tag:theconversation.com,2011:/ca/topics/cosmology-series-19966/articlesCosmology series – The Conversation2015-09-14T20:16:51Ztag:theconversation.com,2011:article/469882015-09-14T20:16:51Z2015-09-14T20:16:51ZWe are lucky to live in a universe made for us<figure><img src="https://images.theconversation.com/files/94602/original/image-20150914-1210-1et5w5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Like a cosmic roulette wheel, we exist because of a very lucky combination of factors.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>To a human, the universe might seem like a very inhospitable place. In the vacuum of space, you would rapidly suffocate, while on the surface of a star you would be burnt to a crisp. As far as we know, all life is confined to a sliver of an atmosphere surrounding the rocky planet we inhabit.</p>
<p>But while the origin of life on Earth remains mysterious, there are bigger questions to answer. Namely: why do the laws of physics permit any life at all? </p>
<p>Hang on, <em>the laws of physics</em>? Surely they are a universal given and life just gets on with it? </p>
<p>But remember that the universe is built of fundamental pieces, particles and forces, which are the building blocks of everything we see around us. And we simply don’t know why these pieces have the properties they do. </p>
<p>There are many observational facts about our universe, such as electrons weighing almost nothing, while some of their quark cousins are thousands of times more massive. And gravity being incredibly weak compared to the immense forces that hold atomic nuclei together. </p>
<p>Why is our universe built this way? We just don’t know.</p>
<h2>But what if…?</h2>
<p>This means we can ask “what if” questions. What if the electron was massive and quarks were fleeting? What if electromagnetism was stronger than the nuclear strong force? If so, what would that universe be like?</p>
<p>Let’s consider <a href="http://www.rsc.org/periodic-table/element/6/carbon">carbon</a>, an element forged in the hearts of massive stars, and an element essential to life as we know it.</p>
<p>Initial calculations of such stellar furnaces showed that they were apparently inefficient in making carbon. Then the British astronomer <a href="http://www.scientificamerican.com/article/hoyle-state-primordial-nucleus-behind-elements-life/">Fred Hoyle realised</a> the carbon nucleus possesses a special property, a resonance, that enhanced the efficiency.</p>
<p>But if the strength of the <a href="http://www.livescience.com/48575-strong-force.html">strong nuclear force</a> was only fractionally different, it would wipe out this property and leave the universe relatively devoid of carbon – and, thus, life. </p>
<p>The story doesn’t end there. Once carbon is made, it is ripe to be transmuted into heavier elements, particularly <a href="http://www.rsc.org/periodic-table/element/8/oxygen">oxygen</a>. It turns out that oxygen, due to the strength of the strong nuclear force, lacks the particular resonance properties that enhanced the efficiency of carbon creation.</p>
<p>This prevents all of the carbon being quickly consumed. The specific strength of the strong force has thus resulted in a universe with an almost equal mix of carbon and oxygen, a bonus for life on Earth. </p>
<h2>Death of a universe</h2>
<p>This is but a single example. We can play “what if” games with the properties of all of the fundamental bits of the universe. With each change we can ask, “What would the universe be like?”</p>
<p>The answers are quite stark. Straying just a little from the convivial conditions that we experience in our universe typically leads to a sterile cosmos. </p>
<p>This might be a bland universe, without the complexity required to store and process the information central to life. Or a universe that expands too quickly for matter to condense into stars, galaxies and planets. Or one that completely re-collapses again in a matter of moments after being born. Any complex life would be impossible!</p>
<p>The questions do not end there. In our universe, we live with the comfort of a certain mix of space and time, and a seemingly understandable mathematical framework that underpins science as we know it. Why is the universe so predictable and understandable? Would we be able to ask such a question if it wasn’t?</p>
<p>Our universe appears to balance on a knife-edge of stability. But why?</p>
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<a href="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=386&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=386&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=386&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=485&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=485&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=485&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">We appear to be very lucky to live in a universe that accommodates life.</span>
<span class="attribution"><span class="source">Zdenko Zivkovic/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>One of a multiverse</h2>
<p>To some, science will simply fix it all. Perhaps, if we discover the “Theory of Everything”, uniting quantum mechanics with Einstein’s relativity, all of the relative masses and strengths of the fundamental pieces will be absolutely defined, with no mysteries remaining. To others, this is little more than wishful thinking.</p>
<p>Some seek solace in a creator, an omnipotent being that finely-tuned the properties of the universe to allow us to be here. But the move from the scientific into the supernatural leaves many uncomfortable.</p>
<p>There is, however, another possible solution, one guided by the murky and confused musings at the edge of science. Super-strings or M-theory (or whatever these will evolve into) suggest that the fundamental properties of the universe are not unique, but are somehow chosen by some cosmic roll of the dice when it was born. </p>
<p>This gives us a possible explanation of the seemingly special properties of the universe in which we live.</p>
