tag:theconversation.com,2011:/au/topics/quantum-mechanics-157/articlesQuantum mechanics – The Conversation2024-03-26T17:01:56Ztag:theconversation.com,2011:article/2262572024-03-26T17:01:56Z2024-03-26T17:01:56ZHow long before quantum computers can benefit society? That’s Google’s US$5 million question<figure><img src="https://images.theconversation.com/files/583117/original/file-20240320-26-rmpub2.jpg?ixlib=rb-1.1.0&rect=5%2C0%2C3828%2C2160&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/quantum-computer-black-background-3d-render-1571871052">Bartlomiej K. Wroblewski / Shutterstock</a></span></figcaption></figure><p>Google and the XPrize Foundation have launched a competition worth US$5 million (£4 million) to develop <a href="https://blog.google/technology/research/google-gesda-and-xprize-launch-new-competition-in-quantum-applications/">real-world applications for quantum computers</a> that benefit society – by speeding up progress on one of the UN Sustainable Development Goals, for example. The principles of quantum physics suggest quantum computers could perform very fast calculations on particular problems, so this competition may expand the range of applications where they have an advantage over conventional computers.</p>
<p>In our everyday lives, the way nature works can generally be described by what we call <a href="https://en.wikipedia.org/wiki/Classical_physics#:%7E:text=Classical%20physical%20concepts%20are%20often,of%20quantum%20mechanics%20and%20relativity.">classical physics</a>. But nature behaves very differently at tiny quantum scales – below the size of an atom. </p>
<p>The race to harness quantum technology can be viewed as a new industrial revolution, progressing from devices that use the properties of classical physics to those utilising the <a href="https://www.energy.gov/science/doe-explainsquantum-mechanics#:%7E:text=Quantum%20mechanics%20is%20the%20field,%E2%80%9Cwave%2Dparticle%20duality.%E2%80%9D">weird and wonderful properties of quantum mechanics</a>. Scientists have spent decades trying to develop new technologies by harnessing these properties. </p>
<p>Given how often we are told that <a href="https://projects.research-and-innovation.ec.europa.eu/en/horizon-magazine/quantum-technologies">quantum technologies</a> will revolutionise our everyday lives, you may be surprised that we still have to search for practical applications by offering a prize. However, while there are numerous examples of success using quantum properties for enhanced precision in sensing and timing, there has been a surprising lack of progress in the development of quantum computers that outdo their classical predecessors.</p>
<p>The main bottleneck holding up this development is that the software – using <a href="https://www.nature.com/articles/npjqi201523">quantum algorithms</a> –
needs to demonstrate an advantage over computers based on classical physics. This is commonly known as <a href="https://theconversation.com/what-is-quantum-advantage-a-quantum-computing-scientist-explains-an-approaching-milestone-marking-the-arrival-of-extremely-powerful-computers-213306">“quantum advantage”</a>.</p>
<p>A crucial way quantum computing differs from classical computing is in using a property known as <a href="https://spectrum.ieee.org/what-is-quantum-entanglement">“entanglement”</a>. Classical computing <a href="https://web.stanford.edu/class/cs101/bits-bytes.html">uses “bits”</a> to represent information. These bits consist of ones and zeros, and everything a computer does comprises strings of these ones and zeros. But quantum computing allows these bits to be in a <a href="https://azure.microsoft.com/en-gb/resources/cloud-computing-dictionary/what-is-a-qubit">“superposition” of ones and zeros</a>. In other words, it is as if these ones and zeros occur simultaneously in the quantum bit, or qubit.</p>
<p>It is this property which allows computational tasks to be performed all at once. Hence the belief that quantum computing can offer a significant advantage over classical computing, as it is able to perform many computing tasks at the same time. </p>
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<a href="https://theconversation.com/what-is-quantum-advantage-a-quantum-computing-scientist-explains-an-approaching-milestone-marking-the-arrival-of-extremely-powerful-computers-213306">What is quantum advantage? A quantum computing scientist explains an approaching milestone marking the arrival of extremely powerful computers</a>
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<h2>Notable quantum algorithms</h2>
<p>While performing many tasks simultaneously should lead to a performance increase over classical computers, putting this into practice has proven more difficult than theory would suggest. There are actually only a few notable quantum algorithms which can perform their tasks better than those using classical physics.</p>
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<p>The most notable are the <a href="https://www.st-andrews.ac.uk/physics/quvis/simulations_html5/sims/cryptography-bb84/Quantum_Cryptography.html">BB84 protocol</a>, developed in 1984, and <a href="https://www.nature.com/articles/s41598-021-95973-w">Shor’s algorithm</a>, developed in 1994, both of which use entanglement to outperform classical algorithms on particular tasks. </p>
<p>The BB84 protocol is a cryptographic protocol – a system for ensuring secure, private communication between two or more parties which is considered more secure than comparable classical algorithms.</p>
<p>Shor’s algorithm uses entanglement to demonstrate how current <a href="https://www.rand.org/pubs/commentary/2023/09/when-a-quantum-computer-is-able-to-break-our-encryption.html#:%7E:text=One%20of%20the%20most%20important,secure%20internet%20traffic%20against%20interception.">classical encryption protocols can be broken</a>, because they are based on the factorisation of very large numbers. <a href="https://ieeexplore.ieee.org/document/365700">There is also evidence</a> that it can perform certain calculations faster than similar algorithms designed for conventional computers. </p>
<p>Despite the superiority of these two algorithms over conventional ones, few advantageous quantum algorithms have followed. However, researchers have not given up trying to develop them. Currently, there are a couple of main directions in research.</p>
<h2>Potential quantum benefits</h2>
<p>The first is to use quantum mechanics to assist in what are called <a href="https://arxiv.org/abs/2312.02279">large-scale optimisation tasks</a>. Optimisation – finding the best or most effective way to solve a particular task – is vital in everyday life, from ensuring traffic flow runs effectively, to managing operational procedures in factory pipelines, to streaming services deciding what to recommend to each user. It seems clear that quantum computers could help with these problems.</p>
<p>If we could reduce the computational time required to perform the optimisation, it could save energy, reducing the carbon footprint of the many computers currently performing these tasks around the world and the data centres supporting them.</p>
<p>Another development that could offer wide-reaching benefits is to use quantum computation to simulate systems, such as combinations of atoms, that behave according to quantum mechanics. Understanding and predicting how quantum systems work in practice could, for example, lead to better drug design and medical treatments. </p>
<p>Quantum systems could also lead to improved electronic devices. As computer chips get smaller, quantum effects take hold, potentially reducing the devices’s performance. A better fundamental understanding of quantum mechanics could help avoid this.</p>
<p>While there has been significant investment in building quantum computers, there has been less focus on ensuring they will directly benefit the public. However, that now appears to be changing.</p>
