </p>
<h2>Time is a funny thing</h2>
<p>In 1905, Albert Einstein, through his special theory of relativity, told us the speed of clocks’ ticking is relative, dependent on how the clocks are moving. In his 1915 general theory, he told us gravity too can influence the relative rates of clock ticks.</p>
<p><a href="https://articles.adsabs.harvard.edu/pdf/1939ApJ....90..634W">By the 1930s</a>, physicists realised the expanding space of the cosmos, which is described in the language of Einstein’s general relativity, also influences the universe of ticks and tocks.</p>
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Read more:
<a href="https://theconversation.com/timeline-the-history-of-gravity-54528">Timeline: the history of gravity</a>
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</em>
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<p>Due to the finite speed of light, as we look through our telescopes, we are peering into the past. The further we look, the further back into the life of the Universe we see. But in our expanding Universe, the further back we look, the more time space has had to stretch, and the more the relative nature of clock ticks grows.</p>
<p>The prediction of Einstein’s mathematics is clear: we should see the distant universe playing out in slow motion.</p>
<h2>Tick-tock supernova clock</h2>
<p>Measuring this slow-motion universe is difficult, as nature does not provide standard clocks across the cosmos whose relative ticks could be compared. </p>
<p>It took until the 1990s for astronomers to discover and understand the tick of <a href="https://arxiv.org/pdf/astro-ph/9707260.pdf">suitable clocks</a>: a particular kind of exploding star, a supernova. Each supernova explosion was surprisingly similar, brightening rapidly and then fading away over a matter of weeks. </p>
<p>Supernovae are similar, but not identical, meaning their rate of brightening and fading was not a standard clock. But by the close of the 20th century, astronomers were taking another look at these exploding stars, using them <a href="https://supernova.lbl.gov">to chart the expansion of the Universe</a>. (This expansion turned out to be accelerating, leading to the <a href="https://www.nobelprize.org/prizes/physics/2011/press-release/">unexpected discovery of dark energy</a>.)</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/from-dark-gravity-to-phantom-energy-whats-driving-the-expansion-of-the-universe-60433">From dark gravity to phantom energy: what's driving the expansion of the universe?</a>
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</p>
<hr>
<p>To achieve this goal, astronomers had to iron out peculiarities of each supernova, putting them on an equal footing, matching them to a standard intrinsic brightness and a standard clock. </p>
<p>They found the flash of more distant supernovae was stretched precisely in line with Einstein’s predictions. The most distant observed supernovae, exploding when the Universe was half its present age, brightened and faded <a href="https://arxiv.org/pdf/0804.3595.pdf">twice as slowly as more recent supernovae</a>.</p>
<h2>The trouble with quasars</h2>
<p>Supernovae are not the only variable objects in the cosmos. </p>
<p><a href="https://www.wired.com/2010/08/0805first-quasar-located/">Quasars were discovered in the 1960s</a>, and are thought to be supermassive black holes, some many billions of times more massive than the Sun, lurking at the hearts of galaxies. Matter swirls around these black holes on its journey to oblivion inside, heating up and glowing brightly as it does so.</p>
<p>Quasars are <a href="https://phys.org/news/2023-05-astronomers-explore-luminous-quasar.html#:%7E:text=J1144%20was%20detected%20in%20June,a%20redshift%20greater%20than%200.4.">extremely bright</a>, some burning furiously when the <a href="https://phys.org/news/2023-02-hundreds-high-redshift-quasars.html">Universe was an infant</a>. Quasars are also variable, varying in luminosity as matter turbulently tumbles on its way to destruction. </p>
<p>Because quasars are so bright, we can see them at much greater distances than supernovae. So the impact of expanding space and time dilation should be more pronounced.</p>
<p>However, searches for the expected signal have turned up blank. Samples of hundreds of quasars observed over decades definitely varied, but it seemed that the variations of those nearby and those far away were identical. </p>
<p>Some suggested that this demonstrated that the variability of quasars is not intrinsic but is instead due to black holes scattered through the Universe, <a href="https://arxiv.org/pdf/2204.09143.pdf">magnifying some quasars</a> by the action of gravity. More outlandishly, others have claimed that the lack of the expected cosmological signal is a clear sign that we have <a href="https://www.mdpi.com/2218-1997/1/3/307">cosmology all wrong</a> and need to go back to the drawing board. </p>
<h2>New data, new approaches</h2>
<p>In 2023, a new set of quasar data was <a href="https://arxiv.org/pdf/2201.02762.pdf">published</a>. This presented 190 quasars originally identified in the highly successful Sloan Digital Sky Survey but observed over two decades in multiple colours – green, red and infrared light. </p>
<p>The data sampling was mixed, with lots of observations over some times, and less over others. But the wealth of this data meant the astronomers, led by graduate student <a href="https://astro.illinois.edu/directory/profile/stone28">Zachary Stone at the University of Illinois</a>, could statistically characterise each quasar’s variability as what is known as a “<a href="https://arxiv.org/pdf/1312.3966.pdf">damped random walk</a>”. This characterisation assigned a time scale, a tick, to each quasar.</p>
<p>Like each supernova, each quasar is different, and the observed variability can depend upon their intrinsic properties. But with this new data, we could match similar quasars with each other, removing the impact of these differences. As had been done for supernovae before, we had standardised the tick-tock of quasars.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3prF2V_a2gY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The only remaining influence on the observed variability of quasars was the expansion of space, and we unambiguously revealed this signature. Quasars obeyed the rules of the Universe exactly as Einstein’s theory predicted. </p>
<p>Due to their brightness, however, the influence of this cosmic time dilation could be seen much further. The most distant quasars, seen when the Universe was only a tenth of its present age, were ticking away time five times more slowly than today.</p>
<p>At its heart, this is a story about how <a href="https://scitechdaily.com/einstein-proven-right-yet-again-theory-of-general-relativity-passes-a-range-of-precise-tests/">Einstein is right again</a>, and how his mathematical description of the cosmos is the best we have. It puts to rest ideas of a sea of cosmic black holes, or that we truly inhabit a static, unchanging universe. And this is precisely how science advances.</p><img src="https://counter.theconversation.com/content/208621/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Lewis receives funding from the Australian Research Council.</span></em></p>Bright, flickering galaxies called quasars were thought to pose a problem for our understanding of the cosmos – but new research shows Einstein was right yet again.Geraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2065752023-06-18T20:08:12Z2023-06-18T20:08:12ZWhy is the sky dark at night? The 200-year history of a question that transformed our understanding of the Universe<figure><img src="https://images.theconversation.com/files/528678/original/file-20230527-19-36mvgt.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C3390%2C2841&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://esawebb.org/images/potm2301a/">ESA/Webb, NASA & CSA, A. Martel</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>As dawn rose over the German city of Bremen on May 7 1823, <a href="https://link.springer.com/referenceworkentry/10.1007/978-1-4419-9917-7_1031">Heinrich Olbers</a> put the finishing touches to an article that left his name in history. After the deaths of his wife and daughter, Dr Olbers had recently given up his work as an opthalmologist to devote himself to his nocturnal passions: the stars, the Moon, meteorites and comets. </p>
<p>Like many of his peers, Olbers trained himself in astronomy. He gained a <a href="https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_27/July_1885/Some_Self-Made_Astronomers">solid reputation</a> in the academic world and spent long nights observing the sky from the observatory on the second floor of his house.</p>
<p>On that morning, Olbers had come to a strange conclusion: based on all that was known about the Universe at that time, the night sky should not have been dark. In fact, the entire heavens should have been glowing as brightly as the Sun.</p>
<p>Olbers was <a href="https://ui.adsabs.harvard.edu/abs/1990IAUS..139....3H/abstract">not the first</a> to note this paradox. But his name is the one we attach to it today. The enigma of the night sky’s darkness has echoed down the centuries from Olbers and the poet Edgar Allan Poe to 20th-century astronomers and space probes today.</p>
<h2>Finite light in an infinite Universe</h2>
<p>Like many of his contemporaries, Olbers followed <a href="https://doi.org/10.1063/1.881049">Isaac Newton and René Descartes</a> in believing the Universe was infinite.</p>
<p>If the Universe were finite and static, the force of gravity should draw all the stars together at a central point. But if the Universe stretched on forever, gravitational forces would on average be balanced in all directions. </p>
<p>But Olbers realised this model of the cosmos was inconsistent with observations. In a limitless Universe filled with an infinite number of stars, wherever we look at night our gaze should land on the surface of a star, in much the same way as every line of sight in a forest ends at a tree.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of densely packed tree trunks in a forest" src="https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/528760/original/file-20230529-17-zhp9e7.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">In an infinite forest, every line of sight leads to a tree trunk. In an infinite Universe, is the same true for stars?</span>
<span class="attribution"><a class="source" href="https://pxhere.com/fr/photo/1273647">PXHere</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This is the problem Olbers raised in his <a href="https://www.biodiversitylibrary.org/page/2471191#page/163/mode/1up">paper</a> of May 7 1823: the cosmological model of the time suggested every point in the sky should be as bright as the surface of the Sun. There should be no night.</p>
<p>Olbers proposed a solution: the light from more distant stars was absorbed by dust or other material floating in space. The English astronomer John Herschel later pointed out this couldn’t be right, because anything absorbing that much light would eventually heat up enough to glow.</p>
<p>When Olbers died on March 2 1840, at the age of 81, the riddle we know today as Olbers’ paradox was unsolved.</p>
<h2>A poet’s intuition</h2>
<p>Eight years later, on the other side of the Atlantic Ocean, poet and writer Edgar Allan Poe <a href="https://articles.adsabs.harvard.edu/pdf/1994QJRAS..35..177C">thought he had found an answer</a>. On February 3 1848, he gave a public lecture about his ideas to 60 people at the New York Society Library.</p>
<p>Veering between metaphysics and science, Poe argued the cosmos had emerged from a single state of matter (“Oneness”) that fragmented and dispersed under the action of a repulsive force.</p>
<p>This meant the Universe was a finite sphere of matter. If the finite universe is populated by a sufficiently small number of stars, then we won’t see one in every direction we look. The night can be dark again. </p>
<p>Even if we assume the Universe is infinite, if it began at some point in the past then the <a href="https://academic.oup.com/book/32357">time taken by light to reach us</a> would limit the size of the amount of the Universe we can see. This travel time would create a horizon beyond which distant stars would remain inaccessible. </p>
<p>Poe’s audience at the New York Society Library did not give him the rapturous reception he had hoped for. Later the same year, he published his theories in the prose poem <a href="https://www.eapoe.org/works/editions/eurekac.htm">Eureka</a>, which was little circulated.</p>
<p>The following year, on October 7 1849, Poe died at the age of 40. It would be more than a century before scientists confirmed his intuitions about the enigma of the dark night sky.</p>
<h2>Two and a half facts</h2>
<p>In the first half of the 20th century many new theories of the cosmos were developed, spurred on by Einstein’s theory of general relativity, which explained gravity, space and time in new ways. In the second half of the century, these cosmological theories began to be tested with observations.</p>
<p>In 1963, <a href="https://articles.adsabs.harvard.edu/pdf/1993QJRAS..34..157L">British astronomer Peter Scheuer</a> argued that cosmology was based on only “two and a half facts”: </p>
<ul>
<li>fact 1: the night sky is dark, which had been known for some time</li>
<li>fact 2: galaxies are <a href="https://en.wikipedia.org/wiki/Hubble%27s_law">moving away from each other</a>, as shown by Hubble’s observations published in 1929</li>
<li>fact 2.5: the content of the Universe is probably evolving as cosmic time unfolds. </li>
</ul>
<p>Strong controversies on the interpretation of facts 2 and 2.5 agitated the scientific community in the 1950s and 1960s. Was the Universe essentially stationary, or had it begun in an enormous explosion – a Big Bang? Supporters of both sides conceded, however, they needed to explain the darkness of the night sky. </p>
<h2>The lifetime of stars</h2>
<p>British cosmologist Edward Harrison <a href="https://www.nature.com/articles/204271b0">resolved the conflict</a> in 1964. He showed that the main factor determining the brightness of the night sky is actually the finite age of the stars. </p>
<p>The number of stars in the observable Universe is <a href="https://www.esa.int/Science_Exploration/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe">extremely large</a>, but it is finite. This limited number, each burning for a limited time, spread over a gigantic volume, lets darkness manifest itself between the stars. </p>
<p>Harrison later <a href="https://www.nature.com/articles/322417a0">realised</a> this solution had already been proposed not only by Edgar Allan Poe, but by British physicist Lord Kelvin in 1901. </p>
<p>Observations in the 1980s confirmed the resolution proposed by Poe, Kelvin and Harrison. Olbers’ paradox had <a href="https://ui.adsabs.harvard.edu/link_gateway/1986SSRv...44..169W/ADS_PDF">finally been put to rest</a>.</p>
<h2>Fossil light</h2>
<p>Or perhaps not quite. Viewed from a different angle, there is another resolution to the paradox: the night sky is not actually so dark after all. </p>
<p>After the discovery of the expansion of the Universe in the late 1920s, scientists realised the Universe could have started off extremely compact, dense and hot. This is the “hot Big Bang” model we have today.</p>
<p>One core prediction of this model is the existence of “fossil light” released in the cosmic dawn. This fossil light should be observable today – but not with the naked eye, as the expanding Universe would have shifted it to longer wavelengths. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=323&fit=crop&dpr=1 600w, https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=323&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=323&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=406&fit=crop&dpr=1 754w, https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=406&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/528761/original/file-20230529-19-ipn9fu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=406&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When seen via microwave radiation, the sky is dominated by our Milky Way galaxy. But behind it we can see the fainter glow of the cosmic microwave background.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/images/pia13239-plancks-view-of-the-whole-sky">ESA, HFI & LFI consortia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This radiation – the cosmic microwave background – was <a href="https://ui.adsabs.harvard.edu/abs/1965ApJ...142..419P/abstract">detected in 1964</a>. Now measured with <a href="https://doi.org/10.1051/0004-6361/201833880">exquisite accuracy</a>, the cosmic background radiation is the most common light in the Universe. </p>
<p>We now know the cosmos is also illuminated by <a href="https://ui.adsabs.harvard.edu/abs/1967ApJ...148..377P">a second, much fainter background light</a>, produced by galaxies as they form and evolve. This light is referred to as the cosmic ultraviolet, optical and infrared background. </p>
<p>So we can also answer Olbers’ paradox by saying the sky is not dark, but faintly glimmers with the <a href="https://journals.sagepub.com/doi/10.1177/0003702818767133">dim relic radiation</a> of all that has been over the finite lifetime of the Universe.</p>
<h2>New answers, new questions</h2>
<p>In 2023, Olbers’ paradox has evolved into a rich field of research. In our own work, we carry out ever-more precise measurements of the brightness of the night sky, and simulate the stars of the cosmos with supercomputers. We can now determine the <a href="https://academic.oup.com/mnras/article/503/2/2033/6152275">number of stars</a> in the sky with great accuracy. </p>
<p>Nevertheless, puzzles remain. Last year the New Horizons space probe, out beyond the orbit of Pluto and away from the dust of the inner Solar System, found the sky is <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac573d/pdf">twice as bright</a> as we expected it to be.</p>
<p>And so the question of the darkness of the sky lives on, crossing ages and cultures.</p><img src="https://counter.theconversation.com/content/206575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Biteau receives funding from University Paris-Saclay, CNRS (Centre National de la Recherche) and ANR (Agence National de la Recherche). </span></em></p><p class="fine-print"><em><span>Alberto Domínguez receives funding from Ministerio de Ciencia e Innovación (Spain) and Banco Santander - Universidad Complutense de Madrid.</span></em></p><p class="fine-print"><em><span>David Valls-Gabaud receives funding from the CNRS (Centre National de la Recherche Scientifique) and CNES (Centre National d'Etudes Spatiales).</span></em></p><p class="fine-print"><em><span>José Fonseca receives funding from Fundação para a Ciência e Tecnologia. </span></em></p><p class="fine-print"><em><span>Juan Garcia-Bellido receives funding from MICINN (Spain) through various research projects.</span></em></p><p class="fine-print"><em><span>Simon Driver receives funding from the Australian Research Council which supports studies of the Extragalactic Background Light (EBL). Simon is also a member of the Hubble Space Telescope SkySURF program (measuring the EBL) and a member of the Messier team (a potential space mission which includes, as part of its science case, studies of the EBL).</span></em></p><p class="fine-print"><em><span>Hervé Dole 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 darkness of the night sky seems so obvious as to need no explanation – yet it has intrigued and baffled scientists for centuries.Jonathan Biteau, Maître de conférence en physique des astroparticules, Université Paris-SaclayAlberto Domínguez, Investigador en Astrofísica, Universidad Complutense de MadridDavid Valls-Gabaud, Astrophysicien, Directeur de recherches au CNRS, Observatoire de ParisHervé Dole, Astrophysicien, Professeur, Vice-président, art, culture, science et société, Université Paris-SaclayJosé Fonseca, Assistant Research, Universidade do PortoJuan Garcia-Bellido, Catedratico de Fisica Teórica, Universidad Autónoma de MadridSimon Driver, ARC Laureate Fellow and Winthrop Research Professor at the International Centre for Radio Astronomy Research, UWA., The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2052422023-05-11T20:08:28Z2023-05-11T20:08:28ZHow fast is the Universe really expanding? Multiple views of an exploding star raise new questions<figure><img src="https://images.theconversation.com/files/525519/original/file-20230511-27-dajgjd.jpg?ixlib=rb-1.1.0&rect=0%2C898%2C2400%2C1498&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2015/46/3671-Image.html?keyword=Refsdal">NASA / ESA / P Kelly</a></span></figcaption></figure><p>How did we get here? Where are we going? And how long will it take? These questions are as old as humanity itself, and, if they’ve already been asked by other species elsewhere in the Universe, potentially very much older than that.</p>
<p>They are also some of the fundamental questions we are trying to answer in the study of the Universe, called cosmology. One cosmological conundrum is how fast the Universe is expanding, which is measured by a number called the Hubble constant. And there is quite a bit of tension around it.</p>