<p>We are not the only universe, but just one in a semi-infinite sea of universes, each with their own peculiar set of physical properties, laws and particles, lifetimes and ultimately mathematical frameworks. As we have seen, the vast majority of these other universes in the overall multiverse are dead and sterile. </p>
<p>They only way we can exist to ask the question “why are we here?” is that we happen to find ourselves in a universe conducive to our very existence. In any other universe, we simply wouldn’t be around to wonder why we didn’t exist.</p>
<p>If the multiverse picture is correct, we have to accept that the fundamental properties of the universe were ultimately dished out in a game of cosmic roulette, a spin of the wheel that we appear to have won.</p>
<p>Thus we truly live in a fortunate universe.</p><img src="https://counter.theconversation.com/content/46988/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>If some of the laws of physics were only infinitesimally different, we would simply not exist. It almost looks like the universe itself was built for life. But how can that be?Geraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/464932015-09-04T16:55:36Z2015-09-04T16:55:36ZFive myths about gravitational waves<figure><img src="https://images.theconversation.com/files/93044/original/image-20150826-7663-1d6skza.jpg?ixlib=rb-1.1.0&rect=0%2C476%2C2000%2C1350&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Elegant but elusive. Simulation of merging black holes showing gravitational waves.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:This_visualization_shows_what_Einstein_envisioned.jpg">NASA/ESA/wikimedia</a></span></figcaption></figure><p>Rumours are swirling around that scientists working at the <a href="http://space.mit.edu/LIGO/more.html">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a> in the US have detected gravitational waves, which are <a href="https://theconversation.com/rippling-space-time-how-to-catch-einsteins-gravitational-waves-7058">ripples in space-time</a>. Is it possible? After all, in 2014, scientists behind the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) telescope, made an extraordinary claim that they had <a href="https://www.cfa.harvard.edu/news/2014-05">detected them</a>. Initially hailed as the most groundbreaking discovery of the century, it later proved a <a href="http://arxiv.org/abs/1502.00612">false alarm</a>: the signal was merely galactic dust.</p>
<p>So are we likely to ever find gravitational waves? And would they really provide irrefutable evidence for the Big Bang? Here are five common myths and misconceptions about gravitational waves.</p>
<h2>1. Setbacks are just due to teething problems</h2>
<p>It may seem like the search for gravitational waves has only just begun, but it has actually been going on for decades without success. </p>
<p>Gravitational waves are pulsating perturbations, or “ripples” produced in the fabric of space-time as a massive object moves through it. As they propagate, they stretch and squash objects, albeit on subatomic scale. Scientists have therefore been trying to demonstrate the existence of gravitational waves by looking at how nearby objects are affected. </p>
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<img alt="" src="https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93903/original/image-20150904-14653-1bggolm.gif?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">A passing gravitational wave stretches and squashes objects in its path.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Gravitational_wave#/media/File:GravitationalWave_PlusPolarization.gif">wikimedia</a></span>
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</figure>
<p>In 1968, American physicist <a href="http://www.nytimes.com/2000/10/09/us/joseph-weber-dies-at-81-a-pioneer-in-laser-theory.html">Joseph Weber</a> claimed he had detected gravitational waves in this way using his esoteric detector made up of enormous aluminium cylinders. This was sadly <a href="http://physics.aps.org/story/v16/st19">later disproved</a>. </p>
<p>These days, scientists prefer using <a href="https://theconversation.com/rippling-space-time-how-to-catch-einsteins-gravitational-waves-7058">laser interferometry</a> to search for gravitational waves. It works by splitting a laser beam in two perpendicular directions and sending each down a long vacuum tunnel. The two paths are then reflected back by mirrors to the point they started, where a detector is placed. If the waves are disturbed by gravitational waves on their way, the recombined beams would be different from the original.</p>
<p>Ground-based interferometers, <a href="http://space.mit.edu/LIGO/more.html">like the Laser Interferometer Gravitational-Wave Observatory (LIGO)</a>, have arms that are about four kilometres long. Future space-based interferometers like the Deci-hertz Interferometer Gravitational Wave Observatory <a href="http://iopscience.iop.org/article/10.1088/1742-6596/122/1/012006/meta;jsessionid=FDBA35DE8AC0B9D01FCE8759208C71DD.c1">(DECIGO)</a> and the Evolved Laser Interferometer Space Antenna <a href="https://www.elisascience.org/articles/lisa-pathfinder/lpf-mission">(eLISA)</a> will use laser arms spanning up to a million kilometres. These experiments are expected to launch within the next decade.</p>
<h2>2. The waves come from the early universe</h2>
<p>The strongest sources of gravitational waves are in fact astrophysical processes, which are happening all the time.</p>
<p>The most dominant of these sources is the rotation of pairs of white dwarfs or black holes (so-called “binary systems”). Such pairs are thought to gradually lose energy by emitting gravitational waves. This was <a href="http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=3thehulsetaylor">demonstrated</a> by the discovery of the famous <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/press.html">Hulse-Taylor pulsar</a> in 1974. The pulsar provided indirect evidence of gravitational waves as it was losing energy at a rate which had been predicted by the general theory of relativity (the waves themselves were not seen).</p>