<p>Whether we will all have quantum computers in our homes within the next 20 years remains doubtful. But, given the current financial commitment to making quantum computation a practical reality, it seems that society is finally in a better position to make use of them. What precise form will this take? There’s US$5 million dollars on the line to find out.</p><img src="https://counter.theconversation.com/content/226257/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Lowe 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>Quantum computing has huge promise from a technical perspective, but the practical benefits are less clear.Adam Lowe, Lecturer, School of Computer Science and Digital Technologies, Aston UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2243722024-03-03T19:19:44Z2024-03-03T19:19:44ZGravity experiments on the kitchen table: why a tiny, tiny measurement may be a big leap forward for physics<figure><img src="https://images.theconversation.com/files/579074/original/file-20240301-30-ecsdm7.jpg?ixlib=rb-1.1.0&rect=3%2C16%2C2131%2C1536&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/string-theory-physical-processes-quantum-entanglement-733672807">Shutterstock</a></span></figcaption></figure><p>Just over a week ago, European physicists <a href="https://www.science.org/doi/10.1126/sciadv.adk2949">announced</a> they had measured the strength of gravity on the smallest scale ever. </p>
<p>In a clever tabletop experiment, researchers at Leiden University in the Netherlands, the University of Southampton in the UK, and the Institute for Photonics and Nanotechnologies in Italy measured a force of around 30 attonewtons on a particle with just under half a milligram of mass. An attonewton is a billionth of a billionth of a newton, the standard unit of force.</p>
<p>The researchers <a href="https://www.eurekalert.org/news-releases/1035222">say</a> the work could “unlock more secrets about the universe’s very fabric” and may be an important step toward the next big revolution in physics. </p>
<p>But why is that? It’s not just the result: it’s the method, and what it says about a path forward for a branch of science critics say may be trapped in a loop of <a href="https://www.prospectmagazine.co.uk/ideas/technology/38913/is-particle-physics-at-a-dead-end">rising costs and diminishing returns</a>.</p>
<h2>Gravity</h2>
<p>From a physicist’s point of view, gravity is an extremely weak force. This might seem like an odd thing to say. It doesn’t feel weak when you’re trying to get out of bed in the morning!</p>
<p>Still, compared with the other forces that we know about – such as the electromagnetic force that is responsible for binding atoms together and for generating light, and the strong nuclear force that binds the cores of atoms – gravity exerts a relatively weak attraction between objects. </p>
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<p>And on smaller scales, the effects of gravity get weaker and weaker.</p>
<p>It’s easy to see the effects of gravity for objects the size of a star or planet, but it is much harder to detect gravitational effects for small, light objects.</p>
<h2>The need to test gravity</h2>
<p>Despite the difficulty, physicists really want to test gravity at small scales. This is because it could help resolve a century-old mystery in current physics.</p>
<p>Physics is dominated by two extremely successful theories. </p>
<p>The first is general relativity, which describes gravity and spacetime at large scales. The second is quantum mechanics, which is a theory of particles and fields – the basic building blocks of matter – at small scales. </p>
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Read more:
<a href="https://theconversation.com/approaching-zero-super-chilled-mirrors-edge-towards-the-borders-of-gravity-and-quantum-physics-162785">Approaching zero: super-chilled mirrors edge towards the borders of gravity and quantum physics</a>
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<p>These two theories are in some ways contradictory, and physicists don’t understand what happens in situations where both should apply. One goal of modern physics is to combine general relativity and quantum mechanics into a theory of “quantum gravity”. </p>
<p>One example of a situation where quantum gravity is needed is to fully understand black holes. These are predicted by general relativity – and we have observed huge ones in space – but tiny black holes may also arise at the quantum scale. </p>
<p>At present, however, we don’t know how to bring general relativity and quantum mechanics together to give an account of how gravity, and thus black holes, work in the quantum realm.</p>
<h2>New theories and new data</h2>
<p>A number of approaches to a potential theory of quantum gravity have been developed, including <a href="https://theconversation.com/explainer-string-theory-2983">string theory</a>, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5567241/">loop quantum gravity</a> and <a href="https://link.springer.com/article/10.1007/s41114-019-0023-1">causal set theory</a>.</p>
<p>However, these approaches are entirely theoretical. We currently don’t have any way to test them via experiments.</p>
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<p>To empirically test these theories, we’d need a way to measure gravity at very small scales where quantum effects dominate.</p>
<p>Until recently, performing such tests was out of reach. It seemed we would need very large pieces of equipment: even bigger than the world’s largest particle accelerator, the Large Hadron Collider, which sends high-energy particles zooming around a 27-kilometre loop before smashing them together. </p>
<h2>Tabletop experiments</h2>
<p>This is why the recent small-scale measurement of gravity is so important.</p>
<p>The experiment conducted jointly between the Netherlands and the UK is a “tabletop” experiment. It didn’t require massive machinery.</p>
<p>The experiment works by floating a particle in a magnetic field and then swinging a weight past it to see how it “wiggles” in response.</p>
<p>This is analogous to the way one planet “wiggles” when it swings past another.</p>
<p>By levitating the particle with magnets, it can be isolated from many of the influences that make detecting weak gravitational influences so hard.</p>
<p>The beauty of tabletop experiments like this is they don’t cost billions of dollars, which removes one of the main barriers to conducting small-scale gravity experiments, and potentially to making progress in physics. (The latest proposal for a bigger successor to the Large Hadron Collider would <a href="https://www.nature.com/articles/d41586-024-00353-9">cost US$17 billion</a>.)</p>
<h2>Work to do</h2>
<p>Tabletop experiments are very promising, but there is still work to do.</p>
<p>The recent experiment comes close to the quantum domain, but doesn’t quite get there. The masses and forces involved will need to be even smaller, to find out how gravity acts at this scale. </p>
<p>We also need to be prepared for the possibility that it may not be possible to push tabletop experiments this far.</p>
<p>There may yet be some technological limitation that prevents us from conducting experiments of gravity at quantum scales, pushing us back toward building bigger colliders.</p>
<h2>Back to the theories</h2>
<p>It’s also worth noting some of the theories of quantum gravity that might be tested using tabletop experiments are very radical.</p>
<p>Some theories, such as loop quantum gravity, suggest <a href="https://theconversation.com/time-might-not-exist-according-to-physicists-and-philosophers-but-thats-okay-181268">space and time may disappear</a> at very small scales or high energies. If that’s right, it may not be possible to carry out experiments at these scales.</p>
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<p>After all, experiments as we know them are the kind of thing that happen at a particular place, across a particular interval of time. If theories like this are correct, we may need to rethink the very nature of experimentation so we can make sense of it in situations where space and time are absent.</p>
<p>On the other hand, the very fact we can perform straightforward experiments involving gravity at small scales may suggest that space and time are present after all.</p>