<p>In two new papers led by my colleague Patrick Kelly at the University of Minnesota, we have successfully used a new technique – involving light from an exploding star that arrived at Earth via multiple winding routes through the expanding Universe – to measure the Hubble constant. The papers are published in <a href="http://www.science.org/doi/10.1126/sciadv.abh1322">Science</a> and <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ac4ccb">The Astrophysical Journal</a>.</p>
<p>And if our results don’t quite resolve the tension, they do give us another clue – and more questions to ask.</p>
<h2>Standard candles and the expanding Universe</h2>
<p>We have known since the 1920s that the Universe is expanding.</p>
<p>Around 1908, US astronomer Henrietta Leavitt found a way to measure the intrinsic brightness of a kind of star called a Cepheid variable – not how bright they appear from Earth, which depends on distance and other factors, but how bright they really are. Cepheids grow brighter and dimmer in a regular cycle, and Leavitt showed the intrinsic brightness was related to the length of this cycle.</p>
<p>Leavitt’s Law, as it is now called, lets scientists use Cepheids as “standard candles”: objects whose intrinsic brightness is known, and therefore, whose distance can be calculated.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525524/original/file-20230511-15-3vncam.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The standard candle principle: all of these lights have the same ‘intrinsic brightness’, but the more distant ones appear dimmer.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>How does this work? Imagine it is night, and you are standing on a long, dark street with only a few light poles going down the road. Now imagine every light pole has the same type of light bulb, with the same power. You’ll notice the distant ones appear fainter than the nearby ones. </p>
<p>We know that light fades proportionately to its distance, in something called the inverse-square law for light. Now, if you can measure how bright each light appears to you, and if you already know how bright it should be, you can then figure out how far away each light pole is.</p>
<p>In 1929, another US astronomer, Edwin Hubble, was able to find a number of these Cepheid stars in other galaxies and measure their distance – and from those distances and other measurements, he could determine that the Universe was expanding. </p>
<h2>Different methods give different results</h2>
<p>This standard candle method is a powerful one, allowing us to measure the vast Universe. We are always looking for different candles that can be better measured, and seen at much greater distances.</p>
<p>Some recent efforts to measure the Universe further from Earth, like the SH0ES project I was a part of, led by Nobel laureate Adam Riess, have used Cepheids alongside a type of exploding star called a Type Ia supernova, which can also be used as a standard candle.</p>
<p>There are also other methods to measure Hubble’s constant, such as one that uses the cosmic microwave background – relic light or radiation that began to travel through the Universe shortly after the Big Bang.</p>
<p>The problem is that these two measurements, one nearby using supernovae and Cepheids, and one much farther away using the microwave background, differ by nearly 10%. Astronomers call this difference the Hubble tension, and have been looking for new measurement techniques to resolve it.</p>
<h2>A new method: gravitational lensing</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=489&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=489&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=489&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=614&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=614&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525533/original/file-20230511-27-3vncam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=614&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Each of the four yellow dots is a separate image of Supernova Refsdal, which lies behind the bright blob of a galaxy cluster in the centre of the picture.</span>
<span class="attribution"><span class="source">NASA / ESA / P Kelly</span></span>
</figcaption>
</figure>
<p>In our new work, we have successfully used a new technique to measure this expansion rate of the Universe. The work is based on a supernova called Supernova Refsdal. </p>
<p>In 2014, our team spotted multiple images of the same supernova – the first time such a “lensed” supernova had been observed. Instead of the Hubble Space Telescope seeing one supernova, we saw five!</p>
<p>How does this happen? The light from the supernova went out in all directions, but it travelled through space warped by the enormous gravitational fields of a huge cluster of galaxies, which bent some of the light’s path in such a way that it ended up coming to Earth via multiple routes. Each appearance of the supernova had reached us along a different path through the Universe. </p>
<p>Imagine three trains leaving the same station at the same time. However, one goes directly to the next station, the other makes a wide trip through the mountains, and another via the coast. They all leave and arrive at the same stations, but take different trips and so while they leave at the same time, they will arrive at different times. </p>
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<figcaption>
<span class="caption">Multiple views of a single supernova – spread across time and space – allowed scientists to measure how fast the Universe is expanding.</span>
<span class="attribution"><a class="source" href="http://www.science.org/doi/10.1126/sciadv.abh1322">P.L. Kelly et al., Science 10.1126/science.abh1322 (2023)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>So our lensed images show the same supernova, that exploded at one certain point in time, but each image has travelled a different path. By looking at the arrival at Earth of each appearance of the supernova – one of which happened in 2015, after the exploding star had been spotted already – we were able to measure their travel time, and therefore how much the Universe had grown while the image was in transit.</p>
<h2>Are we there yet?</h2>
<p>This gave us a different, but unique measurement of the growth of the Universe. In the papers, we find this measurement is closer to the cosmic microwave background measurement, rather than the nearby Cepheid and supernova measurement. However, based on its location, it should be closer to the Cepheid and supernova measurement.</p>
<p>While this does not settle the debate at all, it gives us another clue to look at. There could be a problem with the supernova value, or our understanding of galaxy clusters and the models to apply to lensing, or something else entirely.</p>
<p>Like the kids in the back of the car on a road trip asking “are we there yet”, we still don’t know.</p><img src="https://counter.theconversation.com/content/205242/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brad E Tucker receives funding from the Australian Research Council and Australian Capital Territory government. </span></em></p>Different measures of the rate of the Universe’s expansion give different results – and a new measurement technique only makes matters more complicated.Brad E Tucker, Astrophysicist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2048242023-05-10T12:05:23Z2023-05-10T12:05:23ZStephen Hawking and I created his final theory of the cosmos – here’s what it reveals about the origins of time and life<figure><img src="https://images.theconversation.com/files/525085/original/file-20230509-27-2ly6rr.jpeg?ixlib=rb-1.1.0&rect=38%2C5%2C1230%2C841&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hawking and the author. </span> <span class="attribution"><span class="source">Photograph: Thomas Hertog and Jonathan Wood</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The late physicist Stephen Hawking first asked me to work with him to develop “a new quantum theory of the Big Bang” in 1998. What started out as a doctoral project evolved over some 20 years into an intense collaboration that ended <a href="https://theconversation.com/stephen-hawking-martin-rees-looks-back-on-colleagues-spectacular-success-against-all-odds-93379">only with his passing</a> on March 14 2018. </p>
<p>The enigma at the centre of our research throughout this period was how the Big Bang could have created <a href="https://theconversation.com/the-multiverse-our-universe-is-suspiciously-unlikely-to-exist-unless-it-is-one-of-many-200585">conditions so perfectly hospitable to life</a>. Our answer is being <a href="https://www.penguin.co.uk/books/440139/on-the-origin-of-time-by-hertog-thomas/9781911709084">published in a new book</a>, On the Origin of Time: Stephen Hawking’s Final Theory.</p>
<p>Questions about the ultimate origin of the cosmos, or universe, take physics out of its comfort zone. Yet this was exactly where Hawking liked to venture. The prospect — or hope — to crack the riddle of cosmic design drove much of Hawking’s research in cosmology. “To boldly go where Star Trek fears to tread” was his motto – and also his screen saver. </p>
<p>Our shared scientific quest meant that we inevitably grew close. Being around him, one could not fail to be influenced by his determination and optimism that we could tackle mystifying questions. He made me feel as if we were writing our own creation story, which, in a sense, we did.</p>
<p>In the old days, it was thought that the apparent design of the cosmos meant there had to be a designer – a God. Today, scientists instead point to the laws of physics. These laws have a number of striking life-engendering properties. Take the amount of matter and energy in the universe, the delicate ratios of the forces, or the number of spatial dimensions. </p>
<p>Physicists <a href="https://www.sciencedirect.com/science/article/pii/S0370157319300511">have discovered</a> that if you tweak these properties ever so slightly, it renders the universe lifeless. It almost feels as if the universe is a fix – even a big one. </p>
<p>But where do the laws of physics come from? From Albert Einstein to Hawking in his earlier work, most 20th-century physicists regarded the mathematical relationships that underlie the physical laws as eternal truths. In this view, the apparent design of the cosmos is a matter of mathematical necessity. The universe is the way it is because nature had no choice. </p>
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<p>Around the turn of the 21st century, a different explanation emerged. Perhaps we live in a multiverse, an enormous space that spawns a patchwork of universes, each with its own kind of Big Bang and physics. It would make sense, statistically, for a few of these universes to be life-friendly.</p>
<p>However, soon such multiverse musings got caught in a <a href="https://theconversation.com/the-multiverse-how-were-tackling-the-challenges-facing-the-theory-201729">spiral of paradoxes</a> and no verifiable predictions.</p>
<h2>Turning cosmology inside out</h2>
<p>Can we do better? Yes, Hawking and I found out, but only by relinquishing the idea, inherent in multiverse cosmology, that our physical theories can take a God’s-eye view, as if standing outside the entire cosmos. </p>
<p>It is an obvious and seemingly tautological point: cosmological theory must account for the fact that we exist within the universe. “We are not angels who view the universe from the outside,” Hawking told me. “Our theories are never decoupled from us.”</p>
<p>We set out to rethink cosmology from an observer’s perspective. This required adopting the strange rules of <a href="https://theconversation.com/great-mysteries-of-physics-4-does-objective-reality-exist-202550">quantum mechanics</a>, which governs the microworld of particles and atoms. </p>
<p>According to quantum mechanics, particles can be in several possible locations at the same time – a property called superposition. It is only when a particle is observed that it (randomly) picks a definite position. Quantum mechanics also involves random jumps and fluctuations, such as particles popping out of empty space and disappearing again. </p>
<p>In a quantum universe, therefore, a tangible past and future emerge out of a haze of possibilities by means of a continual process of observing. Such quantum observations don’t need to be carried out by humans. The environment or even a single particle can “observe”. </p>
<p>Countless such quantum acts of observation constantly transform what might be into what does happen, thereby drawing the universe more firmly into existence. And once something has been observed, all other possibilities become irrelevant.</p>
<figure class="align-center ">
<img alt="Image of the Carina nebula." src="https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&rect=0%2C32%2C3573%2C2010&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=437&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=437&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=437&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Star-forming region in our galaxy.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, and STScI</span></span>
</figcaption>
</figure>
<p>We discovered that when looking back at the earliest stages of the universe through a quantum lens, there’s a deeper level of evolution in which even the laws of physics change and evolve, in sync with the universe that is taking shape. What’s more, this meta-evolution has a Darwinian flavor. </p>
<p>Variation enters because random quantum jumps cause frequent excursions from what’s most probable. Selection enters because some of these excursions can be amplified and frozen, thanks to quantum observation. The interplay between these two competing forces – variation and selection – in the primeval universe produced a branching tree of physical laws. </p>
<p>The upshot is a profound revision of the fundamentals of cosmology. Cosmologists usually start by assuming laws and initial conditions that existed at the moment of the Big Bang, then consider how today’s universe evolved from them. But we suggest that these laws are themselves the result of evolution. </p>
<p>Dimensions, forces, and particle species transmute and diversify in the furnace of the hot Big Bang – somewhat analogous to how biological species emerge billions of years later – and acquire their effective form over time. </p>
<p>Moreover, the randomness involved means that the outcome of this evolution – the specific set of physical laws that makes our universe what it is – <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.73.123527">can only be understood in retrospect</a>.</p>
<p>In some sense, the early universe was a superposition of an enormous number of possible worlds. But we are looking at the universe today at a time when humans, galaxies and planets exist. That means we see the history that led to our evolution. </p>
<p>We observe parameters with “lucky values”. But we are wrong to assume they were somehow designed or always like that. </p>
<h2>The trouble with time</h2>
<p>The crux of our hypothesis is that, reasoning backward in time, evolution towards more simplicity and less structure continues all the way. Ultimately, even time and, with it, the physical laws fade away. </p>
<p>This view is especially borne out of the holographic form of our theory. The “<a href="https://www.theguardian.com/science/shortcuts/2017/jan/31/guide-to-holographic-principle-of-universe">holographic principle</a>” in physics predicts that just as a hologram appears to have three dimensions when it is in fact encoded in only two dimensions, the evolution of the entire universe is similarly encoded on an abstract, timeless surface. </p>
<p>Hawking and I view time and causality <a href="https://theconversation.com/great-mysteries-of-physics-1-is-time-an-illusion-201026">as “emergent qualities”</a>, having no prior existence but arising from the interactions between countless quantum particles. It’s a bit like how temperature emerges from many atoms moving collectively, even though no single atom has temperature. </p>
<p>One ventures back in time by zooming out and taking a fuzzier look at the hologram. Eventually, however, one loses all information encoded in the hologram. This would be the origin of time - the Big Bang. </p>
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<p>For almost a century, we have studied the origin of the universe against the stable background of immutable laws of nature. But our theory reads the universe’s history from within and as one that includes, in its earliest stages, the genealogy of the physical laws. It isn’t the laws as such but their capacity to transmute that has the final word. </p>
<p>Future cosmological observations may find evidence of this. For instance, precision observations of <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">gravitational waves</a> – ripples in the fabric of spacetime – may reveal signatures of some of the early branches of the universe. If spotted, Hawking’s cosmological finale may well prove to be his greatest scientific legacy.</p><img src="https://counter.theconversation.com/content/204824/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Hertog is professor of theoretical physics at KU Leuven (Belgium). </span></em></p>The enigma at the centre of our 20-year collaboration was how the Big Bang could have created conditions so perfectly hospitable to lifeThomas Hertog, Professor of physics, KU LeuvenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2042452023-05-05T17:04:27Z2023-05-05T17:04:27ZThe Euclid spacecraft will transform how we view the ‘dark universe’<figure><img src="https://images.theconversation.com/files/524112/original/file-20230503-26-6f6as6.jpg?ixlib=rb-1.1.0&rect=17%2C8%2C5973%2C2964&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Euclid is set to launch this year on a rocket built by SpaceX.</span> <span class="attribution"><a class="source" href="https://www.esa.int/ESA_Multimedia/Search?SearchText=euclid&result_type=images">Work performed by ATG under contract for ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The European Space Agency’s (ESA) <a href="https://www.esa.int/Science_Exploration/Space_Science/Euclid_overview">Euclid satellite</a> completed the first part of its long journey into space on May 1 2023, when it <a href="https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_arrives_at_launch_site">arrived in Florida on a boat from Italy</a>. It is scheduled to lift off on a Falcon 9 rocket, built by SpaceX, from Cape Canaveral in early July.</p>
<p>Euclid is designed to provide us with a better understanding of the “mysterious” components of our universe, known as dark matter and dark energy. </p>
<p>Unlike the normal matter we experience here on Earth, <a href="https://www.nasa.gov/audience/forstudents/9-12/features/what-is-dark-matter.html">dark matter</a> neither reflects nor emits light. It binds galaxies together and is thought to make up about 80% of all the mass in the universe. We’ve known about it for a century, but its true nature remains an enigma. </p>
<p><a href="https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy">Dark energy</a> is similarly puzzling. Astronomers have shown that the expansion of the universe over the last five billion years has been <a href="https://iopscience.iop.org/article/10.1086/300499/fulltext/">accelerating faster than expected</a>. Many believe <a href="https://iopscience.iop.org/article/10.1086/307221/meta">this acceleration</a> is driven by an unseen force, which has been dubbed dark energy. This makes up about 70% of the energy in the universe. </p>
<p>Euclid will map this “dark universe”, using a suite of scientific instruments to shed light on different aspects of dark energy and dark matter. </p>
<h2>A light in the dark</h2>
<p>After launch, Euclid will undertake a month-long journey to a region in space called the <a href="https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/">second Earth-Sun Lagrangian point</a>, which is five times further from us than the Moon. It’s where the gravitational pull of the Sun and the Earth balance out and provides a stable vantage point for Euclid to observe the universe. Euclid will join the <a href="https://webb.nasa.gov">James Webb Space Telescope (JWST)</a> at this point and will be the perfect companion to that amazing space observatory.</p>
<p>My involvement in Euclid began in 2007 when I was invited by ESA to participate in an independent concept advisory team to assess two competing mission proposals called SPACE and DUNE. </p>
<p>Both used different techniques, and therefore different instruments, to study the dark universe, and ESA was struggling to decide between them. Both were compelling concepts and our team decided that both had merit, especially to provide a vital cross-check between them. Euclid was thus <a href="https://sci.esa.int/web/cosmic-vision/-/42437-study-missions">born from the best of both concepts</a>.</p>
