tag:theconversation.com,2011:/nz/topics/theoretical-physics-7109/articlesTheoretical physics – The Conversation2023-07-26T12:15:06Ztag:theconversation.com,2011:article/2058912023-07-26T12:15:06Z2023-07-26T12:15:06ZMeasuring helium in distant galaxies may give physicists insight into why the universe exists<figure><img src="https://images.theconversation.com/files/537554/original/file-20230714-21948-g2t785.jpg?ixlib=rb-1.1.0&rect=60%2C0%2C6698%2C4489&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New measurements from Japan's Subaru telescope have helped researchers study the matter-antimatter asymmetry problem. </span> <span class="attribution"><a class="source" href="https://media.gettyimages.com/id/1335056886/photo/andromeda-galaxy-surrounded-by-stars.jpg?s=612x612&w=0&k=20&c=yhgVDZmt3gODQx_vm9nzfweVT8-WzwwOpxJehbnynrI=">Javier Zayas Photography/Moment via Getty</a></span></figcaption></figure><p>When theoretical physicists like myself say that we’re studying why the universe exists, we sound like philosophers. But new data collected by researchers using Japan’s <a href="https://subarutelescope.org/en/">Subaru telescope</a> has revealed insights into that very question.</p>
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<a href="https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cylindrical building sitting on a cliff overlooking a sunset." src="https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/538069/original/file-20230718-7668-yp1ts1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Japan’s Subaru telescope, located on Mauna Kea in Hawaii.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Subaru_Telescope._Mauna_Kea_Summit_-_panoramio.jpg">Panoramio/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p><a href="https://science.nasa.gov/astrophysics/focus-areas/what-powered-the-big-bang">The Big Bang</a> <a href="https://theconversation.com/how-could-an-explosive-big-bang-be-the-birth-of-our-universe-128430">kick-started the universe</a> as we know it 13.8 billion years ago. <a href="https://www.slac.stanford.edu/pubs/beamline/26/1/26-1-sather.pdf">Many theories</a> in particle physics suggest that for all the matter created at the universe’s conception, an equal amount of antimatter should have been created alongside it. Antimatter, like matter, has mass and takes up space. However, antimatter particles exhibit the opposite properties of their corresponding matter particles. </p>
<p>When pieces of matter and antimatter collide, they <a href="https://home.cern/science/physics/matter-antimatter-asymmetry-problem">annihilate each other in a powerful explosion</a>, leaving behind only energy. The puzzling thing about theories that predict the creation of an equal balance of matter and antimatter is that if they were true, the two would have totally annihilated each other, leaving the universe empty. So there must have been more matter than antimatter at the birth of the universe, because the universe isn’t empty – it’s full of stuff that’s made of matter like galaxies, stars and planets. A little bit of antimatter <a href="https://www.energy.gov/science/doe-explainsantimatter">exists around us</a>, but it is very rare. </p>
<p>As a <a href="https://inspirehep.net/authors/2064347">physicist working on Subaru data</a>, I’m interested in this so-called <a href="https://home.cern/science/physics/matter-antimatter-asymmetry-problem">matter-antimatter asymmetry problem</a>. In our <a href="https://doi.org/10.1103/PhysRevLett.130.131001">recent study</a>, my collaborators and I found that the telescope’s new measurement of the amount and type of helium in faraway galaxies may offer a solution to this long-standing mystery.</p>
<h2>After the Big Bang</h2>
<p>In the first milliseconds after the Big Bang, the universe was hot, dense and full of elementary particles like protons, neutrons and electrons <a href="https://www.space.com/25126-big-bang-theory.html">swimming around in a plasma</a>. Also present in this pool of particles were <a href="https://theconversation.com/explainer-the-elusive-neutrino-431">neutrinos</a>, which are very tiny, weakly interacting particles, and antineutrinos, their antimatter counterparts.</p>
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<a href="https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image showing a burst of light and color against black space and stars." src="https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537553/original/file-20230714-27-ymcvpp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The Big Bang created fundamental particles that make up other particles like protons and neutrons. Neutrinos are another type of fundamental particle.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/big-bang-conceptual-image-royalty-free-illustration/639549057?phrase=the%20big%20bang">Alfred Pasieka/Science Photo Library via Getty Images</a></span>
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<p>Physicists believe that just one second after the Big Bang, the nuclei of light <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">elements like hydrogen</a> and helium began to form. This process is known as <a href="https://w.astro.berkeley.edu/%7Emwhite/darkmatter/bbn.html">Big Bang Nucleosynthesis</a>. The nuclei formed were about <a href="https://science.howstuffworks.com/dictionary/astronomy-terms/big-bang-theory5.htm">75% hydrogen nuclei and 24% helium nuclei</a>, plus small amounts of heavier nuclei. </p>
<p>The physics community’s <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/bbnuc.html">most widely accepted theory</a> on the formation of these nuclei tells us that neutrinos and antineutrinos played a fundamental role in the creation of, in particular, helium nuclei. </p>
<p>Helium creation in the early universe happened in a two-step process. First, neutrons and protons converted from one to the other in a <a href="https://ned.ipac.caltech.edu/level5/March04/Steigman3/Steigman2.html">series of processes</a> involving neutrinos and antineutrinos. As the universe cooled, these processes stopped and the <a href="https://ned.ipac.caltech.edu/level5/March04/Steigman3/Steigman2.html">ratio of protons to neutrons was set</a>. </p>
<p>As theoretical physicists, we can create models to test how the ratio of protons to neutrons depends on the relative number of neutrinos and antineutrinos in the early universe. If <a href="https://doi.org/10.1103/PhysRevLett.130.131001">more neutrinos were present</a>, then our models show more protons and fewer neutrons would exist as a result. </p>
<p>As the universe cooled, hydrogen, helium and other elements <a href="https://ned.ipac.caltech.edu/level5/March04/Steigman3/Steigman2.html">formed from these protons and neutrons</a>. Helium is made up of two protons and two neutrons, and hydrogen is just one proton and no neutrons. So the fewer the neutrons available in the early universe, the less helium would be produced.</p>
<p>Because the nuclei formed during Big Bang Nucleosynthesis <a href="https://doi.org/10.1103/PhysRevLett.130.131001">can still be observed today</a>, scientists can infer how many neutrinos and antineutrinos were present during the early universe. They do this by looking specifically at galaxies that are rich in light elements like hydrogen and helium.</p>
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<img alt="A diagram showing how protons and neutrons form helium atoms." src="https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537555/original/file-20230714-25-rbf648.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">In a series of high-energy particle collisions, elements like helium are formed in the early universe. Here, D stands for deuterium, an isotope of hydrogen with one proton and one neutron, and γ stands for photons, or light particles. In the series of chain reactions shown, protons and neutrons fuse to form deuterium, then these deuterium nuclei fuse to form helium nuclei.</span>
<span class="attribution"><span class="source">Anne-Katherine Burns</span></span>
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<h2>A clue in helium</h2>
<p>Last year, the Subaru Collaboration – a group of Japanese scientists working on the Subaru telescope – released data on <a href="https://doi.org/10.3847/1538-4357/ac9ea1">10 galaxies</a> far outside of our own that are almost exclusively made up of hydrogen and helium. </p>
<p>Using a technique that allows researchers to distinguish different elements from one another <a href="https://theconversation.com/explainer-seeing-the-universe-through-spectroscopic-eyes-37759">based on the wavelengths of light</a> observed in the telescope, the Subaru scientists determined exactly how much helium exists in each of these 10 galaxies. Importantly, they found less helium than the previously accepted theory predicted. </p>
<p>With this new result, my collaborators and I worked backward to find the <a href="https://doi.org/10.1103/PhysRevLett.130.131001">number of neutrinos and antineutrinos</a> necessary to produce the helium abundance found in the data. Think back to your ninth grade math class when you were asked to solve for “X” in an equation. What my team did was essentially the more sophisticated version of that, where our “X” was the number of neutrinos or antineutrinos.</p>
<p>The previously accepted theory predicted that there should be the same number of neutrinos and antineutrinos in the early universe. However, when we tweaked this theory to give us a prediction that matched the new data set, <a href="https://doi.org/10.1103/PhysRevLett.130.131001">we found that</a> the number of neutrinos was greater than the number of antineutrinos.</p>
<h2>What does it all mean?</h2>
<p>This analysis of new helium-rich galaxy data has a far-reaching consequence – it can be used to explain the asymmetry between matter and antimatter. The Subaru data points us directly to a source for that imbalance: neutrinos. In this study, my collaborators and I proved that this new measurement of helium is consistent with there being more neutrinos then antineutrinos in the early universe. Through <a href="https://doi.org/10.1103/PhysRevLett.130.131001">known and likely particle physics processes</a>, the asymmetry in the neutrinos could propagate into an asymmetry in all matter. </p>
<p>The result of our study is a common type of result in the theoretical physics world. Basically, we discovered a viable way in which the matter-antimatter asymmetry could have been produced, but that doesn’t mean it definitely was produced in that way. The fact that the data fits with our theory is a hint that the theory we’ve proposed might be the correct one, but this fact alone doesn’t mean that it is. </p>
<p>So, are these tiny little neutrinos the key to answering the age old question, “Why does anything exist?” According to this new research, they just might be.</p><img src="https://counter.theconversation.com/content/205891/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anne-Katherine Burns 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 way particles interacted while the universe was forming seconds after the Big Bang could explain why the universe exists the way it does – a physicist explains matter-antimatter asymmetry.Anne-Katherine Burns, Ph.D. Candidate in Theoretical Particle Physics, University of California, IrvineLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2030102023-05-15T15:43:17Z2023-05-15T15:43:17ZTheory of everything: how progress in physics depends on asking the right questions<figure><img src="https://images.theconversation.com/files/524343/original/file-20230504-29-15yttd.jpg?ixlib=rb-1.1.0&rect=152%2C197%2C5838%2C5793&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Calabi-Yau manifold: a proposed structure of extra dimensions of space in string theory. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/calabiyau-manifold-structure-extra-dimensions-space-1228700050">vchal/Shutterstock</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/64353c62de066f001110361d" frameborder="0" width="100%" height="190px"></iframe>
<p><iframe id="tc-infographic-807" class="tc-infographic" height="100px" src="https://cdn.theconversation.com/infographics/807/1668471fb1e76a459995c87bd439c36b04b754ac/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>When I began my undergraduate physics degree (around 20 years ago), “What is the <a href="https://theconversation.com/great-mysteries-of-physics-do-we-really-need-a-theory-of-everything-203534">theory of everything</a>?” was a question that I heard often. It was used as a label for how theoretical physicists were trying to develop a deeper understanding of the elementary building blocks of our universe and the forces that govern their dynamics.</p>
<p>But is it a good question? Is it helpful in guiding scientists towards the discoveries that will advance our understanding to the next level? After all, good science relies on asking good questions. Or is it just <a href="https://bigthink.com/starts-with-a-bang/theories-of-everything/">“wishful thinking”</a>?</p>
<p>Arguably, the question “What is the theory of everything?” reminds us that good science doesn’t have to start with the best questions. Let me explain what I mean.</p>
<p>Suppose we play a game. I have a deck of cards, and each card is printed with the name and a photograph of a different animal. I choose a card, and your job is to ask questions to find out which animal I have chosen. Of course, to ask a discerning question, you first need to know something about animals.</p>
<p>The first time you play, you may not be familiar with which animals are in the deck, and your first question is “Does it live in the sea?”. My answer is “No,” and the game continues. Then it is your turn to pick a card. You look carefully through the deck to make your choice, and you realise that it only contains land animals. “Does it live in the sea?” seemed like a good question to start with, but it was not.</p>
<p>We take turns, and the more we play, the quicker we seem to figure out which card has been chosen. Why? We have become better at asking good questions.</p>
<p>The role that questions play in scientific research is similar. We start from some level of understanding, and we ask questions based on that level of understanding to try to improve it. As our understanding builds, we refine our questions and get more insightful answers.</p>
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<img alt="" src="https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513939/original/file-20230307-20-pgea9d.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">
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<p><em>This is article is accompanied by a podcast series called <a href="https://podfollow.com/great-mysteries-of-physics">Great Mysteries of Physics</a> which uncovers the greatest mysteries facing physicists today – and discusses the radical proposals for solving them.</em></p>
<hr>
<p>This is how progress is made. The same is true of asking “What is the theory of everything?”: the goodness of a scientific question is not immutable.</p>
<h2>Why a ‘theory of everything’?</h2>
<p>The <a href="https://home.cern/tags/standard-model#:%7E:text=The%20Standard%20Model%20of%20particle,of%20scientists%20around%20the%20world.">Standard Model of Particle Physics</a>, one <a href="https://theconversation.com/the-standard-model-of-particle-physics-may-be-broken-an-expert-explains-182081">of the pillars of modern science</a>, is a success of reductionism - the idea that things can be explained by breaking them down into smaller parts.</p>
<p>The model, which is written in a mathematical language called <a href="https://www.damtp.cam.ac.uk/user/tong/whatisqft.html">quantum field theory</a>, describes how elementary particles move around and interact with one another. It explains the nature of three out of four of the known fundamental forces: electromagnetism, and the weak and strong forces that govern processes on subatomic scales. It does not include gravity, the fourth force.</p>
<p>The model accounts for <a href="https://theconversation.com/great-mysteries-of-physics-4-does-objective-reality-exist-202550">quantum mechanics</a>, which describes the probabilistic nature of the dynamics of subatomic particles, and Einstein’s special theory of relativity, which describes what happens when relative speeds are close to the speed of light – no small achievement.</p>
<p>The assumption in asking “What is the theory of everything?” is that the Standard Model will one day be found to be embedded within a larger structure (with more elemental ingredients) that provides us with a unified explanation of the fundamental forces including gravity. Gravity, in fact, is this question’s ultimate focus. </p>
<p>But the question “What is the theory of everything?” gives very little guidance as to what such a theory of everything might look like. We need some better questions.</p>
<p>Now, there are good reasons to expect that such a unified explanation of the fundamental forces might exist: the Standard Model includes the celebrated Higgs mechanism, from which the <a href="https://theconversation.com/higgs-boson-ten-years-after-its-discovery-why-this-particle-could-unlock-new-physics-beyond-the-standard-model-186076">Higgs boson</a> arises. It explains why fundamental particles known as the W and Z bosons, which transmit the weak force, acquire a mass. It also explains why the photon, which transmits the electromagnetic force, does not.</p>
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<img alt="CMS experiment at Cern." src="https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524347/original/file-20230504-17-wd6j6c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&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">CMS experiment at Cern.</span>
<span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>As a result, electromagnetism and the weak force, which is involved in the nuclear fusion that powers stars, behave differently at low energies: the electromagnetic force acts over very large distances, whereas the weak force acts only over very short distances. The Higgs mechanism also explains why, at higher energies, these two forces start to behave as a single “electroweak” force. This is called electroweak unification.</p>
<p>Now, if electromagnetism and the weak force combine in this way, why not all the forces in the Standard Model? Unifying these two with the strong force, the force that holds the ingredients of atomic nuclei together, is the aim of grand unified theories. Theoretical ideas such as <a href="https://home.cern/science/physics/supersymmetry">supersymmetry</a>, which postulates a symmetry between force carriers and matter particles, suggest that <a href="https://bigthink.com/starts-with-a-bang/theories-of-everything/">the strength of these three forces could get tantalisingly close at high enough energies</a>.</p>
<p>And if the electromagnetic, weak and strong forces turn out to be unified, why not gravity, too?</p>
<p>Gravity is described by <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">Einstein’s General Theory of Relativity</a>, which applies on large scales or at low energies. But if we want a consistent quantum theory of gravity that applies on the smallest scales, quantum field theory isn’t enough. We need mathematical frameworks that can consistently incorporate both general relativity and quantum mechanics.</p>
<p>The “everything” in a “theory of everything” refers to all the known forces of nature: electromagnetism, the weak force, the strong force, and gravity (and new, <a href="https://theconversation.com/new-physics-latest-results-from-cern-further-boost-tantalising-evidence-170133">hypothetical forces</a>, too) and the particles that they act between. The “theory” refers to the existence of some common mathematical framework that describes all of the “everything”.</p>
<p>One such common mathematical framework is <a href="https://theconversation.com/stephen-hawking-had-pinned-his-hopes-on-m-theory-to-fully-explain-the-universe-heres-what-it-is-93440">string theory</a>, which supposes that the most fundamental building blocks of the universe are tiny strings that vibrate in extra spatial dimensions beyond the three of our everyday experience. </p>
<h2>Better questions</h2>
<p>Questions are the guide to scientific inquiry. The question “What is the theory of everything?” only speculates at a destination, but it gives very little direction.</p>
<p>Frameworks such as supersymmetry and string theory were not developed to answer the question “What is the theory of everything?” directly. They were motivated by better questions about what a theory of all the fundamental forces needs to explain and what it might look like, questions like: Why is there a huge discrepancy between the energy scales of the Standard Model and quantum gravity? Why do quantum mechanics and general relativity seem to be incompatible?</p>
<p>But the “whys” that theoretical physicists ask develop as our understanding develops, and the questions that we are now posing are getting us even closer than ever to an understanding of all the known forces of nature. </p>
<p>These new “whys” hint at <a href="https://doi.org/10.48550/arXiv.2006.06872">remarkable connections between very different areas of physics and mathematics</a>: Why does the physics of holograms seem to help us to understand gravity? Why does this seem to be connected to the properties of large collections of random numbers? Why do the rules of quantum information seem to explain the physics of black holes?</p>
<p>But this is not a case of “out with the old and in with the new”. Instead, these new questions have been reached by building on what has been learnt from developing and studying possible “Theories of Everything”, like string theory.</p>
<p>And these new questions are good questions. The exciting thing is that they still may not be the best questions, and having them to guide us doesn’t necessarily mean that we know where we will end up. That is what scientific discovery is all about.</p>
<p><em>You can listen to Great Mysteries of Physics via any of the apps listed above, our <a href="https://feeds.acast.com/public/shows/638f4b009a65b10011b94c5e">RSS feed</a>, or find out how else to listen here. You can also read a <a href="https://cdn.theconversation.com/static_files/files/2634/MoP__Ep6_-_Theory_of_Everything_TRANSCRIPT.docx.pdf?1681292977">transcript of the episode here</a>.</em></p><img src="https://counter.theconversation.com/content/203010/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Millington is a Senior Research Fellow in the Particle Theory Group at the University of Manchester, UK, where he holds a UK Research and Innovation Future Leaders Fellowship and a Royal Society International Exchanges Grant. Peter Millington is a Member of the Institute of Physics, UK and serves on the Institute of Physics High Energy Particle Physics Group Committee.</span></em></p>Good questions guide good science, but that doesn’t mean we know where we’ll end up.Peter Millington, Senior Research Fellow and UKRI Future Leaders Fellow in the Particle Theory Group, Department of Physics and Astronomy, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1919272022-10-06T17:51:10Z2022-10-06T17:51:10ZWhat is quantum entanglement? A physicist explains the science of Einstein’s ‘spooky action at a distance’<figure><img src="https://images.theconversation.com/files/488150/original/file-20221004-12421-klkh40.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5064%2C3294&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When two particles are entangled, the state of one is tied to the state of the other. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/quantum-entanglement-conceptual-artwork-royalty-free-illustration/1333715460">Victor de Schwanberg/Science Photo Library via Getty Images</a></span></figcaption></figure><p>The <a href="https://theconversation.com/nobel-prize-physicists-share-prize-for-insights-into-the-spooky-world-of-quantum-mechanics-191884">2022 Nobel Prize in physics</a> recognized three scientists who made groundbreaking contributions in understanding one of the most mysterious of all natural phenomena: quantum entanglement.</p>
<p>In the simplest terms, quantum entanglement means that aspects of one particle of an entangled pair depend on aspects of the other particle, no matter how far apart they are or what lies between them. These particles could be, for example, electrons or photons, and an aspect could be the state it is in, such as whether it is “spinning” in one direction or another.</p>
<p>The strange part of quantum entanglement is that when you measure something about one particle in an entangled pair, you immediately know something about the other particle, even if they are millions of light years apart. This odd connection between the two particles is instantaneous, <a href="https://doi.org/10.1103/PhysRev.47.777">seemingly breaking a fundamental law of the universe</a>. Albert Einstein famously called the phenomenon “spooky action at a distance.”</p>
<p>Having spent the better part of <a href="https://scholar.google.com/citations?user=r8sBeycAAAAJ&hl=en&oi=ao">two decades conducting experiments rooted in quantum mechanics</a>, I have come to accept its strangeness. Thanks to ever more precise and reliable instruments and the work of this year’s Nobel winners, <a href="https://scholar.google.com/citations?user=-6d6dV4AAAAJ&hl=en&oi=sra">Alain Aspect</a>, <a href="https://scholar.google.com/citations?user=BDm2SGcAAAAJ&hl=en&oi=ao">John Clauser</a> and <a href="https://scholar.google.com/citations?user=cuqIY0oAAAAJ&hl=en&oi=ao">Anton Zeilinger</a>, physicists now integrate quantum phenomena into their knowledge of the world with an exceptional degree of certainty.</p>