<p>Which will prove true? The best way to find out is to keep going with tabletop experiments, and to push them as far as they can go.</p><img src="https://counter.theconversation.com/content/224372/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>A new measurement of gravity at small scales hints at an alternative to billion-dollar experiments for the future of physics.Sam Baron, Associate Professor, Philosophy of Science, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2185952024-01-24T19:06:45Z2024-01-24T19:06:45ZAustralia may spend hundreds of millions of dollars on quantum computing research. Are we chasing a mirage?<figure><img src="https://images.theconversation.com/files/571090/original/file-20240124-19-t230yk.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3880%2C2052&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/background-pattern-vNCBkSX3Nbo">Dynamic Wang / Unsplash</a></span></figcaption></figure><p>The Australian government is going all in on quantum computing. After investing more than $100 million on “quantum technology” <a href="https://ministers.treasury.gov.au/ministers/jane-hume-2020/media-releases/111-million-investment-back-australias-quantum-technology">in 2021</a>, it is now <a href="https://www.innovationaus.com/govt-uses-secret-eoi-in-search-for-quantum-computer/">reportedly</a> considering spending up to $200 million on purchasing a “quantum computer” from a US company. </p>
<p>Is this a sensible decision? You might think so, if you read reports from <a href="https://www.zdnet.com/article/quantum-computers-eight-ways-quantum-computing-is-going-to-change-the-world/">media</a>, industry and <a href="https://www.industry.gov.au/publications/national-quantum-strategy/appendix-categories-quantum-technologies">government</a> predicting that quantum computers will revolutionise many fields of science. Two common examples given are drastically accelerating the <a href="https://spectrum.ieee.org/lithium-air-battery-quantum-computing">design of better batteries</a> and <a href="https://www.mckinsey.com/industries/life-sciences/our-insights/pharmas-digital-rx-quantum-computing-in-drug-research-and-development">drug discovery</a>. </p>
<p>Given the scale of investment, from governments around the world and also private companies, you might think quantum computers are a sure bet to reach these amazing goals. Unfortunately, in the words of US quantum computing theorist Scott Aaronson, the reality is “<a href="https://x.com/DulwichQuantum/status/1740842486262849884?s=20">much iffier</a>”.</p>
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<h2>What’s so iffy about quantum computing?</h2>
<p>In a recent <a href="https://www.pnas.org/doi/10.1073/pnas.2313269120">perspective article</a> in the Proceedings of the National Academy of Sciences, French physicist Xavier Waintal warned of weaknesses in “the quantum house of cards”. Waintal notes that “a simple task such as multiplying 3 by 5 is beyond existing quantum hardware” and that a useful quantum computer might “require an improvement by a factor of one billion” on the error rate of current devices.</p>
<p><a href="https://spectrum.ieee.org/quantum-computing-skeptics">Skeptical voices such as Waintal’s are growing louder</a> as success still seems a long way off, despite huge investments of time and effort. While companies like IBM and Google are still spending on quantum computing, China’s tech giants are <a href="https://www.reuters.com/technology/baidu-donate-quantum-computing-lab-equipment-beijing-institute-2024-01-03/">dumping their own quantum computing labs</a>.</p>
<p>It’s possible that a chain of breakthroughs could occur over the next few years, leading to useful quantum computers. We have seen other technologies, such as traditional computing chips, make huge improvements in short amounts of time. </p>
<p>However, improvements in traditional computing have resulted from massive investment over many decades. Before we can decide whether such a large investment is worth it for quantum computers, we need a clear understanding of their applications. </p>
<h2>What would quantum computers really be good for?</h2>
<p>One application that first drew attention to the idea of quantum computers (in the 1990s) is their ability to <a href="https://pubs.aip.org/aapt/ajp/article-abstract/73/6/521/1041912/Shor-s-factoring-algorithm-and-modern-cryptography?redirectedFrom=fulltext">break some kinds of encryption</a> commonly used to store and transmit data. However, <a href="https://link.springer.com/chapter/10.1007/978-3-031-33386-6_10">new encryption methods</a> have since been developed that would be safe from quantum computers.</p>
<p>Now attention has moved to the potential ability of quantum computers to solve problems in biology and chemistry, such as drug discovery and battery design. The idea is that biology and chemistry are governed by <a href="https://www.ted.com/talks/tim_duignan_why_simple_salt_water_is_so_much_more_than_it_seems">the same laws of quantum mechanics</a> that control the workings of quantum computers.</p>
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<p>This argument seems plausible, but it has some problems. One is that, although chemistry and biology do follow the laws of quantum mechanics, in many cases their behaviours are almost indistinguishable from non-quantum ones. </p>
<p>In fact, there is <a href="https://arxiv.org/abs/2208.02199">no guarantee</a> that quantum computers will be able to outperform current computers when applied to problems in biology and chemistry. </p>
<p>It’s possible that once we have built a quantum computer we will be able to find ways to make it solve problems in biology and chemistry faster than a normal computer, but it’s far from guaranteed.</p>
<h2>Can AI outdo quantum computers?</h2>
<p>Quantum computing advocates are not alone in wanting to better simulate chemistry and biology. Many other scientists are working on this problem as well.</p>
<p>For example, quantum chemistry and molecular simulation are two very active research fields. These scientists are making rapid progress on solving many of the problems that supposedly justify the development of quantum computers. </p>
<p>Most excitingly, these fields are taking advantage of recent developments in artificial intelligence to massively improve the scale and accuracy with which they can simulate biology and chemistry. In <a href="https://arxiv.org/abs/2401.00096">one recent example</a>, researchers trained an AI algorithm on a huge dataset and used it to study a large range of chemical and biological systems with impressive accuracy and speed.</p>
<h2>Quantum alternatives</h2>
<p>“Useful” quantum computers are still some distance away, if they ever eventuate. And even if they are built, they may not be as useful as their advocates hope. </p>
<p>So while it’s reasonable for our government to invest in quantum computing research, we should be realistic about what we hope to get out of it. And we shouldn’t neglect other avenues in the quest to understand chemistry and biology at the most fundamental levels.</p>
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<a href="https://theconversation.com/australia-has-a-national-quantum-strategy-what-does-that-mean-205232">Australia has a National Quantum Strategy. What does that mean?</a>
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<p>Just as a smart investment strategy is to diversity, we should do the same with our research funding, backing many different potentially exciting technologies. We should be humble about our ability to know which research directions are the most promising, as the future is incredibly hard to predict. If it wasn’t, we wouldn’t need a quantum computer in the first place.</p><img src="https://counter.theconversation.com/content/218595/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy Duignan receives funding from Australian Research Council. </span></em></p>Quantum computers are proving extremely difficult to build, and there is no guarantee they will live up to their designers’ hopes.Timothy Duignan, Lecturer, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2180652024-01-19T13:03:16Z2024-01-19T13:03:16ZCould quantum physics be the key that unlocks the secrets of human behaviour?<figure><img src="https://images.theconversation.com/files/561544/original/file-20231124-25-m6quk8.jpg?ixlib=rb-1.1.0&rect=11%2C5%2C3982%2C2389&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/concept-human-intelligence-brain-on-blue-294471983">ESB Professional / Shutterstock</a></span></figcaption></figure><p>Human behaviour is an enigma that fascinates many scientists. And there has been much discussion over the role of probability in explaining how our minds work.</p>