<p>Euclid is designed to study the whole universe so needs instruments with wide fields of view. The wider the field of view of the imaging instrument, the more of the universe it can observe. To do this, Euclid uses a relatively small telescope compared to JWST. In size, Euclid is roughly the size of a truck compared to the aircraft-sized JWST. But Euclid also carries some of the biggest digital cameras deployed in space with fields of view hundreds of times greater than JWST’s. </p>
<h2>Shapes and colours</h2>
<p>The <a href="https://arxiv.org/pdf/1608.08603.pdf">Euclid VIS (or visible) instrument</a>, built mostly in the UK, is designed to measure the positions and shapes of as many galaxies as possible to look for subtle correlations in this data caused by the gravitational lensing of the light, as it travels to us through the intervening dark matter. This gravitational lensing effect is weak, only one part in a hundred thousand for most galaxies, thus requiring lots of galaxies to see the effect in high definition. Thus VIS will produce Hubble telescope-like image quality over a third of the night sky. </p>
<p>VIS, however, can’t measure the colours of objects. This is needed to measure their distance through the <a href="https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift">redshift effect</a>, where light from those objects is shifted to longer, or redder, wavelengths in a way that relates to their distance from us. Some of this data will need to come from existing and planned ground-based observatories, but Euclid also carries the <a href="https://arxiv.org/pdf/2203.01650.pdf">NISP (Near-Infra Spectrometer and Photometer)</a> instrument which is specifically designed to measure the infrared colours and spectra, and therefore redshifts, for the most distant galaxies that Euclid will see. </p>
<p>To measure dark energy, NISP will exploit a relative new technique called <a href="https://svs.gsfc.nasa.gov/13768">Baryon Acoustic Oscillations (BAO)</a> that provides an accurate measurement of the expansion history of the universe over its last 10 billion years. That history is vital for testing possible models of dark energy including suggested modifications to Einstien’s Theory of General Relativity. </p>
<figure class="align-center ">
<img alt="The Whirlpool Galaxy, known as M51, and a companion galaxy." src="https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=523&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=523&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524144/original/file-20230503-26-56rt5t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=523&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Euclid will gather information on the shapes and other properties of galaxies in the sky.</span>
<span class="attribution"><a class="source" href="https://esahubble.org/images/heic0506a/">NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Treasure trove</h2>
<p>Such an experiment takes an army of scientists and not everyone is solely working on dark matter and dark energy. Like JWST, Euclid will be a treasure-trove of new discoveries in many areas of astronomy. The Euclid consortium needs hundreds of people to help develop the sophisticated software needed to merge the space data with the ground-based data, and extract, to high accuracy, the shapes and colours of billions of galaxies. </p>
<p>This software has also been checked and verified using some of the largest simulations of the universe that have ever been constructed. After arriving at L2, Euclid will undergo several months of testing, validation and calibration to ensure the instruments and telescope are working as expected. We are all familiar with such nervous waiting after the recent JWST launch. </p>
<p>Once ready, Euclid will embark on a five-year survey of 15,000 square degrees of the sky with about 2,000 scientists from across the world collecting results along the way. However, the true power of Euclid will only be realised once we have all this data together and analysed carefully. That could take another five years, taking us well into next decade before we have our final dark answers. The SpaceX launch therefore only feels like the half-way point in the Euclid story.</p>
<p>I will travel to Florida this summer to see the launch of Euclid. I will be joined by hundreds of my colleagues who have dedicated their careers to building this amazing telescope and experiment. Seeing the project come together in this way makes me proud to call myself a “Euclidian”.</p><img src="https://counter.theconversation.com/content/204245/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bob Nichol previously received funding from UKSA as part of his leadership roles in the Euclid Consortium. He has not received any funding from UKSA since 2020.</span></em></p>A spacecraft set to launch this year will throw a spotlight on the mysterious ‘dark side’ of the universe.Robert Nichol, Pro Vice-Chancellor and Executive Dean, University of SurreyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2041092023-04-20T20:01:55Z2023-04-20T20:01:55ZNew look at ‘Einstein rings’ around distant galaxies just got us closer to solving the dark matter debate<figure><img src="https://images.theconversation.com/files/521998/original/file-20230420-3121-axsfat.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C2000%2C1320&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">ESA / Hubble & NASA</span></span></figcaption></figure><p>Physicists believe most of the matter in the universe is made up of an invisible substance that we only know about by its indirect effects on the stars and galaxies we can see.</p>
<p>We’re not crazy! Without this “dark matter”, the universe as we see it would make no sense. </p>
<p>But the nature of dark matter is a longstanding puzzle. However, <a href="https://www.nature.com/articles/s41550-023-01943-9">a new study</a> by Alfred Amruth at the University of Hong Kong and colleagues, published in Nature Astronomy, uses the gravitational bending of light to bring us a step closer to understanding. </p>
<h2>Invisible but omnipresent</h2>
<p>The reason we think dark matter exists is that we can see the effects of its gravity in the behaviour of galaxies. Specifically, dark matter seems to make up about 85% of the universe’s mass, and most of the distant galaxies we can see appear to be surrounded by a halo of the mystery substance.</p>
<p>But it’s called dark matter because it doesn’t give off light, or absorb or reflect it, which makes it incredibly difficult to detect. </p>
<p>So what is this stuff? We think it must be some kind of unknown fundamental particle, but beyond that we’re not sure. All attempts to detect dark matter particles in laboratory experiments so far have failed, and physicists have been debating its nature for decades.</p>
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Read more:
<a href="https://theconversation.com/why-do-astronomers-believe-in-dark-matter-122864">Why do astronomers believe in dark matter?</a>
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<p>Scientists have proposed two leading hypothetical candidates for dark matter: relatively heavy characters called weakly interacting massive particles (or WIMPs), and extremely lightweight particles called axions. In theory, WIMPs would behave like discrete particles, while axions would behave a lot more like waves due to quantum interference. </p>
<p>It has been difficult to distinguish between these two possibilities – but now light bent around distant galaxies has offered a clue.</p>
<h2>Gravitational lensing and Einstein rings</h2>
<p>When light travelling through the universe passes a massive object like a galaxy, its path is bent because – according to Albert Einstein’s theory of general relativity – the gravity of the massive object distorts space and time around itself.</p>
<p>As a result, sometimes when we look at a distant galaxy we can see distorted images of other galaxies behind it. And if things line up perfectly, the light from the background galaxy will be smeared out into a circle around the closer galaxy. </p>
<p>This distortion of light is called “gravitational lensing”, and the circles it can create are called “Einstein rings”.</p>
<p>By studying how the rings or other lensed images are distorted, astronomers can learn about the properties of the dark matter halo surrounding the closer galaxy. </p>
<h2>Axions vs WIMPs</h2>
<p>And that’s exactly what Amruth and his team have done in their new study. They looked at several systems where multiple copies of the same background object were visible around the foreground lensing galaxy, with a special focus on one called HS 0810+2554.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=589&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=589&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=589&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=740&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=740&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522004/original/file-20230420-2407-ijctq6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=740&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">Multiple images of a background image created by gravitational lensing can be seen in the system HS 0810+2554.</span>
<span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2020/05/4613-Image?news=true">Hubble Space Telescope / NASA / ESA</a></span>
</figcaption>
</figure>
<p>Using detailed modelling, they worked out how the images would be distorted if dark matter were made of WIMPs vs how they would if dark matter were made of axions. The WIMP model didn’t look much like the real thing, but the axion model accurately reproduced all features of the system.</p>
<p>The result suggests axions are a more probable candidate for dark matter, and their ability to explain lensing anomalies and other astrophysical observations has scientists buzzing with excitement. </p>
<h2>Particles and galaxies</h2>
<p>The new research builds on previous studies that have also pointed towards axions as the more likely form of dark matter. For example, <a href="https://doi.org/10.1093/mnras/sty271">one study</a> looked at the effects of axion dark matter on the cosmic microwave background, while <a href="https://doi.org/10.1093/mnras/stx1941">another</a> examined the behaviour of dark matter in dwarf galaxies. </p>
<p>Although this research won’t yet end the scientific debate over the nature of dark matter, it does open new avenues for testing and experiment. For example, future gravitational lensing observations could be used to probe the wave-like nature of axions and potentially measure their mass.</p>
<p>A better understanding of dark matter will have implications for what we know about particle physics and the early universe. It could also help us to understand better how galaxies form and change over time. </p>
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Read more:
<a href="https://theconversation.com/explainer-standard-model-of-particle-physics-2539">Explainer: Standard Model of Particle Physics</a>
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</em>
</p>
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<img src="https://counter.theconversation.com/content/204109/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rossana Ruggeri 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>For decades physicists have argued over the nature of the elusive dark matter that pervades the Universe. A clever new study uses gravitational lensing to bring new evidence to the debate.Rossana Ruggeri, Research Fellow in Cosmology, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2033082023-04-18T16:12:00Z2023-04-18T16:12:00ZBuilding telescopes on the Moon could transform astronomy – and it’s becoming an achievable goal<figure><img src="https://images.theconversation.com/files/520796/original/file-20230413-117-illn0w.jpeg?ixlib=rb-1.1.0&rect=3%2C1%2C1013%2C570&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The far side of the Moon is an attractive place to carry out astronomy.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/11747">NASA / Ernie Wright</a></span></figcaption></figure><p>Lunar exploration is undergoing a renaissance. <a href="https://en.wikipedia.org/wiki/List_of_missions_to_the_Moon">Dozens of missions</a>, organised by multiple space agencies – and increasingly by commercial companies – are set to visit the Moon by the end of this decade. Most of these will involve small robotic spacecraft, but NASA’s ambitious <a href="https://theconversation.com/astronauts-are-returning-to-the-moon-but-they-wont-be-repeating-the-apollo-missions-202489">Artemis programme</a>, aims to return humans to the lunar surface by the middle of the decade.</p>
<p>There are various reasons for all this activity, including geopolitical posturing and the search for lunar resources, such as <a href="https://www.technologyreview.com/2020/05/19/1001857/how-moon-lunar-mining-water-ice-rocket-fuel/">water-ice at the lunar poles</a>, which can be extracted and turned into hydrogen and oxygen propellant for rockets. However, science is also sure to be a major beneficiary. </p>
<p>The Moon <a href="https://esamultimedia.esa.int/docs/HRE/03_PhysicalSciences_Planetary_Science.pdf">still has much to tell us</a> about the origin and evolution of the solar system. It also has scientific value as a platform for observational astronomy. </p>
<p>The potential role for astronomy of Earth’s natural satellite was discussed at a <a href="https://royalsociety.org/science-events-and-lectures/2023/02/astronomy-moon/">Royal Society meeting</a> earlier this year. The meeting itself had, in part, been sparked by the enhanced access to the lunar surface now in prospect.</p>
<h2>Far side benefits</h2>
<p>Several types of astronomy would benefit. The most obvious is radio astronomy, which can be conducted from the side of the Moon that always faces away from Earth – the far side. </p>
<p>The lunar far side is permanently shielded from the radio signals generated by humans on Earth. During the lunar night, it is also protected from the Sun. These characteristics make it probably <a href="https://royalsocietypublishing.org/toc/rsta/2021/379/2188?volume=379&vol=379&issue=2188&publicationCode=rsta">the most “radio-quiet” location in the whole solar system</a> as no other planet or moon has a side that permanently faces away from the Earth. It is therefore ideally suited for radio astronomy.</p>
<p>Radio waves are a form of electromagnetic energy – as are, for example, infrared, ultraviolet and visible-light waves. They are defined by having different wavelengths in the electromagnetic spectrum. </p>
<p>Radio waves with wavelengths longer than about 15m are blocked by Earth’s <a href="https://en.wikipedia.org/wiki/Ionosphere">ionoshere</a>. But radio waves at these wavelengths reach the Moon’s surface unimpeded. For astronomy, this is the last unexplored region of the electromagnetic spectrum, and it is best studied from the lunar far side.</p>
<p>Observations of the cosmos at these wavelengths come under the umbrella of “low frequency radio astronomy”. These wavelengths are uniquely able to probe the structure of the early universe, especially the cosmic “<a href="https://en.wikipedia.org/wiki/Chronology_of_the_universe#Dark_Ages">dark ages</a>” – an era before the first galaxies formed. </p>
<p>At that time, most of the matter in the universe, excluding the mysterious <a href="https://en.wikipedia.org/wiki/Dark_matter">dark matter</a>, was in the form of neutral hydrogen atoms. These emit and absorb radiation with a characteristic wavelength of 21cm. Radio astronomers have been using this property to study hydrogen clouds in our own galaxy – the Milky Way – since the 1950s. </p>
<p>Because the universe is constantly expanding, the 21cm signal generated by hydrogen in the early universe has been shifted to much longer wavelengths. As a result, hydrogen from the cosmic “dark ages” will appear to us with wavelengths greater than 10m. The lunar far side may be the only place where we can study this. </p>
<p>The astronomer Jack Burns provided a good summary of the relevant <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2019.0564">science background</a> at the recent Royal Society meeting, calling the far side of the moon a “pristine, quiet platform to conduct low radio frequency observations of the early Universe’s Dark Ages, as well as space weather and magnetospheres associated with habitable exoplanets”.</p>
<h2>Signals from other stars</h2>
<p>As Burns says, another potential application of far side radio astronomy is trying to detect radio waves from charged particles trapped by magnetic fields – <a href="https://en.wikipedia.org/wiki/Magnetosphere">magnetospheres</a> – of planets orbiting other stars. </p>
<p>This would help to assess how capable these exoplanets are of hosting life. Radio waves from exoplanet magnetospheres would probably have wavelengths greater than 100m, so they would require a radio-quiet environment in space. Again, the far side of the Moon will be the best location.</p>
<p>A similar argument can be made for <a href="https://www.smithsonianmag.com/science-nature/why-astronomers-want-build-seti-observatory-moon-180975966/">attempts to detect signals from intelligent aliens</a>. And, by opening up an unexplored part of the radio spectrum, there is also the possibility of making serendipitous discoveries of new phenomena.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520108/original/file-20230410-5761-65x14.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s conception of the LuSEE-Night radio astronomy experiment on the Moon (credit: Nasa/Tricia Talbert)</span>
</figcaption>
</figure>
<p>We should get an indication of the potential of these observations when NASA’s <a href="https://physics.berkeley.edu/news/lusee-night-will-attempt-first-its-kind-measurements-dark-ages-universe">LuSEE-Night mission</a> lands on the lunar far side in 2025 or 2026. </p>
<h2>Crater depths</h2>
<p>The Moon also offers opportunities for other types of astronomy as well. Astronomers have lots of experience with optical and infrared telescopes operating in free space, such as the <a href="https://www.nasa.gov/mission_pages/hubble/main/index.html">Hubble telescope</a> and <a href="https://webb.nasa.gov">JWST</a>. However, the stability of the lunar surface may confer advantages for these types of instrument.</p>
<p>Moreover, there are <a href="https://en.wikipedia.org/wiki/Permanently_shadowed_crater">craters</a> at the lunar poles that receive no sunlight. Telescopes that observe the universe at infrared wavelengths are very sensitive to heat and therefore have to operate at low temperatures. JWST, for example, needs a huge sunshield to protect it from the sun’s rays. On the Moon, a natural crater rim could provide this shielding for free. </p>
<figure class="align-center ">
<img alt="A permanently shadowed lunar crater" src="https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/520990/original/file-20230414-20-s56de3.jpeg?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">Permanently shadowed craters at the lunar poles could eventually host infrared telescopes.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2019/inside-dark-polar-moon-craters-water-not-as-invincible-as-expected-scientists-argue">LROC / ASU / NASA</a></span>
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</figure>
<p>The Moon’s low gravity may also enable the <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2019.0570">construction of much larger telescopes</a> than is feasible for free-flying satellites. These considerations have led the astronomer Jean-Pierre Maillard to suggest that the Moon may be the <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2020.0212">future of infrared astronomy</a>. </p>
<p>The cold, stable environment of permanently shadowed craters may also have advantages for the next generation of instruments to detect <a href="https://arxiv.org/abs/2205.07255">gravitational waves</a> – “ripples” in space-time caused by processes such as exploding stars and colliding black holes. </p>
<p>Moreover, for billions of years the Moon has been bombarded by charged particles from the sun – solar wind – and galactic cosmic rays. The lunar surface may contain a <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2019.0562">rich record of these processes</a>. Studying them could yield insights into the evolution of both the Sun and the Milky Way. </p>
<p>For all these reasons, astronomy stands to benefit from the current renaissance in lunar exploration. In particular, astronomy is likely to benefit from the infrastructure built up on the Moon as lunar exploration proceeds. This will include both transportation infrastructure – rockets, landers and other vehicles – to access the surface, as well as humans and robots on-site to construct and maintain astronomical instruments.</p>