<p>However, even until the 1970s, researchers were still divided over whether quantum entanglement was a real phenomenon. And for good reasons – who would dare contradict the great Einstein, who himself doubted it? It took the development of new experimental technology and bold researchers to finally put this mystery to rest.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cat sitting in a box." src="https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488154/original/file-20221004-18-6uzgqx.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">According to quantum mechanics, particles are simultaneously in two or more states until observed – an effect vividly captured by Schrödinger’s famous thought experiment of a cat that is both dead and alive simultaneously.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cat_in_a_box_2.jpg#/media/File:Cat_in_a_box_2.jpg">Michael Holloway/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Existing in multiple states at once</h2>
<p>To truly understand the spookiness of quantum entanglement, it is important to first understand <a href="https://doi.org/10.1103/RevModPhys.71.S288">quantum superposition</a>. Quantum superposition is the idea that particles exist in multiple states at once. When a measurement is performed, it is as if the particle selects one of the states in the superposition.</p>
<p>For example, many particles have an attribute called spin that is measured either as “up” or “down” for a given orientation of the analyzer. But until you measure the spin of a particle, it simultaneously exists in a superposition of spin up and spin down.</p>
<p>There is a probability attached to each state, and it is possible to predict the average outcome from many measurements. The likelihood of a single measurement being up or down depends on these probabilities, <a href="https://theconversation.com/could-schrodingers-cat-exist-in-real-life-our-research-may-provide-the-answer-147752">but is itself unpredictable</a>.</p>
<p>Though very weird, the mathematics and a vast number of experiments have shown that quantum mechanics correctly describes physical reality.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of Albert Einstein" src="https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=774&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=774&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=774&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=973&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=973&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488577/original/file-20221006-18-bitlqh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=973&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Albert Einstein, Boris Podolsky and Nathan Rosen pointed out an apparent problem with quantum entanglement in 1935 that prompted Einstein to describe quantum entanglement as ‘spooky action at a distance.’</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Einstein-formal_portrait-35.jpg#/media/File:Einstein-formal_portrait-35.jpg">Sophie Dela/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>Two entangled particles</h2>
<p>The <a href="https://doi.org/10.1103/PhysRev.48.696">spookiness of quantum entanglement</a> emerges from the reality of quantum superposition, and was clear to the founding fathers of quantum mechanics who developed the theory in the 1920s and 1930s.</p>
<p>To create entangled particles you essentially break a system into two, where the sum of the parts is known. For example, you can split a particle with spin of zero into two particles that necessarily will have opposite spins so that their sum is zero. </p>
<p>In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen <a href="https://doi.org/10.1103/PhysRev.47.777">published a paper</a> that describes a thought experiment designed to illustrate a <a href="https://doi.org/10.1103/PhysRev.47.777">seeming absurdity of quantum entanglement</a> that challenged a foundational law of the universe.</p>
<p>A <a href="https://doi.org/10.1103/PhysRev.48.696">simplified version of this thought experiment</a>, attributed to David Bohm, considers the decay of a particle called the pi meson. When this particle decays, it produces an electron and a positron that have opposite spin and are moving away from each other. Therefore, if the electron spin is measured to be up, then the measured spin of the positron could only be down, and vice versa. This is true even if the particles are billions of miles apart.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two blue circles with an arrow pointing up and an arrow pointing down." src="https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488317/original/file-20221005-23-t916hd.jpg?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">Entanglement can be created between a pair of particles with one measured as spin up and the other as spin down.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/spin-quantum-physics-and-computing-concept-royalty-free-image/1346594645?phrase=particle%20spin%20physics&adppopup=true">atdigit/iStock via Getty Images</a></span>
</figcaption>
</figure>
<p>This would be fine if the measurement of the electron spin were always up and the measured spin of the positron were always down. But because of quantum mechanics, the spin of each particle is both part up and part down until it is measured. Only when the measurement occurs does the quantum state of the spin “collapse” into either up or down – instantaneously collapsing the other particle into the opposite spin. This seems to suggest that the particles communicate with each other through some means that moves faster than the speed of light. But according to the laws of physics, nothing can travel faster than the speed of light. Surely the measured state of one particle cannot instantaneously determine the state of another particle at the far end of the universe?</p>
<p>Physicists, including Einstein, proposed a number of alternative interpretations of quantum entanglement in the 1930s. They theorized there was some unknown property – dubbed hidden variables – <a href="https://doi.org/10.1103/PhysRev.47.777">that determined the state of a particle before measurement</a>. But at the time, physicists did not have the technology nor a definition of a clear measurement that could test whether quantum theory needed to be modified to include hidden variables.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of John Stuart Bell in front of a chalkboard." src="https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=609&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=609&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=609&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=766&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=766&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488613/original/file-20221006-18-cedhj0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=766&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">John Bell, an Irish physicist, came up with the means to test the reality of whether quantum entanglement relied on hidden variables.</span>
<span class="attribution"><a class="source" href="https://cds.cern.ch/record/1823937">CERN</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Disproving a theory</h2>
<p>It took until the 1960s before there were any clues to an answer. John Bell, a brilliant Irish physicist who did not live to receive the Nobel Prize, devised a scheme to test whether the notion of hidden variables made sense.</p>
<p><a href="https://doi.org/10.1103/PhysicsPhysiqueFizika.1.195">Bell produced</a> an equation now known as Bell’s inequality that is always correct – and only correct – for hidden variable theories, and not always for quantum mechanics. Thus, if Bell’s equation was found not to be satisfied in a real-world experiment, local hidden variable theories can be ruled out as an explanation for quantum entanglement.</p>
<p>The experiments of the 2022 Nobel laureates, particularly those of <a href="https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.49.91">Alain Aspect</a>, were the first <a href="https://doi.org/10.1038/18296">tests of the Bell inequality</a>. The experiments used entangled photons, rather than pairs of an electron and a positron, as in many thought experiments. The results conclusively ruled out the existence of hidden variables, a mysterious attribute that would predetermine the states of entangled particles. Collectively, these and <a href="https://www.nature.com/articles/nature15759">many</a> <a href="https://doi.org/10.1038/35057215">follow-up</a> <a href="https://doi.org/10.1103/PhysRevD.14.2543">experiments</a> have vindicated quantum mechanics. Objects can be correlated over large distances in ways that physics before quantum mechanics can not explain.</p>
<p>Importantly, there is also no conflict with <a href="https://www.ams.org/journals/bull/1935-41-04/S0002-9904-1935-06046-X/S0002-9904-1935-06046-X.pdf">special relativity, which forbids faster-than-light communication</a>. The fact that measurements over vast distances are correlated does not imply that information is transmitted between the particles. Two parties far apart performing measurements on entangled particles <a href="https://www.forbes.com/sites/startswithabang/2020/01/02/no-we-still-cant-use-quantum-entanglement-to-communicate-faster-than-light/?sh=730ad18c4d5d">cannot use the phenomenon to pass along information</a> faster than the speed of light.</p>
<p>Today, physicists <a href="https://doi.org/0.1103/PhysRevLett.103.217402">continue to research quantum entanglement</a> and <a href="https://theconversation.com/a-quantum-computing-future-is-unlikely-due-to-random-hardware-errors-126503">investigate potential</a> <a href="https://theconversation.com/the-search-for-dark-matter-gets-a-speed-boost-from-quantum-technology-153604">practical applications</a>. Although quantum mechanics can predict the probability of a measurement with incredible accuracy, many researchers remain skeptical that it provides a complete description of reality. One thing is certain, though. Much remains to be said about the mysterious world of quantum mechanics.</p><img src="https://counter.theconversation.com/content/191927/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andreas Muller receives funding from the National Science Foundation. </span></em></p>A multitude of experiments have shown the mysterious phenomena of quantum mechanics to be how the universe functions. The scientists behind these experiments won the 2022 Nobel Prize in physics.Andreas Muller, Associate Professor of Physics, University of South FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1787762022-04-24T14:02:41Z2022-04-24T14:02:41ZTime travel could be possible, but only with parallel timelines<figure><img src="https://images.theconversation.com/files/458680/original/file-20220419-14894-hnv3v4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3840%2C2155&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If time travel were possible, it would mean the existence of parallel timelines.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/time-travel-could-be-possible--but-only-with-parallel-timelines" width="100%" height="400"></iframe>
<p>Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore — you can always go back and change it. But <a href="https://doi.org/10.21468/SciPostPhysLectNotes.10">is time travel really possible in our universe</a>, or is it just science fiction?</p>
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Read more:
<a href="https://theconversation.com/curious-kids-is-time-travel-possible-for-humans-140703">Curious Kids: is time travel possible for humans?</a>
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<p>Our modern understanding of time and causality comes from <a href="http://dx.doi.org/10.1007/978-3-319-55182-1">general relativity</a>. Theoretical physicist Albert Einstein’s theory combines space and time into a single entity — “spacetime” — and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.</p>
<p>For decades, physicists have been trying to <a href="http://dx.doi.org/10.1007/978-3-319-72754-7">use general relativity to figure out if time travel is possible</a>. It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.</p>
<h2>Arguments against time travel</h2>
<p>There are two main issues which make us think these equations may be unrealistic. The first issue is a practical one: building a time machine seems to require <a href="https://doi.org/10.1007/978-1-4939-3210-8_3">exotic matter</a>, which is matter with negative energy. All the matter we see in our daily lives has positive energy — matter with negative energy is not something you can just find lying around. From quantum mechanics, we know that such matter can theoretically be created, but <a href="https://doi.org/10.1103/PhysRevD.51.4277">in too small quantities and for too short times</a>.</p>
<p>However, there is no proof that it is impossible to create exotic matter in sufficient quantities. Furthermore, other equations may be discovered that allow time travel without requiring exotic matter. Therefore, this issue may just be a limitation of our current technology or understanding of quantum mechanics.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="an illustration of a person standing in a barren landscape underneath a clock" src="https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/459107/original/file-20220421-18-3nvtk0.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">Time travel appears to contradict logic.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>The other main issue is less practical, but more significant: it is the observation that time travel seems to contradict logic, in the form of <a href="https://doi.org/10.1103/PhysRevD.102.064062">time travel paradoxes</a>. There are several types of such paradoxes, but the most problematic are <a href="https://doi.org/10.21468/SciPostPhysLectNotes.10">consistency paradoxes</a>. </p>
<p>A popular trope in science fiction, consistency paradoxes happen whenever there is a certain event that leads to changing the past, but the change itself prevents this event from happening in the first place.</p>
<p>For example, consider a scenario where I enter my time machine, use it to go back in time five minutes, and destroy the machine as soon as I get to the past. Now that I destroyed the time machine, it would be impossible for me to use it five minutes later.</p>
<p>But if I cannot use the time machine, then I cannot go back in time and destroy it. Therefore, it is not destroyed, so I can go back in time and destroy it. In other words, the time machine is destroyed if and only if it is not destroyed. Since it cannot be both destroyed and not destroyed simultaneously, this scenario is inconsistent and paradoxical.</p>
<h2>Eliminating the paradoxes</h2>
<p>There’s a common misconception in science fiction that paradoxes can be “created.” Time travellers are usually warned not to make significant changes to the past and to avoid meeting their past selves for this exact reason. Examples of this may be found in many time travel movies, such as the <em>Back to the Future</em> trilogy.</p>
<p>But in physics, a paradox is not an event that can actually happen — it is a purely theoretical concept that points towards an inconsistency in the theory itself. In other words, consistency paradoxes don’t merely imply time travel is a dangerous endeavour, they imply it simply cannot be possible.</p>
<p>This was one of the motivations for theoretical physicist Stephen Hawking to formulate his <a href="http://dx.doi.org/10.1103/PhysRevD.46.603">chronology protection conjecture</a>, which states that time travel should be impossible. However, this conjecture so far remains unproven. Furthermore, the universe would be a much more interesting place if instead of eliminating time travel due to paradoxes, we could just eliminate the paradoxes themselves.</p>
<p>One attempt at resolving time travel paradoxes is theoretical physicist Igor Dmitriyevich Novikov’s <a href="http://dx.doi.org/10.1103/PhysRevD.42.1915">self-consistency conjecture</a>, which essentially states that you can travel to the past, but you cannot change it. </p>
<p>According to Novikov, if I tried to destroy my time machine five minutes in the past, I would find that it is impossible to do so. The laws of physics would somehow conspire to preserve consistency.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FWG3Dfss3Jc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The first time travel scene in the 1985 film ‘Back to the Future.’</span></figcaption>
</figure>
<h2>Introducing multiple histories</h2>
<p>But what’s the point of going back in time if you cannot change the past? My recent work, together with my students Jacob Hauser and Jared Wogan, shows that there are time travel paradoxes that Novikov’s conjecture cannot resolve. This takes us back to square one, since if even just one paradox cannot be eliminated, time travel remains logically impossible.</p>
<p>So, is this the final nail in the coffin of time travel? Not quite. We showed that allowing for <a href="https://arxiv.org/abs/2110.02448">multiple histories</a> (or in more familiar terms, parallel timelines) can resolve the paradoxes that Novikov’s conjecture cannot. In fact, it can resolve any paradox you throw at it.</p>
<p>The idea is very simple. When I exit the time machine, I exit into a different timeline. In that timeline, I can do whatever I want, including destroying the time machine, without changing anything in the original timeline I came from. Since I cannot destroy the time machine in the original timeline, which is the one I actually used to travel back in time, there is no paradox.</p>
<p><a href="https://doi.org/10.21468/SciPostPhysLectNotes.10">After working on time travel paradoxes for the last three years</a>, I have become increasingly convinced that time travel could be possible, but only if our universe can allow multiple histories to coexist. So, can it?</p>
<p>Quantum mechanics certainly seems to imply so, at least if you subscribe to Everett’s <a href="http://dx.doi.org/10.1103/PhysRevD.44.3197">“many-worlds” interpretation</a>, where one history can “split” into multiple histories, one for each possible measurement outcome – for example, whether <a href="https://youtu.be/IOYyCHGWJq4">Schrödinger’s cat</a> is alive or dead, or whether or not I arrived in the past.</p>
<p>But these are just speculations. My students and I are currently working on finding a concrete theory of time travel with multiple histories that is fully compatible with general relativity. Of course, even if we manage to find such a theory, this would not be sufficient to prove that time travel is possible, but it would at least mean that time travel is not ruled out by consistency paradoxes.</p>
<p>Time travel and parallel timelines almost always go hand-in-hand in science fiction, but now we have proof that they must go hand-in-hand in real science as well. General relativity and quantum mechanics tell us that time travel might be possible, but if it is, then multiple histories must also be possible.</p><img src="https://counter.theconversation.com/content/178776/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Barak Shoshany 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>Scientifically speaking, for time travel to exist, so must parallel timelines. This theory addresses the paradoxes that arise when studying the possibility of time travel.Barak Shoshany, Assistant Professor, Physics, Brock UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1810282022-04-14T12:13:39Z2022-04-14T12:13:39ZA decade of science and trillions of collisions show the W boson is more massive than expected – a physicist on the team explains what it means for the Standard Model<figure><img src="https://images.theconversation.com/files/458000/original/file-20220413-16-ptwkj1.jpg?ixlib=rb-1.1.0&rect=235%2C188%2C5006%2C3143&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Measuring the mass of W bosons took 10 years – and the result was not what physicists expected.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/balls-balancing-on-scale-royalty-free-image/1284113909">PM Images/Digital Vision via Getty Images</a></span></figcaption></figure><p>“You can do it quickly, you can do it cheaply, or you can do it right. We did it right.” These were some of the opening remarks from David Toback, leader of the Collider Detector at Fermilab, as he announced the results of a decadelong experiment to <a href="https://doi.org/10.1126/science.abk1781">measure the mass of a particle called the W boson</a>.</p>
<p>I am a <a href="https://physics.ucdavis.edu/directory/faculty/john-conway">high energy particle physicist</a>, and I am part of the team of hundreds of scientists that built and ran the Collider Detector at Fermilab in Illinois – known as CDF.</p>
<p>After trillions of collisions and years of data collection and number crunching, the CDF team found that the W boson has <a href="https://doi.org/10.1126/science.abk1781">slightly more mass than expected</a>. Though the discrepancy is tiny, the results, described in a paper published in Science on April 7, 2022, have <a href="https://doi.org/10.1038/d41586-022-01014-5">electrified the particle physics world</a>. If the measurement is correct, it is <a href="https://theconversation.com/2021-a-year-physicists-asked-what-lies-beyond-the-standard-model-173132">yet another strong signal</a> that there are missing pieces to the physics puzzle of how the universe works.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing many particles." src="https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=574&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=574&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=574&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=721&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=721&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458003/original/file-20220413-17-m5k8mw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=721&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Standard Model of particle physics describes the particles that make up the mass and forces of the universe.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg#/media/File:Standard_Model_of_Elementary_Particles.svg">MissMJ/WikimediaCommons</a></span>
</figcaption>
</figure>
<h2>A particle that carries the weak force</h2>
<p>The <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">Standard Model of particle physics</a> is science’s current best framework for the basic laws of the universe and <a href="https://www.iop.org/explore-physics/physics-stepping-stones/standard-model">describes three basic forces</a>: the electromagnetic force, the weak force and the strong force. </p>
<p>The strong force holds atomic nuclei together. But some nuclei are unstable and undergo radioactive decay, slowly releasing energy by emitting particles. This process is driven by the weak force, and since the early 1900s, physicists sought an explanation for why and how atoms decay.</p>
<p>According to the Standard Model, forces are transmitted by particles. In the 1960s, a series of <a href="https://www.routledge.com/Weak-Neutral-Currents-The-Discovery-Of-The-Electro-weak-Force/Cline/p/book/9780367216139">theoretical and experimental breakthroughs</a> proposed that the weak force is transmitted by particles called W and Z bosons. It also postulated that a third particle, the Higgs boson, is what gives all other particles – including W and Z bosons – mass.</p>
<p>Since the advent of the Standard Model in the 1960s, scientists have been working their way down the list of predicted yet undiscovered particles and measuring their properties. In 1983, two experiments at CERN in Geneva, Switzerland, <a href="https://doi.org/10.1016/0370-2693(83)90860-2">captured the first evidence of the existence of the W boson</a>. It appeared to have the mass of roughly a medium-sized atom such as bromine. </p>
<p>By the 2000s, there was just one piece missing to complete the Standard Model and tie everything together: the Higgs boson. I helped search for the Higgs boson on three successive experiments, and at last we <a href="https://home.cern/science/physics/higgs-boson">discovered it in 2012</a> at the Large Hadron Collider at CERN. </p>
<p>The Standard Model was complete, and all the measurements we made hung together beautifully with the predictions.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large yellow tube surrounded by electronics." src="https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458007/original/file-20220413-14-a1ml2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Collider Detector at Fermilab collected data from trillions of collisions that produced millions of W bosons.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Collider_Detector_at_Fermilab.jpg#/media/File:Collider_Detector_at_Fermilab.jpg">Bodhita/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Measuring W bosons</h2>
<p>Testing the Standard Model is fun – you just smash particles together at very high energies. These collisions briefly produce heavier particles that then decay back into lighter ones. Physicists use huge and very sensitive detectors at places like Fermilab and CERN to measure the properties and interactions of the particles produced in these collisions. </p>
<p>In CDF, W bosons are produced about <a href="http://www.hep.ph.ic.ac.uk/%7Ewstirlin/plots/crosssections2012_v5.pdf">one out of every 10 million times</a> when a proton and an antiproton collide. Antiprotons are the antimatter version of protons, with exactly the same mass but opposite charge. Protons are made of smaller fundamental particles called quarks, and antiprotons are made of antiquarks. It is the collision between quarks and antiquarks that <a href="https://inspirehep.net/literature/261813">create W bosons</a>. W bosons decay so fast that they are impossible to measure directly. So physicists track the energy produced from their decay to measure the mass of W bosons.</p>