<p>However, scientists are also looking for gravitational waves created shortly after the universe was born, called primordial gravitational waves, which are much more elusive.</p>
<h2>3. BICEP2 could one day ‘see’ gravitational waves</h2>
<p>One of BICEP2’s goals was try to detect the signature of primordial gravitational waves imprinted in the temperature of the <a href="http://www.bbc.co.uk/science/space/universe/sights/cosmic_microwave_background_radiation">Cosmic Microwave Background</a> (CMB). This radiation contains light that first emerged from the soup of elementary particles when the universe was just 300,000 years old, long before the first stars were born.</p>
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<img alt="" src="https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93910/original/image-20150904-14639-10j4bed.jpg?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">
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<span class="caption">The cosmic microwave background, as measured by the Planck satellite.</span>
<span class="attribution"><span class="source">ESA/Planck Collaboration</span></span>
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</figure>
<p>When light waves vibrate in a certain direction, we say that it has a specific <em>polarisation</em>. If gravitational waves were present at the time when the CMB was born, they should leave behind a unique swirly pattern – a curling in the polarisation of the light – dubbed “B modes”. </p>
<p>Therefore, the B modes are only indirect evidence for gravitational waves. This is an important point: Experiments like BICEP2 will never be able to observe gravitational waves themselves, only the fingerprints they left behind.</p>
<p>Even dusting for these fingerprints is not easy. B-modes are typically masked by much stronger signals from dust emission and an effect called <a href="http://www.cfhtlens.org/public/what-gravitational-lensing">gravitational lensing</a>, which mixes different types of polarisation patterns. Eliminating these and many other contaminants is a most delicate task, often relying on results from other experiments. </p>
<p>This complex challenge will be tackled by the next generation of BICEP-like experiments such as the <a href="http://www.princeton.edu/act/">Atacama Cosmology Telescope</a> (ACT) and its planned successor AdvACT. They will be able to measure CMB to scales beyond the reach of Planck, and would have learned valuable lessons from BICEP in the modelling of dust and other contaminants. The prospects for detecting B-mode within the decade look very promising.</p>
<p>Some have even speculated that space interferometers <a href="http://arxiv.org/abs/1201.0983">might be able to</a> detect primordial waves, perhaps by subtracting the waves detected from known astrophysical processes.</p>
<h2>4. Gravitational waves would ‘prove’ the Big Bang</h2>
<p>The earliest source of gravitational waves is not the Big Bang, but rather <em>cosmological inflation</em>: a period during which the universe underwent a brief flash of exponential expansion just after the Big Bang. </p>
<p>The gravitational waves that BICEP2 claimed to have detected are the by-product of this burst of accelerating expansion of the universe. This is in accordance with general relativity, which <a href="http://www.space.com/11848-gravity-wave-detector-space-time.html">predicts that an accelerating body emits gravitational waves</a> (similar to the way an accelerating charge emits electromagnetic waves).</p>
<p>Inflation is currently regarded as the leading model of the early universe. While many key predictions of inflation have been verified, the predicted existence of primordial gravitational waves remains elusive. If they are observed, they will tell us directly about the energy scale at which inflation occurred, bringing us closer to understanding the Big Bang. But they would not prove the Big Bang, which is a mathematical singularity that we are yet to understand.</p>
<h2>5. We just need one experiment to detect them</h2>
<p>Strong statistical evidence for gravitational waves will certainly require more than one experiment. Like light waves, gravitational waves come in a spectrum of frequencies. The two detection techniques (B-modes and laser interferometry) are searching for waves at different frequencies – 15 orders of magnitude apart. </p>
<p>The simplest theory of inflation predicts a background of primordial gravitational waves with a particular frequency spectrum, in other words we know what the amplitude should be in each frequency. So, if scientists could detect gravitational waves on two of these very different frequencies, it would be strong evidence for inflation that is difficult to refute even by the most hardline sceptic. </p>
<h2>So is the search worth it?</h2>
<p>It is highly unlikely that the first generation of space interferometers would achieve the sensitivity required to detect primordial gravitational waves. Exactly what such a signal would look like is unknown and could, in principle, be forever out of reach by any future interferometers. </p>
<p>Nevertheless, if we could detect astrophysical gravitational waves directly, this would open up new ways to test the validity of Einstein’s theory of general relativity, which is used to describe gravitation in modern physics. The theory, which has been <a href="http://phys.org/news/2014-06-gun-gravity.html">questioned in recent years</a>), predicts the existence of gravitational waves.</p>
<p>It would also provide new insights into the evolution of stars, galaxies and black holes that we could never get any other way.</p>
<p><em>Read other articles in our cosmology series <a href="https://theconversation.com/uk/topics/cosmology-series">here</a></em>.</p>
<p>_This article was updated on January 12, 2016 to reflect latest developments.