<p>But there is also a tension here: human activities on the lunar far side may create unwanted radio interference, and plans to extract water-ice from shadowed craters might make it difficult for those same craters to be used for astronomy. As my colleagues and I recently <a href="https://arxiv.org/abs/2212.01363">argued</a>, we will need to ensure that lunar locations that are uniquely valuable for astronomy are protected in this new age of lunar exploration.</p><img src="https://counter.theconversation.com/content/203308/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Crawford is a member of the UK Space Agency's Space Exploration Advisory Committee (SEAC) and has advised the European Space Agency on lunar exploration policy. He is chair of COSPAR sub-commission B3 (Moon), and a member of the Moon Village Association which aims to foster international cooperation in lunar exploration. He was a co-organiser of the recent Royal Society meeting "Astronomy from the Moon."</span></em></p>The current race to the Moon is opening up opportunities for lunar astronomy.Ian Crawford, Professor of Planetary Science and Astrobiology, Birkbeck, University of London, Honorary Associate Professor, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2008292023-03-05T19:19:56Z2023-03-05T19:19:56ZWhat are the best conditions for life? Exploring the multiverse can help us find out<figure><img src="https://images.theconversation.com/files/513318/original/file-20230303-18-ugje3l.jpeg?ixlib=rb-1.1.0&rect=12%2C0%2C4013%2C3024&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Israel Pina / Unsplash</span></span></figcaption></figure><p>Is our universe all there is, or could there be more? Is our universe just one of a countless multitude, all together in an all-encompassing multiverse? </p>
<p>And if there are other universes, what would they be like? Could they be habitable?</p>
<p>This might feel like speculation heaped upon speculation, but it’s not as crazy as you might think. </p>
<p>My colleagues and I have been exploring what other parts of the multiverse might be like – and what these hypothetical neighbouring universes can tell us about the conditions that make life possible, and how they arise.</p>
<h2>What-if universes</h2>
<p>Some physicists <a href="https://www.space.com/25100-multiverse-cosmic-inflation-gravitational-waves.html">contend</a> that a burst of rapid expansion at the cosmic dawn known as inflation makes some form of multiverse inevitable. Our universe would really just be one of many. </p>
<p>In this theory, each new universe crystallises out of the seething background of inflation, imprinted with its own unique mix of physical laws.</p>
<p>If physical laws similar to ours govern these other universes, then we can come to grips with them. Well, at least in theory. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513319/original/file-20230303-14-sdad7i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&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">The history of our universe. Other universes with slightly different laws of physics may also have crystallised from the early period of inflation.</span>
<span class="attribution"><a class="source" href="http://map.gsfc.nasa.gov/media/060915/index.html">NASA</a></span>
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</figure>
<p>Within our universe, physics is governed by rules that tell us how things should interact with each other, and constants of nature, such as the speed of light, that dictate the strengths of these interactions. So, we can imagine hypothetical “what-if” universes where we change these properties and explore the consequences within mathematical equations.</p>
<p>This might sound simple, but the rules we tinker with are the fundamental makeup of the universe. If we imagine a universe where, say, the electron is a hundred times heavier than in our universe, then what would its consequences be for stars, planets and even life?</p>
<h2>What does life need?</h2>
<p>We recently tackled this question in a series of papers where we considered habitability across the multiverse. Of course, habitability is a complex concept, but we think life requires a few choice ingredients to get going.</p>
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<strong>
Read more:
<a href="https://theconversation.com/the-multiverse-is-huge-in-pop-culture-right-now-but-what-is-it-and-does-it-really-exist-181781">The multiverse is huge in pop culture right now – but what is it, and does it really exist?</a>
</strong>
</em>
</p>
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<p>Complexity is one of those ingredients. For life on Earth, that complexity comes from the elements of the periodic table, which can be mixed and arranged into a myriad of different molecules. We are living molecular machines. </p>
<p>But a stable environment and a steady flow of energy are also essential. It is no surprise that Earthly life began on the surface of a rocky planet, with an abundance of chemical elements, bathed in the light of a long-lived stable star.</p>
<h2>Tweaking the fundamental forces</h2>
<p>Do similar environments exist across the extent of the multiverse? We started our theoretical exploration by considering the <a href="https://www.mdpi.com/2218-1997/8/12/651">abundance of chemical elements</a>. </p>
<p>In our universe, other than primordial hydrogen and helium that were formed in the Big Bang, all elements arise through the lives of stars. They are either generated through the nuclear reactions in stellar cores, or in the supreme violence of supernovae, when a massive star tears itself apart at the end of its life.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/we-are-lucky-to-live-in-a-universe-made-for-us-46988">We are lucky to live in a universe made for us</a>
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</p>
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<p>All these processes are governed by the four fundamental forces in the universe. Gravity squeezes the stellar core, driving it to immense temperatures and densities. Electromagnetism tries to force atomic nuclei apart, but if they can get close enough, the strong nuclear force can bind them into a new element. Even the weak nuclear force, which can flip a proton into a neutron, plays an important role in the ignition of the stellar furnace.</p>
<p>The masses of the fundamental particles, such as electrons and quarks, can also play a pivotal role. </p>
<p>So, to explore these hypothetical universes, we have many dials we can adjust. The changes to the fundamental universe flow through to the rest of physics.</p>
<h2>The carbon–oxygen balance</h2>
<p>To tackle the immense complexity of this problem, we chopped the various pieces of physics into manageable chunks: <a href="https://www.mdpi.com/2218-1997/9/1/4">stars and atmospheres</a>, <a href="https://www.mdpi.com/2218-1997/9/1/2">planets and plate tectonics</a>, the <a href="https://www.mdpi.com/2218-1997/9/1/42">origins of life</a>, and more. And then we pinned the chunks together to tell an overall story about habitability across the multiverse.</p>
<p>A complex picture emerges. Some factors can strongly influence the habitability of a universe. </p>
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<strong>
Read more:
<a href="https://theconversation.com/does-a-planet-need-plate-tectonics-to-develop-life-61303">Does a planet need plate tectonics to develop life?</a>
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<p>For example, the ratio of carbon to oxygen, something set by a particular chain of nuclear reactions in the heart of a star, appears to be particularly important. </p>
<p>Straying too far from the value in our universe, where there are roughly equal amounts of the two elements, results in environments where it would be extremely difficult for life to emerge and thrive. </p>
<p>But the abundance of other elements appears to be less important. As long as they are stable, which does depend on the balance of the fundamental forces, they can play a pivotal role in the building blocks of life.</p>
<h2>More complexity to explore</h2>
<p>We have only been able to take a broad-brush approach to unravel habitability across the multiverse, sampling the space of possibilities in very discrete steps. </p>
<p>Furthermore, to make the problem manageable, we had to take several theoretical shortcuts and approximations. So we are only at the first stage of understanding the conditions for life across the multiverse.</p>
<p>In the next steps, the full complexity of alternative physics of other universes needs to be considered. We will need to understand the influence of the fundamental forces at the small scale and extrapolate it to the large scale, onto the formation of stars and eventually planets. </p>
<h2>A word of caution</h2>
<p>The notion of a multiverse is still only a hypothesis, an idea that has yet to be tested. In truth, we don’t yet know if it is an idea that <em>can</em> be tested. </p>
<p>And we don’t know if the physical laws could be different across the multiverse and, if they are, just how different they could be. </p>
<p>We may be at the start of a journey that will reveal our ultimate place within infinity – or we may be heading for a scientific dead end.</p><img src="https://counter.theconversation.com/content/200829/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Lewis receives funding from Australian Research Council. </span></em></p>Some physicists think we live in a multiverse, surrounded by universes not quite like our own. What does that mean for life?Geraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1976212023-03-03T00:13:56Z2023-03-03T00:13:56ZHumans are still hunting for aliens. Here’s how astronomers are looking for life beyond Earth<figure><img src="https://images.theconversation.com/files/508029/original/file-20230203-12-uvmpl6.jpg?ixlib=rb-1.1.0&rect=302%2C315%2C4072%2C2733&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">zhengzaishuru/Shutterstock</span></span></figcaption></figure><p>We have long been fascinated with the idea of alien life. The earliest written record presenting the idea of “aliens” is seen in the satiric work of Assyrian writer <a href="https://blogs.scientificamerican.com/life-unbounded/the-first-alien/">Lucian of Samosata</a> dated to 200 AD.</p>
<p>In one novel, Lucian <a href="https://www.yorku.ca/inpar/lucian_true_tale.pdf">writes of a journey to the Moon</a> and the bizarre life he imagines living there – everything from three-headed vultures to fleas the size of elephants.</p>
<p>Now, 2,000 years later, we still write stories of epic adventures beyond Earth to meet otherworldly beings (<a href="https://www.britannica.com/topic/The-Hitchhikers-Guide-to-the-Galaxy-novel-by-Adams">Hitchhiker’s Guide</a>, anyone?). Stories like these entertain and inspire, and we are forever trying to find out if science fiction will become science fact.</p>
<h2>Not all alien life is the same</h2>
<p>When looking for life beyond Earth, we are faced with two possibilities. We might find basic microbial life hiding somewhere in our Solar System; or we will identify signals from intelligent life somewhere far away.</p>
<p>Unlike in <a href="https://www.britannica.com/topic/Star-Wars-film-series">Star Wars</a>, we’re not talking far, far away in another galaxy, but rather around other nearby stars. It is this second possibility which really excites me, and should excite you too. A detection of intelligent life would fundamentally change how we see ourselves in the Universe. </p>
<p>In the last 80 years, programs dedicated to the search for extraterrestrial intelligence (SETI) have worked tirelessly searching for cosmic “hellos” in the form of radio signals.</p>
<p>The reason we think any intelligent life would communicate via radio waves is due to the waves’ ability to travel vast distances through space, rarely interacting with the dust and gas in between stars. If anything out there is trying to communicate, it’s a pretty fair bet they would do it through radio waves. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=134&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=134&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=134&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=169&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=169&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505679/original/file-20230121-18-zi7kes.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=169&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 three radio facilities used in the Breakthrough Listen Initiative. Left to Right: 100m Robert C. Byrd Green Bank Telescope, 64m Murriyang (Parkes) Radio Telescope, 64-antenna MeerKAT array.</span>
<span class="attribution"><span class="source">NRAO, CSIRO, MeerKAT</span></span>
</figcaption>
</figure>
<h2>Listening to the stars</h2>
<p>One of the most exciting searches to date is <a href="https://breakthroughinitiatives.org/initiative/1">Breakthrough Listen</a>, the largest scientific research program dedicated to looking for evidence of intelligent life beyond Earth.</p>
<p>This is one of many projects funded by US-based Israeli entrepreneurs Julia and Yuri Milner, with some serious dollars attached. Over a ten-year period a total amount of <a href="https://breakthroughinitiatives.org/initiative/1">US$100 million</a> will be invested in this effort, and they have a mighty big task at hand. </p>
<p>Breakthrough Listen is currently targeting the closest one million stars in the hope of identifying any unnatural, alien-made radio signals. Using telescopes around the globe, from the 64-metre Murriyang Dish (Parkes) here in Australia, to the 64-antenna MeerKAT array in South Africa, the search is one of epic proportions. But it isn’t the only one. </p>
<p>Hiding away in the Cascade Mountains north of San Francisco sits the <a href="https://www.seti.org/ata">Allen Telescope Array</a>, the first radio telescope built from the ground up specifically for SETI use.</p>
<p>This unique facility is another exciting project, able to search for signals every day of the year. This project is currently upgrading the hardware and software on the original dish, including the ability to target several stars at once. This is a part of the non-profit research organisation, the SETI Institute.</p>
<h2>Space lasers!</h2>
<p>The SETI Institute is also looking for signals that would be best explained as “space lasers”.</p>
<p>Some astronomers hypothesise that intelligent beings might use massive lasers to communicate or even to propel spacecraft. This is because even here on Earth we’re investigating <a href="https://www.nasa.gov/feature/goddard/2022/the-future-of-laser-communications/">laser communication</a> and laser-propelled <a href="https://www.insidescience.org/news/new-light-sail-design-would-use-laser-beam-ride-space">light sails</a>.</p>
<p>To search for these mysterious flashes in the night sky, we need speciality instruments in locations around the globe, which are currently being developed and deployed. This is a research area I’m excited to watch progress and eagerly await results. </p>
<p>As of writing this article, sadly no alien laser signals have been found yet.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/do-aliens-exist-we-asked-five-experts-161811">Do aliens exist? We asked five experts</a>
</strong>
</em>
</p>
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<h2>Out there, somewhere</h2>
<p>It’s always interesting to ponder who or what might be living out in the Universe, but there is one problem we must overcome to meet or communicate with aliens. It’s the speed of light.</p>
<p>Everything we rely on to communicate via space requires light, and it can only travel so fast. This is where my optimism for finding intelligent life begins to fade. The Universe is big – <em>really</em> big.</p>
<p>To put it in perspective, humans started using radio waves to communicate across large distances in 1901. That <a href="https://ethw.org/Milestones:Reception_of_Transatlantic_Radio_Signals,_1901">first transatlantic signal</a> has only travelled 122 light years, reaching just 0.0000015% of the stars in our Milky Way.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image of a spiral galaxy with a box on the lower right corner centred on a tiny blue dot" src="https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505680/original/file-20230121-16-884k8k.jpeg?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 little blue dot in the centre of the square is the current extent of human broadcasts just in our own galaxy.</span>
<span class="attribution"><a class="source" href="https://www.planetary.org/space-images/extent-of-human-radio-broadcasts">Adam Grossman/Nick Risinger</a></span>
</figcaption>
</figure>
<p>Did your optimism just fade too? That is okay, because here is the wonderful thing… we don’t have to find life to know it is out there, somewhere.</p>
<p>When we consider the <a href="https://theconversation.com/how-many-stars-are-there-in-space-165370">trillions of galaxies</a>, septillion of stars, and likely many more planets just in the observable Universe, it feels near impossible that we are alone.</p>
<p>We can’t fully constrain the parameters we need to estimate how many other lifeforms might be out there, as famously proposed by Frank Drake, but using our best estimates and <a href="https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/numerical-testbed-for-hypotheses-of-extraterrestrial-life-and-intelligence/0C97E7803EEB69323C3728F02BA31AFA">simulations</a> the current best answer to this is tens of thousands of possible civilisations out there. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/frank-drake-has-passed-away-but-his-equation-for-alien-intelligence-is-more-important-than-ever-189935">Frank Drake has passed away but his equation for alien intelligence is more important than ever</a>
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<p>The Universe <a href="https://theconversation.com/is-space-infinite-we-asked-5-experts-165742">might even be infinite</a>, but that is too much for my brain to comprehend on a weekday.</p>
<h2>Don’t forget the tiny aliens</h2>
<p>So, despite keenly listening for signals, we might not find intelligent life in our lifetimes. But there is hope for aliens yet.</p>
<p>The ones hiding in plain sight, on the planetary bodies of our Solar System. In the coming decades we’ll explore the moons of Jupiter and Saturn like never before, with missions hunting to find traces of basic life.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505682/original/file-20230121-23485-sxmcy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Jupiter and the icy moon Europa. Concept art of the Europa Clipper mission currently under development.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>Mars will continue to be explored – eventually by humans – which could allow us to uncover and retrieve samples from new and unexplored regions.</p>
<p>Even if our future aliens are only tiny microbes, it would still be nice to know we have company in this Universe.</p>
<hr>
<p><em>Correction: this article has been amended to clarify that Julia and Yuri Milner are no longer Russian citizens.</em></p><img src="https://counter.theconversation.com/content/197621/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sara Webb 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>To date, we have not heard from any aliens. Nor have we seen any – but here are the fascinating projects working to change that.Sara Webb, Postdoctoral Research Fellow, Centre for Astrophysics and Supercomputing, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2003432023-02-22T19:04:55Z2023-02-22T19:04:55Z‘We just discovered the impossible’: how giant baby galaxies are shaking up our understanding of the early Universe<figure><img src="https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&rect=21%2C24%2C1978%2C1319&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Images of six candidate massive galaxies, seen 500–800 million years after the Big Bang.</span> <span class="attribution"><span class="source">NASA / ESA / CSA / I. Labbe</span>, <span class="license">Author provided</span></span></figcaption></figure><p>“Look at this,” says Erica’s message. She is poring over the very first images from the brand new James Webb Space Telescope (JWST). </p>
<p>It is July 2022, barely a week after those first images from the revolutionary super telescope were released. Twenty-five years in the making, a hundred to a thousand times more powerful than any previous telescope, one of the biggest and most ambitious scientific experiments in human history: it is hard to not speak in superlatives, and it is all true. </p>
<p>The telescope took decades to build, because it had to be made foldable to fit on top of a rocket and be sent into the coldness of space, 1.5 million kms from Earth. Here, far from the heat glow of the Earth, JWST can detect the faintest infrared light from the distant universe. </p>
<p>Little did I know that among the pictures is a small red dot that will shake up our understanding of how the first galaxies formed after the Big Bang. After months of analysis, my colleagues and I just <a href="https://www.nature.com/articles/s41586-023-05786-2">published our results in Nature</a>.</p>
<h2>Hunting new kinds of galaxies</h2>
<p>Erica and I are on the hunt to discover new types of galaxies. Galaxies that the venerable Hubble Space Telescope had missed, even after decades of surveying the sky. </p>
<p>She and I go back 15 years. We met when she was a first-year student at a Californian liberal arts college and I was a freshly minted PhD straight out of university, just starting my first gig as a researcher in Los Angeles. JWST was only a distant rumor.</p>