<p>In the 40 years since scientists first detected evidence of the W boson, successive experiments have attained ever more precise measurements of its mass. But it is only since the measurement of the Higgs boson – since it gives mass to all other particles – that researchers could check the measured mass of W bosons against the <a href="https://doi.org/10.1007/JHEP12(2013)084">mass predicted by the Standard Model</a>. The prediction and the experiments always matched up – until now.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing two circles near a line." src="https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=567&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=567&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=567&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=713&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=713&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458024/original/file-20220413-23-edjk9x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=713&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 new measurement of the W boson (red circle) is much farther from the mass predicted by the Standard Model (purple line) and also greater than the preliminary measurement from the experiment.</span>
<span class="attribution"><a class="source" href="https://www.science.org/doi/10.1126/science.abk1781">CDF Collaboration via Science Magazine</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Unexpectedly heavy</h2>
<p>The CDF detector at Fermilab is excellent at accurately measuring W bosons. From 2001 to 2011, the accelerator collided protons with antiprotons trillions of times, producing millions of W bosons and recording as much data as possible from each collision.</p>
<p>The Fermilab team published <a href="https://inspirehep.net/literature/1097099">initial results</a> using a fraction of the data in 2012. We found the mass to be slightly off, but close to the prediction. The team then spent a decade painstakingly analyzing the full data set. The process included numerous internal cross-checks and required years of computer simulations. To avoid any bias creeping into the analysis, nobody could see any results until the full calculation was complete.</p>
<p>When the physics world finally saw the result on April 7, 2022, we were all surprised. Physicists measure elementary particle masses in units of millions of electron volts – shortened to MeV. The W boson’s mass <a href="https://doi.org/10.1126/science.abk1781">came out to be 80,433 MeV</a> – 70 MeV higher than what the Standard Model predicts it should be. This may seem like a tiny excess, but the measurement is accurate to within 9 MeV. This is a deviation of nearly eight times the margin of error. When my colleagues and I saw the result, our reaction was a resounding “wow!” </p>
<h2>What this means for the Standard Model</h2>
<p>The fact that the measured mass of the W boson doesn’t match the predicted mass within the Standard Model could mean three things. Either the math is wrong, the measurement is wrong or there is something missing from the Standard Model.</p>
<p>First, the math. In order to calculate the W boson’s mass, physicists use the mass of the Higgs boson. CERN experiments have allowed physicists to <a href="https://doi.org/10.1007/JHEP10(2012)140">measure the Higgs boson mass</a> to within a quarter-percent. Additionally, theoretical physicists have been <a href="https://doi.org/10.1103/PhysRevD.96.093005">working on the W boson mass calculations for decades</a>. While the math is sophisticated, the prediction is solid and not likely to change.</p>
<p>The next possibility is a flaw in the experiment or analysis. Physicists all over the world are already reviewing the result to try to poke holes in it. Additionally, future experiments at CERN may eventually achieve a more precise result that will either confirm or refute the Fermilab mass. But in my opinion, the experiment is as good a measurement as is currently possible.</p>
<p>That leaves the last option: There are unexplained particles or forces causing the upward shift in the W boson’s mass. Even before this measurement, some theorists had <a href="https://doi.org/10.1126/science.abk1781">proposed potential new particles or forces</a> that would result in the observed deviation. In the coming months and years, I expect a raft of new papers seeking to explain the puzzling mass of W bosons. </p>
<p>As a particle physicist, I am confident in saying that there must be more physics waiting to be discovered beyond the Standard Model. If this new result holds up, it will be the latest in a series of findings showing that the Standard Model and real-world measurements often <a href="https://theconversation.com/proof-of-new-physics-from-the-muons-magnetic-moment-maybe-not-according-to-a-new-theoretical-calculation-157829">don’t quite match</a>. It is these mysteries that give physicists new clues and new reasons to keep searching for fuller understanding of matter, energy, space and time.</p>
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<p class="fine-print"><em><span>John Conway receives funding from US Department of Energy and US National Science Foundation</span></em></p>A decadelong experiment produced the most accurate measurement yet of the mass of W bosons. These particles are responsible for the weak force, and the result is more evidence for undiscovered physics.John Conway, Professor of Physics, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1573912021-04-23T17:38:33Z2021-04-23T17:38:33ZWarp drives: Physicists give chances of faster-than-light space travel a boost<figure><img src="https://images.theconversation.com/files/396639/original/file-20210422-24-1x8nzax.jpg?ixlib=rb-1.1.0&rect=37%2C19%2C1119%2C804&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Faster than light travel is the only way humans could ever get to other stars in a reasonable amount of time. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Wormhole_travel_as_envisioned_by_Les_Bossinas_for_NASA.jpg">Les Bossinas/NASA/Wikimedia Commons</a></span></figcaption></figure><p>The closest star to Earth is Proxima Centauri. It is about 4.25 light-years away, or about 25 trillion miles (40 trillion km). The fastest ever spacecraft, the now- in-space <a href="https://blogs.nasa.gov/parkersolarprobe/2018/10/29/parker-solar-probe-becomes-fastest-ever-spacecraft/">Parker Solar Probe</a> will reach a top speed of 450,000 mph. It would take just 20 seconds to go from Los Angeles to New York City at that speed, but it would take the solar probe about 6,633 years to reach Earth’s nearest neighboring solar system. </p>
<p>If humanity ever wants to travel easily between stars, people will need to go faster than light. But so far, faster-than-light travel is possible only in science fiction. </p>
<p>In Issac Asimov’s <a href="https://asimov.fandom.com/wiki/Foundation">Foundation series</a>, humanity can travel from planet to planet, star to star or across the universe using jump drives. As a kid, I read as many of those stories as I could get my hands on. I am now a theoretical physicist and study nanotechnology, but I am still fascinated by the ways humanity could one day travel in space. </p>
<p>Some characters – like the astronauts in the movies “Interstellar” and “Thor” – use <a href="https://www.space.com/20881-wormholes.html">wormholes to travel between solar systems</a> in seconds. Another approach – familiar to “Star Trek” fans – is warp drive technology. Warp drives are theoretically possible if still far-fetched technology. Two recent papers <a href="https://www.msn.com/en-au/news/techandscience/engineers-have-proposed-the-first-model-for-a-physically-possible-warp-drive/ar-BB1ed4KQ">made headlines</a> in March when <a href="https://doi.org/10.1088/1361-6382/abe692">researchers claimed</a> to <a href="https://doi.org/10.1088/1361-6382/abdf6e">have overcome</a> one of the many challenges that stand between the theory of warp drives and reality. </p>
<p>But how do these theoretical warp drives really work? And will humans be making the jump to warp speed anytime soon?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A circle on a flat blue plane with the surface dipping down in front and rising up behind." src="https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=278&fit=crop&dpr=1 600w, https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=278&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=278&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=349&fit=crop&dpr=1 754w, https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=349&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/396642/original/file-20210422-15-1fbhdiq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=349&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 2-dimensional representation shows the flat, unwarped bubble of spacetime in the center where a warp drive would sit surrounded by compressed spacetime to the right (downward curve) and expanded spacetime to the left (upward curve).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Alcubierre.png#/media/File:Alcubierre.png">AllenMcC/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>Compression and expansion</h2>
<p>Physicists’ current understanding of spacetime comes from Albert Einstein’s <a href="https://www.space.com/17661-theory-general-relativity.html">theory of General Relativity</a>. General Relativity states that space and time are fused and that nothing can travel faster than the speed of light. General relativity also describes how mass and energy warp spacetime – hefty objects like stars and black holes curve spacetime around them. This curvature is what you feel as gravity and why many spacefaring heroes worry about “getting stuck in” or “falling into” a gravity well. Early science fiction writers <a href="https://www.tor.com/2018/07/05/the-father-of-science-fiction-the-best-of-john-w-campbell/">John Campbell</a> and Asimov saw this warping as a way to skirt the speed limit. </p>
<p>What if a starship could compress space in front of it while expanding spacetime behind it? “Star Trek” took this idea and named it the warp drive. </p>
<p>In 1994, Miguel Alcubierre, a Mexican theoretical physicist, showed that compressing spacetime in front of the spaceship while expanding it behind was <a href="https://doi.org/10.1088/0264-9381/11/5/001">mathematically possible within the laws of General Relativity</a>. So, what does that mean? Imagine the distance between two points is 10 meters (33 feet). If you are standing at point A and can travel one meter per second, it would take 10 seconds to get to point B. However, let’s say you could somehow compress the space between you and point B so that the interval is now just one meter. Then, moving through spacetime at your maximum speed of one meter per second, you would be able to reach point B in about one second. In theory, this approach does not contradict the laws of relativity since you are not moving faster than light in the space around you. Alcubierre showed that the warp drive from “Star Trek” was in fact theoretically possible.</p>
<p>Proxima Centauri here we come, right? Unfortunately, Alcubierre’s method of compressing spacetime had one problem: it requires negative energy or negative mass.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A 2–dimensional diagram showing how matter warps spacetime" src="https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=260&fit=crop&dpr=1 600w, https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=260&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=260&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=327&fit=crop&dpr=1 754w, https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=327&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/396645/original/file-20210422-16-1yaplky.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=327&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 2–dimensional representation shows how positive mass curves spacetime (left side, blue earth) and negative mass curves spacetime in an opposite direction (right side, red earth).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:One-sided_spacetime_curvatures.png#/media/File:One-sided_spacetime_curvatures.png">Tokamac/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>A negative energy problem</h2>
<p>Alcubierre’s warp drive would work by creating a bubble of flat spacetime around the spaceship and curving spacetime around that bubble to reduce distances. The warp drive would require either negative mass – a theorized type of matter – or a ring of negative energy density to work. Physicists have never observed negative mass, so that leaves negative energy as the only option. </p>
<p>To create negative energy, a warp drive would use a huge amount of mass to create an imbalance between particles and antiparticles. For example, if an electron and an antielectron appear near the warp drive, one of the particles would get trapped by the mass and this results in an imbalance. This imbalance results in negative energy density. Alcubierre’s warp drive would use this negative energy to create the spacetime bubble. </p>
<p>But for a warp drive to generate enough negative energy, you would need a lot of matter. Alcubierre estimated that a warp drive with a 100-meter bubble would <a href="https://doi.org/10.1088/0264-9381/11/5/001">require the mass of the entire visible universe</a>. </p>
<p>In 1999, physicist Chris Van Den Broeck showed that expanding the volume inside the bubble but keeping the surface area constant would <a href="https://doi.org/10.1088/0264-9381/16/12/314">reduce the energy requirements significantly</a>, to just about the mass of the sun. A significant improvement, but still far beyond all practical possibilities.</p>
<h2>A sci-fi future?</h2>
<p>Two recent papers – one by <a href="https://doi.org/10.1088/1361-6382/abdf6e">Alexey Bobrick and Gianni Martire</a> and another by <a href="https://doi.org/10.1088/1361-6382/abe692">Erik Lentz</a> – provide solutions that seem to bring warp drives closer to reality.</p>
<p>Bobrick and Martire realized that by modifying spacetime within the bubble in a certain way, they could remove the need to use negative energy. This solution, though, does not produce a warp drive that can go faster than light. </p>
<p>[<em>Over 100,000 readers rely on The Conversation’s newsletter to understand the world.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=100Ksignup">Sign up today</a>.]</p>
<p>Independently, Lentz also proposed a solution that does not require negative energy. He used a different geometric approach to solve the equations of General Relativity, and by doing so, he found that a warp drive wouldn’t need to use negative energy. Lentz’s solution would allow the bubble to travel faster than the speed of light.</p>
<p>It is essential to point out that these exciting developments are mathematical models. As a physicist, I won’t fully trust models until we have experimental proof. Yet, the science of warp drives is coming into view. As a science fiction fan, I welcome all this innovative thinking. In the <a href="https://www.youtube.com/watch?v=7-Q9CxKtZUA">words of Captain Picard</a>, things are only impossible until they are not.</p><img src="https://counter.theconversation.com/content/157391/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mario Borunda 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>If humanity wants to travel between stars, people are going to need to travel faster than light. New research suggests that it might be possible to build warp drives and beat the galactic speed limit.Mario Borunda, Associate Professor of Physics, Oklahoma State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1580702021-04-15T19:51:56Z2021-04-15T19:51:56ZNew warp drive research dashes faster than light travel dreams – but reveals stranger possibilities<figure><img src="https://images.theconversation.com/files/395179/original/file-20210415-19-1xil815.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">shutterstock</span> </figcaption></figure><p>In 1994, physicist Miguel Alcubierre <a href="https://arxiv.org/abs/gr-qc/0009013">proposed</a> a radical technology that would allow faster than light travel: the <a href="https://en.wikipedia.org/wiki/Alcubierre_drive">warp drive</a>, a hypothetical way to skirt around the universe’s ultimate speed limit by bending the fabric of reality.</p>
<p>It was an intriguing idea – even NASA has been <a href="https://ntrs.nasa.gov/citations/20110015936">researching</a> it at the Eagleworks laboratory – but Alcubierre’s proposal contained problems that seemed insurmountable. Now, a recent <a href="https://arxiv.org/abs/2102.06824">paper</a> by US-based physicists Alexey Bobrick and Gianni Martire has resolved many of those issues and <a href="https://phys.org/news/2021-03-potential-real-physical-warp.html">generated</a> a <a href="https://www.popularmechanics.com/science/a35718463/scientists-say-physical-warp-drive-is-possible/">lot</a> of <a href="https://www.sciencealert.com/engineers-have-proposed-the-first-model-for-a-physical-warp-drive">buzz</a>.</p>
<p>But while Bobrick and Martire have managed to substantially demystify warp technology, their work actually suggests that faster-than-light travel will remain out of reach for beings like us, at least for the time being. </p>
<p>There is, however, a silver lining: warp technology may have radical applications beyond space travel.</p>
<h2>Across the universe?</h2>
<p>The story of warp drives starts with Einstein’s crowning achievement: general relativity. The equations of general relativity capture the way in which spacetime – the very fabric of reality – bends in response to the presence of matter and energy which, in turn, explains how matter and energy move. </p>
<p>General relativity places two constraints on interstellar travel. First, nothing can be accelerated past the speed of light (around 300,000 km per second). Even travelling at this dizzying speed it would still take us four years to arrive at Proxima Centauri, the nearest star to our Sun.</p>
<p>Second, the clock on a spaceship travelling close to the speed of light would slow down relative to a clock on Earth (this is known as time dilation). Assuming a constant state of acceleration, this makes it possible to travel the stars. One can reach a distant star that is 150 lightyears away within one’s lifetime. The catch, however, is that upon one’s return more than 300 years will have passed on Earth.</p>
<h2>A new hope</h2>
<p>This is where Alcubierre came in. He argued that the mathematics of general relativity allowed for “warp bubbles” – regions where matter and energy were arranged in such a way as to bend spacetime in front of the bubble and expand it to the rear in a way that allowed a “flat” area inside the bubble to travel faster than light. </p>
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<strong>
Read more:
<a href="https://theconversation.com/dont-stop-me-now-superluminal-travel-in-einsteins-universe-49439">Don't stop me now! Superluminal travel in Einstein's universe</a>
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<p>To get a sense of what “flat” means in this context, note that spacetime is sort of like a rubber mat. The mat curves in the presence of matter and energy (think of putting a bowling ball on the mat). Gravity is nothing more than the tendency objects have to roll into the the dents created by things like stars and planets. A flat region is like a part of the mat with nothing on it.</p>
<p>Such a drive would also avoid the uncomfortable consequences of time dilation. One could potentially make a round trip into deep space and still be greeted by one’s nearest and dearest at home.</p>
<h2>A spacetime oddity</h2>
<p>How does Alcubierre’s device work? Here discussion often relies on analogies, because the maths is so complex.</p>
<p>Imagine a rug with a cup on it. You’re on the rug and you want to get to the cup. You could move across the rug, or tug the rug toward you. The warp drive is like tugging on spacetime to bring your destination closer. </p>
<p>But analogies have their limits: a warp drive doesn’t really drag your destination toward you. It contracts spacetime to make your path shorter. There’s just less rug between you and the cup when you switch the drive on.</p>
<p>Alcubierre’s suggestion, while mathematically rigorous, is difficult to understand at an intuitive level. Bobrick and Martire’s work is set to change all that. </p>
<h2>Starship bloopers</h2>
<p>Bobrick and Martire show that any warp drive must be a shell of material in a constant state of motion, enclosing a flat region of spacetime. The energy of the shell modifies the properties of the spacetime region inside it. </p>
<p>This might not sound like much of a discovery, but until now it was unclear what warp drives might be, physically speaking. Their work tells us that a warp drive is, somewhat surprisingly, like a car. A car is also a shell of energy (in the form of matter) that encloses a flat region of spacetime. The difference is that getting inside a car does not make you age faster. That, however, is the kind of thing a warp drive might do.</p>
<p>Using their simple description, Bobrick and Martire demonstrate a method for using Einstein’s general relativity equations to find spacetimes that allow for arrangements of matter and energy that would act as warp bubbles. This gives us a mathematical key for finding and classifying warp technologies. </p>
<p>Their work manages to address one of the core problems for warp drives. To make the equations balance, Alcubierre’s device runs on “negative energy” – but we are yet to discover any viable sources of negative energy in the real world. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=325&fit=crop&dpr=1 600w, https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=325&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=325&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/395193/original/file-20210415-23-1ibugvi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A two-dimensional visualization of an Alcubierre drive. Expanding and contracting regions of spacetime on opposite sides of the central flat region cause it to move.</span>
<span class="attribution"><a class="source" href="https://appliedphysics.org/physical-warp-drives/">Applied Physics</a></span>
</figcaption>
</figure>
<p>Worse, the negative energy requirements of Alcubierre’s device are immense. By some estimates, the entire energy in the known universe would be needed (though later work brings the number down a bit).</p>
<p>Bobrick and Martire show a warp drive could be made from positive energy (i.e. “normal” energy) or from a mixture of negative and positive energy. That said, the energy requirements would still be immense. </p>
<p>If Bobrick and Martire are right, then a warp drive is just like any other object in motion. It would be subject to the universal speed limit enforced by general relativity after all, and it would need some kind of conventional propulsion system to make it accelerate. </p>
<p>The news gets worse. Many kinds of warp drive can only modify the spacetime inside in a certain way: by slowing down the clock of the passenger in exactly the way that makes a trip into deep space a problem.</p>
<p>Bobrick and Martire do show that some warp drives could travel faster than light, but only if they are created already travelling at that speed – which is no help for any ordinary human hoping for a bit of interstellar tourism. </p>
<h2>The end game</h2>
<p>Remember that a warp drive can modify the region of flat spacetime it encloses. It can, in particular, speed up or slow down a clock inside the drive. </p>
<p>Consider what it would mean to have such an object available. Want to put someone with a terminal illness on ice? Stick them in a warp drive and slow their clock down. From their perspective, a few years will pass, while a hundred years will pass on Earth — time enough to find a cure.</p>
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<strong>
Read more:
<a href="https://theconversation.com/the-art-and-beauty-of-general-relativity-51042">The art and beauty of general relativity</a>
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</p>
<hr>
<p>Want to grow your crops overnight? Stick them in a warp drive and speed the clock up. A few days will pass for you, and a few weeks will pass for your seedlings.</p>
<p>There are even more exotic possibilities: by rotating the spacetime inside a drive one may be able to produce a battery capable of holding huge amounts of energy. </p>
<p>Faster-than-light travel remains a distant dream. But warp technology would be revolutionary in its own right.</p><img src="https://counter.theconversation.com/content/158070/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sam Baron receives funding from the Australian Research Council. </span></em></p>Bending space into warp bubbles to travel faster than light may never be a reality, but distorting the flow of time just might be possible.Sam Baron, Associate professor, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1507302020-12-09T13:18:16Z2020-12-09T13:18:16ZFragments of energy – not waves or particles – may be the fundamental building blocks of the universe<figure><img src="https://images.theconversation.com/files/373145/original/file-20201204-17-cnef4y.jpg?ixlib=rb-1.1.0&rect=0%2C26%2C4895%2C3323&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New mathematics have shown that lines of energy can be used to describe the universe. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/%E7%B2%92%E5%AD%90%E7%B7%9A%E6%A2%9D-royalty-free-image/1167012631?adppopup=true">zf L/Moment via Getty Images</a></span></figcaption></figure><p>Matter is what makes up the universe, but what makes up matter? This question has long been tricky for those who think about it – especially for the physicists. Reflecting recent trends in physics, my <a href="https://scholar.google.com/citations?hl=en&user=aBZ6HqMAAAAJ">colleague Jeffrey Eischen</a> <a href="https://scholar.google.com/citations?hl=en&user=FrIFYKoAAAAJ">and I</a> have described an updated way to think about matter. We propose that matter is not made of <a href="https://en.wikipedia.org/wiki/Particle">particles</a> or <a href="https://en.wikipedia.org/wiki/Electromagnetic_radiation">waves</a>, as was long thought, but – more fundamentally – that matter is made of <a href="https://physicsessays.org/browse-journal-2/product/1829-14-larry-m-silverberg-and-jeffrey-w-eischen-on-a-new-field-theory-formulation-and-a-space-time-adjustment-that-predict-the-same-precession-of-mercury-and-the-same-bending-of-light-as-general-relativity.html">fragments of energy</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graphic showing images representing earth, air, fire, water and aether." src="https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=251&fit=crop&dpr=1 754w, https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=251&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/373142/original/file-20201204-13-1t489d6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=251&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 ancient times, five elements were thought to be the building blocks of reality.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/set-of-main-elements-royalty-free-illustration/979105476?adppopup=true">IkonStudio/iStock via Getty Images</a></span>