<p>Probability is a mathematical framework designed to tell us how likely an event is to occur – and works well for many everyday situations. For example, it describes the outcome of a coin toss as ½ – or 50% – because throwing either heads or tails is equally probable. </p>
<p><a href="https://www.aeaweb.org/articles?id=10.1257/000282803322655392">Yet research has shown</a> that human behaviour can’t be fully captured by these traditional or “classical” laws of probability. Could it instead be explained by the way probability works in the more mysterious world of quantum mechanics?</p>
<p>Mathematical probability is also a vital component of quantum mechanics, the branch of physics that describes how nature behaves at the scale of atoms or sub-atomic particles. However, as we’ll see, in the quantum world, probabilities follow very different rules.</p>
<p><a href="https://jbusemey.pages.iu.edu/quantum/Quantum%20Cognition%20Notes.htm">Discoveries over the last two decades</a> have shed light on a crucial role for “quantumness” in human cognition – how the human brain processes information to acquire knowledge or understanding. These findings also have potential implications for the development of artificial intelligence (AI). </p>
<h2>Human ‘irrationality’</h2>
<p>Nobel laureate <a href="https://en.wikipedia.org/wiki/Daniel_Kahneman">Daniel Kahnemann</a> and other cognitive scientists have carried out work on what they describe as the “irrationality” of human behaviour. When behavioural patterns do not strictly follow the rules of classical probability theory from a mathematical perspective, they are deemed “irrational”.</p>
<p>For example, <a href="https://journals.sagepub.com/doi/abs/10.1111/j.1467-9280.1992.tb00678.x">a study found</a> that a majority of students who have passed an end-of-term exam favour going on holiday afterwards. Likewise, a majority of those who have failed also want to go for a holiday. </p>
<p>If a student doesn’t know their result, classical probability would predict that they would opt for the holiday because it is the preferred option whether they have passed or failed. Yet in the experiment, a majority of students preferred not to go on holiday if they didn’t know how they’d done. </p>
<p>Intuitively, it’s not hard to understand that students might not want to go on holiday if they are going to be worrying about their exam results the whole time. But classical probability does not accurately capture the behaviour, so it is described as irrational. Many similar violations of classical probability rules have been observed in cognitive science.</p>
<h2>Quantum brain?</h2>
<p>In classical probability, when a sequence of questions is asked, then the answers do not depend on the order in which the questions are posed. By contrast, in quantum physics, the answers to a series of questions can depend crucially on the order in which they are asked. </p>
<p>One example is the measurement of the <a href="https://en.wikipedia.org/wiki/Spin_(physics)">spin of an electron</a> in two different directions. If you first measure the spin in the horizontal direction and then in the vertical direction, you will get one outcome. </p>
<p>The outcomes will generally be different when the order is reversed, because of a well known feature of quantum mechanics. Simply measuring a property of a quantum system can affect the thing that’s being measured (in this case an electron’s spin) and hence the outcome of any subsequent experiments. </p>
<p>Order dependence can also be seen in human behaviour. For example, in a <a href="https://academic.oup.com/poq/article-abstract/66/1/80/1866700">study published 20 years ago about the effects that question order has on respondents’ answers</a>, subjects were asked whether they thought the previous US president, Bill Clinton, was honest. They were then asked if his vice president, Al Gore, seemed honest. </p>
<p>When the questions were delivered in this order, a respective 50% and 60% of respondents answered that they were honest. But when the researchers asked respondents about Gore first and then Clinton, a respective 68% and 60% responded that they were honest. </p>
<p>On an everyday level, it might seem that human behaviour is not consistent because it often violates the rules of classical probability theory. However, <a href="https://www.nature.com/articles/s41598-023-43403-4">this behaviour does appear to fit</a> with the way probability works in quantum mechanics. </p>
<p>Observations of this kind have led cognitive scientist <a href="https://en.wikipedia.org/wiki/Jerome_Busemeyer">Jerome Busemeyer</a> and many others to recognise that quantum mechanics can, on the whole, explain human behaviour in a more consistent way.</p>
<p>Based on this astonishing hypothesis, a new research field called “quantum cognition” has arisen within the area of cognitive sciences. </p>
<p>How it is possible that thought processes are dictated by quantum rules? Is our brain working like a quantum computer? No one yet knows the answers, but the empirical data strongly appears to suggest that our thoughts follow quantum rules.</p>
<h2>Dynamic behaviour</h2>
<p>In parallel to these exciting developments, over the past two decades my collaborators and I have developed a framework for modelling – or simulating – the dynamics of people’s cognitive behaviour <a href="https://www.worldscientific.com/worldscibooks/10.1142/12533">as they digest “noisy”</a> (that is, imperfect) information from the outside world.</p>
<p>We again found that mathematical techniques developed for <a href="https://iopscience.iop.org/article/10.1088/0305-4470/39/4/008/meta">modelling the quantum world</a> could be applied to modelling how the human brain processes noisy data. </p>
<p>These principles can be applied to other behaviour in biology, beyond just the brain. <a href="https://royalsocietypublishing.org/doi/10.1098/rspa.2022.0809">Green plants</a>, for example, have the <a href="https://royalsocietypublishing.org/doi/10.1098/rsfs.2016.0098">remarkable ability</a> to extract and analyse chemical and other information from their environments and to adapt to changes.</p>
<p>My rough estimate, based on <a href="https://www.nature.com/articles/s41598-020-76588-z">a recent experiment</a> on common bean plants, suggests that they can <a href="https://www.nature.com/articles/s41598-020-76588-z">process this external information</a> more efficiently than the best computer we have today. </p>
<p>In this context, efficiency means that the plant is consistently able to <a href="https://royalsocietypublishing.org/doi/10.1098/rspa.2022.0809">reduce the uncertainty</a> about its external environment to the greatest extent possible in its circumstances. This could, for example, encompass easily detecting the direction that light is coming from, so that the plant can grow towards it. The efficient processing of information by an organism is also linked to saving energy, which is important for its survival.</p>
<p>Similar rules may apply to the human brain, particularly to how our state of mind changes when detecting outside signals. All of this is important for the current trajectory of technological development. If our behaviour is best described by the way probability works in quantum mechanics, then to accurately replicate human behaviour in machines, AI systems should probably follow quantum rules, not classical ones. </p>
<p>I’ve called this idea <a href="https://www.nature.com/articles/s41598-023-43403-4">artificial quantum intelligence (AQI)</a>. A great deal of research is needed to develop practical applications from such an idea. </p>
<p>But an AQI could help get us to the goal of AI systems that behave more like a real person.</p><img src="https://counter.theconversation.com/content/218065/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dorje C Brody receives funding from Engineering and Physical Science Research Council (EP/X019926/1) and the John