_</p><img src="https://counter.theconversation.com/content/46493/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Siri Chongchitnan 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>Gravitational waves: are they worth the hype?Siri Chongchitnan, Lecturer in Mathematics, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/461572015-09-03T13:18:46Z2015-09-03T13:18:46ZThe fate of the universe: heat death, Big Rip or cosmic consciousness?<figure><img src="https://images.theconversation.com/files/93520/original/image-20150901-13443-kp3nxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes will be all that remains before the universe enters heath death. But the story doesn't end there...</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Future_of_an_expanding_universe#/media/File:BlackHole.jpg">NASA/ESA/wikimedia</a></span></figcaption></figure><p>By piecing together an increasing number of clues, cosmologists are getting closer to understanding what the future and ultimate fate of the universe will be. And I’m afraid the news is not good. Star formation will cease and black holes will take over until they eventually evaporate into nothingness. There could even be a “Big Rip” on the horizon. But for those who don’t mind waiting another 10<sup>10<sup>50</sup></sup> years or so, things may start to look up as a number of bizarre events could take place.</p>
<p>But before we consider random events in the very far future, let’s start with what we know about the past and the present. </p>
<h2>The past</h2>
<p>The reason we can investigate the past evolution of the universe is that, in some regards, astronomy is analogous to archaeology. Explicitly: the further we peer away from our home planet, the further back in time we see in to the universe. And when we look far back in time, we observe that galaxies are closer together than they are at present. Although only <a href="https://theconversation.com/one-funeral-at-a-time-big-bang-denial-and-the-search-for-truth-11127">one strand of evidence among many</a>, this observation – coupled with Einstein’s theory of general relativity – means that the <a href="https://theconversation.com/god-the-big-bang-next-please-1871">universe started with a Big Bang</a> and has been expanding ever since. </p>
<h2>The present</h2>
<p>Late last century, one of the most pressing issues in modern cosmology was to measure the deceleration rate of the universe. Given the amount of mass observed in the cosmos it was thought that it might be enough to cause an eventual contraction of the expansion. </p>
<p>Remarkably, two independent teams of scientists found the exact opposite. The universe was not slowing down in its expansion, it was accelerating. This <a href="https://theconversation.com/nobel-prize-win-tells-us-the-universe-is-accelerating-what-does-that-mean-3753">profound discovery</a> lead to the Nobel prize in physics in 2011. However, understanding the implications of it remains challenging. </p>
<p>One way to think about the accelerating universe is that there must be some kind of material (or field) that permeates the universe that exerts a negative pressure (or a repulsive gravity). We call this <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">dark energy</a>. </p>
<p>This may sound a bit far-fetched, but independent experiments have been conducted to corroborate the acceleration of the universe and the existence of dark energy. From 2006, I was involved in the <a href="http://wigglez.swin.edu.au/site/">WiggleZ Dark Energy Survey</a> – a scientific experiment to independently confirm the acceleration. Not only did we find that the acceleration is happening, but we provided compelling evidence that the cause of this was dark energy. We observed that dark energy was retarding the growth of massive superclusters of galaxies. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93521/original/image-20150901-13422-kchauj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The growth rate of superclusters like Virgo is providing strong evidence for the existence of dark energy.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:6_Virgo_Supercluster_%28blank%29.png">Andrew Z. Colvin/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We therefore suggested that <a href="http://wigglez.swin.edu.au/site/prmay2011_files/wigglez_mediarelease.pdf">dark energy is real</a>. If the concept of dark energy and its repulsive gravitation force is too weird, then an alternative to consider is that perhaps our theory of gravitation needs to be modified. This might be achieved in a similar way that relativity advanced Newtonian gravitation. Either way, we need new physics to explain it. </p>
<h2>The future</h2>
<p>Before turning to the very distant future, I will mention another relevant survey: <a href="http://www.gama-survey.org">GAMA</a>. Using that survey, we found that <a href="https://theconversation.com/dont-panic-but-the-universe-is-slowly-dying-45779">the universe is slowly “dying”</a>. Put another way: the peak era of star formation is well behind us, and the universe is already fading.</p>
<p>The more “immediate” future can be predicted with some certainty. Five billion years from now, the <a href="http://www.scientificamerican.com/article/the-sun-will-eventually-engulf-earth-maybe/">sun will enter its red giant phase</a>. Depressingly, no more than two more billion years after that, it will consume Earth.</p>