</figcaption>
</figure>
<h2>From five to one</h2>
<p>The ancient Greeks conceived of <a href="https://en.wikipedia.org/wiki/Classical_element">five building blocks of matter</a> – from bottom to top: earth, water, air, fire and aether. Aether was the matter that filled the heavens and explained the rotation of the stars, as observed from the Earth vantage point. These were the first most basic elements from which one could build up a world. Their conceptions of the physical elements did not change dramatically for nearly 2,000 years. </p>
<p>Then, about 300 years ago, <a href="https://en.wikipedia.org/wiki/Isaac_Newton">Sir Isaac Newton</a> introduced the idea that all matter exists at points called <a href="https://en.wikipedia.org/wiki/Particle">particles</a>. One hundred fifty years after that, <a href="https://en.wikipedia.org/wiki/James_Clerk_Maxwell">James Clerk Maxwell</a> introduced the <a href="https://en.wikipedia.org/wiki/Electromagnetic_radiation">electromagnetic wave</a> – the underlying and often invisible form of magnetism, electricity and light. The particle served as the building block for mechanics and the wave for electromagnetism – and the public settled on the particle and the wave as the two building blocks of matter. Together, the particles and waves became the building blocks of all kinds of matter.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A drawing of Issac Newton next to a tree and the moon." src="https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1434&fit=crop&dpr=1 600w, https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1434&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1434&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1802&fit=crop&dpr=1 754w, https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1802&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/373171/original/file-20201205-23-1s0ejqw.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1802&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sir Issac Newton, credited with developing the particle theory.</span>
<span class="attribution"><span class="source">Christopher Terrell</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This was a vast improvement over the ancient Greeks’ five elements, but was still flawed. In a famous series of experiments, known as the <a href="https://en.wikipedia.org/wiki/Double-slit_experiment">double-slit experiments</a>, light sometimes acts like a particle and at other times acts like a wave. And while the theories and math of waves and particles allow scientists to make incredibly accurate predictions about the universe, the rules break down at the largest and tiniest scales. </p>
<p>Einstein proposed a remedy in his theory of <a href="https://en.wikipedia.org/wiki/General_relativity">general relativity</a>. Using the mathematical tools available to him at the time, Einstein was able to better explain certain physical phenomena and also resolve a longstanding <a href="https://en.wikipedia.org/wiki/Equivalence_principle">paradox relating to inertia and gravity</a>. But instead of improving on particles or waves, he eliminated them as he proposed the warping of space and time.</p>
<p>Using newer mathematical tools, my colleague and I have demonstrated a new theory that may accurately describe the universe. Instead of basing the theory on the warping of space and time, we considered that there could be a building block that is more fundamental than the particle and the wave. Scientists understand that particles and waves are existential opposites: A particle is a source of matter that exists at a single point, and waves exist everywhere except at the points that create them. My colleague and I thought it made logical sense for there to be an underlying connection between them. </p>
<figure class="align-center ">
<img alt="A painting of a child staring up at the stars" src="https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372997/original/file-20201204-19-19qmasy.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">A new building block of matter can model both the largest and smallest of things – from stars to light.</span>
<span class="attribution"><span class="source">Christopher Terrell</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Flow and fragments of energy</h2>
<p>Our theory begins with a new fundamental idea – that energy always “flows” through regions of space and time. </p>
<p>Think of energy as made up of lines that fill up a region of space and time, flowing into and out of that region, never beginning, never ending and never crossing one another.</p>
<p>Working from the idea of a universe of flowing energy lines, we looked for a single building block for the flowing energy. If we could find and define such a thing, we hoped we could use it to accurately make predictions about the universe at the largest and tiniest scales. </p>
<p>There were many building blocks to choose from mathematically, but we sought one that had the features of both the particle and wave – concentrated like the particle but also spread out over space and time like the wave. The answer was a building block that looks like a concentration of energy – kind of like a star – having energy that is highest at the center and that gets smaller farther away from the center. </p>
<p>Much to our surprise, we discovered that there were only a limited number of ways to describe a concentration of energy that flows. Of those, we found just one that works in accordance with our mathematical definition of flow. We named it a <a href="https://youtu.be/W31lEn7v4X0">fragment of energy</a>. For the math and physics aficionados, it is defined as A = -⍺/<em>r</em> where ⍺ is intensity and <em>r</em> is the distance function. </p>
<p>Using the fragment of energy as a building block of matter, we then constructed the math necessary to solve physics problems. The final step was to test it out.</p>
<h2>Back to Einstein, adding universality</h2>
<figure class="align-left ">
<img alt="A graphic showing the orbit of mercury shifting over time." src="https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/373143/original/file-20201204-21-19ca7b1.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">General relativity was the first theory to accurately predict the slight rotation of Mercury’s orbit.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Tests_of_general_relativity#/media/File:Apsidendrehung.png">Rainer Zenz via Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>More than 100 years ago, Einstein had turned to <a href="https://en.wikipedia.org/wiki/Tests_of_general_relativity">two legendary problems</a> in physics to validate general relativity: the ever-so-slight yearly <a href="https://aether.lbl.gov/www/classes/p10/gr/PrecessionperihelionMercury.htm">shift – or precession – in Mercury’s orbit</a>, and the <a href="https://www.cnet.com/news/albert-einstein-gravitational-lensing-general-relativity-white-dwarf-sahu-stein-2051-b/">tiny bending of light as it passes the Sun</a>.</p>
<p>These problems were at the two extremes of the size spectrum. Neither wave nor particle theories of matter could solve them, but general relativity did. The theory of general relativity warped space and time in such way as to cause the trajectory of Mercury to shift and light to bend in precisely the amounts seen in astronomical observations. </p>
<p>If our new theory was to have a chance at replacing the particle and the wave with the presumably more fundamental fragment, we would have to be able to solve these problems with our theory, too. </p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<p>For the precession-of-Mercury problem, we modeled the Sun as an enormous stationary fragment of energy and Mercury as a smaller but still enormous slow-moving fragment of energy. For the bending-of-light problem, the Sun was modeled the same way, but the photon was modeled as a minuscule fragment of energy moving at the speed of light. In both problems, we calculated the trajectories of the moving fragments and got the same answers as those predicted by the theory of general relativity. We were stunned. </p>
<p>Our initial work demonstrated how a new building block is capable of accurately modeling bodies from the enormous to the minuscule. Where particles and waves break down, the fragment of energy building block held strong. The fragment could be a single potentially universal building block from which to model reality mathematically – and update the way people think about the building blocks of the universe.</p><img src="https://counter.theconversation.com/content/150730/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Larry M. Silverberg 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>Field theory describes the universe as energy flowing along unending lines. With this perspective, it is possible to define a new fundamental building block of matter.Larry M. Silverberg, Professor of Mechanical and Aerospace Engineering, North Carolina State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1468402020-09-29T19:59:05Z2020-09-29T19:59:05ZCurious Kids: could our entire reality be part of a simulation created by some other beings?<figure><img src="https://images.theconversation.com/files/359745/original/file-20200924-22-pvzq.jpg?ixlib=rb-1.1.0&rect=22%2C367%2C3811%2C5386&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Unsplash</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><blockquote>
<p><strong>Is it possible the whole observable universe is just a thing kept in a container, in a room where there are some other extraterrestrial beings much bigger than us? Kanishk, Year 9</strong></p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Hi Kanishk!</p>
<p>I’m going to interpret your question in a slightly different way.</p>
<p>Let’s assume these extraterrestrial beings have a computer on which our universe is being “simulated”. Simulated worlds are pretend worlds – a bit like the worlds on Minecraft or Fortnite, which are both simulations created by us.</p>
<p>If we think about it like this, it also helps to suppose these “beings” are similar to us. They’d have to at least understand us to be able to simulate us.</p>
<p>By narrowing the question down, we’re now asking: is it possible we’re living in a <a href="https://www.scientificamerican.com/article/are-we-living-in-a-computer-simulation/">computer simulation</a> run by beings like us? University of Oxford professor <a href="https://nickbostrom.com/">Nick Bostrom</a> has thought a lot about this exact question. And he <a href="https://www.youtube.com/watch?v=nnl6nY8YKHs">argues</a> the answer is “yes”.</p>
<p>Not only does Bostrom think it’s possible, he thinks there’s a decent probability it’s true. Bostrom’s theory is known as the Simulation Hypothesis.</p>
<h2>A simulated world that feels real</h2>
<p>I want you to imagine there are many civilisations like ours dotted all around the universe. Also imagine many of these civilisations have developed advanced technology that lets them create computer simulations of a time in their own past (a time before they developed the technology).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=840&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=840&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=840&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1056&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1056&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359742/original/file-20200924-16-eiyg96.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1056&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Do you think our whole world could be created by someone using more advanced technology than we have today?</span>
<span class="attribution"><span class="source">Yash Raut/Unsplash</span></span>
</figcaption>
</figure>
<p>The people in these simulations are just like us. They are conscious (aware) beings who can touch, taste, move, smell and feel happiness and sadness. However, they have no way of proving they’re in a simulation and no way to “break out”.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-time-travel-possible-for-humans-140703">Curious Kids: is time travel possible for humans?</a>
</strong>
</em>
</p>
<hr>
<h2>Hedge your bets</h2>
<p>According to Bostrom, if these simulated people (who are so much like us) don’t realise they’re in a simulation, then it’s possible you and I are too.</p>
<p>Suppose I guess we’re not in a simulation and you guess we are. Who guessed best? </p>
<p>Let’s say there is just one “real” past. But these futuristic beings are also running many simulations of the past — different versions they made up.</p>
<p>They could be running any number of simulations (it doesn’t change the point Bostrom is trying to make) — but let’s go with 200,000. Our guessing-game then is a bit like rolling a die with 200,000 sides. </p>
<p>When I guess we <em>are not</em> simulated, I’m betting the die will be a specific number (let’s make it 2), because there can only be one possible reality in which we’re not simulated. </p>
<p>This means in every other scenario <em>we are</em> simulated, which is what you guessed. That’s like betting the die will roll anything other than 2. So your bet is a far better one.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359743/original/file-20200924-20-12zqekv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Simulated or not simulated, would you bet on it?</span>
<span class="attribution"><span class="source">Ian Gonzalez/Unsplash</span></span>
</figcaption>
</figure>
<h2>Are we simulated?</h2>
<p>Does that mean we’re simulated? Not quite. </p>
<p>The odds are only against my guess if we are assuming these beings exist and are running simulations.</p>
<p>But, how likely is it there are beings so advanced they can run simulations with people who are “conscious” like us in the first place? Suppose this is very unlikely. Then it would also be unlikely our world is simulated. </p>
<p>Second, how likely is it such beings would run simulations even if they <em>could</em>? Maybe they have no interest in doing this. This, too, would mean it’s unlikely we are simulated. </p>
<h2>Laying out all our options</h2>
<p>Before us, then, are three possibilities:</p>
<ol>
<li><p>there are technologically advanced beings who can (and do) run many simulations of people like us (likely including us)</p></li>
<li><p>there are technologically advanced beings who can run simulations of people like us, but don’t do this for whatever reason</p></li>
<li><p>there are no beings technologically advanced enough to run simulations of people like us.</p></li>
</ol>
<p>But are these really the only options available? The answer seems to be “yes”.</p>
<p>You might disagree by bringing up one of several theories suggesting our universe is not a simulation. For example, what if we’re all here because of the Big Bang (as science suggests), rather than by a simulation? </p>
<p>That’s a good point, but it actually fits within the Simulation Hypothesis, under options 2 and 3 — in which we’re not simulated. It doesn’t go against it. This is why the theory leaves us with only three options, one of which then must be true. </p>
<p>So which is it? Sadly, we don’t have enough evidence to help us decide. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-started-the-big-bang-79845">Curious Kids: what started the Big Bang?</a>
</strong>
</em>
</p>
<hr>
<h2>The principle of indifference</h2>
<p>When we’re faced with a set of options and there is not enough evidence to believe one over the others, we should give an equal “credence” to each option. Generally speaking, credence is how likely you believe something to be true based on the evidence available.</p>
<p>Giving equal credence in cases such as the Simulation Hypothesis is an example of what philosophers call the “<a href="https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100001616">principle of indifference</a>”. </p>
<p>Suppose you place a cookie on your desk and leave the room. When you come back, it’s gone. In the room with you were three people, all of which are strangers to you.</p>
<p>You have to start by piecing together what you know. You know someone in the room took the cookie. If you knew person A had been caught stealing cookies in the past, you could guess it was probably them. But on this occasion, you don’t know anything about these people.</p>
<p>Would it be fair to accuse anyone in particular? No. </p>
<h2>Our universe, expanding</h2>
<p>And so it is with the simulation argument. We don’t have enough information to help us select between the three options.</p>
<p>What we do know is if option 1 is true, then we’re very likely to be in a simulation. In options 2 and 3, we’re not. Thus, Bostrom’s argument seems to imply our credence of being simulated is roughly 1 in 3. </p>
<p>To put this into perspective, your credence in getting “heads” when you flip a coin should be 1 in 2. And your credence in winning the <a href="https://phys.org/news/2016-01-mathematician-real-chances-powerball-largest.html">largest lottery in the world</a> should be around 1 in 300,000,000 (if you believe it isn’t rigged). </p>
<p>If that makes you a little nervous, it’s worth remembering we might make discoveries in the future that could change our credences. What that information might be and how we might discover it, however, remains unknown.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/SYAG9dAfy8U?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Famous astrophysicist Neil deGrasse Tyson has said it’s “hard to argue against” Bostrum’s Simulation Hypothesis.</span></figcaption>
</figure><img src="https://counter.theconversation.com/content/146840/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sam Baron receives funding from the Australian Research Council</span></em></p>Philosopher Nick Bostrom’s theory suggests there’s a one-in-three probability we live in a simulation.Sam Baron, Associate professor, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/934222018-03-15T04:03:11Z2018-03-15T04:03:11ZHawking tackled the biggest question of all: how did the universe begin?<figure><img src="https://images.theconversation.com/files/210448/original/file-20180315-113455-q04j32.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hawking had a cult-like following among academics and non-academics alike. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/kosalabandara/7958144996/">kosalabandara/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>With the death of Stephen Hawking, the world has lost an adventurer.</p>
<p>I was one of the many who first encountered the deep ideas of cosmology through Hawking’s book A Brief History of Time, and found myself inspired. To his readers Hawking revealed a whole new world — showing how physics can address some of the deep questions of our existence, all the way to the deepest of all: how did the universe begin?</p>
<p>Physics is often perceived to be dry and devoid of imagination, but as researchers we realise that could not be further from the truth. In research, we routinely throw assumptions in the bin, play with “what if” scenarios, and rely on insight and creativity to explore new ideas that could take us beyond the bounds of the physics we already know. Stephen Hawking was a master at this. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-timeline-of-stephen-hawkings-remarkable-life-93364">A timeline of Stephen Hawking's remarkable life</a>
</strong>
</em>
</p>
<hr>
<h2>Theory of everything</h2>
<p>What made Hawking such a trailblazer were his attempts to merge quantum physics and general relativity. </p>
<p>The situation in modern physics is both powerful and dire. We have two incredibly strong theories that have passed every test we can throw at them, and yet we can’t unify them. </p>
<p><a href="https://theconversation.com/from-newton-to-einstein-the-origins-of-general-relativity-50013">General relativity</a> is our theory of gravity, with thanks to Einstein, and <a href="https://theconversation.com/explainer-quantum-physics-570">quantum physics</a> is our theory of everything else – in particular, how particles interact. Both have been tested to incredible precision and have become everyday tools. We use general relativity to make our GPS system accurate, and quantum physics is used to design key elements of all high technology. </p>
<p>However, we still have no theory that combines the two, and this has perplexed physicists for a century. Merging the two theories engaged Einstein for the latter half of his life to no avail.</p>
<p>The quest for a quantum theory of gravity that can also explain the whole universe, is known as the search for a “theory of everything”, or “ToE”.</p>
<p>Hawking’s most famous insight was to take seriously the question of what would happen if you took a quantum system and put it near the event horizon of a black hole. Even without a final theory of quantum gravity, he revealed that in some special circumstances you can calculate solutions anyway.</p>
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<strong>
Read more:
<a href="https://theconversation.com/tributes-pour-in-for-stephen-hawking-the-famous-theoretical-physicist-who-died-at-age-76-93363">Tributes pour in for Stephen Hawking, the famous theoretical physicist who died at age 76</a>
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<h2>The ‘mind of God’</h2>
<p>Hawking famously <a href="https://www.smh.com.au/national/professor-stephen-hawking-one-of-the-worlds-most-brilliant-physicists-20180314-h0xgr5.html">described</a> the quest for a theory of everything in analogy to God:</p>
<blockquote>
<p>If we do discover a theory of everything… it would be the ultimate triumph of human reason — for then we would truly know the mind of God.</p>
</blockquote>
<p>He was forced to explain this line many times. As a devout atheist he made it clear that he didn’t mean we would understand a deity, but rather that we would be able to explain, using physics, the birth of the universe itself, and all of the processes within it, thus demonstrating there is no need for a god. </p>
<p>In his own <a href="https://www.scientificamerican.com/article/hawking-vs-god/">words</a>: </p>
<blockquote>
<p>God may exist, but science can explain the universe without the need for a creator.</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210457/original/file-20180315-113455-awfz0k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Stephen Hawking speaking on centre stage via video link during the Web Summit 2017 Opening Cermony at Altice Arena in Lisbon.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/websummit/38189325632/">websummit/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>How the big bang banged</h2>
<p>We know that nothing, not even light, can escape a black hole’s gravitational pull. Nevertheless, Hawking discovered that black holes should “glow”. The light they emit is now known as “<a href="https://arxiv.org/pdf/hep-th/0409024.pdf">Hawking radiation</a>”.</p>
<p>But if light can’t escape from black holes, how can they glow? </p>
<p>The event horizon of a black hole is the point of no return. Once you are within the event horizon you can never escape, and no light you emit will ever be seen outside. The reason black holes can glow is because no light actually emerges from inside the event horizon. The light gets created just outside of it, thanks to the black hole’s interaction with the quantum vacuum. </p>
<p>This leads to another question, because another important rule of physics is conservation of energy; you can’t create something from nothing. So in order to glow, the black hole has to pay a price, and it pays with the only currency it has – its mass. </p>
<p>As the black hole emits light it gets lighter, and the lighter the black hole the more dramatically it shines, which accelerates its demise, until it evaporates into nothing in an intense flash of radiation.</p>
<p>As spectacular as that may be, it may seem a trifle esoteric: why should we care how black holes behave? Well, the theories Hawking was developing also have implications for the question of how the universe began. Hawking proposed a mechanism, through quantum physics, by which a universe could be born. In other words, he proposed an answer to how the big bang banged.</p>
<h2>The symphony of space</h2>
<p>Hawking became one of the world’s most recognisable physicists. His fame saw him appear frequently in popular culture including on the Simpsons and Star Trek (where he played himself). Not only a superb researcher, he was a brilliant communicator, and this set him apart from his peers. His <a href="http://www.hawking.org.uk/a-brief-history-of-time.html">A Brief History of Time</a> sold more than 10 million copies and was translated into at least 35 languages. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210453/original/file-20180315-113465-rju9fe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Hawking held a party to celebrate the New Horizon Spacecraft passing by Pluto in 2015.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/epicfireworks/19605192156/">epicfireworks/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>One of the fantastic things about A Brief History of Time was that it made complex ideas simple, but also didn’t shy away from giving the gory details. Hawking showed respect to his readers and to their potential to understand – perhaps having higher expectations of them than they had of themselves. As a result, he was able to convey a great feeling of the depth of thought behind the theories.</p>