Templeton Foundation (62210). The opinions expressed in this publication are those of the author and do not necessarily reflect the views of the John Templeton Foundation.</span></em></p>Human behaviour is often irrational if viewed through the lens of “classical” physics and probability theory.Dorje C. Brody, Professor of Mathematics, University of SurreyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2158042023-10-19T04:59:00Z2023-10-19T04:59:00ZQuantum computers in 2023: how they work, what they do, and where they’re heading<figure><img src="https://images.theconversation.com/files/554450/original/file-20231018-29-xrpphz.jpg?ixlib=rb-1.1.0&rect=17%2C43%2C5757%2C3800&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A complex cooling rig is needed to maintain the ultracold working temperatures required by a superconducting quantum computer.</span> <span class="attribution"><a class="source" href="https://newsroom.ibm.com/media-quantum-innovation">IBM</a></span></figcaption></figure><p>In June, an IBM computing executive claimed <a href="https://www.nytimes.com/2023/06/14/science/ibm-quantum-computing.html">quantum computers were entering the “utility” phase</a>, in which high-tech experimental devices become useful. In September, Australia’s Chief Scientist Cathy Foley went so far as to declare “<a href="https://www.chiefscientist.gov.au/news-and-media/its-time-australia-leverage-our-resources-and-tech-skills-prosper-new-economy">the dawn of the quantum era</a>”. </p>
<p>This week, Australian physicist <a href="https://www.abc.net.au/news/science/2023-10-16/prime-minister-science-prize-michelle-simmons-quantum-physics/102979096">Michelle Simmons won the nation’s top science award</a> for her work on developing silicon-based quantum computers.</p>
<p>Obviously, quantum computers are having a moment. But – to step back a little – what exactly <em>are</em> they? </p>
<h2>What is a quantum computer?</h2>
<p>One way to think about computers is in terms of the kinds of numbers they work with.</p>
<p>The digital computers we use every day rely on whole numbers (or <em>integers</em>), representing information as strings of zeroes and ones which they rearrange according to complicated rules. There are also analogue computers, which represent information as continuously varying numbers (or <em>real numbers</em>), manipulated via electrical circuits or spinning rotors or moving fluids.</p>
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<a href="https://theconversation.com/theres-a-way-to-turn-almost-any-object-into-a-computer-and-it-could-cause-shockwaves-in-ai-62235">There's a way to turn almost any object into a computer – and it could cause shockwaves in AI</a>
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<p>In the 16th century, the Italian mathematician Girolamo Cardano invented another kind of number called <em>complex numbers</em> to solve seemingly impossible tasks such as finding the square root of a negative number. In the 20th century, with the advent of quantum physics, it turned out complex numbers also naturally describe the fine details of light and matter.</p>
<p>In the 1990s, physics and computer science collided when it was discovered that some problems could be solved much faster with algorithms that work directly with complex numbers as encoded in quantum physics. </p>
<p>The next logical step was to build devices that work with light and matter to do those calculations for us automatically. This was the birth of quantum computing.</p>
<h2>Why does quantum computing matter?</h2>
<p>We usually think of the things our computers do in terms that mean something to us — balance my spreadsheet, transmit my live video, find my ride to the airport. However, all of these are ultimately computational problems, phrased in mathematical language. </p>
<p>As quantum computing is still a nascent field, most of the problems we know quantum computers will solve are phrased in abstract mathematics. Some of these will have “real world” applications we can’t yet foresee, but others will find a more immediate impact.</p>
<p>One early application will be cryptography. Quantum computers will be able to crack today’s internet encryption algorithms, so we will need quantum-resistant cryptographic technology. Provably secure cryptography and a fully quantum internet would use quantum computing technology.</p>
<figure class="align-center ">
<img alt="A microscopic view of a square, iridescent computer chip against an orange background." src="https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554626/original/file-20231018-19-68uhls.jpeg?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">
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<span class="caption">Google has claimed its Sycamore quantum processor can outperform classical computers at certain tasks.</span>
<span class="attribution"><span class="source">Google</span></span>
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<p>In materials science, quantum computers will be able to simulate molecular structures at the atomic scale, making it faster and easier to discover new and interesting materials. This may have significant applications in batteries, pharmaceuticals, fertilisers and other chemistry-based domains.</p>
<p>Quantum computers will also speed up many difficult optimisation problems, where we want to find the “best” way to do something. This will allow us to tackle larger-scale problems in areas such as logistics, finance, and weather forecasting.</p>
<p>Machine learning is another area where quantum computers may accelerate progress. This could happen indirectly, by speeding up subroutines in digital computers, or directly if quantum computers can be reimagined as learning machines.</p>
<h2>What is the current landscape?</h2>
<p>In 2023, quantum computing is moving out of the basement laboratories of university physics departments and into industrial research and development facilities. The move is backed by the chequebooks of multinational corporations and venture capitalists. </p>
<p>Contemporary quantum computing prototypes – built by <a href="https://www.ibm.com/quantum">IBM</a>, <a href="https://quantumai.google/">Google</a>, <a href="https://ionq.com/">IonQ</a>, <a href="https://www.rigetti.com/">Rigetti</a> and others – are still some way from perfection. </p>
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<a href="https://theconversation.com/error-correcting-the-things-that-go-wrong-at-the-quantum-computing-scale-84846">Error correcting the things that go wrong at the quantum computing scale</a>
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<p>Today’s machines are of modest size and susceptible to errors, in what has been called the “<a href="https://thequantuminsider.com/2023/03/13/what-is-nisq-quantum-computing/">noisy intermediate-scale quantum</a>” phase of development. The delicate nature of tiny quantum systems means they are prone to many sources of error, and correcting these errors is a major technical hurdle.</p>
<p>The holy grail is a large-scale quantum computer which can correct its own errors. A whole ecosystem of research factions and commercial enterprises are pursuing this goal via diverse technological approaches. </p>
<h2>Superconductors, ions, silicon, photons</h2>
<p>The current leading approach uses loops of electric current inside superconducting circuits to store and manipulate information. This is the technology adopted by <a href="https://quantumai.google/hardware">Google</a>, <a href="https://www.ibm.com/topics/quantum-computing">IBM</a>, <a href="https://www.rigetti.com/what-we-build">Rigetti</a> and others. </p>
<p>Another method, the “trapped ion” technology, works with groups of electrically charged atomic particles, using the inherent stability of the particles to reduce errors. This approach has been spearheaded by <a href="https://ionq.com/technology">IonQ</a> and <a href="https://www.honeywell.com/us/en/company/quantum">Honeywell</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration showing glowing dots and patterns of light." src="https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=519&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=519&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=519&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=653&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=653&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554627/original/file-20231018-29-hte4r6.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=653&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">An artist’s impression of a semiconductor-based quantum computer.</span>