<p>Somehow, many years later, our paths crossed again, and now Assistant Professor Erica Nelson of the University of Colorado and I are finding ourselves at the tip of the spear attacking the first data of a very real JWST. </p>
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Read more:
<a href="https://theconversation.com/two-experts-break-down-the-james-webb-space-telescopes-first-images-and-explain-what-weve-already-learnt-186738">Two experts break down the James Webb Space Telescope's first images, and explain what we've already learnt</a>
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<p>“UFOs”, she calls the new galaxies, and I can read a giant grin between the lines: <a href="https://arxiv.org/abs/2208.01630">“Ultra-red Flattened Objects”</a>, because they all look like flying saucers. In the colour images they appear very red because all the light is coming out in the infrared, while the galaxies are invisible at wavelengths humans can see. </p>
<p>Infrared is JWST’s superpower, allowing it to spy the most distant galaxies. Ultraviolet and visible light from the first stars and galaxies that formed after the Big Bang is stretched out by the expansion of the universe as it travels towards us, so by the time the light reaches us we see it as infrared light. </p>
<h2>Impossibly early, impossibly massive galaxies</h2>
<p>All of Erica’s galaxies look like saucers, except one. I stare at the little red dot on the screen. That is no UFO. And then it hits me: this is something very different. Much more important. </p>
<p>I run the analysis software on the little pinprick and it spits out two numbers: distance 13.1 billion light years, mass 100 billion stars, and I nearly spit out my coffee. We just discovered the impossible. Impossibly early, impossibly massive galaxies. </p>
<p>At this distance, the light took 13 billion years to reach us, so we are seeing the galaxies at a time when the universe was only 700 million years old, barely 5% of its current age of 13.8 billion years. If this is true, this galaxy has formed as many stars as our present-day Milky Way. In record time. </p>
<p>And where there is one, there are more. One day later I had found six. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&rect=21%2C24%2C1978%2C1319&q=45&auto=format&w=1000&fit=clip"><img alt="Pixelated images of six reddish dots against dark backgrounds." src="https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&rect=21%2C24%2C1978%2C1319&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/511593/original/file-20230222-22-uxqf8q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Images of six candidate massive galaxies, seen 500–800 million years after the Big Bang.</span>
<span class="attribution"><span class="source">NASA / ESA / CSA / I. Labbe</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Astronomy’s missing link?</h2>
<p>Could we have discovered astronomy’s missing link? There has been a long-standing puzzle in galaxy formation. As we look out in space and back in time, we see the “corpses” of fully formed, mature galaxies appear seemingly out of nowhere around 1.5 billion years after the Big Bang. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/is-the-james-webb-space-telescope-finding-the-furthest-oldest-youngest-or-first-galaxies-an-astronomer-explains-187915">Is the James Webb Space Telescope finding the furthest, oldest, youngest or first galaxies? An astronomer explains</a>
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<p>These galaxies have stopped forming stars. Dead galaxies, we call them, and some astronomers are obsessed with them. The stellar ages of these dead galaxies suggest they must have formed much earlier in the Universe, but Hubble has never been able to spot their earlier, living stages. </p>
<p>Early dead galaxies are truly bizarre creatures, packing as many stars as the Milky Way, but in a size 30 times smaller. Imagine an adult, weighing 100 kilos, but standing 6cm tall. Our little red dots are equally bizarre. They look like baby versions of the same galaxies, also weighing in at 100 kilos, with a height of 6cm. </p>
<h2>Too many stars, too early</h2>
<p>There is a problem, however. These little red dots have too many stars, too early. Stars form out of hydrogen gas, and fundamental cosmological (“Big Bang”) theory makes hard predictions on how much gas is available to form stars. </p>
<p>To produce these galaxies so quickly, you almost need all the gas in the universe to turn into stars at near 100% efficiency. And that is very hard, which is the scientific term for impossible. This discovery could transform our understanding of how the earliest galaxies in the universe formed. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=427&fit=crop&dpr=1 600w, https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=427&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=427&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/511591/original/file-20230222-16-4ylne.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&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">The six galaxies and their surroundings in the sky.</span>
<span class="attribution"><span class="source">NASA / ESA / CSA / I. Labbe</span>, <span class="license">Author provided</span></span>
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<p>The implication is that there is different channel, a fast track, that produces monster galaxies very quickly, very efficiently. A fast track for the top 1%.</p>
<p>In a way, each of these candidates can be considered a “black swan”. The confirmation of even one would rule out our current “all swans are white” model of galaxy formation, in which all early galaxies grow slowly and gradually. </p>
<h2>Checking the fingerprints</h2>
<p>The first step to solve this mystery is to confirm the distances with spectroscopy, where we put the light of each of these galaxies through a prism, and split it into its rainbow-like fingerprint. This will tell us the distance to 0.1% accuracy. </p>
<p>It will also tell us what is producing the light, whether it is stars or something else more exotic. </p>
<p>By chance, about a month ago, JWST already targeted one of the six candidate massive galaxies and it turned out to be a distant baby quasar. A quasar is a phenomenon that occurs when gas falls into a supermassive black hole at the centre of a galaxy and starts to shine brightly. </p>
<p>This is really exciting on the one hand, because the origin of supermassive black holes in galaxies is not understood either, and finding baby quasars might just hold the key. On the other hand, quasars can outshine their entire host galaxy, so it is impossible to tell how many stars are there and whether the galaxy is really that massive. </p>
<p>Could that be the answer for all of them? Baby quasars everywhere? Probably not, but it will take another year to investigate the remaining galaxies and find out. </p>
<p>One black swan down, five to go.</p><img src="https://counter.theconversation.com/content/200343/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ivo Labbe receives funding from ARC in the form of a Future Fellowship, to conduct research with the James Webb Space Telescope.</span></em></p>The discovery of massive, early galaxies could force scientists to rethink how the first galaxies formed after the Big Bang.Ivo Labbe, ARC Future Fellow / Associate Professor, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1997852023-02-15T19:07:04Z2023-02-15T19:07:04ZThe largest structures in the Universe are still glowing with the shock of their creation<figure><img src="https://images.theconversation.com/files/515372/original/file-20230315-16-i6oy82.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Screenshot at</span> </figcaption></figure><p>On the largest scales, the Universe is ordered into a web-like pattern: galaxies are pulled together into clusters, which are connected by <a href="https://theconversation.com/a-thread-of-the-cosmic-web-astronomers-spot-a-50-million-light-year-galactic-filament-151569">filaments</a> and separated by voids. These clusters and filaments contain dark matter, as well as regular matter like gas and galaxies. </p>
<p>We call this the “<a href="https://bigthink.com/hard-science/cosmic-web/">cosmic web</a>”, and we can see it by mapping the locations and densities of galaxies from large surveys made with optical telescopes. </p>
<p>We think the cosmic web is also permeated by magnetic fields, which are created by energetic particles in motion and in turn guide the movement of those particles. Our theories predict that, as gravity draws a filament together, it will cause shockwaves that make the magnetic field stronger and create a glow that can be seen with a radio telescope.</p>
<p>In <a href="http://www.science.org/doi/10.1126/sciadv.ade7233">new research published in Science Advances</a>, we have for the first time observed these shockwaves around pairs of galaxy clusters and the filaments that connect them.</p>
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Read more:
<a href="https://theconversation.com/explainer-radio-astronomy-7420">Explainer: radio astronomy</a>
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<p>In the past, we have only ever observed these radio shockwaves directly from <a href="https://theconversation.com/we-found-some-strange-radio-sources-in-a-distant-galaxy-cluster-theyre-making-us-rethink-what-we-thought-we-knew-187631">collisions between galaxy clusters</a>. However, we believe they exist around small groups of galaxies, as well as in cosmic filaments. </p>
<p>There are still gaps in our knowledge of these magnetic fields, such as how strong they are, how have they evolved, and what their role is in the formation of this cosmic web. </p>
<p>Detecting and studying this glow could not only confirm our theories for how the large-scale structure of the Universe has formed, but help answer questions about cosmic magnetic fields and their significance. </p>
<h2>Digging into the noise</h2>
<p>We expect this radio glow to be both very faint and spread over large areas, which means it is very challenging to detect it directly. </p>
<p>What’s more, the galaxies themselves are much brighter and can hide these faint cosmic signals. To make it even more difficult, the noise from our telescopes is usually many times larger than the expected radio glow. </p>
<p>For these reasons, rather than <em>directly</em> observing these radio shockwaves, we had to get creative, using a technique known as stacking. This is when you average together images of many objects too faint to see individually, which decreases the noise, or rather enhances the average signal above the noise. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a stack of several faint images next to a single sharper version of the image." src="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&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">‘Stacking’ many images together can make the signal of interest brighter than the background noise.</span>
<span class="attribution"><span class="source">Tessa Vernstrom</span>, <span class="license">Author provided</span></span>
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<p>So what did we stack? We found more than 600,000 pairs of galaxy clusters that are near each other in space, and so are likely to be connected by filaments. We then aligned our images of them so that any radio signal from the clusters or the region between them – where we expect the shockwaves to be – would add together. </p>
<p>We first used this method in <a href="https://academic.oup.com/mnras/article/505/3/4178/6273648">a paper published in 2021</a> with data from two radio telescopes: the <a href="https://www.mwatelescope.org/">Murchison Widefield Array</a> in Western Australia and the <a href="https://leo.phys.unm.edu/%7Elwa/index.html">Owens Valley Radio Observatory Long Wavelength Array</a> in New Mexico. These were chosen not only because they covered nearly all the sky but also because they operated at low radio frequencies where this signal is expected to be brighter. </p>
<p>In the first project, we made an exciting discovery: we found a glow between the pairs of clusters! However, because it was an <em>average</em> of many clusters, all containing many galaxies, it was difficult to say for sure the signal was coming from the cosmic magnetic fields, rather than other sources like galaxies. </p>
<h2>A ‘shocking’ revelation</h2>
<p>Normally the magnetic fields in clusters are jumbled up due to turbulence. However, these shock waves force the magnetic fields into order, which means the radio glow they emit is highly <a href="https://www.sciencefocus.com/science/what-is-polarised-light/">polarised</a>. </p>
<p>We decided to try the stacking experiment on maps of polarised radio light. This has the advantage of helping to determine what is causing the signal.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-thread-of-the-cosmic-web-astronomers-spot-a-50-million-light-year-galactic-filament-151569">A thread of the cosmic web: astronomers spot a 50 million light-year galactic filament</a>
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<p>Signals from regular galaxies are only 5% polarised or less, while signals from shockwaves can be 30% polarised or more.</p>
<p>In our <a href="http://www.science.org/doi/10.1126/sciadv.ade7233">new work</a>, we used radio data from the <a href="https://gmims.ok.ubc.ca/">Global Magneto Ionic Medium Survey</a> as well as the <a href="https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_at_a_glance">Planck</a> satellite to repeat the experiment. These surveys cover almost the entire sky and have both polarised and regular radio maps. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=758&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">Stacking cluster pairs: the two dark spots aligned vertically are the clusters and show depolarisation due to turbulence, while the outer areas and the area between the clusters is highly polarised.</span>
<span class="attribution"><span class="source">Tessa Vernstrom using Planck data</span>, <span class="license">Author provided</span></span>
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<p>We detected very clear rings of polarised light surrounding cluster pairs. This means the centres of the clusters are depolarised, which is expected as they are very turbulent environments. </p>
<p>However, on the edges of the clusters the magnetic fields are put in order thanks to the shockwaves, meaning we see this ring of polarised light. </p>
<p>We also found an excess of highly polarised light between the clusters, much more than you would expect from just galaxies. We can interpret this as light from the shocks in the connecting filaments. This is the first time such emission has been found in this kind of environment. </p>
<p>We compared our results with state-of-the-art cosmological simulations, the first of their kind to predict not just the total signal of the radio emission but the <em>polarised</em> signal as well. Our data agreed very well with these simulations, and by combining them we are able to understand the magnetic field signal left over from the early Universe.</p>
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<iframe src="https://player.vimeo.com/video/798306932" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Cosmological simulation showing the gas temperature, radio emission from shocks, and magnetic field lines. Credit: F Vazza (Univ Bologna) / D Wittor (Hamburger Sternwarte) / J West (NRC) / ICRAR.</span></figcaption>
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<p>In future we would like to repeat this detection for different times over the history of the Universe. We still do not know the origin of these cosmic magnetic fields, but further observations like this can help us to figure out where they came from and how they have evolved. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/we-found-some-strange-radio-sources-in-a-distant-galaxy-cluster-theyre-making-us-rethink-what-we-thought-we-knew-187631">We found some strange radio sources in a distant galaxy cluster. They're making us rethink what we thought we knew.</a>
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<img src="https://counter.theconversation.com/content/199785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tessa Vernstrom works for the International Centre for Radio Astronomy Research at the University of Western Australia and is also affiliated with CSIRO Space & Astronomy.</span></em></p><p class="fine-print"><em><span>Christopher Riseley works for Alma Mater Studiorum - Università di Bologna. He is also affiliated with the Istituto Nazionale di Astrofisica (INAF) and CSIRO Space & Astronomy. He is supported by funding from the European Research Council (ERC) under the ERC Starting Grant 'DRANOEL', number 714245.</span></em></p>Astronomers have detected a radio glow caused by shockwaves in the gigantic filaments between galaxy clusters in the ‘cosmic web’ which pervades the Universe.Tessa Vernstrom, Senior research fellow, The University of Western AustraliaChristopher Riseley, Research Fellow, Università di BolognaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1998312023-02-15T17:16:17Z2023-02-15T17:16:17ZBlack holes may be the source of mysterious dark energy that makes up most of the universe<figure><img src="https://images.theconversation.com/files/509870/original/file-20230213-4443-xsmxpu.jpg?ixlib=rb-1.1.0&rect=313%2C0%2C2251%2C1483&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">black hole</span> </figcaption></figure><p><a href="https://www.nasa.gov/vision/universe/starsgalaxies/black_hole_description.html">Black holes</a> could explain a mysterious form of energy that makes up most of the universe, according to astronomers. The existence of <a href="https://en.wikipedia.org/wiki/Dark_energy">“dark energy”</a> has been inferred from observations of stars and galaxies, but no one has been able to explain what it is, or where it comes from.</p>
<p>The stuff, or matter, that makes up the familiar world around us is just 5% of everything in the universe. Another 27% is <a href="https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy">dark matter</a>, a shadowy counterpart of ordinary matter which does not emit, reflect or absorb light. However, the majority of the cosmos – around 68% – is dark energy.</p>
<p>The new evidence that black holes could be the source of dark energy is described in <a href="https://iopscience.iop.org/article/10.3847/2041-8213/acb704">a scientific paper</a> published in The Astrophysical Journal Letters. The study is the work of 17 astronomers in nine countries and was led by the University of Hawaii. The collaboration included researchers in the UK, based at STFC RAL Space, The Open University, and Imperial College London.</p>
<p>Searching through data spanning nine billion years of cosmic history, the astronomers have uncovered the first evidence of <a href="https://physicsworld.com/a/cosmological-coupling-is-making-black-holes-bigger-study-suggests/">“cosmological coupling”</a>, which would mean that the growth of black holes over time is linked to the expansion of the universe itself.</p>
<p>The idea that black holes might contain something called <a href="https://en.wikipedia.org/wiki/Vacuum_energy">vacuum energy</a> (a manifestation of dark energy) is not particularly new and in fact was discussed theoretically as far back as the 1960s. But this latest work assumes this energy (and therefore the mass of the black holes) would increase with time as the universe expands as a result of cosmological coupling.</p>
<p>The team calculated how much of the dark energy in the universe could be attributed to this process. They found that black holes could potentially explain the total amount of dark energy we measure in the universe today. The result could solve one of the most fundamental problems in modern cosmology.</p>
<h2>Rapid expansion</h2>
<p><a href="https://hubblesite.org/contents/articles/the-big-bang">Our universe began in a Big Bang</a> around 13.7 billion years ago. The energy from this explosion of space and time caused the universe to expand rapidly, with all the galaxies flying away from each other. However, we expect that this expansion would gradually slow down because of the effect of gravity on all the stuff in the cosmos.</p>
<p>This is the version of the universe we thought we lived in until the late 1990s, when the Hubble space telescope discovered something strange. Observations of distant exploding stars showed that, in the past, the universe <a href="https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe">was actually expanding more slowly than it is today</a>. </p>
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<figcaption><span class="caption">The new discovery is explained by Chris Pearson of RAL Space and The Open University.</span></figcaption>
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<p>So the expansion of the universe has not been slowing due to gravity, as everyone thought, but instead has been accelerating. This was highly unexpected and astronomers struggled to explain it.</p>