<p>Millions of readers engrossed in his book left with a sense of wonder, even if they fell short of full understanding. Like listening to a symphony, you can appreciate the beauty and complexity of the music without knowing how to play any of the instruments. </p>
<p>Hawking played the symphony of space into words on a page, which left people with the feeling they had experienced something profound, even if they hadn’t fully understood it.</p>
<h2>Be curious</h2>
<p>That Hawking survived until age 76 is truly remarkable. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=925&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=925&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=925&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210458/original/file-20180315-113452-1ihamyj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1163&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Stephen Hawking in San Francisco at the amyotrophic lateral sclerosis (ALS) convention in the mid 1980s.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/wwworks/3728608454/">wwworks/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Diagnosed with amyotrophic lateral sclerosis (ALS) as a 22 year old, he was given only two years to live. </p>
<p>Rather than being defeated by such a diagnosis he dove into research with an urgency perhaps inspired by his limited time. He determined to do something significant with his time remaining, and thus attacked some of the most profound and challenging questions in physics. </p>
<p>To the benefit of humankind he did not succumb to the disease and was able to continue researching for another half-century. That he refused to let physical difficulties deter him from his life’s work is an inspiration to us all. </p>
<p>He was also a real character, and is famous for placing high-profile bets on big physics questions (which he usually lost). In 1974 he bet that the x-ray source at the centre of our galaxy, Cygnus X-1, was not a black hole, but conceded the loss due to overwhelming evidence by 1990. </p>
<p>From our modern perspective it’s astonishing to realise that all of his early research on black holes was done before we were even sure they existed. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/stephen-hawking-martin-rees-looks-back-on-colleagues-spectacular-success-against-all-odds-93379">Stephen Hawking: Martin Rees looks back on colleague's spectacular success against all odds</a>
</strong>
</em>
</p>
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<p>One of Hawking’s most fascinating bets was about the “information paradox”. The fact that black holes can evaporate turned out to be extremely perplexing, because all the information about what went into them is lost as the black hole vanishes. In quantum physics you can’t destroy information, thus the paradox. </p>
<p>Although Hawking conceded this bet very publicly in 2004, most physicists would still argue that the answer is unresolved. Recently it has seen a resurgence of interest with the “firewall paradox” and Hawking himself was adding new ideas to the debate even in his last few years.</p>
<p>As we say farewell to one of the greatest thinkers of our time, I leave you with some of his best advice:</p>
<blockquote>
<p>Look up at the stars and not down at your feet. Try to make sense of what you see, and wonder about what makes the universe exist. Be curious.</p>
</blockquote>
<p>With Stephen Hawking’s passing, humanity has lost a brilliant mind and an inspirational human being.</p><img src="https://counter.theconversation.com/content/93422/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tamara Davis receives funding from the Australian Research Council.</span></em></p>Stephen Hawking was a highly creative scientist, pushing past assumptions and playing with “what if” scenarios to take physics to new levels.Tamara Davis, Professor, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/933632018-03-14T06:09:08Z2018-03-14T06:09:08ZTributes pour in for Stephen Hawking, the famous theoretical physicist who died at age 76<p>Acclaimed British theoretical physicist, cosmologist and author Stephen Hawking has died aged 76. Hawking is best known for his work on black holes, which revolutionised our understanding of the universe. </p>
<p>Hawking passed away today peacefully at his home in Cambridge, his family confirmed in a <a href="https://www.theaustralian.com.au/news/world/stephen-hawking-dies-aged-76/news-story/ee7cdd9728ca1fc625770d731576b91f">statement</a>:</p>
<blockquote>
<p>We are deeply saddened that our beloved father passed away today. He was a great scientist and an extraordinary man whose work and legacy will live on for many years. </p>
<p>His courage and persistence with his brilliance and humour inspired people across the world. He once said, “It would not be much of a universe if it wasn’t home to the people you love.” We will miss him forever.</p>
</blockquote>
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<strong>
Read more:
<a href="https://theconversation.com/a-timeline-of-stephen-hawkings-remarkable-life-93364">A timeline of Stephen Hawking's remarkable life</a>
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</p>
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<p>Hawking was born on January 8, 1942, in Oxford, England. In 1963 he was diagnosed with ALS, a form of Motor Neurone Disease, and later confined to a wheelchair and forced to communicate via a computerised voice. But he continued his theoretical work and was outspoken on many things over much of his life.</p>
<p>Tributes have been pouring in on social media for the scientist, who made complex science accessible to everyone in his 1988 bestselling book <a href="https://www.theguardian.com/science/2018/mar/14/a-brief-history-of-stephen-hawkings-brief-history-of-time">A Brief History of Time</a>.</p>
<p>Among those early to pay tribute were the American astrophysicist Neil deGrasse Tyson and NASA.</p>
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<p>Others to pay tribute include Microsoft CEO Satya Nadella and the Prime Minister of India, Narendra Modi.</p>
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<p>Hawking’s acclaimed book, A Brief History of Time, was <a href="http://www.imdb.com/title/tt0103882/">made into a documentary</a> in 1991, directed by Errol Morris, who also paid tribute.</p>
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<h2>Australian reaction</h2>
<p>There have been reactions too from the world of Astronomy in Australia.</p>
<h2><a href="https://theconversation.com/profiles/alan-duffy-95986">Alan Duffy</a>, Associate Professor and Research Fellow, Swinburne University of Technology</h2>
<p>Professor Stephen Hawking was an inspiration to me to become not just a scientist but a communicator of that science.</p>
<p>His work as a cosmologist, and discoveries in black hole physics were legendary. His best-known prediction, named by the community as Hawking Radiation, transformed black holes from inescapable gravitational prisons into objects that instead shrink and fade away over time. </p>
<p>His writings were inspirational to many scientists and enriched the lives of millions with the latest science and cosmic perspectives. He was also wonderfully funny with a fantastic media savviness that propelled him into A-list celebrity stardom as few other scientists before.</p>
<p>Through it all, of course, his illness made his achievements near-superhuman. How he manipulated Einstein’s equations in his mind when he could no longer hold a pen I can’t even begin to imagine. </p>
<p>While his many contributions will live on there is no doubt that science and the wider world is the poorer for his passing.</p>
<hr>
<h2><a href="https://theconversation.com/profiles/jonti-horner-3355">Jonti Horner</a>, Professor (Astrophysics), University of Southern Queensland</h2>
<p>I think Stephen Hawking’s biggest achievement was getting people talking and interested in some very complex and challenging ideas about the universe and our place in it.</p>
<p>I remember the fuss when his book A Brief History of Time came out, and how it became such a big deal in the UK. It was amazing how widely read and discussed it was, particularly given its content (stuff that is usually portrayed as being really difficult and/or boring).</p>
<p>It was a fantastic example of how even the most complex and challenging ideas can capture the imagination, when they’re explained in the right way. Above and beyond the great research he did, his impact as a communicator was fantastic. </p>
<p>He definitely did a lot to bring those kind of concepts into the mainstream, and doubtless inspired a whole new generation of cosmologists and astronomers. That is probably the best legacy any scientist could ask for!</p>
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<h2><a href="https://theconversation.com/profiles/lisa-harvey-smith-6452">Lisa Harvey-Smith</a>, Group Leader - Australia Telescope National Facility Science, CSIRO</h2>
<p>Stephen Hawking was undoubtedly an intellectual giant, making leaps of reasoning that sometimes led to startling insights into the nature of the physical world. His finding that black holes slowly dissolve will probably be his greatest scientific legacy.</p>
<p>But he was much more than a skilled cosmologist. His greatest impact came from taking the time to carefully explain his theories to the public, engaging millions with his bestselling books. </p>
<p>As a 15-year-old, his most successful book A Brief History of Time had me captivated with relativity and quantum theory. This is the true strength of his legacy. </p>
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<h2><a href="https://theconversation.com/profiles/matthew-bailes-4276">Matthew Bailes</a>, ARC Laureate Fellow, Swinburne University of Technology, Swinburne University of Technology, and Director of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)</h2>
<p>Like many of the great theorists, Stephen Hawking had the ability to use very simple thought experiments to make predictions about the behaviour of the universe. </p>
<p>My favourite was his insight into evaporating black holes, which combined general relativity and quantum mechanics. </p>
<p>His ability to remain engaged with the scientific community despite his physical condition was a testament to his rare talent.</p>
<p>Hawking also recognised the enormous potential of the universe to be teeming with life and the advances in technology that might permit its detection in the near future. Hence his support for Breakthrough Listen, the search for alien life in the Universe.</p>
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<h2><a href="https://theconversation.com/profiles/steven-tingay-7618">Steven Tingay</a>, John Curtin Distinguished Professor (Radio Astronomy), Curtin University</h2>
<p>As an astrophysicist who has spent a significant fraction of my career working on the observational aspects of black holes using radio telescopes, and hoping to continue that with the billion dollar Square Kilometre Array over the next decade, Stephen Hawking’s work to understand the physics of black holes is close to my heart.</p>
<p>His mathematical and physical insights into black holes have been astonishing, which at some level synthesised general relativity and quantum mechanics. </p>
<p>Hawking’s work has inspired deep questions in physics and astrophysics, which has had a bearing on plans to build telescopes to explore the Universe, including the Square Kilometre Array in Australia.</p>
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<h2><a href="https://theconversation.com/profiles/alice-gorman-4234">Alice Gorman</a>, Senior Lecturer in archaeology and space studies, Flinders University</h2>
<p>There are few scientists who reach as far into popular culture as Stephen Hawking did. His research tackled the biggest of big questions – the nature of time, space and the universe we live in. </p>
<p>Sometimes it feels like science is losing ground in the modern world, but people still look to the stars for answers about who we are and how we come to be here. </p>
<p>Hawking’s bestselling A Brief History of Time made cosmology accessible to people and brought black holes out of the shadows and into the public imagination.</p>
<p>Personally I’ll miss his appearances on <a href="http://bigbangtheory.wikia.com/wiki/Stephen_Hawking">The Big Bang Theory</a>, where he could out-nerd the nerds, and also provide some often necessary common sense. It was always great to see a world-class scientist just having fun.</p><img src="https://counter.theconversation.com/content/93363/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alice Gorman is a Co-Deputy Chair of the Board of the Space Industry Association of Australia.</span></em></p><p class="fine-print"><em><span>Matthew Bailes receives funding from the Australian Research Council to perform fundamental science and is the Director of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav). One of OzGrav's aims is to promote the benefits of fundamental science and use the allure of black holes and relativity to attract young people to careers in STEM, and educate the general public.</span></em></p><p class="fine-print"><em><span>Steven Tingay receives funding from Curtin University, Western Australian Government, Australian Government, US Government. He is a member of the ALP.</span></em></p><p class="fine-print"><em><span>Alan Duffy, Jonti Horner, and Lisa Harvey-Smith do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Stephen Hawking inspired people with his work on black holes and other mysteries of the universe. Many were quick to pay tribute to the theoretical physicist who died today in the UK, aged 76.Alan Duffy, Associate Professor and Research Fellow, Swinburne University of TechnologyAlice Gorman, Senior Lecturer in archaeology and space studies, Flinders UniversityJonti Horner, Professor (Astrophysics), University of Southern QueenslandLisa Harvey-Smith, Astronomer at CSIRO, CSIROMatthew Bailes, ARC Laureate Fellow, Swinburne University of Technology., Swinburne University of TechnologySteven Tingay, John Curtin Distinguished Professor (Radio Astronomy), Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/665432016-10-08T00:51:40Z2016-10-08T00:51:40ZPhysicists explore exotic states of matter inspired by Nobel-winning research<figure><img src="https://images.theconversation.com/files/140958/original/image-20161007-21414-ajgt9v.jpg?ixlib=rb-1.1.0&rect=61%2C267%2C284%2C181&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Things are kind of different on the quantum level.</span> <span class="attribution"><span class="source">Nandini Trivedi</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The 2016 Nobel Prize in physics has been awarded to <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2016/thouless-facts.html">David Thouless</a>, <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2016/haldane-facts.html">Duncan Haldane</a> and <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2016/kosterlitz-facts.html">Michael Kosterlitz</a>, three theoretical physicists whose research used the unexpected mathematical lens of <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2016/popular-physicsprize2016.pdf">topology to investigate phases of matter and the transitions between them</a>.</p>
<p>Topology is a branch of mathematics that deals with understanding shapes of objects; it’s interested in “invariants” that don’t change when a shape is deformed, like the number of holes an object has. Physics is the study of matter and its properties. The Nobel Prize winners were the first to make the connection between these two worlds.</p>
<p>Everyone is used to the idea that a material can take various familiar forms such as a solid, liquid or gas. But the Nobel Prize recognizes other surprising phases of matter – called topological phases – that the winners proposed theoretically and experimentalists have since explored.</p>
<p>Topology is opening up new platforms for observing and understanding these new states of matter in many branches of physics. I work with theoretical aspects of cold atomic gases, a field which has only developed in the years since Thouless, Haldane and Kosterlitz did their groundbreaking theoretical work. Using lasers and atoms to emulate complex materials, cold atom researchers have begun to realize some of the laureates’ predictions – with the promise of much more to come.</p>
<h2>Cold atoms get us to quantum states of matter</h2>
<p>All matter is made up of building blocks, such as atoms. When many atoms come together in a material, they start to interact. As the temperature changes, the state of matter starts to change. For instance, water is a liquid until a fixed temperature, when it turns into vapor (373 degrees Kelvin; 212 degrees Fahrenheit; 100 degrees Celsius); and if you cool, solid ice forms at a fixed temperature (273K; 32°F; 0°C). The laws of physics give us a theoretical limit to how low the temperature can get. This lowest possible temperature is called absolute zero (0K) (and equals -460°F or -273°C).</p>
<p>Classical physics governs our everyday world. Classical physics tells us that if we cool atoms to really low temperatures, they stop their normally constant vibrating and come to a standstill.</p>
<p>But really, as we cool atoms down to temperatures approaching close to 0K, we leave the regime of classical physics – quantum mechanics begins to govern what we see. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nAGPAb4obs8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Atoms start to behave not as individual particles but as waves in the world of quantum physics.</span></figcaption>
</figure>
<p>In the quantum mechanical world, if an object’s position becomes sharply defined then its momentum becomes highly uncertain, and vice versa. Thus, if we cool atoms down, the momentum of each atom decreases, and the quantum uncertainty of its position grows. Instead of being able to pinpoint where each atom is, we can now only see a blurry space somewhere within which the atom must be. At some point, the neighboring uncertain positions of nearby atoms start overlapping and the atoms lose their individual identities. Surprisingly, the distinct atoms become a single entity, and behave as <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2001/">one coherent unit</a> – a discovery that won a previous Nobel.</p>
<p>This new, amazing way atoms organize themselves at very low temperatures results in new properties of matter; it’s no longer a classical solid in which the atoms occupy periodic well-defined positions, like eggs in a carton.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=581&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=581&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=581&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=730&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=730&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140881/original/image-20161007-21416-dcixy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=730&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Supercooled atoms are highly coherent.</span>
<span class="attribution"><span class="source">Nandini Trivedi</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Instead, the material is now in a new quantum state of matter in which each atom has become a wave with its position no longer identifiable. And yet the atoms are not moving around chaotically. Instead, they are highly coherent, with a new kind of quantum order. Just like laser beams, the coherent matter waves of superfluids, superconductors and magnets <a href="http://doi.org/10.1126/science.275.5300.637">can produce interference patterns</a>.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=586&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=586&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=586&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=737&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=737&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140883/original/image-20161007-21454-154tkox.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=737&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">As temperatures rise, materials lose their quantum order.</span>
<span class="attribution"><span class="source">Nandini Trivedi</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Physicists have known about quantum order in superfluids and magnets in three dimensions since the middle of the last century. We understand that the order is lost at a critical temperature due to thermal fluctuations. But in two dimensions the situation is different. Early theoretical work showed that thermal fluctuations would destroy the quantum order even at very low temperatures. </p>
<p>What Thouless, Haldane and Kosterlitz addressed were two important questions: What is the nature of the quantum ordered state of superfluids, superconductors and magnets in low dimensions? What is the nature of the phase transition from the ordered to the disordered state in two dimensions? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=317&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=317&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=317&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140892/original/image-20161007-21421-1gllk4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The whirl of a topological defect, a vortex or an anti-vortex, can be felt no matter how far you go from the eye of the storm.</span>
<span class="attribution"><span class="source">Nandini Trivedi</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Thinking about defects</h2>
<p>Kosterlitz and Thouless’s innovation was to show that topological defects – vortex and anti-vortex whirls and swirls – are crucial to understand the magnetic and superfluid states of matter in two dimensions. These defects are not just local perturbations in the quantum order; they produce a winding or circulation as one goes around it. The vorticity, which measures how many times one winds around, is measured in integer units of the circulation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=248&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=248&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=248&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=312&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=312&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140906/original/image-20161007-21430-w2slpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=312&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On the left, a vortex is bound up with an anti-vortex. On the right, more and more defects unbind upon increasing the temperature, and the material enters a disordered state.</span>
<span class="attribution"><span class="source">Nandini Trivedi</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Kosterlitz and Thouless showed that at low temperatures, a vortex is bound up with an anti-vortex so the order survives. As the temperature increases, these defects unbind and grow in number and that drives a transition from an ordered to a disordered state. </p>
<p>It’s been possible to visualize the vortices in cold atomic gases that Kosterlitz and Thouless originally proposed, <a href="http://doi.org/10.1038/nature04851">bringing to life the topological defects they theoretically proposed</a>. In my own research, <a href="http://doi.org/10.1038/nphys983">we’ve been able to extend these ideas</a> to quantum phase transitions driven by increasing interactions between the atoms rather than by temperature fluctuations.</p>
<h2>Figuring out step-wise changes in materials</h2>
<p>The second part of the Nobel Prize went to Thouless and Haldane for discovering new topological states of matter and for showing how to describe them in terms of topological invariants. </p>
<p>Physicists knew about the existence of a phenomenon called the quantum Hall effect, first observed in two dimensional electrons in semiconductors. The Hall conductance, which is the ratio of the transverse voltage and the current, was observed to change in very precise integer steps as the magnetic field was increased. This was puzzling because real materials are disordered and messy. How could something so precise be seen in experiments?</p>
<p>It turns out that the current flows only in narrow channels at the edges and not within the bulk of the material. The number of channels is controlled by the magnetic field. Every time an additional channel or lane gets added to the highway, the conductance increase by a very precise integer step, with a precision of one part in billion. </p>
<p>Thouless’ insight was to show that the flow of electrons at the boundaries has a topological character: the flow is not perturbed by defects – the current just bends around them and continues with its onward flow. This is similar to strong water flow in a river that bends around boulders.</p>
<p>Thouless figured out that here was a new kind of order, represented by a topological index that counts the number of edge states at the boundary. That’s just like how the number of holes (zero in a sphere, one in a doughnut, two in glasses, three in a pretzel) define the topology of a shape and the robustness of the shape so long as it is deformed smoothly and the number of holes remains unchanged. </p>
<h2>Global, not local, properties</h2>
<p>Interacting topological states are even more remarkable and truly bizarre in that they harbor fractionalized excitations. We’re used to thinking of an electron, for instance, with its charge of e as being indivisible. But, in the presence of strong interactions, as in the fractional quantum Hall experiments, the electron indeed fractionalizes into three pieces each carrying a third of a charge! </p>