<span class="attribution"><a class="source" href="https://www.sqc.com.au">Silicon Quantum Computing</a></span>
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<p>A third route of exploration is to confine electrons within tiny particles of semiconductor material, which could then be melded into the well-established silicon technology of classical computing. <a href="https://sqc.com.au/">Silicon Quantum Computing</a> is pursuing this angle.</p>
<p>Yet another direction is to use individual particles of light (photons), which can be manipulated with high fidelity. A company called PsiQuantum is designing <a href="https://www.nature.com/articles/s41467-023-36493-1">intricate “guided light” circuits</a> to perform quantum computations. </p>
<p>There is no clear winner yet from among these technologies, and it may well be a hybrid approach that ultimately prevails.</p>
<h2>Where will the quantum future take us?</h2>
<p>Attempting to forecast the future of quantum computing today is akin to predicting flying cars and ending up with cameras in our phones instead. Nevertheless, there are a few milestones that many researchers would agree are likely to be reached in the next decade.</p>
<p>Better error correction is a big one. We expect to see a transition from the era of noisy devices to small devices that can sustain computation through active error correction.</p>
<p>Another is the advent of post-quantum cryptography. This means the establishment and adoption of cryptographic standards that can’t easily be broken by quantum computers.</p>
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<a href="https://theconversation.com/quantum-computers-threaten-our-whole-cybersecurity-infrastructure-heres-how-scientists-can-bulletproof-it-196065">Quantum computers threaten our whole cybersecurity infrastructure: here's how scientists can bulletproof it</a>
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<p>Commercial spin-offs of technology such as quantum sensing are also on the horizon.</p>
<p>The demonstration of a genuine “quantum advantage” will also be a likely development. This means a compelling application where a quantum device is unarguably superior to the digital alternative.</p>
<p>And a stretch goal for the coming decade is the creation of a large-scale quantum computer free of errors (with active error correction). </p>
<p>When this has been achieved, we can be confident the 21st century will be the “quantum era”.</p><img src="https://counter.theconversation.com/content/215804/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Ferrie receives funding from the Australian Research Council. He is a co-founder of quantum startup Eigensystems. </span></em></p>After decades of hype, quantum computers are on the verge of becoming useful. Here’s a refresher on why they’re such a big dealChristopher Ferrie, Senior Lecturer, UTS Chancellor's Postdoctoral Research and ARC DECRA Fellow, University of Technology SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2110672023-09-24T12:10:23Z2023-09-24T12:10:23ZWhy Einstein must be wrong: In search of the theory of gravity<figure><img src="https://images.theconversation.com/files/548379/original/file-20230914-27-fu6fow.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6000%2C2497&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As new and powerful telescopes gather new data about the universe, they reveal the limits of older theories.</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/why-einstein-must-be-wrong-in-search-of-the-theory-of-gravity" width="100%" height="400"></iframe>
<p>Einstein’s theory of gravity — <a href="https://www.space.com/17661-theory-general-relativity.html">general relativity</a> — has been very successful for more than a century. However, it has theoretical shortcomings. This is not surprising: the theory predicts its own failure at spacetime singularities inside black holes — and the <a href="https://www.einstein-online.info/en/spotlight/avoiding_the_big_bang/">Big Bang itself</a>. </p>
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<a href="https://theconversation.com/our-understanding-of-black-holes-has-changed-over-time-172816">Our understanding of black holes has changed over time</a>
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<p>Unlike physical theories describing the other three fundamental forces in physics — the electromagnetic and the strong and weak nuclear interactions — the general theory of relativity has only been tested in weak gravity. </p>
<p>Deviations of gravity from general relativity are by no means excluded nor tested everywhere <a href="https://doi.org/10.1038/s41550-022-01808-7">in the universe</a>. And, according to theoretical physicists, deviation must happen.</p>
<h2>Deviations and quantum mechanics</h2>
<p>According to Einstein, our universe originated in a Big Bang. Other singularities hide inside black holes: Space and time cease to have meaning there, while quantities such as energy density and pressure become infinite. These signal that Einstein’s theory is failing there and must be replaced with a more fundamental one.</p>
<p>Naively, spacetime singularities should be resolved by quantum mechanics, which apply at very small scales.</p>
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<a href="https://theconversation.com/will-we-have-to-rewrite-einsteins-theory-of-general-relativity-50057">Will we have to rewrite Einstein's theory of general relativity?</a>
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<p>Quantum physics relies on two simple ideas: <a href="https://www.quantamagazine.org/what-is-a-particle-20201112/">point particles</a> make no sense; and the <a href="https://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">Heisenberg uncertainty principle</a>, which states that one can never know the value of certain pairs of quantities with absolute precision — for example, the position and velocity of a particle. This is because particles should not be thought of as points but as waves; at small scales they behave as waves of matter.</p>
<p>This is enough to understand that a theory that embraces both general relativity and quantum physics should be free of such pathologies. However, all attempts to blend general relativity and quantum physics necessarily introduce deviations from Einstein’s theory. </p>
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<a href="https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a black circle surrounded with a ring of light" src="https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=358&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=358&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=358&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=450&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=450&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548820/original/file-20230918-27-exi2b0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=450&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A photo of the 1919 complete solar eclipse.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1098/rsta.1920.0009">(Arthur Eddington/Philosophical Transactions of the Royal Society)</a></span>
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<p>Therefore, Einstein’s gravity cannot be the ultimate theory of gravity. Indeed, it was not long after the introduction of general relativity by Einstein in 1915 that Arthur Eddington, best known for verifying this theory in the <a href="https://doi.org/10.1098/rsnr.2020.0040">1919 solar eclipse</a>, started searching for alternatives just to see how things could be different. </p>
<p>Einstein’s theory has survived all tests to date, accurately predicting various results from the <a href="https://doi.org/10.12942/lrr-2014-4">precession of Mercury’s orbit to the existence of gravitational waves</a>. So, where are these deviations from general relativity hiding?</p>
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<a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">Gravitational waves discovered: top scientists respond</a>
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<h2>Cosmology matters</h2>