<p>After that, the relative strength of dark energy and how it might vary over time becomes important. The stronger and faster the repulsive force of dark energy is, the more likely it is that the universe will experience a <a href="http://www.telegraph.co.uk/news/science/science-news/11715091/Big-Rip-will-end-the-universe-scientists-claim.html">Big Rip</a>. Put bluntly: the Big Rip is what happens when the repulsive force of dark energy is able to overcome gravitation (and everything else). Bodies that are gravitationally bound (such as our local supercluster, our own Milky Way galaxy, our solar system, and eventually ourselves) <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.91.071301">become ripped apart</a> and all that is left is (probably) lonesome patches of vacuum.</p>
<p>The data from the WiggleZ survey and other experiments do not rule out the Big Rip, but push it in to the exceptionally far future (if at all). </p>
<p>Somewhat more pressing is the heat death of the universe. As the universe carries on expanding, we will no longer be able to observe galaxies outside our local group (100 million years from now). Star formation will then cease in about <a href="http://arxiv.org/abs/astro-ph/9701131">1-100 trillion years</a> as the supply of gas needed will be exhausted. While there will be some stars around, these will run out of fuel in some 120 trillion years. All that is left at that point is stellar remnants: black holes, neutron stars, & white dwarfs being the prime examples. One hundred quintillion (10<sup>20</sup>) years from now, most of these objects will be swallowed up by the supermassive <a href="https://theconversation.com/explainer-black-holes-7431">black holes</a> at the heart of galaxies. </p>
<p>In this way, the universe will get darker and quieter until there’s not much going on. What happens next will depend on how fast the matter in the universe decays. It is thought that protons, which make up atoms along with neutrons and electrons, spontaneously decay into subatomic particles if you just wait long enough. The time for all ordinary matter to disappear has been calculated to be 10<sup>40</sup> years from now. Beyond this, only black holes will remain. And even <a href="http://journals.aps.org/prd/abstract/10.1103/PhysRevD.13.198">they will evaporate away</a> after some 10<sup>100</sup> years. </p>
<p>At this point, the universe will be nearly a vacuum. Particles that remain, like electrons and light particles (photons), are then very far apart due to the universe’s expansion and rarely – if at all – interact. This is the true death of the universe, dubbed the “heat death”. </p>
<p>The idea comes from the <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html">second law of thermodynamics</a>, which states that entropy – a measure of “disorder” or the number of ways a system can be arranged – always increases. Any system, including the universe, will eventually evolve into a state of maximum disorder – just like a sugar cube will always dissolve in a cup of tea but would take an insanely long time to randomly go back to an orderly cube structure. When all the energy the in the cosmos is uniformly spread out, there is no more heat or free energy to fuel processes that consume energy, such as life.</p>
<h2>Boltzmann Brains and new Big Bangs</h2>
<p>All of the above seem very bleak to say the least. So I will end this article on a highly speculative, <a href="http://arxiv.org/abs/1405.0298">probably wrong</a>, completely untestable, but more positive, note. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93514/original/image-20150901-13401-gr8hdc.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">
<figcaption>
<span class="caption">Fishy? The far future of the universe could rather bizarre.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/akrockefeller/13892653941/in/photolist-naDu1e-6YrhaZ-4GXcBN-dJu9p4-aCRcEK-h7eHjh-dPu5Dj-dJu49c-dYqyPu-dPotf8-dQ9ijS-pGKkVe-p8ndvK-oRK77J-oRK73q-66vM1x-c2bt3J-oRJymP-9qKL2b-dYqzeW">AK Rockefeller/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>According to the strange rules of quantum mechanics, random things can pop up from a vacuum. And it is not just a mathematical quirk: the existence of particles suddenly coming into existence and then disappearing again is seen constantly in particle physics experiments. However, there is no reason why so-called “quantum fluctuations” could not give rise to an entire atom. </p>
<p>There has even been speculation that a “brain”, dubbed a <a href="https://www.newscientist.com/article/mg22229692.600-quantum-twist-could-kill-off-the-multiverse/">Boltzmann brain</a>, could be created in this context. The timescale for such a thing to appear? Well, that has been computed at <a href="http://iopscience.iop.org/article/10.1088/1475-7516/2007/01/022">10<sup>10<sup>50</sup></sup> years</a>.</p>
<p>And a new Big Bang? That could be on the way <a href="http://arxiv.org/abs/hep-th/0410270">in some 10<sup>10<sup>10<sup>56</sup></sup></sup> years</a>. </p>