<p>Haldane discovered a whole new paradigm: in a chain of spins with one unit of magnetic moment, the edge spins are fractionalized into units of one-half. Remarkably, the global topological properties of the chain completely determine the unusual behavior at the edges. Haldane’s remarkable predictions have been verified by experiments on solid state materials containing one-dimensional chains of magnetic ions.</p>
<p>Topological states are new additions to the list of phases of matter, such as, solid, liquid, gas, and even superfluids, superconductors and magnets. The laureates’ ideas have opened the floodgates for prizeworthy predictions and observations of topological insulators and topological superconductors. The <a href="http://doi.org/10.1038/nature13915">cold atomic gases present opportunities</a> beyond what can be achieved in materials because of the greater variety of atomic spin states and highly tunable interactions. Beyond the rewards of untangling fascinating aspects of our physical world, this research opens the possibility of using topologically protected states for quantum computing.</p><img src="https://counter.theconversation.com/content/66543/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nandini Trivedi 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>Forget solid, liquid, gas. This research used advanced math to theorize about topological phases of matter. And over the years experiments with matter and cold atoms have been validating the ideas.Nandini Trivedi, Professor of Physics, The Ohio State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/459662015-09-28T05:32:25Z2015-09-28T05:32:25ZUnderstanding the hidden dimensions of modern physics through the arts<figure><img src="https://images.theconversation.com/files/95705/original/image-20150922-16698-1kqvv6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Can the arts be a bridge to other worlds?</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/parksdh/9713995081/in/photolist-fNoLiP-D77HM-rUT5cx-pnTCYC-nmjt4Z-4tFJRm-4LsuM-hPBoYS-e3kE6B-96QyBj-jeXEcA-fky24x-vT4uBk-4tzBVc-nrZNnP-c8XrUy-9oTKUr-sQstBQ-5Bpk4Q-cC2gjf-aaoMeg-bqbJVx-4G2K3S-oyApa-nqhCRj-yNTFq-qqqTCV-nwXu22-ikpUps-xp4eDm-7uWEfq-eCxuRJ-7dpYrk-eiZAyY-cgyH7u-odVRjt-qrqX1C-dMta5V-cQczT5-owkJCB-u7LcTn-cQczWE-wMpZzc-wfghta-9EBncx-wqgCaK-qgC6m1-wN3ymr-bsKgrw-bsKibw">Daniel Parks</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Sometimes, the hardest job for a theoretical physicist is telling the story. The work in this field can be conducted entirely in the abstract, leaving outsiders (and the odd insider) bewildered, but there might be some assistance in the visualisation techniques developed by certain artists and writers. Cutting-edge theories are often motivated by aesthetics and simplicity, after all, and so the idea of a synergy between artists and scientists does not seem all that far-fetched. One clear example where the combination can work comes in the exploration and understanding of extra dimensions. </p>
<p>You may have heard that scientists often talk of these “other worlds”, but (hopefully), your everyday reality takes place in three dimensions of space, and one dimension of time. Physicists marry together these dimensions because of Albert Einstein’s special theory of relativity; it enables us to describe a point in (1+3) dimensions of (time+space) with four coordinates: (t, x, y, z). But from an abstract point of view, it makes a lot of sense to then ask: why just four? And in fact, many theories in physics can easily be formulated without being too specific about the number of dimensions. We can call it 1+D instead and open up the the possibility of more than three spatial dimensions: (t, x, y, z….). </p>
<p>But that’s where it gets hard, of course. Extra spatial dimensions are very hard to imagine, and even the scientists working with them (<a href="http://thequantummessenger.com">such as myself</a>) have a hard time visualising them. Now, this in itself is not proof that they do not exist. We also find it hard to imagine infinities, for instance, and <a href="http://www.physics.org/article-questions.asp?id=124">super-positions of quantum mechanical states</a>, but both these concepts are seen in nature. </p>
<h2>Hidden truths</h2>
<p>Physicists have of course <a href="http://thequantummessenger.com/index.php/2015/08/14/adding-dimensions-with-art-and-prose-1/#_ftn2">come up with tests</a> which allow for the existence of other dimensions, but the trouble is that this delivers results which imply we’re happily bumping along with the ones we’re all very familiar with.</p>
<p>But before concluding that this invalidates the whole discussion about more dimensions already, there are ways to get around this result. We already <a href="http://home.web.cern.ch/about/physics/extra-dimensions-gravitons-and-tiny-black-holes">knew</a> that the new dimensions would have to be very different from the ones we experience – otherwise we would be able to see them. In much the same way they may not show up in those tests which use <a href="http://thequantummessenger.com/index.php/2015/08/14/adding-dimensions-with-art-and-prose-1/#_ftnref2">force laws</a>. They may be very small, for instance, and folded away to make them invisible to us. Size and energy are inversely related in particle theories, so the smaller the dimensions are, the less likely it is that we will be able to probe them directly. </p>
<p>A popular example of how this works is by an ant on a piece of rope. From far away, the piece of rope seems one-dimensional, but only when you zoom in you can see that in the ant’s world the surface it sits on is really 2D. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/96034/original/image-20150924-17062-ou2c8h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Our ability to perceive even our own dimensions can be flawed.</span>
<span class="attribution"><a class="source" href="http://www.alexameade.com/">Alexa Meade</a></span>
</figcaption>
</figure>
<p>This limited ability to perceive dimensions even in our familiar world can be seen in the <a href="http://www.alexameade.com/">work of artist Alexa Meade</a>, who paints 3D installations and renders them 2D to our primitive eyes. And to start visualising extra dimensions instead, scientists may also take inspiration from the arts. </p>
<h2>Slicing</h2>
<p>A good starting point is to turn the question on its head: in <a href="https://www.youtube.com/watch?v=RxcMa4lay5Q">the 1884 novella Flatland</a> EA Abbott wrote about creatures living in fewer dimensions, instead of more. The creatures of his 2D world experienced 3D through cross sections of objects passing through. An illustration from the book appears below.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=220&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=220&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=220&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=277&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=277&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93542/original/image-20150901-13419-qp08bc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=277&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Flatland, A Romance of Many Dimensions, EA Abbott</span></span>
</figcaption>
</figure>
<p>In exactly the same way we may use a computer to show what a cross section of a 4D image would look like in 3D, or in 2D. A 4D cube (a hypercube) may for instance be represented with this slicing method: </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=294&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=294&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=294&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=370&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=370&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93540/original/image-20150901-13412-woiv6p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=370&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Thomas Banchoff, Brown University</span></span>
</figcaption>
</figure>
<p>Interestingly, both are slices of the same object, but in the top set of images the slicing was started on a corner, and in the second one with a square. </p>
<p>EA Abbott wrote about slicing, but there may have been another way in which his flat creatures observed the 3D sphere. If the 3D sun had shone over it, a shadow would have been cast over the plane: this defines the linear perspective method. It has a foundation in ancient Greece, and modern artists still follow the <a href="https://www.khanacademy.org/humanities/renaissance-reformation/early-renaissance1/beginners-renaissance-florence/v/linear-perspective-brunelleschi-s-experiement">techniques developed by Renaissance architect Filippo Brunelleschi</a>, perhaps most famous for building the gigantic dome of on Florence cathedral. Jean-François Colonna has some <a href="http://www.lactamme.polytechnique.fr/">great examples of extra dimensional objects</a> created using the perspective method which have all the trappings of abstract art.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93541/original/image-20150901-13392-ws979j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">from http://www.drawspace.com/</span></span>
</figcaption>
</figure>
<h2>Light and shade</h2>
<p>In the same way that the light from our sun casts shadows on 2D surfaces, that is, in parallel lines, we may consider a hypothetical 4D sun which casts a shadow of a 4D object onto our 3D world. This is hard to visualise, but easy to program on a computer. A hypercube would then look like this: </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=649&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=649&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=649&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=815&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=815&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93539/original/image-20150901-13425-q8lpfi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=815&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">from Wolfram Mathworld</span></span>
</figcaption>
</figure>
<p>This is called a Schlegel diagram. Perhaps it is not immediately obvious how this is related to a shadow, but considering its contour lines may help.</p>
<p>If you can imagine adding one dimension, you can imagine adding several. Descriptions of string theory, for example, only make sense when formulated in as many as 11 dimensions. And though the result may grow in complexity with the number of dimensions, the techniques looked at here are not limited to 4D. </p>
<p>Difficulties with visualizing physical theories have never proved to be a valid basis for their rejection, but they have been an obstacle to understanding. The techniques developed for visualizing extra dimensions form a good example of how physicists may borrow and extrapolate techniques developed in the arts world, and how interdisciplinary collaborations may be beneficial to both fields.</p><img src="https://counter.theconversation.com/content/45966/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Djuna Croon receives funding from the University of Sussex. </span></em></p>Is a novella published 130 years ago our best bet for explaining the worlds of 4D and beyond?Djuna Croon, PhD Researcher, University of SussexLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/409672015-06-18T20:10:28Z2015-06-18T20:10:28ZFrom Newton to Hawking and beyond: a short history of the Lucasian Chair<figure><img src="https://images.theconversation.com/files/85484/original/image-20150618-23256-bqqg2r.jpg?ixlib=rb-1.1.0&rect=216%2C281%2C1762%2C1474&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Isaac Newton was the most famous Lucasian Professor, but many other colourful figures have also occupied 'Newton's Chair'.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Isaac_Newton,_English_School,_1715-20.jpg#/media/File:Isaac_Newton,_English_School,_1715-20.jpg">Bonhams/Wikimedia</a></span></figcaption></figure><p>On July 1 physicist <a href="http://www2.ph.ed.ac.uk/%7Emec/">Michael Cates</a> will be the 19th person to sit in what is perhaps the most <a href="http://www.cambridge.org/au/academic/subjects/general-science/history-science/newton-hawking-history-cambridge-universitys-lucasian-professors-mathematics">prestigious “chair” in science</a> when he assumes the post of the <a href="https://en.wikipedia.org/wiki/Lucasian_Professor_of_Mathematics">Lucasian Professor of Mathematics</a> at Cambridge University. </p>
<p>Although sometimes called “Newton’s chair” after its most famous holder, Sir Isaac was not the only brilliant mind, nor the most colourful individual, to occupy the post.</p>
<p>The Lucasian Chair was founded in 1663 at the bequest of <a href="https://en.wikipedia.org/wiki/Henry_Lucas_(died_1663)">Henry Lucas</a> (1640-1648), who was a member of Parliament for Cambridge University. In his will, he <a href="http://www.cambridge.org/au/academic/subjects/general-science/history-science/newton-hawking-history-cambridge-universitys-lucasian-professors-mathematics">provided</a> “a yearly stipend and salarie for a professor […] of mathematicall sciences in the said Vniversitie” to “honor that greate body” and assist “that parte of learning which hitherto hath not bin provided for”. </p>
<p>The Lucasian Chair has been held by a fascinating procession of scientists, including</p>
<ul>
<li>Physicist and mathematician <a href="http://www.biography.com/people/isaac-newton-9422656">Issac Newton</a> (who held the chair from 1669 to 1702)</li>
<li>Astronomer <a href="http://www.britannica.com/biography/George-Biddell-Airy">George Biddell Airy</a> (1826 to 1828)</li>
<li>Mathematician and computing pioneer <a href="http://www.cbi.umn.edu/about/babbage.html">Charles Babbage</a> (1828 to 1839)</li>
<li>Physicist and mathematician <a href="http://www.giffordlectures.org/lecturers/george-gabriel-stokes">George Stokes</a> (1849 to 1903)</li>
<li>Physicist <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-bio.html">Paul Dirac</a> (1932 to 1969)</li>
<li>Theoretical physicist <a href="http://www.britannica.com/biography/Stephen-W-Hawking">Stephen Hawking</a> (1979 to 2009) and most recently, </li>
<li>Theoretical physicist <a href="http://www.damtp.cam.ac.uk/people/m.b.green/">Michael Green</a> (2009 to 2015). </li>
</ul>
<p>It also has the unusual distinction of having been held by a famous – though fictitious and wholly artificial person – Star Trek: The Next Generation’s <a href="http://en.memory-alpha.wikia.com/wiki/Data">Data</a>, in the series’ final episode, “<a href="http://www.imdb.com/title/tt0111281/">All Good Things…</a>”. But that is another quantum timeline.</p>
<h2>Smart seat</h2>
<p>The first Lucasian Professor, <a href="http://www.britannica.com/biography/Isaac-Barrow">Isaac Barrow</a>, held both the Regius Professorship of Greek and Gresham Chair in geometry. </p>
<p>Sadly, Barrow’s early ardour for mathematics had waned by the time he took up the Chair in 1663. His “method of tangents”, though, was seen as ground breaking at the time. This proto-calculus set the scene for his brilliant successor: Isaac Newton.</p>
<p><a href="http://www.biography.com/people/isaac-newton-9422656">Newton</a> was elected to the Chair after his <em>anni mirabiles</em> of 1666. According to <a href="https://royalsociety.org/library/moments/newton-apple/">William Stukeley’s 1752 biography</a>, that is the year Newton inferred the law of gravity by observing an apple falling in his orchard as he “sat in contemplative mood”. </p>
<p>While Lucasian Professor, Newton developed his most important contributions to science, in particular the masterpieces <a href="http://cudl.lib.cam.ac.uk/view/PR-ADV-B-00039-00001/1">Philosophiae Naturalis Principia Mathematica</a> (1687) and <a href="http://www.gutenberg.org/files/33504/33504-h/33504-h.htm">Opticks</a> (1704).</p>
<p>At the time of Newton’s election in 1669, the Lucasian Chair was one of eight <a href="http://en.wikipedia.org/wiki/List_of_professorships_at_the_University_of_Cambridge">Chairs at Cambridge</a>. The Lucasian Professor is elected, then as now. The election is made by the masters of the Colleges at Cambridge, with the vice chancellor able to break a deadlock if required.</p>
<h2>An uneven history</h2>
<p>Despite its prestige, the history of the Chair is not one of undiluted greatness. </p>
<p>The stories of the post-Newtonian Chairs of William Whiston (from 1702 to 1710), Nicholas Saunderson (1711 to 1739), John Colson (1739 to 1760), Edward Waring (1760 to 1798) and Isaac Milner (1798 to 1820) was largely one of translating, teaching, expanding and developing the great works of former Chair-holder, Newton.</p>
<p>In the latter half of the 19th century, as science became the arena of professional scientists rather than dilettante gentlemen, the Lucasian Chair was sometimes used as a stepping stone to more lucrative or important positions. </p>
<p>Robert Woodhouse (Chair from 1820 to 1822) lasted only two years in the post. He was rewarded for his “conformity” by securing the <a href="http://adsabs.harvard.edu/full/1911Obs....34..341L">Plumian Chair of mathematics</a> and the directorship of the Cambridge astronomical observatory. </p>
<p>His successor, Thomas Turton (from 1822 to 1826), described as “mathematically inert and utterly reliable”, departed to the more prestigious Regius Chair of Divinity (founded in 1540 by Henry VIII) and better paid dean-ships, eventually becoming the Bishop of Ely.</p>
<h2>Dirac and the quantum age</h2>
<p>Nevertheless, while the term might not apply to all holders of the Chair, Paul Dirac (from 1932 to 1969), was indisputably brilliant. In fact, Dirac personified the stereotype of the lone genius. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=886&fit=crop&dpr=1 600w, https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=886&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=886&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1113&fit=crop&dpr=1 754w, https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1113&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/85495/original/image-20150618-23217-1e60wgl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1113&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Paul Dirac was one of the more brilliant Lucasian Professors. He predicted the existence of antimatter before it was first detected.</span>
<span class="attribution"><a class="source" href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-facts.html">Nobel Foundation</a></span>
</figcaption>
</figure>
<p>Einstein <a href="https://books.google.com.au/books?id=zXm1Bso1VREC&pg=PA82&lpg=PA82&dq=Einstein+Dirac+his+balancing+on+the+dizzying+path+between+genius+and&source=bl&ots=OKhIznXMDa&sig=ySmItECFnf8EzVFModWB4g4rLXg&hl=en&sa=X&ved=0CCsQ6AEwAmoVChMI-MHji6-OxgIVU328Ch38FwCQ#v=onepage&q=Einstein%20Dirac%20his%20balancing%20on%20the%20dizzying%20path%20between%20genius%20and&f=false">said of him</a>: “This balancing on the dizzying path between genius and madness is awful.”</p>
<p>By the age of 26, Dirac had, in the period from 1925 to 1928, developed his own theory of quantum mechanics and relativistic quantum theory of the electron, as well as predicted the existence of antimatter. </p>
<p><a href="http://dragonlaughing.tumblr.com/post/120042169749/tale-of-a-strange-man-the-biography-of-physicist">Dirac</a>, like Newton, also made significant contributions to science in his tenure as Lucasian Professor. According to <a href="https://en.wikipedia.org/wiki/John_Polkinghorne">John Polkinghorne</a>, Dirac was once asked about his most fundamental belief, upon which, “<a href="https://books.google.com.au/books?id=dzALOdPG-CAC&printsec=frontcover#v=onepage&q&f=false">he strode to a blackboard and wrote that the laws of nature should be expressed in beautiful equations</a>”.</p>
<h2>Hawking: the stopgap professor?</h2>
<p>Of the more recent holders of the Lucasian Chair, it is the name of Stephen Hawking, who held the Professorship for three decades from 1979 to 2009, that has become most synonymous with the post – and a household name at that. </p>
<p>In an interview with <a href="https://ucdavis.academia.edu/H%C3%A9l%C3%A8neMialet">Hélène Mialet</a>, Hawking said he always assumed he was elected as a stopgap professor because he was not expected to live a long time and his “<a href="http://www.academia.edu/2336920/Reading_Hawking_s_Presence_An_Interview_with_a_Self_Effacing_Man">work would not disgrace the standards expected of the Lucasian chair</a>”. </p>
<p>Nonetheless he confounded his doctors and held the chair until the retirement age of 67.</p>
<p>Hawking had, at the time of his election, hoped the Chair might go to a brilliant scientist who was not already affiliated with or educated at Cambridge. This would have been a remarkable change. </p>
<p>Holders of the Lucasian Chair have all been Cambridge graduates, in addition to being male and British. Only Dirac and Hawking have undergraduate degrees from a university other than Cambridge (Bristol and Oxford, respectively). Dirac alone was not of British birth – he was a Swiss national, though born in England in 1902 and acquiring British nationality in 1919.</p>
<p>The quality of Hawking’s scientific output puts this “stopgap professor” in the Lucasian top-three league, along with Newton and Dirac. </p>
<p>Incidentally, Stephen Hawking played a game of poker with Star Trek’s Data – the fictitious future Lucasian Chair – along with fellow Chair Isaac Newton and Albert Einstein (the latter played by actors, of course) in Star Trek: the Next Generation’s episode “<a href="http://www.imdb.com/title/tt0708700/">Descent</a>”.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mg8_cKxJZJY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Hawking was succeeded by <a href="http://physicsworld.com/cws/article/news/2009/oct/20/string-theorist-takes-over-from-hawking">Michael Green</a>, who was Lucasian Professor from 2009 to this year. Green made long-term contributions to mathematics, including pioneering string theory in 1984. </p>
<h2>What does the future of the chair hold?</h2>
<p>Michael Cates is certainly no stopgap professor. Cates is an expert in the statistical mechanics of “soft materials”, examples of which are: colloids (paint); emulsions (mayonnaise); foams (shaving cream); surfactant solutions (shampoo); and liquid crystals (flat screen TVs). </p>
<p>His models capture the essential physics without including all the, at times confounding, chemical detail. </p>
<p>Prior to his election as Lucasian Professor, Cates held a <a href="https://royalsociety.org/grants/case-studies/michael-cates/">Royal Society Research Professorship</a> at Edinburgh. At age 54, he will likely hold the Chair for more than a decade. It will be fascinating to see what he contributes to mathematics and the ongoing Lucasian history during his tenure.</p>
<p>As for future chairs? If Star Trek is any indication, it will continue to be populated by some of the most brilliant minds in the known universe – although one wonders when it might be finally held by a brilliant woman.</p><img src="https://counter.theconversation.com/content/40967/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Some of history’s most brilliant scientists have occupied the Lucasian Chair, including Newton, Dirac and Hawking. Others were not so stellar.Kevin Orrman-Rossiter, PhD Research Student, History & Philosophy of Science, The University of MelbourneMorgan Saletta, Adjunct Faculty, History and Philosophy of Science and Department of Management and Marketing, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/372782015-02-11T19:27:13Z2015-02-11T19:27:13ZSchrödinger’s cat gets a reality check<figure><img src="https://images.theconversation.com/files/71687/original/image-20150211-25693-z5uat7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If kitty goes in, will she really be alive and dead? </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/29233640@N07/8132455446/in/photolist-doCXF5-86PBZy-aAFX2s-9FcFZV-9Kzc7m-9FfCfd-9EDhZk-9o2yKZ-6Qjby7-aZBhpM-2LCpRM-9FfCbo-drikci-3dEk3a-3KAMMz-8DSVKT-aVxtaK-7J7k8u-4KRXMb-9g9JTR-7M14mC-fpEYk5-4cK1ws-pRv6Zo-6LPcTx-a9s4m-8cV53i-dVcD2p-8MbPXd-7u9oBH-anipoX-2qmUbo-9txn1d-pmxjp5-2qmqcK-4A5nNt-4sEVa6-9hGgaK-4YbUNM-9YvdPd-4cFPfR-4Er2p3-e71X98-mfvLKe-6p2JJx-7uGKfg-6sPmXQ-8Rc7pE-3bn6pG-8hC351">Robert Couse-Baker/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It’s a century-old debate: what is the meaning of the <a href="http://www.britannica.com/EBchecked/topic/637845/wave-function">wave function</a>, the central object of quantum mechanics? Is <a href="http://www.iflscience.com/physics/schr%C3%B6dinger%E2%80%99s-cat-explained">Schrödinger’s cat</a> <em>really</em> dead and alive? </p>
<p>I was recently involved in <a href="https://doi.org/10.1038/nphys3233">an experiment</a> conducted by Andrew White’s Quantum Technology Lab at the University of Queensland that has now provided the most significant evidence on that question in years. And it doesn’t look good for the cat.</p>
<p>To understand the importance of this result, we need to delve into its history. At the root of quantum physics there is something of a reality crisis. Multiple interpretations of the theory exist, and they paint very different pictures of the world. One of the major contentions centres around what we should make of the quantum wave function.</p>
<p>In short, the wave function describes the quantum state of a physical system. But unlike in classical physics, where a complete specification of a state determines all of its properties (for example, a particle’s position and velocity), the quantum state in general only gives probabilistic predictions.</p>
<p>In fact, the wave function seems to describe bizarre situations, like physical systems existing simultaneously in multiple states, such as different positions or velocities. It gives very precise probabilities for the possible outcomes of laboratory experiments, but it defies an intuitive interpretation.</p>