<p>A century of research has given us the standard model of cosmology known as the Λ-Cold Dark Matter <a href="https://lambda.gsfc.nasa.gov/education/graphic_history/univ_evol.html">(ΛCDM) model</a>. Here, Λ stands for either Einstein’s famous cosmological constant or a mysterious dark energy with similar properties. </p>
<p>Dark energy was introduced ad hoc by astronomers to explain the <a href="https://doi.org/10.1103/RevModPhys.75.559">acceleration of the cosmic expansion</a>. Despite fitting cosmological data extremely well until recently, the ΛCDM model is spectacularly incomplete and unsatisfactory from the theoretical point of view. </p>
<p>In the past five years, it has also faced severe <a href="https://doi.org/10.1088/1361-6382/ac086d">observational tensions</a>. The Hubble constant, which determines the age and the distance scale in the universe, can be measured in the early universe using the cosmic microwave background and in the late universe using supernovae as standard candles. </p>
<p>These two measurements give <a href="https://doi.org/10.1088/1361-6382/ac086d">incompatible results</a>. Even more important, the nature of the main ingredients of the ΛCDM model — <a href="https://theconversation.com/the-experiments-trying-to-crack-physics-biggest-question-what-is-dark-energy-52917">dark energy</a>, <a href="https://theconversation.com/why-do-astronomers-believe-in-dark-matter-122864">dark matter</a> and the field driving early universe <a href="https://www.newscientist.com/definition/cosmic-inflation/">inflation</a> (a very brief period of extremely fast expansion originating the seeds for galaxies and galaxy clusters) — remains a mystery.</p>
<p>From the observational point of view, the most compelling motivation for modified gravity is the acceleration of the universe discovered in 1998 with <a href="https://doi.org/10.1086/307221">Type Ia supernovae</a>, whose luminosity is dimmed by this acceleration. The ΛCDM model based on general relativity postulates an extremely exotic dark energy with negative pressure permeating the universe. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="eight bright circles in a dark sky" src="https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548822/original/file-20230918-27-jr07hx.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">Type Ia supernovae were discovered in 1998, and revealed more about the rate of the universe’s acceleration.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/jpl/galex/pia18929/after-the-explosion-investigating-supernova-sites">(Sloan Digital Sky Survey/NASA)</a></span>
</figcaption>
</figure>
<p>Problem is, this dark energy has no physical justification. Its nature is completely unknown, although a <a href="https://doi.org/10.1142/S0219887807001928">plethora of models</a> has been proposed. The proposed alternative to dark energy is a cosmological constant Λ which, according to quantum-mechanical <a href="https://doi.org/10.1103/RevModPhys.61.1">back-of-the-envelope (but questionable) calculations</a>, should be huge. </p>
<p>However, Λ must instead be incredibly fine-tuned to a tiny value to fit the cosmological observations. If dark energy exists, our ignorance of its nature is deeply troubling.</p>
<h2>Alternatives to Einstein’s theory</h2>
<p>Could it be that troubles arise, instead, from wrongly trying to fit the cosmological observations into general relativity, like fitting a person into a pair of trousers that are too small? That we are observing the first deviations from general relativity while the mysterious dark energy simply does not exist? </p>
<p>This idea, <a href="https://doi.org/10.1142/S0218271802002025">first proposed</a> by researchers at the University of Naples, has gained tremendous popularity while the contending dark energy camp remains vigorous. </p>
<p>How can we tell? Deviations from Einstein gravity are <a href="https://doi.org/10.12942/lrr-2014-4">constrained by solar system experiments</a>, the recent observations of <a href="https://doi.org/10.1103/PhysRevLett.116.061102">gravitational waves</a> and the <a href="https://doi.org/10.3847/2041-8213/ab0ec7">near-horizon images of black holes</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/say-hello-to-sagittarius-a-the-black-hole-at-the-center-of-the-milky-way-galaxy-183008">Say hello to Sagittarius A*, the black hole at the center of the Milky Way galaxy</a>
</strong>
</em>
</p>
<hr>
<p>There is now a <a href="https://doi.org/10.1103/RevModPhys.82.451">large literature</a> on theories of gravity alternative to general relativity, going back to Eddington’s 1923 early investigations. A very popular class of alternatives is the so-called scalar-tensor gravity. It is conceptually very simple since it only introduces one additional ingredient (a scalar field corresponding to the simplest, spinless, particle) to Einstein’s geometric description of gravity. </p>
<p>The consequences of this program, however, are far from trivial. A striking phenomenon is the “<a href="https://doi.org/10.1007/s41114-018-0011-x">chameleon effect</a>,” consisting of the fact that these theories can disguise themselves as general relativity in high-density environments (such as in stars or in the solar system) while deviating strongly from it in the low-density environment of cosmology.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-search-for-dark-matter-and-dark-energy-just-got-interesting-46422">The search for 'dark matter' and 'dark energy' just got interesting</a>
</strong>
</em>
</p>
<hr>
<p>As a result, the extra (gravitational) field is effectively absent in the first type of systems, disguising itself as a chameleon does, and is felt only at the largest (cosmological) scales.</p>
<h2>The current situation</h2>
<p>Nowadays the spectrum of alternatives to Einstein gravity has widened dramatically. Even adding a single massive scalar excitation (namely, a spin-zero particle) to Einstein gravity —and keeping the resulting equations “simple” to avoid some known fatal instabilities — has resulted in the much wider class of <a href="https://doi.org/10.1142/S0218271819420069">Horndeski theories</a>, and subsequent generalizations. </p>
<p>Theorists have spent the last decade extracting physical consequences from these theories. The recent detections of <a href="https://doi.org/10.1103/PhysRevLett.116.061102">gravitational waves</a> have provided a way to <a href="https://doi.org/10.1103/PhysRevD.95.084029">constrain the physical class of modifications</a> of Einstein gravity allowed.</p>
<p>However, much work still needs to be done, with the hope that future advances in <a href="https://www.nature.com/articles/s42254-019-0101-z">multi-messenger astronomy</a> lead to discovering modifications of general relativity where gravity is extremely strong.</p><img src="https://counter.theconversation.com/content/211067/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Valerio Faraoni receives funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p><p class="fine-print"><em><span>Andrea Giusti received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Actions (grant agreement No. 895648). </span></em></p>Einstein’s theory of general relativity suggests that our universe originated in a Big Bang. But black holes, and their gravitational forces, challenge the limits of Einstein’s work.Valerio Faraoni, Professor, Physics & Astronomy, Bishop's UniversityAndrea Giusti, Postdoctoral fellow, Swiss Federal Institute of Technology ZurichLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2079742023-07-05T12:23:21Z2023-07-05T12:23:21ZHow splitting sound might lead to a new kind of quantum computer<p>When you turn on a lamp to brighten a room, you are experiencing light energy transmitted as photons, which are small, discrete quantum packets of energy. These photons must obey the sometimes strange laws of quantum mechanics, which, for instance, dictate that photons are indivisible, but at the same time, allow a photon <a href="https://www.cambridge.org/highereducation/books/introduction-to-quantum-mechanics/990799CA07A83FC5312402AF6860311E#overview">to be in two places at once</a>. </p>
<p>Similar to the photons that make up beams of light, indivisible quantum particles <a href="https://news.mit.edu/2010/explained-phonons-0706">called phonons</a> make up a beam of sound. These particles emerge from the collective motion of quadrillions of atoms, much as a “stadium wave” in a sports arena is due to the motion of thousands of individual fans. When you listen to a song, you’re hearing a stream of these very small quantum particles.</p>