<p>To account for this, it was proposed that a “dark energy” was responsible for pushing things apart more strongly than gravity pulled things together. The concept of dark energy was very similar to a mathematical construct Einstein had proposed but later discarded – a <a href="https://en.wikipedia.org/wiki/Cosmological_constant">“cosmological constant”</a> that opposed gravity and kept the universe from collapsing.</p>
<h2>Stellar explosions</h2>
<p>But what is dark energy? The solution, it seems, might lie with another cosmic mystery: black holes. Black holes are commonly born when <a href="https://public.nrao.edu/ask/when-does-a-neutron-star-or-black-hole-form-after-a-supernova/">massive stars explode and die at the ends of their lives</a>. The gravity and pressure in these violent explosions compresses vast amounts of material into a small space. For instance, a star about the same mass as our sun would be squashed into a space of just a few tens of kilometres. </p>
<p>A black hole’s gravitational pull is so strong that not even light can escape it – everything gets sucked in. At the centre of the black hole is a place called a <a href="https://bigthink.com/starts-with-a-bang/singularity-black-hole/">singularity</a>, where matter is crushed into a point of infinite density. The problem is that singularities are a mathematical construct that should not exist.</p>
<figure class="align-center ">
<img alt="The Andromeda galaxy" src="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.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">
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<span class="caption">Dark energy explains why the expansion of the universe is speeding up.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/galex/pia15416.html">NASA/JPL-Caltech</a>, <span class="license">Author provided</span></span>
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<p>The black holes nestled at the centres of galaxies are much heftier than those born when stars die violently. These galactic “supermassive” black holes can weigh millions to billions of times the mass of our Sun.</p>
<p>All black holes increase in size by accumulating matter, by swallowing stars that get too close, or by merging with other black holes. So we expect them to get bigger as the universe gets older.</p>
<p>In the latest paper, the team looked at supermassive black holes in the centres of galaxies and found that these black holes gain mass over billions of years. </p>
<h2>Radical rethink</h2>
<p>The team compared observations of <a href="https://en.wikipedia.org/wiki/Elliptical_galaxy">elliptical galaxies</a>, which lack star formation, in the past and in the present day. These dead galaxies have used up all their fuel so any increase in their black hole mass over this time cannot be ascribed to the normal processes by which black holes grow by accumulating matter.</p>
<p>Instead, the team proposed that these black holes actually contain vacuum energy and that they are “coupled” to the expansion of the universe, so that they increase in mass as the universe expands. </p>
<figure class="align-center ">
<img alt="Visualisation of a black hole" src="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&rect=17%2C34%2C3782%2C2098&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?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">
<figcaption>
<span class="caption">A visualisation of a black hole, which could play a role in dark energy.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2019/nasa-visualization-shows-a-black-hole-s-warped-world">NASA’s Goddard Space Flight Center/Jeremy Schnittman</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This model neatly provides a possible origin for the dark energy in the universe. It also circumvents the mathematical problems that affect some studies of black holes, because it avoids the need for a singularity at the centre.</p>
<p>The team also calculated how much of the dark energy in the universe could be attributed to this process of coupling. They concluded that it would be possible for black holes to provide the necessary amount of vacuum energy to account for all the dark energy that we measure in the universe today. </p>
<p>This would not only explain the origin of dark energy in the universe but would also make us radically rethink our understanding of black holes and their role in the cosmos.</p>
<p>Much more work needs to be done to test and confirm this idea, both from observations of the sky and from theory. But we may at last be seeing a new way to solve the problem of dark energy.</p><img src="https://counter.theconversation.com/content/199831/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Pearson receives funding from STFC and is head of astronomy at STFC RAL Space and a visiting fellow at the Open University </span></em></p><p class="fine-print"><em><span>Dave Clements receives funding from STFC and the UKSA and works at Imperial College London.</span></em></p>Astronomers have found that mysterious dark energy may originate in black holes.Chris Pearson, Astronomy Group Lead, Space Operations Division at RAL Space, and Visiting Fellow, The Open UniversityDave Clements, Reader in Astrophysics, Imperial College LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1989962023-02-02T19:15:43Z2023-02-02T19:15:43ZWhy do black holes twinkle? We studied 5,000 star-eating behemoths to find out<figure><img src="https://images.theconversation.com/files/507733/original/file-20230201-15-6lbgd6.jpg?ixlib=rb-1.1.0&rect=222%2C151%2C2477%2C1637&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Somchat Parkaythong/Shutterstock</span></span></figcaption></figure><p>Black holes are bizarre things, even by the standards of astronomers. Their mass is so great, it bends space around them so tightly that nothing can escape, even light itself.</p>
<p>And yet, despite their famous blackness, some black holes are quite visible. The gas and stars these galactic vacuums devour are sucked into a glowing disc before their one-way trip into the hole, and these discs can shine more brightly than entire galaxies. </p>
<p>Stranger still, these black holes twinkle. The brightness of the glowing discs can fluctuate from day to day, and nobody is entirely sure why.</p>
<p>We piggy-backed on NASA’s asteroid defence effort to watch more than 5,000 of the fastest-growing black holes in the sky for five years, in an attempt to understand why this twinkling occurs. In <a href="https://rdcu.be/c4Je0">a new paper in Nature Astronomy</a>, we report our answer: a kind of turbulence driven by friction and intense gravitational and magnetic fields. </p>
<h2>Gigantic star-eaters</h2>
<p>We study supermassive black holes, the kind that sit at the centres of galaxies and are as massive as millions or billions of Suns. </p>
<p>Our own galaxy, the Milky Way, has one of these giants at its centre, with a mass of about four million Suns. For the most part, the 200 billion or so stars that make up the rest of the galaxy (including our Sun) happily orbit around the black hole at the centre.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/are-black-holes-time-machines-yes-but-theres-a-catch-195418">Are black holes time machines? Yes, but there's a catch</a>
</strong>
</em>
</p>
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<p>However, things are not so peaceful in all galaxies. When pairs of galaxies pull on each other via gravity, many stars may end up tugged too close to their galaxy’s black hole. This ends badly for the stars: they are torn apart and devoured.</p>
<p>We are confident this must have happened in galaxies with black holes that weigh as much as a billion suns, because we can’t imagine how else they could have grown so large. It may also have happened in the Milky Way in the past.</p>
<p>Black holes can also feed in a slower, more gentle way: by sucking in clouds of gas blown out by geriatric stars known as red giants.</p>
<h2>Feeding time</h2>
<p>In our new study, we looked closely at the feeding process among the 5,000 fastest-growing black holes in the Universe. </p>
<p>In earlier studies, we discovered the black holes with the most voracious appetite. Last year, we found a black hole that eats <a href="https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/discovery-of-the-most-luminous-quasar-of-the-last-9-gyr/F7FEDC02A19FE9CA90A116552CC6BE14">an Earth’s-worth of stuff every second</a>. In 2018, we found one that eats <a href="https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/discovery-of-the-most-ultraluminous-qso-using-gaia-skymapper-and-wise/6FB5687AE7326F09557AD625C2889A0F">a whole Sun every 48 hours</a>.</p>
<p>But we have lots of questions about their actual feeding behaviour. We know material on its way into the hole spirals into a glowing “accretion disc” that can be bright enough to outshine entire galaxies. These visibly feeding black holes are called quasars. </p>
<p>Most of these black holes are a long, long way away – much too far for us to see any detail of the disc. We have some images of accretion discs around nearby black holes, but they are merely breathing in some cosmic gas rather than feasting on stars.</p>
<figure class="align-center ">
<img alt="A blobby photo of a red-yellow ring around a central black hole." src="https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507563/original/file-20230201-14-cillry.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">
<figcaption>
<span class="caption">The glowing accretion disc around the black hole Sagittarius A*, at the centre of the Milky Way, was imaged in 2022.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso2208-eht-mwa/">EHT Collaboration</a></span>
</figcaption>
</figure>
<h2>Five years of flickering black holes</h2>
<p>In <a href="https://rdcu.be/c4Je0">our new work</a>, we used data from NASA’s ATLAS telescope in Hawaii. It scans the entire sky every night (weather permitting), monitoring for asteroids approaching Earth from the outer darkness. </p>
<p>These whole-sky scans also happen to provide a nightly record of the glow of hungry black holes, deep in the background. Our team put together a five-year movie of each of those black holes, showing the day-to-day changes in brightness caused by the bubbling and boiling glowing maelstrom of the accretion disc.</p>
<p>The twinkling of these black holes can tell us something about accretion discs. </p>
<p>In 1998, astrophysicists Steven Balbus and John Hawley proposed a theory of “<a href="https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.70.1">magneto-rotational instabilities</a>” that describes how magnetic fields can cause turbulence in the discs. If that is the right idea, then the discs should sizzle in regular patterns. They would twinkle in random patterns that unfold as the discs orbit. Larger discs orbit more slowly with a slow twinkle, while tighter and faster orbits in smaller discs twinkle more rapidly.</p>
<p>But would the discs in the real world prove this simple, without any further complexities? (Whether “simple” is the right word for turbulence in an ultra-dense, out-of-control environment embedded in intense gravitational and magnetic fields where space itself is bent to breaking point is perhaps a separate question.)</p>
<p>Using statistical methods we measured how much the light emitted from our 5,000 discs flickered over time. The pattern of flickering in each one looked somewhat different. </p>
<p>But when we sorted them by size, brightness and colour, we began to see intriguing patterns. We were able to determine the orbital speed of each disc – and once you set your clock to run at the disc’s speed, all the flickering patterns started to look the same. </p>
<p>This universal behaviour is indeed predicted by the theory of “magneto-rotational instabilities”.</p>
<p>That was comforting! It means these mind-boggling maelstroms are “simple” after all. </p>
<p>And it opens new possibilities. We think the remaining subtle differences between accretion discs occur because we are looking at them from different orientations.</p>
<p>The next step is to examine these subtle differences more closely and see whether they hold clues to discern a black hole’s orientation. Eventually, our future measurements of black holes could be even more accurate.</p><img src="https://counter.theconversation.com/content/198996/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Wolf receives funding from the Australian Research Council (ARC). He is a member of the Astronomical Society of Australia (ASA).</span></em></p>While we can’t see inside a black hole, we can spot the intensely bright glowing disc that surrounds one. Now, we might better understand why these discs appear to ‘twinkle’.Christian Wolf, Associate Professor, Astronomy & Astrophysics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1979052023-01-16T22:13:08Z2023-01-16T22:13:08ZAstronomers reveal the most detailed radio image yet of the Milky Way’s galactic plane<figure><img src="https://images.theconversation.com/files/504592/original/file-20230116-19027-nxt92l.jpg?ixlib=rb-1.1.0&rect=264%2C0%2C1930%2C1103&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Combined images from the ASKAP and Parkes radio telescopes.</span> <span class="attribution"><span class="source">R. Kothes (NRC) and the PEGASUS team</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Two major astronomy research programs, called EMU and PEGASUS, have joined forces to resolve one of the mysteries of our Milky Way: where are all the supernova remnants? </p>
<p>A <a href="https://theconversation.com/a-new-australian-supercomputer-has-already-delivered-a-stunning-supernova-remnant-pic-188375">supernova remnant</a> is an expanding cloud of gas and dust marking the last phase in the life of a star, after it has exploded as a supernova. But the number of supernova remnants we have detected so far with radio telescopes is too low. Models predict five times as many, so where are the missing ones? </p>
<p>We have combined observations from two of Australia’s world-leading radio telescopes, the <a href="https://www.csiro.au/en/about/facilities-collections/ATNF/ASKAP-radio-telescope">ASKAP radio telescope</a> and the <a href="https://www.csiro.au/en/about/facilities-collections/atnf/parkes-radio-telescope">Parkes radio telescope, Murriyang</a>, to answer this question.</p>
<h2>The gas between the stars</h2>
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<figcaption>Comparison between the ASKAP/EMU image and the combined ASKAP/EMU plus Parkes/PEGASUS image. <br>Images: R. Kothes (NRC) and E. Carretti (INAF).</figcaption>
</figure>
<p>The new image reveals thin tendrils and clumpy clouds associated with hydrogen gas filling the space between the stars. We can see sites where new stars are forming, as well as supernova remnants.</p>
<p>In just this small patch, only about 1% of the whole Milky Way, we have discovered more than 20 new possible supernova remnants where only seven were previously known. </p>
<p>These discoveries were led by PhD student Brianna Ball from Canada’s University of Alberta, working with her supervisor, Roland Kothes of the National Research Council of Canada, who prepared the image. These new discoveries suggest we are close to accounting for the missing remnants.</p>
<p>So why can we see them now when we couldn’t before?</p>
<figure class="align-center ">
<img alt="The ASKAP radio telescope, showing radio dishes pointed at a blue sky with the sun in the background." src="https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504590/original/file-20230116-18-23rt6s.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ASKAP radio telescope at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory in Western Australia.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<h2>The power of joining forces</h2>
<p>I lead the <a href="http://www.emu-survey.org/">Evolutionary Map of the Universe</a> or EMU program, an ambitious project with ASKAP to make the best radio atlas of the Southern Hemisphere.</p>
<p>EMU will measure about 40 million new distant galaxies and supermassive black holes, to help us understand how galaxies have changed over the history of the universe.</p>
<p>Early EMU data have already led to the discovery of <a href="https://theconversation.com/odd-radio-circles-that-baffled-astronomers-are-likely-explosions-from-distant-galaxies-178290">odd radio circles (or “ORCs”)</a>, and revealed <a href="https://theconversation.com/dancing-ghosts-a-new-deeper-scan-of-the-sky-throws-up-surprises-for-astronomers-165239">rare oddities like the “Dancing Ghosts”</a>.</p>
<p>For any telescope, the resolution of its images depends on the size of its aperture. Interferometers like ASKAP simulate the aperture of a much larger telescope. With 36 relatively small dishes (each 12m in diameter) but a 6km distance connecting the farthest of these, ASKAP mimics a single telescope with a 6km wide dish.</p>
<p>That gives ASKAP a good resolution, but comes at the expense of missing radio emission on the largest scales. In the comparison above, the ASKAP image alone appears too skeletal.</p>
<figure class="align-center ">
<img alt="The Parkes radio telescope, Murriyang, showing the 64 telescope dish." src="https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504591/original/file-20230116-16-v7ugns.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Parkes radio telescope, Murriyang.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>To recover that missing information, we turned to a companion project called PEGASUS, led by Ettore Carretti of Italy’s National Institute of Astrophysics.</p>
<p>PEGASUS uses the 64m diameter Parkes/Murriyang telescope – one of the largest single-dish radio telescopes in the world – to map the sky.</p>
<p>Even with such a large dish, Parkes has rather limited resolution. By combining the information from both Parkes and ASKAP, each fills in the gaps of the other to give us the best fidelity image of this region of our Milky Way galaxy. This combination reveals the radio emission on all scales to help uncover the missing supernova remnants.</p>
<p>Linking the datasets from EMU and PEGASUS will allow us to reveal more hidden gems. In the next few years we will have an unprecedented view of almost the entire Milky Way, about a hundred times larger than this initial image, but with the same level of detail and sensitivity.</p>
<p>We estimate there may be up to 1,500 or more new supernova remnants yet to discover. Solving the puzzle of these missing remnants will open new windows into the history of our Milky Way.</p>
<hr>
<p><em>ASKAP and Parkes are owned and operated by CSIRO, Australia’s national science agency, as part of the Australia Telescope National Facility. CSIRO acknowledge the Wajarri Yamaji people as the Traditional Owners and native title holders of Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory, where ASKAP is located, and the Wiradjuri people as the traditional owners of the Parkes Observatory.</em></p><img src="https://counter.theconversation.com/content/197905/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Hopkins 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>Our galaxy should be full of traces of dead stars. Until now, we have found surprisingly few of these supernova remnants, but a new telescope collaboration is changing that.Andrew Hopkins, Professor of Astronomy, Macquarie UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1908302023-01-12T03:45:24Z2023-01-12T03:45:24ZCurious Kids: what are gravitational waves?<figure><img src="https://images.theconversation.com/files/486718/original/file-20220927-20-rw1bvt.jpg?ixlib=rb-1.1.0&rect=17%2C224%2C1979%2C1568&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">3D visualisation of gravitational waves produced by two orbiting black holes.</span> <span class="attribution"><span class="source">Henze/NASA</span></span></figcaption></figure><blockquote>
<p>What are gravitational waves? – Millie, age 10, Sydney</p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>What a great question Millie! </p>
<p>To answer this we have to travel back in time, to the year 1916. This is the year famous physicist Albert Einstein published his general theory of relativity.</p>
<p>Einstein had figured out how to explain gravity within the Universe using maths. Gravity is the force that keeps us on Earth, and Earth orbiting around the Sun. Until 1916 there had been many theories to try and explain what gravity was and why it exists. But Einstein suggested that gravity was the bending of something called space-time. </p>
<p>You can think of space-time like the fabric of the Universe. It’s what makes up the space we live in. Without it we wouldn’t have a Universe, and that wouldn’t be very fun.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-it-possible-to-see-what-is-happening-in-distant-solar-systems-now-185463">Curious Kids: is it possible to see what is happening in distant solar systems now?</a>
</strong>
</em>
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<h2>A space-time trampoline</h2>
<p>Curved space-time is responsible for the effects of gravity. A trampoline is a great way for us to picture this on a flat surface. </p>