<p>Some of the founders of the theory, such as physicists Niels Bohr and Werner Heisenberg, suggested that until an observation of one or another property is made, questions like “where is this particle, <em>really</em>?” simply don’t make sense. </p>
<p>Under this view, it’s not that the particle is <em>really</em> here or there (and we just don’t know until we look). Rather, for Bohr the very meaning of “position” depends on the existence of a measurement that detects it.</p>
<p>Physicist Erwin Schrödinger’s famous thought experiment was designed to show how, if quantum mechanics is taken literally and to its ultimate implications, even macroscopic systems, like cats, would be in such “superpositions” of states – such as the cat being both dead and alive – which is an apparently absurd conclusion.</p>
<h2>It’s all in your head</h2>
<p>An indeterminate reality was unacceptable for Albert Einstein, who famously said: “Do you really believe the moon exists only when you look at it?” Einstein believed instead that the wave function should be understood as representing our limited information about the actual state of physical systems.</p>
<p>A first blow to Einstein’s view came in 1964, when John S Bell showed that any model that describes an objective reality underlying quantum mechanics must include <a href="http://www.nature.com/news/physics-bell-s-theorem-still-reverberates-1.15435">some sort of non-local connection</a> between distant systems, in an apparent violation of Einstein’s own theory of relativity.</p>
<p>And contrary to Einstein’s wish, in all objective interpretations known to date (such as the <a href="http://physics.about.com/od/quantumphysics/f/manyworldsinterpretation.htm">Many Worlds interpretation</a>, <a href="http://en.wikipedia.org/wiki/Objective_collapse_theory">objective collapse models</a>, and <a href="http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory">de Broglie-Bohm theory</a>), the wave function is a real physical object (with one <a href="http://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013">very recent exception</a>, where the wave function plays no explicit role, but the cat is literally dead and alive in parallel universes).</p>
<p>In 2007, however, Robert Spekkens from the Perimeter Institute published a <a href="http://journals.aps.org/pra/abstract/10.1103/PhysRevA.75.032110">seminal work</a> showing that it was possible to reproduce many of the counter-intuitive aspects of quantum theory with a model where the wave function plays the “epistemic” role Einstein longed for. </p>
<p>Other fragments of quantum theory were later shown to fit similar models, but the question was open whether or not this was possible for all of quantum theory. Could Einstein’s dream be revived?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/71576/original/image-20150210-24682-1dpygv1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Einstein wanted to believe that there was some more fundamental reality underlying quantum mechanics.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/wallyg/136352792/in/photolist-d3QWd-J2up8-khwAYe-aUAVvP-7FGrXj-8d48o1-62tQrZ-5d1HxG-4ne9U5-sM1d9-7YH4Rb-5uY1RY-k9ab9d-bbZGbV-5zL96E-4j1qCF-aEUprf-MknkP-bre1Cq-64VgXa-4bZR2S-7khrJ-Mkcdy-p4KVnu-6Vovge-dsrAi9-66GWQ-dhoVKC-gewkn-9VGz2R-khz3Bo-khxhnH-dS2tix-4fFZ26-7Bb135-7YGSb5-aq7hn2-Gurvx-dSWukX-7mhaTE-crNYoJ-a1poC-MGjVX-dNUSw9-oT1QJw-eErJB5-64Zz3f-6tATdd-baHeYv-oLVo5L">Wally Gobetz/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>To understand what this kind of model is, imagine I hold two decks of cards: one contains only red cards, the other only aces, and I ask you to pick a card from one, without knowing which is which. </p>
<p>In an epistemic interpretation, the wave function would play the role of the deck you pick the card from. It gives you some information about the card – like if you pick from the aces deck, you’re sure to pick an ace of some sort – but this information is not itself a property of the card. In fact, it is possible that you have picked an ace of hearts, which is compatible with both decks.</p>
<p>A wake-up call came in 2012, when <a href="http://www.nature.com/nphys/journal/v8/n6/full/nphys2309.html">Matthew Pusey, Jonathan Barrett and Terry Rudolph showed</a> that in any objective model of quantum theory, the wave function must be a real property of individual systems, unlike the deck of cards. But, their theorem had an extra assumption that has called the implications of the theorem into question. </p>
<h2>Reality check</h2>
<p>However, a series of theorems published within the last year, starting with <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.250403">work from myself and colleagues</a>, puts strong bounds on the viability of epistemic models, even without those extra assumptions. </p>
<p>These theorems consider the fact that some pairs of quantum states cannot be distinguished on a single experiment. This is analogous to not always being able to tell whether a randomly picked card came from the red deck or the ace deck. If you pick a non-ace card, you can be sure it came from the red deck. If you pick a black ace, you can be sure it came from the ace deck. </p>
<p>But if it’s an ace of hearts or an ace of diamonds, it could have come from either. Counting the cards in the decks, we can determine how often this is supposed to happen.</p>
<p>In an epistemic interpretation, the fact we can’t distinguish quantum states should be at least partially accounted for in this way. But the theorems show that this explanation simply cannot work. For some specially constructed quantum states, the “decks” corresponding to them cannot have anywhere near the right amount of cards in common, so to speak.</p>
<p>These predictions were partially confirmed by <a href="http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3233.html">the experiment</a> I was involved with, performed by Martin Ringbauer and the Brisbane team led by <a href="http://www.mostlyquantum.org/?page_id=14">Alessandro Fedrizzi</a>. They followed an improved version of our theorem due to Cyril Branciard, a co-author in the study. </p>
<p>The experiment involved preparing single photons (particles of light) in those specially designed states and subjecting them to a number of alternative measurements. The results give bounds on how well a model like the one outlined above can describe the statistics they observe.</p>
<p>This represents the first large class of quantum models to be ruled out since Bell’s theorem started being tested in the 1980s.</p>
<p>If further experiments confirm the implications of the theorems, viable epistemic models of quantum mechanics will be essentially ruled out. If we want an objective reality, à la Einstein, the wave function <em>must</em> be real, dead and alive cats and all.</p>
<p>But there are alternatives. One could be to reconsider assumptions of the framework used to derive the theorems, perhaps by introducing backwards-in-time causality or parallel universes. However, no approaches of this form have yet managed to produce an epistemic interpretation. </p>
<p>Or else, we can <a href="http://www.nature.com/news/physics-qbism-puts-the-scientist-back-into-science-1.14912">deny that a purely objective description is possible at all</a>. However it may be, the weirdness of quantum mechanics is here to stay.</p><img src="https://counter.theconversation.com/content/37278/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eric Cavalcanti receives funding from the Australian Research Council.</span></em></p>It’s a century-old debate: what is the meaning of the wave function, the central object of quantum mechanics? Is Schrödinger’s cat really dead and alive? I was recently involved in an experiment conducted…Eric Cavalcanti, Associate Professor (ARC Future Fellow), Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/223362014-02-23T19:29:33Z2014-02-23T19:29:33ZAn end in sight in the long search for gravity waves<figure><img src="https://images.theconversation.com/files/42119/original/dxybw6ts-1392940790.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We know gravity waves exist but just haven't detected any... yet.</span> <span class="attribution"><span class="source">www.shutterstock.com</span></span></figcaption></figure><p>Our unfolding understanding of the universe is marked by epic searches and we are now on the brink of discovering something that has escaped detection for many years.</p>
<p>The search for gravity waves has been a <a href="https://theconversation.com/gravity-waves-scientists-wave-back-squeezing-light-beyond-quantum-limit-3342">century long epic</a>. They are a prediction of Einstein’s <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">General Theory of Relativity</a> but for years physicists argued about their theoretical existence.</p>
<p>By 1957 physicists had proved that they must carry energy and cause vibrations. But it was also apparent that waves carrying a million times more energy than sunlight would make vibrations smaller than an atomic nucleus.</p>
<p>Building detectors seemed a daunting task but in the 1960s a maverick physicist <a href="http://physicsworld.com/cws/article/news/2000/oct/10/joseph-weber-1919-to-2000">Joseph Weber</a>, at the University of Maryland, began to design the first detectors. By 1969 he claimed success!</p>
<p>There was excitement and consternation. How could such vast amounts of energy be reconciled with our understanding of stars and galaxies? A scientific gold rush began.</p>
<p>Within two years, ten new detectors had been built in major labs across the planet. But nothing was detected.</p>
<h2>Going to need a better detector</h2>
<p>Some physicists gave up on the field but for the next 40 years a growing group of physicists set about trying to build vastly better detectors.</p>
<p>By the 1980s a worldwide collaboration to build five detectors, called cryogenic resonant bars, was underway, with one detector called NIOBE located at the University of Western Australia.</p>
<p>These were huge metal bars cooled to near <a href="http://physics.about.com/od/glossary/g/absolutezero.htm">absolute zero</a>. They used superconducting sensors that could detect a million times smaller vibration energy than those of Weber.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.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"></a>
<figcaption>
<span class="caption">Gravity waves caused by two rotating black holes.</span>
<span class="attribution"><a class="source" href="http://spaceplace.nasa.gov/lisa-g-waves/en/">Nasa</a></span>
</figcaption>
</figure>
<p>They operated throughout much of the 1990s. If a pair of black holes had collided in our galaxy, or a new black hole had formed, it would have been heard as a gentle ping in the cold bars… but all remained quiet.</p>
<p>What the cryogenic detectors did achieve was an understanding of how quantum physics affects measurement, even of tonne-scale objects. The detectors forced us to come to grips with a new approach to measurement. Today this has grown into a major research field called macroscopic quantum mechanics.</p>
<p>But the null results did not mean the end. It meant that we had to look further into the universe. A black hole collision may be rare in one galaxy but it could be a frequent occurrence if you could listen in to a million galaxies.</p>
<h2>Laser beams will help</h2>
<p>A new technology was needed to stretch the sensitivity enormously, and by the year 2000 this was available: a method called laser interferometry.</p>
<p>The idea was to use laser beams to measure tiny vibrations in the distance between widely spaced mirrors. The bigger the distance the bigger the vibration! And an L-shape could double the signal and cancel out the noise from the laser.</p>
<p>Several teams of physicists including a team at the Australian National University had spent many years researching the technology. Laser beam measurements allowed very large spacing and so new detectors up to 4km in size were designed and constructed in the US, Europe and Japan.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&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 gravity wave facility at Gingin.</span>
<span class="attribution"><a class="source" href="http://www.gravity.uwa.edu.au/">Australian International Gravitational Research Centre.</a></span>
</figcaption>
</figure>
<p>The <a href="http://www.anu.edu.au/physics/ACIGA/">Australian Consortium for Gravitational Astronomy</a> built a research centre on a huge site at Gingin, just north of Perth, in Western Australia, that was reserved for the future southern hemisphere gravitational wave detector.</p>
<p>The world would need this so that triangulation could be used to locate signals.</p>
<h2>Latest detectors</h2>
<p>The new detectors were proposed in two stages. Because they involved formidable technological challenges, the first detectors would have the modest aim of proving that the laser technology could be implemented on a 4km scale, but using relatively low intensity laser light that would mean only a few per cent chance of detecting any signals.</p>
<p>The detectors were housed inside the world’s largest vacuum system, the mirrors had to be 100 times more perfect than a telescope mirror, seismic vibrations had to be largely eliminated, and the laser light had to be the purest light ever created.</p>
<p>A second stage would be a complete rebuild with bigger mirrors, much more laser power and even better vibration control. The second stage would have a sensitivity where coalescing pairs of neutron stars merging to form black holes, would be detectable about 20 to 40 times per year.</p>
<p>Australia has been closely involved with both stages of the US project. CSIRO was commissioned to polish the <a href="http://www.csiro.au/Organisation-Structure/Flagships/Future-Manufacturing-Flagship/Agile-Manufacturing/Intelligent-Manufacturing-Technologies/Gravity-wave-detection.aspx">enormously precise mirrors</a> that were the heart of the first stage detectors.</p>
<h2>A gathering of minds</h2>
<p>The Australian Consortium gathered at Gingin earlier this year to plan a new national project.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Students at work in the labs at Gingin.</span>
<span class="attribution"><span class="source">University of WA</span></span>
</figcaption>
</figure>
<p>Part of that project focusses on an 80 meter scale laser research facility – a sort of mini gravity wave detector – the consortium has developed at the site. Experiments are looking at the physics of the new detectors and especially the forces exerted by laser light.</p>
<p>The team has discovered several new phenomena including one that involves laser photons bouncing off particles of sound called <a href="http://physics.about.com/od/physicsmtop/g/phonon.htm">phonons</a>. This phenomenon turns out to be very useful as it allows new diagnostic tools to prevent instabilities in the new detectors.</p>
<p>The light forces can also be used to make “optical rods” – think of a Star Wars light sabre! These devices can capture more gravitational wave energy – opening up a whole range of future possibilities from useful gadgets to new gravitational wave detectors.</p>
<h2>Final stages of discovery</h2>
<p>The first stage detectors achieved their target sensitivity in 2006 and, as expected, they detected no signals. You would know if they had!</p>
<p>The second stage detectors are expected to begin operating next year. The Australian team is readying itself because the new detectors change the whole game.</p>
<p>For the first time we have firm predictions: both the strength and the number of signals. No longer are we hoping for rare and unknown events.</p>
<p>We will be monitoring a significant volume of the universe and for the first time we can be confident that we will “listen” to the coalescence of binary neutron star systems and the formation of black holes.</p>
<p>Once these detectors reach full sensitivity we should hear signals almost once a week. Exactly when we will reach this point, no one knows. We have to learn how to operate the vast and complex machines.</p>
<p>If you want to place bets on the date of first detection of some gravity wave then some physicists would bet on 2016, probably the majority would bet 2017. A few pessimists would say that we will discover unexpected problems that might take a few years to solve.</p><img src="https://counter.theconversation.com/content/22336/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council, is a member of the Australian Consortium for Gravitational Astronomy and is a member of the LIGO Scientific Collaboration.</span></em></p>Our unfolding understanding of the universe is marked by epic searches and we are now on the brink of discovering something that has escaped detection for many years. The search for gravity waves has been…David Blair, Director, Australian International Gravitational Research Centre, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/221212014-02-12T03:25:58Z2014-02-12T03:25:58ZPhysics: a fundamental force for future security<figure><img src="https://images.theconversation.com/files/40865/original/6bnpsghy-1391660799.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Electricity – just one bright idea to stem from physics.</span> <span class="attribution"><span class="source">Flickr/JonathanCohen</span></span></figcaption></figure><p><em>AUSTRALIA 2025: How will science address the challenges of the future? In collaboration with Australia’s chief scientist <a href="https://theconversation.com/profiles/ian-chubb-5153/profile_bio">Ian Chubb</a>, we’re asking how each science discipline will contribute to Australia now and in the future. Written by luminaries and accompanied by two expert commentaries to ensure a broader perspective, these articles run fortnightly and focus on each of the major scientific areas. In the first of the series, we hold physics – a fundamental discipline – up to the light.</em> <br></p>
<p>What is matter? What is energy? What holds matter together? How do the various constituents of the universe interact at the most basic level? Where does the Earth sit in relation to the rest of the universe? Can we predict the movements of the stars?</p>
<p>Physics gives us the knowledge to address remarkable questions like these. But knowledge is also power: a better understanding of these laws, allows us to improve the ways we interact with, and harness our environment. And if you look at the rapid development in human technology over the past two centuries, it is amazing just how much technological change has been derived from advances in physics.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=580&fit=crop&dpr=1 754w, https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=580&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/40982/original/bvfq8mn9-1391737542.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=580&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nuclear fusion reactor.</span>
<span class="attribution"><a class="source" href="http://www.flickr.com/photos/aglet/9336757122/sizes/l/">Flickr/aglet</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>Perhaps the most clear-cut example in this respect is the dramatic transformation that electricity has brought about in all modern societies. Our whole way of living now is completely dependent upon being able to generate, transmit, and harness electric power in a safe and efficient manner – all of which is ultimately underpinned by our understanding of physics. </p>
<p>Keeping up with the ever growing demand for generating electricity with minimal environmental impact will be a significant challenge in the years to come.</p>
<p>No matter how much we know there is always more to discover – and from every discovery we generate great new and practical technologies. </p>
<h2>Knock-on effects</h2>
<p>Whether physicists studying fundamental principles, such as quantum mechanics, are more likely to invent new devices by applying these principles serendipitously, or by design, doesn’t matter as both approaches work. </p>
<p>What is remarkable is the extent to which fundamental breakthroughs can lead to diverse technological consequences.</p>
<p>Take, for example, the transistor and diode, which are used in electronic watches, calculators, pacemakers, hearing aids, cellular phones, global positioning systems (<a href="https://theconversation.com/explainer-what-is-gps-12248">GPSs</a>), radios, computers and light-emitting diodes (LEDs). They are fundamental building blocks upon which our entire society is constructed.</p>
<p>A similar story can be told about lasers. The diverse applications of the laser include bar code readers, micro/eye surgery, compact disc players and information retrieval and storage, fibre optics (for telecommunication and medical procedures), machining, surveying, laser printers, semiconductor fabrication, holography, and perhaps the greatest potential use, nuclear fusion.</p>
<p>Magnetic resonance imaging (<a href="https://theconversation.com/the-science-of-medical-imaging-magnetic-resonance-imaging-mri-15030">MRI</a>) likewise is now used routinely to identify chemical species in both chemistry and biology, and has been vital for noninvasive glimpses into the body to find tumours, to study thinking processes and to understand blood flow – all based upon the spinning of protons in a magnetic field.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=422&fit=crop&dpr=1 754w, https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=422&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/40864/original/r78y43vr-1391660519.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=422&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<p>From new theories, new technology is created that, in turn, allows more accurate, expanded and novel experimental observations to prove or disprove new theories, which leads on to more technology – and so on, in a cycle. Thus there has always been a deep symbiosis between discovery in physics and the development of new technology.</p>
<h2>Crossing disciplines …</h2>
<p>We all benefit from the contributions of physics, only a fraction of which have been mentioned here – and it’s not just physicists who say so.</p>
<p>The American economists <a href="http://www.nobelprize.org/nobel_prizes/economic-sciences/laureates/2004/prescott-bio.html">Edward Prescott</a> and <a href="http://www.nobelprize.org/nobel_prizes/economic-sciences/laureates/2004/kydland-bio.html">Finn Kydland</a>, who won the Nobel Prize for economics in 2004 in part for pointing out that new technology drives economic booms. Physics is fundamental in this respect.</p>
<p>In 2013, the European Physical Society commissioned an independent <a href="http://c.ymcdn.com/sites/www.eps.org/resource/resmgr/policy/EPS_economyReport2013.pdf">economic analysis</a> covering 29 European countries (including Norway and Switzerland) which showed that over the four-year period 2007-2010 the </p>
<blockquote>
<p>physics-based industrial sector generated £3.8 trillion of turnover, around 15% of total turnover in Europe’s business economy, exceeding that of the contribution made by the entire retail sector.</p>
</blockquote>
<p>The same study found that the sector supported more than 15 million jobs corresponding to more than 13% of overall employment in the business economy of Europe.</p>
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<span class="attribution"><a class="source" href="http://www.flickr.com/photos/carolynwill/2569205162/sizes/l/">Flickr/carolyn.will</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Here in Australia, our industrial base is different from that in the US or Europe, but the same arguments hold.</p>
<p>On the one hand, we all benefit from the downstream consequences of past discoveries in physics. In this sense, anyone who uses a GPS signal, turns on a computer, listens to digital music, receives a computed tomography (<a href="https://theconversation.com/the-science-of-medical-imaging-x-rays-and-ct-scans-15029">CT</a>) scan or an MRI scan, or flicks a light switch is proving the value of the discipline.</p>
<p>But, on the other hand, advances in physics are also used in a more immediate sense by local industry. In recent years, physics has found important Australian applications in financial modelling, minerals exploration, equipment manufacturing, telecommunications and the development of new defence technologies.</p>
<h2>… and crossing oceans</h2>
<p>Physics is no less important here in Australia than it is to people anywhere else.</p>
<p>Its future significance, moreover, should not be underestimated. It is easy to imagine for example that, because it is an established science, all the great discoveries of physics have already been made. This is a deeply mistaken perspective.</p>
<p>Globally, physics is currently entering an extremely vibrant era. Increasing computing power and new instrumentation with unprecedented precision and sensitivity is amplifying our ability to understand complex phenomena.</p>
<p>With new experimental data from the <a href="https://theconversation.com/topics/large-hadron-collider">Large Hadron Collider</a> in Switzerland, which explores the tiniest particles that form the most fundamental building blocks of matter, and from the <a href="https://theconversation.com/topics/square-kilometre-array">Square Kilometre Array</a>, which explores the massive structures that form the universe, modern physics will bring us new insights into longstanding questions – such as the origins and expansion of the universe, the nature of dark matter, and the origins of mass.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/dxJMTSJhHnk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Square Kilometre Array.</span></figcaption>
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<p>At the same time, we are just beginning now to tap into new technologies that are based upon the mysterious wonders of <a href="https://theconversation.com/topics/quantum-mechanics">quantum physics</a>. The ability to manipulate individual atoms, molecules, and photons of light – and to exploit quantum effects that are imperceptible in the macroscopic universe – foreshadows a future where the communication and processing of information is radically enhanced from where we are today.</p>