<p><em>Read other stories from our cosmology series <a href="https://theconversation.com/uk/topics/cosmology-series">here</a></em></p><img src="https://counter.theconversation.com/content/46157/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Pimbblet does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>In about 10100 years, the universe will have passed away in a tragic ‘heat death’. But don’t despair, eventually random conscious brains may pop out in empty space to shake things up.Kevin Pimbblet, Senior Lecturer in Physics, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/464972015-09-02T13:29:06Z2015-09-02T13:29:06ZThe theory of parallel universes is not just maths – it is science that can be tested<figure><img src="https://images.theconversation.com/files/93501/original/image-20150901-25717-1y3igv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Scientists are searching for collisions between different 'universe bubbles' in the cosmic microwave background.</span> <span class="attribution"><a class="source" href="https://pixabay.com/en/globe-earth-country-continents-73397/">Geralt</a></span></figcaption></figure><p>The existence of parallel universes may seem like something cooked up by science fiction writers, with little relevance to modern theoretical physics. But the idea that we live in a “<a href="http://www.astronomy.pomona.edu/Projects/moderncosmo/Sean%27s%20mutliverse.html">multiverse</a>” made up of an infinite number of parallel universes has long been considered a scientific possibility – although <a href="https://www.quantamagazine.org/20150317-sciences-path-from-myth-to-multiverse/">it is still a matter of vigorous debate</a> among physicists. The race is now on to find a way to test the theory, including searching the sky for signs of collisions with other universes.</p>
<p>It is important to keep in mind that the multiverse view is not actually a theory, it is rather a consequence of our current understanding of theoretical physics. This distinction is crucial. We have not waved our hands and said: “Let there be a multiverse”. Instead the idea that the universe is perhaps one of infinitely many is derived from current theories like <a href="https://theconversation.com/explainer-quantum-physics-570">quantum mechanics</a> and <a href="https://theconversation.com/explainer-string-theory-2983">string theory</a>.</p>
<h2>The many-worlds interpretation</h2>
<p>You may have heard the thought experiment of <a href="http://news.nationalgeographic.com/news/2013/08/130812-physics-schrodinger-erwin-google-doodle-cat-paradox-science/">Schrödinger’s cat</a>, a spooky animal who lives in a closed box. The act of opening the box allows us to follow one of the possible future histories of our cat, including one in which it is both dead and alive. The reason this seems so impossible is simply because our human intuition is not familiar with it. </p>
<p>But it is entirely possible according to the strange rules of quantum mechanics. The reason that this can happen is that the space of possibilities in quantum mechanics is huge. Mathematically, a quantum mechanical state is a sum (or superposition) of all possible states. In the case of the Schrödinger’s cat, the cat is the superposition of “dead” and “alive” states. </p>
<p>But how do we interpret this to make any practical sense at all? One popular way is to think of all these possibilities as book-keeping devices so that the only “objectively true” cat state is the one we observe. However, one can just as well choose to accept that all these possibilities are true, and that they exist in different universes of a multiverse.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93451/original/image-20150831-25771-t0149q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Miaaaaultiverse.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/29233640@N07/8132455446">Robert Couse-Baker/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The string landscape</h2>
<p><a href="https://theconversation.com/explainer-string-theory-2983">String theory</a> is one of our most, if not the most promising avenue to be able to <a href="https://www.quantamagazine.org/20140314-betting-on-the-future-of-quantum-gravity/">unify quantum mechanics and gravity</a>. This is notoriously hard because gravitational force is so difficult to describe on small scales like those of atoms and subatomic particles – which is the science of quantum mechanics. But string theory, which states that all fundamental particles are made up of one-dimensional strings, can describe all known forces of nature at once: gravity, electromagnetism and the nuclear forces.</p>
<p>However, for string theory to work mathematically, it requires at least ten physical dimensions. Since we can only observe four dimensions: height, width, depth (all spatial) and time (temporal), the extra dimensions of string theory must therefore be hidden somehow if it is to be correct. To be able to use the theory to explain the physical phenomena we see, these extra dimensions have to be “compactified” by being curled up in such a way that they are too small to be seen. Perhaps for each point in our large four dimensions, there exists six extra indistinguishable directions?</p>
<p>A problem, or some would say, a feature, of string theory is that there are many ways of doing this compactification –<a href="http://events.nytimes.com/2005/06/26/weekinreview/26read.html?ei=5070&en=305a968fba809092&ex=1121918400&pagewanted=print">10<sup>500</sup> possibilities is one number usually touted about</a>. Each of these compactifications will result in a universe with different physical laws – such as different masses of electrons and different constants of gravity. However there are also vigorous <a href="http://content.time.com/time/magazine/article/0,9171,1226142,00.html">objections to the methodology</a> of compactification, so the issue is not quite settled.</p>