<p>Imagine you place a heavy bowling ball in the centre of a trampoline – its mass bends the fabric, and it creates a dip. Now, if we tried to roll a marble across the trampoline, it would roll inwards and around the bowling ball.</p>
<p>That’s all gravity is: the distortion of the space-time fabric, affecting how things move.</p>
<figure class="align-center ">
<img alt="Top: trampoline with bowling ball bending the fabric. Bottom: trampoline with bowling ball bending the fabric, and marble path direction outlined by red arrow." src="https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=618&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=618&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=618&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=776&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=776&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485636/original/file-20220920-23-pg5fnk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=776&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If a heavy thing like a bowling ball stretches the trampoline, a marble will roll towards it in a circle.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This is what Einstein’s famous equations helped to explain – how we can expect space-time to move under different conditions. We know that in the Universe, nothing stands still. Everything is always moving, and when objects speed up through space-time, they can create small ripples, just like a pebble in a pond.</p>
<p>These ripples are what we call gravitational waves. Our Universe is likely full of these tiny waves, like an ocean with waves moving in all different directions.</p>
<p>But unlike the ocean, gravitational waves are incredibly small and won’t be rocking Earth about. When first predicted by Einstein, he doubted if we’d ever be able to detect them because of how teeny tiny they should be.</p>
<p>I would love to know what he would think today. Not only have we detected gravitational waves, but we’ve detected 90 unique events! This is one of the biggest achievements in physics, and how they did it was nothing short of amazing.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-is-cosmic-microwave-background-radiation-185537">Curious Kids: what is cosmic microwave background radiation?</a>
</strong>
</em>
</p>
<hr>
<h2>Squeeze and stretch</h2>
<p>When a gravitational wave passes through Earth, it squeezes or stretches the whole planet in the direction it travels. If we tried to measure it with something like a ruler, the ruler would appear to be the same length because the numbers on the ruler would also be stretched or squeezed, and wouldn’t change.</p>
<p>But scientists have a trick: they can use light, because light can only travel a certain distance over a certain time. If space is stretched out, the light has to travel a little bit farther, and takes longer. Vice versa for when space in squeezed. </p>
<p>The trick to knowing if space has been squeezed or stretched is to measure it in <em>two</em> directions, and calculate the difference. Unfortunately for us it isn’t something that is easy to measure.</p>
<p>The difference in the distance we’re looking for is 1,000 times smaller then a really tiny particle called a proton. To really blow your mind, our bodies have around 10 <em>octillion</em> protons (10,000,000,000,000,000,000,000,000,000). </p>
<p>It’s an insanely small change we needed to detect, but thankfully clever scientists and engineers figured out a way to do it, and you can learn more about these detectors in the video below.</p>
<p>Gravitational waves have given us new eyes to our Universe, allowing us to “see” things like black holes and neutron stars crashing together – because we can finally detect the tiny ripples they create. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/4GbWfNHtHRg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure><img src="https://counter.theconversation.com/content/190830/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sara Webb 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>To understand this question, we need to travel back in time.Sara Webb, Postdoctoral Research Fellow, Centre for Astrophysics and Supercomputing, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1947392022-12-22T19:08:04Z2022-12-22T19:08:04Z10 times this year the Webb telescope blew us away with new images of our stunning universe<figure><img src="https://images.theconversation.com/files/501223/original/file-20221215-25-lu4eme.jpg?ixlib=rb-1.1.0&rect=0%2C21%2C3583%2C2042&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Carina star-forming region imaged by the JWST.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-reveals-cosmic-cliffs-glittering-landscape-of-star-birth/">NASA</a></span></figcaption></figure><p>It is no exaggeration to say the James Webb Space Telescope (JWST) represents a new era for modern astronomy.</p>
<p><a href="https://theconversation.com/nasas-james-webb-space-telescope-has-reached-its-destination-1-5-million-km-from-earth-heres-what-happens-next-175327">Launched on December 25 last year</a> and fully operational since July, the telescope offers glimpses of the universe that were inaccessible to us before. Like the Hubble Space Telescope, the JWST is in space, so it can take pictures with stunning detail free from the distortions of Earth’s atmosphere.</p>
<p>However, while Hubble is in orbit around Earth at an altitude of 540km, the JWST is <em>1.5 million</em> kilometres distant, far beyond the Moon. From this position, away from the interference of our planet’s reflected heat, it can collect light from across the universe far into the infrared portion of the electromagnetic spectrum.</p>
<p>This ability, when combined with the JWST’s larger mirror, state-of-the-art detectors, and many other technological advances, allows astronomers to look back to the universe’s earliest epochs.</p>
<p>As the universe expands, it stretches the wavelength of light travelling towards us, making more distant objects appear redder. At great enough distances, the light from a galaxy is shifted entirely out of the visible part of the electromagnetic spectrum to the infrared. The JWST is able to probe such sources of light right back to the earliest times, nearly 14 billion years ago.</p>
<p>The Hubble telescope continues to be a great scientific instrument and can see at optical wavelengths where the JWST cannot. But the Webb telescope can see much further into the infrared with greater sensitivity and sharpness.</p>
<p>Let’s have a look at ten images that have demonstrated the staggering power of this new window to the universe.</p>
<h2>1. Mirror alignment complete</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A bright six-pointed orange star with text above it stating it's a telescope alignment evaluation image. Inset in the top right corner shows a red blob with two points" src="https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=477&fit=crop&dpr=1 754w, https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=477&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/501219/original/file-20221215-24-vfv1aq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=477&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: The first publicly released alignment image from the JWST. Astronomers jumped on this image to compare it to previous images of the same part of sky like that on the right from the Dark Energy Camera on Earth.</span>
<span class="attribution"><span class="source">NASA/STScI/LegacySurvey/C. Jacobs</span></span>
</figcaption>
</figure>
<p>Despite years of testing on the ground, an observatory as complex as the JWST required extensive configuration and testing once deployed in the cold and dark of space.</p>
<p>One of the biggest tasks was getting <a href="https://theconversation.com/the-james-webb-space-telescope-has-taken-its-first-aligned-image-of-a-star-heres-how-it-was-done-178315">the 18 hexagonal mirror segments</a> unfolded and aligned to within a fraction of a wavelength of light. In March, <a href="https://www.nasa.gov/press-release/nasa-s-webb-reaches-alignment-milestone-optics-working-successfully/">NASA released the first image</a> (centred on a star) from the fully aligned mirror. Although it was just a calibration image, astronomers immediately compared it to existing images of that patch of sky – with considerable excitement.</p>
<h2>2. Spitzer vs MIRI</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two orange images showing a series of bright dots - the left one is much fuzzier than the right one" src="https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=575&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=575&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499165/original/file-20221206-20-qp5q7u.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=575&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This image shows a portion of the ‘Pillars of Creation’ in the infrared (see below); on the left taken with the Spitzer Space Telescope, and JWST on the right. The contrast in depth and resolution is dramatic.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech (left), NASA/ESA/CSA/STScI (right)</span></span>
</figcaption>
</figure>
<p>This early image, taken while all the cameras were being focused, clearly demonstrates the step change in data quality that JWST brings over its predecessors.</p>
<p>On the left is an image from the Spitzer telescope, a space-based infrared observatory with an 85cm mirror; the right, the same field from JWST’s mid-infrared <a href="https://webb.nasa.gov/content/observatory/instruments/miri.html">MIRI camera</a> and 6.5m mirror. The resolution and ability to detect much fainter sources is on show here, with hundreds of galaxies visible that were lost in the noise of the Spitzer image. This is what a bigger mirror situated out in the deepest, coldest dark can do.</p>
<h2>3. The first galaxy cluster image</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two images of hundreds of dots of light on a dark background, with more visible on the right hand side" src="https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=308&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=308&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=308&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=386&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=386&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499268/original/file-20221206-18-h6t99q.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">SMACS 0723 galaxy cluster – from Hubble on the left, and JWST on the right. Hundreds more galaxies are visible in JWST’s infrared image.</span>
<span class="attribution"><span class="source">NASA/STSci</span></span>
</figcaption>
</figure>
<p>The galaxy cluster with the prosaic name of SMACS J0723.3–7327 was a good choice for the first colour images <a href="https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-delivers-deepest-infrared-image-of-universe-yet">released to the public</a> from the JWST.</p>
<p>The field is crowded with galaxies of all shapes and colours. The combined mass of this enormous galaxy cluster, over 4 billion light years away, bends space in such a way that light from distant sources in the background is stretched and magnified, an effect known as <a href="https://hubblesite.org/contents/articles/gravitational-lensing">gravitational lensing</a>.</p>
<p>These distorted background galaxies can be clearly seen as lines and arcs throughout this image. The field is already spectacular in Hubble images (left), but the JWST near-infrared image (right) reveals a wealth of extra detail, including hundreds of distant galaxies too faint or too red to be detected by its predecessor.</p>
<h2>4. Stephan’s Quintet</h2>
<figure class="align-center ">
<img alt="Side-by-side images of four large, luminous circles with thousands of stars in the background and within; the left side has more brightness and sharpness" src="https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/501816/original/file-20221219-26-k4lphv.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">
<figcaption>
<span class="caption">Hubble (l) and JWST (r) images of the group of galaxies known as ‘Stephan’s Quintet’. The inset shows a zoom-in on a distant background galaxy.</span>
<span class="attribution"><span class="source">NASA/STScI</span></span>
</figcaption>
</figure>
<p>These images depict a spectacular group of galaxies known as Stephan’s Quintet, a group that has <a href="https://www.galactic-hunter.com/post/hcg-92-stephan-s-quintet">long been of interest to astronomers</a> studying the way colliding galaxies interact with one another gravitationally.</p>
<p>On the left we see the Hubble view, and the right <a href="https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-sheds-light-on-galaxy-evolution-black-holes">the JWST mid-infrared view</a>. The inset shows the power of the new telescope, with a zoom in on a small background galaxy. In the Hubble image we see some bright star-forming regions, but only with the JWST does the full structure of this and surrounding galaxies reveal itself.</p>
<h2>5. The Pillars of Creation</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two side-by-side images of finger-like protrusions on a multicoloured starry background, wth more detail visible on the right" src="https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=290&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=290&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=290&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=364&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=364&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499170/original/file-20221206-21-drey7v.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=364&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 ‘Pillars of Creation’, a star-forming region of our galaxy, as captured by Hubble (left) and JWST (right).</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2022/nasa-s-webb-takes-star-filled-portrait-of-pillars-of-creation">NASA, ESA, CSA, STScI; Joseph DePasquale (STScI), Anton M. Koekemoer (STScI), Alyssa Pagan (STScI)</a></span>
</figcaption>
</figure>
<p>The so-called Pillars of Creation is one of the most famous images in all of astronomy, <a href="https://hubblesite.org/contents/media/images/3862-Image">taken by Hubble in 1995</a>. It demonstrated the extraordinary reach of a space-based telescope.</p>
<p>It depicts a star-forming region in the Eagle Nebula, where interstellar gas and dust provide the backdrop to a stellar nursery teeming with new stars. The image on the right, taken with the <a href="https://webb.nasa.gov/content/observatory/instruments/nircam.html">JWST’s near-infrared camera</a> (NIRCam), demonstrates a further advantage of infrared astronomy: the ability to peer through the shroud of dust and see what lies within and behind. </p>
<h2>6. The ‘Hourglass’ Protostar</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An orange-and-blue hourglass shape on a dark background, with a blurrier blue image of the same shape in the upper corner" src="https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=612&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=612&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=612&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=769&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=769&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499203/original/file-20221206-14-wz1k2y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=769&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 ‘hourglass protostar’, a star still in the process of accreting enough gas to begin fusing hydrogen. Inset: A much lower resolution view from Spitzer.</span>
<span class="attribution"><span class="source">NASA/STScI/JPL-Caltech/A. Tobin</span></span>
</figcaption>
</figure>
<p>This image depicts another act of galactic creation within the Milky Way. This hourglass-shaped structure is a cloud of dust and gas surrounding a star in the act of formation – a protostar called L1527.</p>
<p>Only visible in the infrared, an “accretion disk” of material falling in (the black band in the centre) will eventually enable the protostar to gather enough mass to start fusing hydrogen, and a new star will be born.</p>
<p>In the meantime, light from the still-forming star illuminates the gas above and below the disk, making the hourglass shape. Our previous view of this came from Spitzer; the amount of detail is once again an enormous leap ahead.</p>
<h2>7. Jupiter in infrared</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A turqoise and blue banded sphere with bright orange patches of light at both poles" src="https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=569&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=569&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=569&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=715&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=715&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499258/original/file-20221206-2958-ashu5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=715&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An infrared view of Jupiter from the JWST. Note the auroral glow at the poles; this is caused by the interaction of charged particles from the sun with Jupiter’s magnetic field.</span>
<span class="attribution"><span class="source">NASA/STScI</span></span>
</figcaption>
</figure>
<p>The Webb telescope’s mission includes imaging the most distant galaxies from the beginning of the universe, but it can look a little closer to home as well.</p>
<p>Although JWST cannot look at Earth or the inner Solar System planets – as it must always face away from the Sun – it can look outward at the more distant parts of our Solar System. This near-infrared image of Jupiter is a beautiful example, as we gaze deep into the structure of the gas giant’s clouds and storms. The glow of auroras at both the northern and southern poles is haunting.</p>
<p>This image was extremely difficult to achieve due to the fast motion of Jupiter across the sky relative to the stars and because of its fast rotation. The success proved the Webb telescope’s ability to track difficult astronomical targets extremely well.</p>
<h2>8. The Phantom Galaxy</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three similar images of spiral galaxy in different colours, with the middle one providing the most detail" src="https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499257/original/file-20221206-2849-7pej0e.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">Hubble visible light (l), JWST infrared (r) and combined (middle) images of the ‘Phantom Galaxy’ M74. The ability to combine visible light information about stars with infrared images of gas and dust allow us to probe such galaxies in exquisite detail.</span>
<span class="attribution"><span class="source">ESA/NASA</span></span>
</figcaption>
</figure>
<p>These images of the so-called <a href="https://esawebb.org/images/potm2208a/">Phantom Galaxy or M74</a> reveal the power of JWST not only as the latest and greatest of astronomical instruments, but as a valuable complement to other great tools. The middle panel here combines visible light from Hubble with infrared from Webb, allowing us to see how starlight (via Hubble) and gas and dust (via JWST) together shape this remarkable galaxy.</p>
<p>Much JWST science is designed to be combined with Hubble’s optical views and other imaging to leverage this principle.</p>
<h2>9. A super-distant galaxy</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Side by side images of a black background with many small galaxies of various shapes glowing faintly" src="https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=311&fit=crop&dpr=1 600w, https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=311&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=311&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=391&fit=crop&dpr=1 754w, https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=391&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/501222/original/file-20221215-24-ap036o.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=391&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">A ‘zoom in’ on a galaxy from one of the universe’s earliest epochs, when the universe was only about 300 million years old (the small red source visible in the centre of the right panel). Galaxies at this distance are impossible to detect in visible light as their emitted radiation has been ‘redshifted’ far into the infrared.</span>
<span class="attribution"><span class="source">NASA/STScI/C. Jacobs</span></span>
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</figure>
<p>Although this galaxy – the small, red blob in the right image – is not among the most spectacularly picturesque our universe has to offer, it is just as interesting scientifically.</p>
<p>This snapshot is from when the universe was a mere 350 million years old, making this among the very first galaxies ever to have formed. Understanding the details of how such galaxies grow and merge to create galaxies like our own Milky Way 13 billion years later is a key question, and one with many remaining mysteries, making discoveries like this highly sought after.</p>