<p>Australian science enjoys a particularly strong international reputation in this area, which is potentially very advantageous given the escalating importance of information processing in the Australian economy, and in a growing range of defence applications.</p>
<p>Because of its vast contributions to society, and its tremendous potential to engender new breakthrough technologies and industries, global research in physics has received steady and dramatic increases in investment over the past century – a trend, which is likely to continue as an ever-growing cohort of companies and societies come to recognise the significance of physics to economic, social and environmental development.</p>
<p>Physics is the field that defined the modern scientific worldview. It helps us to understand the world in its most fundamental aspects. It underpins an enormous amount of our most advanced technological capability. </p>
<p>It is essential, therefore, that we encourage students to study it, gifted, passionate and well-qualified teachers to teach it, and that we nurture outstanding scientists who are actively advancing its frontiers.</p>
<hr>
<h2><a href="https://theconversation.com/profiles/david-jamieson-116005/profile_bio">David Jamieson</a>, Professor of Physics at University of Melbourne</h2>
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<a href="https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/40983/original/cwqmhs6y-1391738826.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=496&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="attribution"><a class="source" href="http://www.flickr.com/photos/justard/11896283115/sizes/l/">Flickr/Just Ard</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
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<p>In cafes around the world many of the clientele are employing the physics of the element silicon, properties of electricity and magnetism from Maxwell’s equations, the passage of light through carefully crafted glass fibres, the equations of <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">General Relativity</a> that describe how gravity shapes space and time for the GPS, and other fundamental physics principles to surf the web, read a newspaper or keep in touch with friends and family.</p>
<p>The same physics principles help us answer the biggest questions we can ask about the origin, evolution and fate of the universe. Australian physicists were deeply involved in the <a href="https://theconversation.com/explainer-the-higgs-boson-particle-280">Higgs boson</a> experiments and understanding the significance of the discoveries.</p>
<p>We are developing ways to control the strange quantum machinery that shapes all matter, promising potentially revolutionary devices for the storage, transmission and manipulation of information. </p>
<p>We are already starting to understand photosynthesis as a quantum mechanical process that we may soon harness to make new sorts of biofuels from sunlight and carbon dioxide. Physics has an essential role to play to deliver the new sources of power needed urgently to make that lifestyle preserve the climate systems that unite all life on our planet.</p>
<p>There is an emerging worldwide trend for the convergence of physics with engineering and medicine which will lead to near-term advances in data management, biomedical materials, new types of imaging, medical prosthetics, and supercomputer modelling of cells and tissues. We can look forward to bionic vision, viral self-assembly and life cams to reinforce memories of important events. </p>
<p>Curious, creative and well-educated people sharing in the international endeavour of physics will shape the world of 2025.</p>
<hr>
<h2><a href="https://theconversation.com/profiles/chennupati-jagadish-113841/profile_bio">Chennupati Jagadish</a>, Laureate Fellow at ANU</h2>
<p>By finding answers to fundamental questions of how our world works – or can work better – physics will continue to set the foundation for future technologies.</p>
<p>Those trained in physics gave us and continue to provide new ideas, materials and machines. Physics skills are the creative backbone of all advanced industrial societies and economies. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=186&fit=crop&dpr=1 600w, https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=186&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=186&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=234&fit=crop&dpr=1 754w, https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=234&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/40984/original/g5yj2vj7-1391738987.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=234&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="attribution"><a class="source" href="http://www.flickr.com/photos/georgiesharp/2512822287/sizes/l/">Flickr/Georgie Sharp</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
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<p>In Australia they have helped to build our cities, located minerals underground and will ensure that we find new resources, from the land, sunlight and oceans, but they could also lead to new and revitalised industries if we exploit them intelligently.</p>
<p>Our engineers and scientists have the capacity to help solve the big challenges and to secure our economic future. Australia can be proud of its achievement in physics, with research excellence in many areas that has been an attractor for many students and young scientists from across the world.</p>
<p>To be technically literate necessitates a good grasp of basic physics and to develop technology for commercial advantage requires high level physics skills. </p>
<p>To ensure that Australia benefits commercially from technological breakthroughs and their commercial exploitation, it is vital that our population is physics and science literate, through a focus on physics teaching in our schools and in higher education.</p>
<hr>
<p><br>
<strong>This article is part of the <a href="https://theconversation.com/topics/australia-2025-series">Australia 2025: smart science series</a>, co-published with the <a href="http://www.chiefscientist.gov.au/2014/02/australia-2025-smart-science/">Office of the Chief Scientist</a>. <br>
Further reading:<br>
<a href="https://theconversation.com/australias-future-depends-on-a-strong-science-focus-today-22075">Australia’s future depends on a strong science focus today</a><br>
<a href="https://theconversation.com/proteins-to-plastics-chemistry-as-a-dynamic-discipline-22123">Proteins to plastics: chemistry as a dynamic discipline</a><br>
<a href="https://theconversation.com/optimising-the-future-with-mathematics-22122">Optimising the future with mathematics</a><br>
<a href="https://theconversation.com/australia-can-nurture-growth-and-prosperity-through-biology-22255">Australia can nurture growth and prosperity through biology</a><br>
<a href="https://theconversation.com/a-healthy-future-lets-put-medical-science-under-the-microscope-23190">A healthy future? Let’s put medical science under the microscope</a><br>
<a href="https://theconversation.com/groundbreaking-earth-sciences-for-a-smart-and-lucky-country-22254">Groundbreaking earth sciences for a smart – and lucky – country</a><br>
<a href="https://theconversation.com/to-reach-for-the-stars-australia-must-focus-on-astronomy-22124">To reach for the stars, Australia must focus on astronomy</a><br>
<a href="https://theconversation.com/marine-science-challenges-for-a-growing-blue-economy-22845">Marine science: challenges for a growing ‘blue economy’</a><br>
<a href="https://theconversation.com/building-the-nation-will-be-impossible-without-engineers-23191">Building the nation will be impossible without engineers</a><br>
<a href="https://theconversation.com/australias-got-ict-talent-so-how-do-we-make-the-most-of-it-22842">Australia’s got ICT talent – so how do we make the most of it?</a><br>
<a href="https://theconversation.com/agriculture-in-australia-growing-more-than-our-farming-future-22843">Agriculture in Australia: growing more than our farming future</a></strong> </p><img src="https://counter.theconversation.com/content/22121/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michelle Simmons receives funding from the Australian Research Council and was Chair of the Australian Academy’s National Committee for Physics until 2012.</span></em></p><p class="fine-print"><em><span>Chennupati Jagadish receives funding from the Australian Research Council. He is affiliated with Australian Academy of Science.</span></em></p><p class="fine-print"><em><span>David Jamieson receives funding from the Australian Research Council and is a Chief Investigator in the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology.</span></em></p>AUSTRALIA 2025: How will science address the challenges of the future? In collaboration with Australia’s chief scientist Ian Chubb, we’re asking how each science discipline will contribute to Australia…Michelle Simmons, Professor of Physics, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/194092013-11-04T06:16:17Z2013-11-04T06:16:17ZTheoretical physics – like sex, but with no need to experiment<figure><img src="https://images.theconversation.com/files/34234/original/28mrjw83-1383312244.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Plotting world domination.</span> <span class="attribution"><span class="source">meneldur</span></span></figcaption></figure><p>There are not many professions where people routinely ask you to justify your work, but theoretical physics is one of them. In the wake of the <a href="https://theconversation.com/nobel-prize-in-physics-goes-to-discovery-of-the-higgs-boson-19014">recent Nobel Prize</a> to Peter Higgs and François Englert for their research on the Higgs Boson, this scrutiny has intensified. Richard Feynman once quipped, “Physics is like sex. Sure, it may give some practical results, but that’s not why we do it.” I will attempt a more comprehensive answer.</p>
<p>Theoretical physicists construct theories of nature. For a theory to be true it must be both consistent with itself and consistent with nature. The first aspect can be verified with mathematics, the second with experiment. Thus physics is based on a checks-and-balance system between these two approaches. Without theorists, experimentalists would not have anything to test. Without experimentalists, theorists would not have anything to explain. I personally chose theory because experimental physics appeared too difficult.</p>
<p>This process of scientific exploration is like geographical exploration. There is the reward of fame for discovering the new and wonderful balanced against the risk of wasting your time (though physics research contains less likelihood of a snakebite). Popular lore can be sometimes dramatically overturned, like the interdiction against sailing too far away, lest you fall off the edge of the world. We now know that the history, composition and future of the universe are vastly different than imagined only a few generations ago.</p>
<h2>Explorers of the universe</h2>
<p>People easily understand the benefits of geographic exploration: beside the practical benefits of obtaining new resources, there is the joy of discovering what was unknown. In most cases this might be as banal as exploring the woods behind your house but the feeling of discovery is the same. And occasionally one can discover something truly new. Isaac Newton was the first theoretical physicist (although in his own time his profession was called “natural philosophy”) and likened his work to “finding a shiny pebble on the beach”. In his case, the shiny pebbles formed our basis for understanding nature.</p>
<p>Why do people not universally share this joy of scientific discovery? Probably because the language nature speaks is mathematics - one that most people are not fluent in. Unfamiliarity breeds distrust, and I think this may be the reason society has developed a prejudice against scientists. The “mad” or “evil” scientists are staple archetypes of popular culture, yet the vast majority of physicists I know actively hope that their discoveries will benefit society. </p>
<p>To compound this, I sense that people often consider physics to be mathematical poetry: at best amusing, but at worst a waste of time completely removed from reality. By contrast the work of medical researchers is never questioned since we are all lamentably familiar with disease, illness and death. I believe more people will appreciate physics as they understand today’s technology is based on yesterday’s theory.</p>
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<a href="https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34240/original/4cqfyxd2-1383312456.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Solving the universe’s mysteries.</span>
<span class="attribution"><span class="source">dullhunk</span></span>
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<p>Sometimes an application is immediately obvious: it did not take a leap of the imagination to envisage that Einstein’s equation E=mc<sup>2</sup> (equating mass with energy) could be, and was, used to produce the weapon of mass destruction that is the atomic bomb. More often, however, the purpose is not apparent at the time of the theoretical breakthrough. “People love chopping wood. In this activity one immediately sees results,” commented Einstein. </p>
<h2>In translation</h2>
<p>In 1850 William Gladstone, then the Chancellor of the Exchqeuer, asked British physicist Michael Faraday what the practical value of electricity was. “One day sir, you may tax it,” was Faraday’s retort. Electricity has obviously had a major effect on society, but so have the two pillars of modern physics - quantum theory and relativity. While each brilliantly solved problems in their respective domains, neither had any obvious practical application.</p>
<p>In the 1940s Bardeen, Brattain and Shockley developed the “transfer resistor,” or transistor. They exploited a basic property of quantum mechanics called “tunneling” wherein electrons can travel to regions where classical physics deems not possible. In the two seconds it took you to read this sentence on your screen, you were benefited by the performance of billions of transistors. When theoretical physicists in the early 1900s first realised that position and momentum could not be measured simultaneously they could hardly have forseen the digital technology revolution made possible by transistors.</p>
<p>The other prime example of using purely theoretical physics for something practical is the Global Positioning System (GPS). The GPS configuration consists of 24 satellites in high orbits around the Earth. The timing between your GPS receiver and these satellites can determine your position on the surface of the Earth to within a few meters. To achieve this level of precision, the clock ticks from the satellites must be known to an accuracy of billionths of a second. Einstein’s theories of relativity allow us to achieve that high accuracy. If these effects were not properly taken into account, your GPS data would be wrong after only two minutes, and the errors will keep growing. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34237/original/zczdn9p3-1383312376.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
<span class="attribution"><span class="source">meneldur</span></span>
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<p>There are occasionally even unintended practical byproducts. In 1989 physicist Tim Berners-Lee proposed merging the technologies of personal computers, computer networking and hypertext into a powerful and easy to use global information system. The name of this network was the World Wide Web (WWW), and his supervisor’s response was, “Vague but exciting.” There is a plaque at CERN, Europe’s particle-physics lab, at the exact place where Berners-Lee’s server stood, a modest acknowledgement to one of the most important achievements in recent history.</p>
<p>Because of its lack of direct application to industry, theoretical physics is often underrepresented in the awarding of government and private grants. Recently there have been positive developments with the introduction of the Kavli Foundation, the Yuri Milner Fundamental Physics Prize Foundation, the Foundational Questions Institute and the Simons Foundation - all of which financially support research in fundamental physics. I hope that other benefactors follow their example and support such investigations - what better publicity than to claim that you sponsored the next Einstein?</p>
<p>Apart from practical applications, there is simple pleasure of understanding how the universe works. Oscar Wilde once poetically observed, “We are all in the gutter, but some of us are looking at the stars.” Feynman phrased it differently. Asked by a Swedish encyclopedia for a picture of him playing a drum, to paint a more “human” portrait of the physicist, his reply is legendary: </p>
<blockquote>
<p>Theoretical physics is a human endeavour, one of the higher developments of human beings — and this perpetual desire to prove that people who do it are human by showing that they do other things that a few other humans do (like playing bongo drums) is insulting to me. I am human enough to tell you to go to hell.</p>
</blockquote>
<p>My favourite audience is young children. They are born theoretical physicists, insisting on repeatedly asking “why?” often to the exasperation of their parents. I have been asked all varieties of questions from children, but not a single one has asked me what the purpose of learning about nature was. There are many educational agencies currently investigating how to instill children with a sense of curiosity, but I think the more accurate question is to ask why children lose their curiosity during their transition into adulthood.</p>
<p>The next time I am asked by anyone what the purpose of theoretical physics is I will reply with the following: maybe my research in theoretical physics will lead to something useful, and maybe it won’t. But theoretical physicists comprise the few atoms in the universe that know where they came from.</p><img src="https://counter.theconversation.com/content/19409/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Jackson 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 are not many professions where people routinely ask you to justify your work, but theoretical physics is one of them. In the wake of the recent Nobel Prize to Peter Higgs and François Englert for…Mark Jackson, Postdoctoral Researcher, Centre de Cosmologie Physique de ParisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/180572013-09-10T13:48:43Z2013-09-10T13:48:43ZLHC celebrates five years of not destroying the world<figure><img src="https://images.theconversation.com/files/31093/original/pqv3vm2x-1378817603.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Universe's secrets are revealed in a dark corner in Switzerland.</span> <span class="attribution"><span class="source">timtom.ch</span></span></figcaption></figure><p>Five years ago, at breakfast time, the world waited anxiously for news from CERN, the European Organization for Nuclear Research. The first nervy bunch of protons were due to be fired around the European lab’s latest and biggest particle accelerator, the Large Hadron Collider (LHC), as it kicked into action.</p>
<p>Some “mercifully deluded people” – as Jeremy Paxman put it – feared the <a href="http://blog.sciencemuseum.org.uk/insight/2013/07/15/cern-60-years-of-not-destroying-the-world/">LHC would do no end of mischief</a>. There was talk of planet-swallowing black holes, the transformation of the Earth into a new state of “strange” matter, and even the prospect of the obliteration of the entire universe. But for those of more sensible dispositions, the LHC’s first beam was an occasion for great excitement.</p>
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<p>As the protons sped all the way round the 27km tunnel under the countryside between Lake Geneva and the Jura Mountains, thousands of physicists and engineers celebrated decades of hard work, incredible ingenuity and sheer ambition. Together they had created the largest-ever scientific experiment.</p>
<p>After the LHC was switched on, project leader Lyn Evans said, “We can now look forward to a new era of understanding about the origins and evolution of the universe.”</p>
<p>Operating a massive particle accelerator requires much more than flicking a switch – thousands of individual elements have to all come together, synchronised in time to less than a billionth of a second. </p>
<p>University College London’s physicist Jon Butterworth recalls a “particularly bizarre memory” from that day. Relaxing in a Westminster pub after an exhausting LHC event in London, Butterworth found he could follow live updates from his own <a href="http://atlas.ch/">ATLAS</a> experiment on the pub’s TV.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=583&fit=crop&dpr=1 754w, https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=583&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/31091/original/2gpwdgt7-1378817374.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=583&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Time for a rest.</span>
<span class="attribution"><span class="source">CERN</span></span>
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</figure>
<p>Particle physics continued to make news. The following fortnight’s joy turned to dismay as an accident involving six tonnes of liquid helium erupting violently in the tunnel – euphemistically referred to as “the incident” – damaged around half a mile of the collider, closing the LHC for a year.</p>
<p>Since then, besides the brief setback that was “<a href="http://www.telegraph.co.uk/science/large-hadron-collider/6514155/Large-Hadron-Collider-broken-by-bread-dropped-by-passing-bird.html">baguette-gate</a>”, a bizarre episode when the collider was sabotaged by a baguette-wielding bird, the LHC has been producing great work. Hundreds of scientific papers have been published by the CERN experiments, on topics as diverse as searches for dark matter candidates, the production of the primordial state of matter (known as quark-gluon plasma) and precision measurements of matter-antimatter asymmetries.</p>
<p>However, it was on July 4 last year, that the LHC snared its first major catch with the <a href="http://blog.sciencemuseum.org.uk/insight/2012/07/04/higgs-boson-discovered/">discovery of the Higgs boson</a> – as one of the most significant scientific finds of the century. The Higgs boson was one of the longest-sought prizes in science - it was almost fifty years ago in 1964 that three groups of theorists laid the ground-work for what would become the final piece of the theory known as the Standard Model of Particle Physics. They proposed an energy field, filling the entire Universe that gives mass to fundamental particles.</p>
<p>This “Higgs mechanism” neatly explained why the weak nuclear force was so weak and why light is able to travel over infinite reaches of space. It also laid the groundwork for the unification of the weak and electromagnetic forces into a single “electroweak” force, in a coup similar to James Clerk-Maxwell’s unification of electricity and magnetism in the 19th century.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=529&fit=crop&dpr=1 600w, https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=529&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=529&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=664&fit=crop&dpr=1 754w, https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=664&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/31090/original/8np8zwfb-1378817317.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=664&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Peter Higgs at CERN’s public announcement of the Higgs Boson, 4 July 2012. Credit: CERN.</span>
<span class="attribution"><span class="source">CERN</span></span>
</figcaption>
</figure>
<p>However, like air, the Higgs field itself is invisible; the only way to know if it is there is to create a disturbance in it, like a breeze or a sound. It was Peter Higgs who first suggested that if the field existed, it would be possible to create such a disturbance, which would show up as a new particle. Hence, the boson was named after him, much to the irritation of some of the other five theorists responsible for the theory.</p>
<p>The LHC’s discovery of the Higgs closed a chapter in the development of fundamental physics, placing the keystone into the great arch of the Standard Model. The LHC is currently being upgraded so that in 2015 it will reopen at almost double its previous energy. What every scientist is now aching for is a sign of something new, physics <a href="http://blog.sciencemuseum.org.uk/insight/2013/07/19/standard-model-stands-firm/">beyond the Standard Model</a>, and most probably beyond our wildest aspirations.</p><img src="https://counter.theconversation.com/content/18057/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rupert Cole and Harry Cliff are working on "Collider" a new exhibition opening on November 13 at London's Science Museum, which may benefit from this article in the form of a few more visits to an excellent science exhibition. And Harry Cliff works on a CERN experiment. </span></em></p><p class="fine-print"><em><span>Other than that, Rupert Cole and Harry Cliff do not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.</span></em></p>Five years ago, at breakfast time, the world waited anxiously for news from CERN, the European Organization for Nuclear Research. The first nervy bunch of protons were due to be fired around the European…Rupert Cole, PhD student in the history and philosophy of science, UCLHarry Cliff, Particle Physicist and Science Museum Fellow, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.