<p>But given this, the obvious question is: which of these landscape of possibilities do we live in? String theory itself does not provide a mechanism to predict that, which makes it useless as we can’t test it. But fortunately, an idea from our study of early universe cosmology has turned this bug into a feature. </p>
<h2>The early universe</h2>
<p>During the very early universe, just after the Big Bang, the universe underwent a <a href="http://www.ctc.cam.ac.uk/outreach/origins/inflation_zero.php">period of accelerated expansion</a> called inflation. Inflation was invoked originally to explain why the current observational universe is <a href="http://www.physicsoftheuniverse.com/topics_bigbang_inflation.html">almost uniform in temperature</a>. However, the theory also predicted a spectrum of temperature fluctuations around this equilibrium which was later confirmed by several spacecraft such as <a href="http://aether.lbl.gov/www/projects/cobe/">Cosmic Background Explorer</a>, <a href="http://map.gsfc.nasa.gov/">Wilkinson Microwave Anisotropy Probe</a> and the <a href="http://www.esa.int/Our_Activities/Space_Science/Planck">PLANCK spacecraft</a>.</p>
<p>While the exact details of the theory are still being hotly debated, inflation is widely accepted by physicists. However, a consequence of this theory is that there must be other parts of the universe that are still accelerating. However, due to the quantum fluctuations of space-time, some parts of the universe never actually reach the end state of inflation. This means that the universe is, at least according to our current understanding, eternally inflating. Some parts can therefore end up becoming other universes, which could become other universes etc. This mechanism generates a infinite number of universes.</p>
<p>By combining this scenario with string theory, there is a possibility that each of these universes possesses a different compactification of the extra dimensions and hence has different physical laws. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93458/original/image-20150831-25714-1r7rvpt.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">
<figcaption>
<span class="caption">The cosmic microwave background. Scoured for gravitational waves and signs of collisions with other universes.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:WMAP_2010_41GHz.png">NASA / WMAP Science Team/wikimedia</a></span>
</figcaption>
</figure>
<h2>Testing the theory</h2>
<p>The universes predicted by string theory and inflation live in the same physical space (unlike the many universes of quantum mechanics which live in a mathematical space), they can overlap or collide. Indeed, they inevitably must collide, <a href="http://discovermagazine.com/2009/oct/04-will-our-universe-collide-with-neighboring-one">leaving possible signatures</a> in the cosmic sky which we can try to search for.</p>
<p>The exact details of the signatures depends intimately on the models – ranging from <a href="http://fqxi.org/community/articles/display/155">cold or hot spots</a> in the cosmic microwave background to anomalous voids in the distribution of galaxies. Nevertheless, since collisions with other universes must occur in a particular direction, a general expectation is that any signatures will break the uniformity of our observable universe. </p>
<p>These signatures are actively being pursued by scientists. Some are looking for it directly through <a href="https://www.ucl.ac.uk/news/news-articles/1108/110802-first-test-of-multiverse">imprints in the cosmic microwave background</a>, the afterglow of the Big Bang. However, no such signatures are yet to be seen. Others are looking for indirect support such as gravitational waves, which are ripples in space-time as massive objects pass through. Such waves could directly prove the existence of inflation, which ultimately strengthens the support for the multiverse theory. </p>
<p>Whether we will ever be able to prove their existence is hard to predict. But given the massive implications of such a finding it should definitely be worth the search.</p>
<p><em>Read other articles from our cosmology series <a href="https://theconversation.com/uk/topics/cosmology-series">here</a>.</em></p><img src="https://counter.theconversation.com/content/46497/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eugene Lim receives funding from UK STFC and FQXi.</span></em></p>The idea that our universe is just one in a ‘multiverse’ of parallel universes is increasingly gathering attention from cosmologists. But can we ever test the theory?Eugene Lim, Lecturer in theoretical particle physics & cosmology, King's College LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/469532015-09-01T18:00:28Z2015-09-01T18:00:28ZMove over Milky Way, elliptical galaxies are the most habitable in the cosmos<figure><img src="https://images.theconversation.com/files/93548/original/image-20150901-13422-iotrh.jpg?ixlib=rb-1.1.0&rect=12%2C505%2C2846%2C2204&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Elliptical galaxy SDSS J162702.56+432833.9 could be full of life.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Elliptical_galaxy#/media/File:SDSS_J162702.56%2B432833.9.jpg">NASA/ESA/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The search for extraterrestrial life is surely one of the most important tasks we humans can undertake. However, the cosmos is vast and we don’t really have any idea which bits of it are actually habitable. But what if we could target the search? We have built the <a href="http://iopscience.iop.org/2041-8205/810/1/L2/article;jsessionid=35758CF547C6B0BE721637C07F4EB179.c1">first-ever “cosmobiological” model</a> mapping the galaxies in our local universe to help us understand which ones are habitable. Surprisingly, we found that our own galaxy was not one of the top candidates.</p>