<p>It is also a view only the JWST can achieve. Astronomers did not know quite what to expect; an image of this galaxy taken with Hubble would appear blank, as the light of the galaxy is stretched far into the infrared by the expansion of the universe. </p>
<h2>10. This giant mosaic of Abell 2744</h2>
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<a href="https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An irregularly shaped image of hundreds of glowing dots on a dark background" src="https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=530&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=530&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=530&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">An image of the galaxy cluster Abell 2744 created by combining many different JWST exposures. In this tiny part of the sky (a fraction of a full Moon) almost every one of the thousands of objects shown is a distant galaxy.</span>
<span class="attribution"><span class="source">Lukas Furtak (Ben-Gurion University of the Negev) from images from the GLASS/UNCOVER teams</span></span>
</figcaption>
</figure>
<p>This image (<a href="https://images.theconversation.com/files/499261/original/file-20221206-12-pevvt.jpeg">click here for full view</a>) is a mosaic (many individual images stitched together) centred on the giant Abell 2744 galaxy cluster, colloquially known as “Pandora’s Cluster”. The sheer number and variety of sources that the JWST can detect is mind boggling; with the exception of a handful of foreground stars, every spot of light <em>represents an entire galaxy</em>.</p>
<p>In a patch of dark sky no larger than a fraction of the full Moon there are umpteen thousands of galaxies, really bringing home the sheer scale of the universe we inhabit. Professional and amateur astronomers alike can spend hours scouring this image for oddities and mysteries.</p>
<p>Over the coming years, JWST’s ability to look so deep and far back into the universe will allow us to answer many questions about how we came to be. Just as exciting are the discoveries and questions we can not yet foresee. When you peel back the veil of time as only this new telescope can, these unknown unknowns are certain to be fascinating.</p>
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Read more:
<a href="https://theconversation.com/how-the-james-webb-space-telescope-has-revealed-a-surprisingly-bright-complex-and-element-filled-early-universe-podcast-196649">How the James Webb Space Telescope has revealed a surprisingly bright, complex and element-filled early universe – podcast</a>
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<img src="https://counter.theconversation.com/content/194739/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Colin Jacobs' work is funded by the Australian Research Council grant FL180100060. He is a member of the Australian Greens.</span></em></p><p class="fine-print"><em><span>Karl Glazebrook receives funding for JWST research from the Australian Research Council through Laureate Fellowship FL180100060.</span></em></p>A year on since the historic launch of the most powerful infrared telescope in human history, we admire and explore some of the best images it delivered in 2022.Colin Jacobs, Postdoctoral Researcher in Astrophysics, Swinburne University of TechnologyKarl Glazebrook, ARC Laureate Fellow & Distinguished Professor, Centre for Astrophysics & Supercomputing, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1949292022-11-21T15:54:25Z2022-11-21T15:54:25ZHow to test if we’re living in a computer simulation<figure><img src="https://images.theconversation.com/files/496450/original/file-20221121-25-963m2s.png?ixlib=rb-1.1.0&rect=0%2C137%2C2000%2C1607&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA, ESA, CSA, STScI</span></span></figcaption></figure><p>Physicists have long struggled to explain why the universe started out with conditions <a href="https://plato.stanford.edu/entries/fine-tuning/">suitable for life to evolve</a>. Why do the physical laws and constants <a href="https://theconversation.com/can-the-laws-of-physics-disprove-god-146638">take the very specific values</a> that allow stars, planets and ultimately life to develop? The expansive force of the universe, dark energy, for example, is much weaker than theory suggests it should be – allowing matter to clump together rather than being ripped apart.</p>
<p>A common answer is that we live in an infinite multiverse of universes, so we shouldn’t be surprised that at least one universe has turned out as ours. But another is that our universe is a computer simulation, with someone (perhaps an advanced alien species) fine-tuning the conditions.</p>
<p>The latter option is supported by a branch of science called <a href="https://arxiv.org/abs/1009.5161">information physics</a>, which suggests that space-time and matter are not fundamental phenomena. Instead, the physical reality is fundamentally made up of bits of information, from which our experience of space-time emerges. By comparison, temperature “emerges” from the collective movement of atoms. No single atom fundamentally has temperature. </p>
<p>This leads to the extraordinary possibility that our entire universe might in fact be a computer simulation. The idea is not that new. In 1989, the legendary physicist, <a href="https://phy.princeton.edu/department/history/faculty-history/john-wheeler">John Archibald Wheeler</a>, suggested that the universe is fundamentally mathematical and it can be seen as emerging from information. He coined the famous aphorism “<a href="https://plus.maths.org/content/it-bit">it from bit</a>”. </p>
<p>In 2003, philosopher <a href="https://nickbostrom.com/">Nick Bostrom</a> from Oxford University in the UK formulated his <a href="https://philpapers.org/rec/BOSAWL">simulation hypothesis</a>. This argues that it is actually highly probable that we live in a simulation. That’s because an advanced civilisation should reach a point where their technology is so sophisticated that simulations would be indistinguishable from reality, and the participants would not be aware that they were in a simulation.</p>
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<p>Physicist <a href="https://meche.mit.edu/people/faculty/SLLOYD@MIT.EDU">Seth Lloyd</a> from the Massachusetts Institute of Technology in the US took the simulation hypothesis to the next level by suggesting that the entire universe <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.88.237901">could be a giant quantum computer</a>.<br>
And in 2016, business magnate Elon Musk concluded “We’re most likely in a simulation” (see video above).</p>
<h2>Empirical evidence</h2>
<p>There is some evidence suggesting that our physical reality could be a simulated virtual reality rather than an objective world that exists independently of the observer.</p>
<p>Any virtual reality world will be based on information processing. That means everything is ultimately digitised or pixelated down to a minimum size that cannot be subdivided further: bits. This appears to mimic our reality according to the theory of quantum mechanics, which rules the world of atoms and particles. It states there is a <a href="https://www.symmetrymagazine.org/article/the-planck-scale">smallest, discrete unit</a> of energy, length and time. Similarly, <a href="https://theconversation.com/explainer-what-are-fundamental-particles-38339">elementary particles</a>, which make up all the visible matter in the universe, are the smallest units of matter. To put it simply, our world is pixelated.</p>
<p>The laws of physics that govern everything in the universe also resemble computer code lines that a simulation would follow in the execution of the program. Moreover, mathematical equations, numbers and geometric patterns <a href="https://theconversation.com/mathematics-is-beautiful-no-really-72921">are present everywhere</a> – the world appears to be entirely mathematical. </p>
<p>Another curiosity in physics supporting the simulation hypothesis is the maximum speed limit in our universe, which is the speed of light. In a virtual reality, this limit would correspond to the speed limit of the processor, or the processing power limit. We know that an overloaded processor slows down computer processing in a simulation. Similarly, Albert Einstein’s <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">theory of general relativity</a> shows that time slows in the vicinity of a black hole.</p>
<p>Perhaps the most supportive evidence of the simulation hypothesis comes from quantum mechanics. This suggest nature isn’t “real”: particles in determined states, such as specific locations, <a href="https://theconversation.com/four-common-misconceptions-about-quantum-physics-192062">don’t seem to exist</a> unless you actually observe or measure them. Instead, they are in a mix of different states simultaneously. Similarly, virtual reality needs an observer or programmer for things to happen. </p>
<p>Quantum “entanglement” also allows two particles to be spookily connected so that if you manipulate one, you automatically and immediately also manipulate the other, no matter how far apart they are – with the effect being seemingly faster than the speed of light, which should be impossible.</p>
<p>This could, however, also be explained by the fact that within a virtual reality code, all “locations” (points) should be roughly equally far from a central processor. So while we may think two particles are millions of light years apart, they wouldn’t be if they were created in a simulation.</p>
<h2>Possible experiments</h2>
<p>Assuming that the universe is indeed a simulation, then what sort of experiments could we deploy from within the simulation to prove this?</p>
<p>It is reasonable to assume that a simulated universe would contain a lot of information bits everywhere around us. These information bits represent the code itself. Hence, detecting these information bits will prove the simulation hypothesis. The recently proposed <a href="https://doi.org/10.1063/1.5123794">mass-energy-information (M/E/I) equivalence principle</a> – suggesting mass can be expressed as energy or information, or vice versa – states that information bits must have a small mass. This gives us something to search for.</p>
<p>I have postulated that information is in fact a fifth form of matter in the universe. I’ve even <a href="https://doi.org/10.1063/5.0064475">calculated the expected information content</a> per elementary particle. These studies led to the publication, in 2022, of <a href="https://doi.org/10.1063/5.0087175">an experimental protocol</a> to test these predictions. The experiment involves erasing the information contained inside elementary particles by letting them and their antiparticles (all particles have “anti” versions of themselves which are identical but have opposite charge) annihilate in a flash of energy – emitting “photons”, or light particles.</p>
<p>I have predicted the exact range of expected frequencies of the resulting photons based on information physics. The experiment is highly achievable with our existing tools, and we <a href="https://www.indiegogo.com/projects/is-the-universe-a-simulation-let-s-test-it--2#/">have launched a crowdfunding site</a>) to achieve it. </p>
<p>There are other approaches too. The late physicist <a href="https://royalsociety.org/people/john-barrow-11044/">John Barrow</a> has argued that a simulation would build up minor computational errors which the programmer would need to fix in order to keep it going. He suggested we might <a href="https://www.simulation-argument.com/barrowsim.pdf">experience such fixing</a> as contradictory experimental results appearing suddenly, such as the constants of nature changing. So monitoring the values of these constants is another option.</p>
<p>The nature of our reality is one of the greatest mysteries out there. The more we take the simulation hypothesis seriously, the greater the chances we may one day prove or disprove it.</p><img src="https://counter.theconversation.com/content/194929/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Melvin M. Vopson 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>There may be ways to check if our universe is just simulated entertainment for an advanced, alien species.Melvin M. Vopson, Senior Lecturer in Physics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1941182022-11-10T17:26:56Z2022-11-10T17:26:56ZWe tested Einstein’s theory of gravity on the scale of the universe – here’s what we found<figure><img src="https://images.theconversation.com/files/494485/original/file-20221109-10696-job7mo.jpeg?ixlib=rb-1.1.0&rect=0%2C272%2C2794%2C2581&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Thousands of galaxies seen by the James Webb Space Telescope.</span> <span class="attribution"><span class="source">Nasa</span></span></figcaption></figure><p>Everything in the universe has gravity – and feels it too. Yet this most common of all fundamental forces is also the one that presents the biggest challenges to physicists. <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">Albert Einstein’s theory of general relativity</a> has been remarkably successful in describing the gravity of stars and planets, but it doesn’t seem to apply perfectly on all scales.</p>
<p>General relativity has passed many years of observational tests, from <a href="https://www.smithsonianmag.com/science-nature/total-solar-eclipse-100-years-ago-proved-einsteins-general-relativity-180972278/">Eddington’s measurement</a> of the deflection of starlight by the Sun in 1919 to the <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">recent detection of gravitational waves</a>. However, gaps in our understanding start to appear when we try to apply it to extremely small distances, where <a href="https://theconversation.com/four-common-misconceptions-about-quantum-physics-192062">the laws of quantum mechanics operate</a>, or when we try to describe the entire universe.</p>
<p>Our new study, <a href="https://www.nature.com/articles/s41550-022-01808-7">published in Nature Astronomy</a>, has now tested Einstein’s theory on the largest of scales. We believe our approach may one day help resolve some of the biggest mysteries in cosmology, and the results hint that the theory of general relativity may need to be tweaked on this scale.</p>
<h2>Faulty model?</h2>
<p>Quantum theory predicts that empty space, the vacuum, is packed with energy. We do not notice its presence because our devices can only measure changes in energy rather than its total amount. </p>
<p>However, according to Einstein, the vacuum energy has a repulsive gravity – it pushes the empty space apart. Interestingly, in 1998, it was discovered that the expansion of the universe is in fact accelerating (a finding awarded with the <a href="https://www.nobelprize.org/prizes/physics/2011/summary/">2011 Nobel prize in physics</a>).
However, the amount of vacuum energy, or dark energy as it has been called, necessary to explain the acceleration is many orders of magnitude smaller than what quantum theory predicts. </p>
<p>Hence the big question, dubbed “the old cosmological constant problem”, is whether the vacuum energy actually gravitates – exerting a gravitational force and changing the expansion of the universe.</p>
<p>If yes, then why is its gravity so much weaker than predicted? If the vacuum does not gravitate at all, what is causing the cosmic acceleration? </p>
<p>We don’t know what dark energy is, but we need to assume it exists in order to explain the universe’s expansion. Similarly, we also need to assume there is a type of invisible matter presence, dubbed dark matter, to explain how galaxies and clusters evolved to be the way we observe them today.</p>
<p>These assumptions are baked into scientists’ standard cosmological theory, called the lambda cold dark matter (LCDM) model – suggesting there is 70% dark energy, 25% dark matter and 5% ordinary matter in the cosmos. And this model has been remarkably successful in fitting all the data collected by cosmologists over the past 20 years.</p>
<p>But the fact that most of the universe is made up of dark forces and substances, taking odd values that don’t make sense, has prompted many physicists to wonder if Einstein’s theory of gravity needs modification to describe the entire universe.</p>
<p>A new twist appeared a few years ago when it became apparent that different ways of measuring the rate of cosmic expansion, dubbed the Hubble constant, give different answers – a problem known as <a href="https://theconversation.com/the-universes-rate-of-expansion-is-in-dispute-and-we-may-need-new-physics-to-solve-it-100154">the Hubble tension</a>.</p>
<p>The disagreement, or tension, is between two values of the Hubble constant. One is the number predicted by the LCDM cosmological model, which has been developed to match <a href="https://theconversation.com/the-cmb-how-an-accidental-discovery-became-the-key-to-understanding-the-universe-45126">the light left over from the Big Bang</a> (the cosmic microwave background radiation). The other is the expansion rate measured by observing exploding stars known as supernovas in distant galaxies. </p>
<figure class="align-center ">
<img alt="Image of the cosmic microwave background." src="https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=468&fit=crop&dpr=1 754w, https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=468&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/494622/original/file-20221110-13-t7kn1l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=468&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cosmic microwave background.</span>
<span class="attribution"><span class="source">Nasa</span></span>
</figcaption>
</figure>
<p>Many theoretical ideas have been proposed for ways of modifying LCDM to explain the Hubble tension. Among them are alternative gravity theories.</p>
<h2>Digging for answers</h2>
<p>We can design tests to check if the universe obeys the rules of Einstein’s theory.
General relativity describes gravity as the curving or warping of space and time, bending the pathways along which light and matter travel. Importantly, it predicts that the trajectories of light rays and matter should be bent by gravity in the same way.</p>
<p>Together with a team of cosmologists, we put the basic laws of general relativity to test. We also explored whether modifying Einstein’s theory could help resolve some of the open problems of cosmology, such as the Hubble tension. </p>
<p>To find out whether general relativity is correct on large scales, we set out, for the first time, to simultaneously investigate three aspects of it. These were the expansion of the universe, the effects of gravity on light and the effects of gravity on matter. </p>
<p>Using a statistical method known as the Bayesian inference, we reconstructed the gravity of the universe through cosmic history in a computer model based on these three parameters. We could estimate the parameters using the cosmic microwave background data from the Planck satellite, supernova catalogues as well as observations of the shapes and distribution of distant galaxies by the <a href="https://www.sdss4.org/">SDSS</a> and <a href="https://www.darkenergysurvey.org/">DES</a> telescopes.
We then compared our reconstruction to the prediction of the LCDM model (essentially Einstein’s model). </p>
<p>We found interesting hints of a possible mismatch with Einstein’s prediction, albeit with rather low statistical significance. This means that there is nevertheless a possibility that gravity works differently on large scales, and that the theory of general relativity may need to be tweaked. </p>
<p>Our study also found that it is very difficult to solve the Hubble tension problem by only changing the theory of gravity. The full solution would probably require a new ingredient in the cosmological model, present before the time when protons and electrons first combined to form hydrogen just after the Big Bang, such as a special form of dark matter, an early type of dark energy or primordial magnetic fields. Or, perhaps, there’s a yet unknown systematic error in the data.</p>
<p>That said, our study has demonstrated that it is possible to test the validity of general relativity over cosmological distances using observational data. While we haven’t yet solved the Hubble problem, we will have a lot more data from new probes in a few years.</p>
<p>This means that we will be able to use these statistical methods to continue tweaking general relativity, exploring the limits of modifications, to pave the way to resolving some of the open challenges in cosmology.</p><img src="https://counter.theconversation.com/content/194118/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kazuya Koyama receives funding from the Science Technology and Facilities Council. </span></em></p><p class="fine-print"><em><span>Levon Pogosian receives funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p>The theory of gravity may need to be altered.Kazuya Koyama, Professor of Cosmology, University of PortsmouthLevon Pogosian, Professor of Physics, Simon Fraser UniversityLicensed as Creative Commons – attribution, no derivatives.