<h2>Ingredients for habitability</h2>
<p>Drawing on our understanding of habitable zones within a galaxy, we proposed that the overall habitability of any galaxy depends on three key astrophysical criteria. One is simply the total number of stars capable of hosting planets, which is roughly related to the size of the galaxy. Another is the total amount of the building blocks of planets and life – such as carbon, oxygen and iron – the so-called astrophysical “metals”. Another is the negative influence of supernova explosions, whose powerful (and poisonous) radiation could potentially <a href="http://www.nature.com/nature/journal/v265/n5592/abs/265318a0.html">inhibit the formation and evolution of complex life</a> on nearby planets.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.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">Not so special anymore. Artist s impression of the Milky Way.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Milky_Way#/media/File:Artist%27s_impression_of_the_Milky_Way_%28updated_-_annotated%29.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Interestingly, the largest survey of its kind ever undertaken, data from the <a href="http://www.sdss.org/">Sloan Digital Sky Survey</a> observes exactly these three key properties for more than 150,000 galaxies in the nearby universe. This data shows that the largest galaxies have the largest amount of metals. Sifting through this data set we found that giant <a href="http://www.space.com/22395-elliptical-galaxies.html">elliptical galaxies</a>, which have a rounded shape rather than spiral arms like our Milky Way, win the “most-likely-to-be-habitable” title. Indeed, each giant elliptical that is at least twice as big as the Milky Way and has a tenth of its supernova rate could potentially host 10,000 times as many habitable (Earth-like) planets. </p>
<p>Our results, <a href="http://iopscience.iop.org/2041-8205/810/1/L2/article;jsessionid=35758CF547C6B0BE721637C07F4EB179.c1">recently published</a> in the Astrophysical Journal Letters, also show that they typically have a low rate of supernova explosions, ensuring that most of these planets remain unmolested by harmful radiation.</p>
<p>This is the first computation that discusses life on cosmological scales, rather than just within individual galaxies like the Milky Way. The model therefore opens up a new avenue, extending the understanding of habitability around individual stars to a true “cosmobiological” context, which allows us to discuss the habitability of the entire universe. </p>
<p>One of the most attractive features of the model is that that data used includes the entire history of all the galaxies in the universe that we see around us. The relationship between the number of stars, amount of metals and rate of supernova explosions essentially acts as the “fingerprint”, uniquely identifying how any given galaxy formed. This is a key bit of information that we need to understand the chances of galactic habitability and which has been missing in this field. </p>
<h2>Are we in the wrong galaxy?</h2>
<p>By all accounts, our Milky Way is a typical <a href="http://cas.sdss.org/dr6/en/proj/basic/galaxies/spirals.asp">spiral galaxy</a> of average size that roughly makes one star like our sun every year. Given that ellipticals are much more hospitable to habitable planets raises the interesting question of whether life here in the Milky Way is just a freak of nature. </p>
<p>Or does the presence of life on at least one planet in the Milky Way imply that these big elliptical galaxies might be absolutely teeming with life?</p>
<p>One drawback is that the nearest elliptical galaxy to the Milky Way, called <a href="http://www.astr.ua.edu/gifimages/maffei1.html">Maffei1</a>, is so far away that any radio signals beamed from this cosmic neighbour would take 9m years to reach us. Surveys such as the <a href="https://theconversation.com/its-not-all-about-aliens-listening-project-may-unveil-other-secrets-of-the-universe-45031">SETI (Search for Extraterrestrial Intelligence)</a> that continually maps the skies for anomalous signals might one day detect such a signal in the far future, a call to us from our (not so) nearest neighbours. </p>
<p><em>Read other articles from our cosmology series <a href="https://theconversation.com/uk/topics/cosmology-series">here</a></em></p><img src="https://counter.theconversation.com/content/46953/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Pratika Dayal does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new model suggests that elliptical galaxies are more likely to be habitable than spiral galaxies like our own. Does that mean we’re a freak event and elsewhere is teeming with life?Pratika Dayal, Addison Wheeler Fellow in Cosmology, Durham UniversityLicensed as Creative Commons – attribution, no derivatives.