<p>Originally conceived to <a href="https://www.wiley.com/en-us/Introduction+to+Solid+State+Physics%2C+8th+Edition-p-9780471415268">explain the heat capacities of solids</a>, phonons are predicted to obey the same rules of quantum mechanics as photons. The technology to generate and detect individual phonons has, however, lagged behind that for photons. </p>
<p>That technology is only now being developed, in part by <a href="https://clelandlab.uchicago.edu/">my research group</a> at the Pritzker School of Molecular Engineering at the University of Chicago. <a href="https://scholar.google.com/citations?user=uE04v0gAAAAJ&hl=en&oi=ao">We are exploring</a> the fundamental quantum properties of sound by splitting phonons in half and entangling them together.</p>
<p>My group’s fundamental research on phonons may one day allow researchers to build a new type of quantum computer, called a mechanical quantum computer.</p>
<h2>Splitting sound with ‘bad’ mirrors</h2>
<p>To explore the quantum properties of phonons, our team uses acoustic mirrors, which can direct beams of sound. Our latest experiments, published in <a href="https://doi.org/10.1126/science.adg8715">a recent issue of Science</a>, however, involve “bad” mirrors, called beam splitters, that reflect about half the sound sent toward them and let the other half through. Our team decided to explore what happens when we direct a phonon at a beam splitter. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a line representing a beam splitter, which a phonon hits. Two dashed lines on either side of the beam splitter line demarcate that the phonon is both reflected off the beam splitter and transmitted to the other side, in superposition." src="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A beam splitter for phonons – the phonon enters a superposition state where it is both reflected and transmitted until it is detected.</span>
<span class="attribution"><span class="source">A.N. Cleland</span></span>
</figcaption>
</figure>
<p>As a phonon is indivisible; it cannot be split. Instead, after interacting with the beam splitter, the phonon ends up in what is called a “<a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">superposition state</a>.” In this state the phonon is, somewhat paradoxically, both reflected and transmitted, and you’re equally likely to detect the phonon in either state. If you intervene and detect the phonon, half the time you will measure that it was reflected and half the time that it was transmitted; in a sense, the state is <a href="https://doi.org/10.1119/1.3243279">selected at random</a> by the detector. Absent the detection process, the phonon will remain in the superposition state of being both transmitted and reflected. </p>
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<figcaption><span class="caption">A brief Ted-Ed explainer on superposition, which happens when particles can exist in multiple places at once.</span></figcaption>
</figure>
<p>This superposition effect was observed many years ago with photons. Our results indicate that phonons have the same property. </p>
<h2>Entangled phonons</h2>
<p>After demonstrating that phonons can go into quantum superpositions just as photons do, my team asked <a href="https://doi.org/10.1126/science.adg8715">a more complex question</a>. We wanted to know what would happen if we sent two identical phonons into the beam splitter, one from each direction. </p>
<p>It turns out that each phonon will go into a similar superposition state of half-transmitted and half-reflected. But because of the physics of the beam splitter, if we time the phonons precisely, they will quantum-mechanically interfere with one another. What emerges is actually a superposition state of two phonons going one way and two phonons going the other – the two phonons are thus <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/entanglement">quantum-mechanically entangled</a>. </p>
<p>In quantum entanglement, each phonon is in a superposition of reflected and transmitted, but the two phonons are locked together. This means detecting one phonon as having been transmitted or reflected forces the other phonon to be in the same state.</p>
<p>So, if you detect, you’ll always detect two phonons, going one way or the other, never one phonon going each way. This same effect for light, the combination of superposition and interference of two photons, is called the <a href="https://doi.org/10.1103/PhysRevLett.59.2044">Hong-Ou-Mandel effect</a>, after the three physicists who first predicted and observed it in 1987. Now, my group has demonstrated this effect with sound. </p>
<h2>The future of quantum computing</h2>
<p>These results suggest that it may now be possible to build a mechanical quantum computer using phonons. There are continuing efforts to build <a href="https://news.mit.edu/2020/explained-quantum-engineering-1210">optical quantum computers</a> that require only the emission, detection and interference of single photons. These are in parallel with efforts to build electrical quantum computers, which through the use of large numbers of entangled particles promise an exponential speedup for certain problems, such as factoring large numbers or simulating quantum systems.</p>
<p>A quantum computer using phonons could be very compact and self-contained, built entirely on a chip similar to that of a laptop computer’s processor. Its small size could make it easier to implement and use, if researchers can further expand and improve phonon-based technologies.</p>
<p>My group’s <a href="https://doi.org/10.1126/science.adg8715">experiments with phonons</a> use qubits – the same technology that powers electronic quantum computers – which means that as the technology for phonons catches up, there’s the potential to integrate phonon-based computers with electronic quantum computers. Doing so could yield new, potentially unique computational abilities.</p><img src="https://counter.theconversation.com/content/207974/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew N. Cleland receives funding from various US federal funding agencies. He is a fellow of the American Physical Society (APS) and the American Association for the Advancement of Science. He is currently Past Chair of the Division of Quantum Information of the APS, and in 2023 held a Fulbright Distinguished Chair. He is a founder and a board member of Spectradyne LLC, a startup company based in Los Angeles that is commercializing electrical and optical detection of nanoparticles in fluids.</span></em></p>Scientists show they can create quantum superpositions of sound particles, pointing to the potential for mechanical quantum computers.Andrew N. Cleland, Professor of Molecular Engineering Innovation and Enterprise, University of Chicago Pritzker School of Molecular EngineeringLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2049952023-05-15T12:33:56Z2023-05-15T12:33:56ZQuantum physics proposes a new way to study biology – and the results could revolutionize our understanding of how life works<figure><img src="https://images.theconversation.com/files/525487/original/file-20230510-21-cnx7u8.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1999%2C1499&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Looking at life at the atomic scale offers a more comprehensive understanding of the macroscopic world.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/colorful-model-of-helix-dna-strand-royalty-free-image/157531306">theasis/E+ via Getty Images</a></span></figcaption></figure><p>Imagine using your cellphone to control the activity of your own cells to treat injuries and disease. It sounds like something from the imagination of an overly optimistic science fiction writer. But this may one day be a possibility through the emerging field of quantum biology.</p>
<p>Over the past few decades, scientists have made incredible progress in understanding and manipulating biological systems at increasingly small scales, from <a href="https://theconversation.com/when-researchers-dont-have-the-proteins-they-need-they-can-get-ai-to-hallucinate-new-structures-173209">protein folding</a> to <a href="https://www.genome.gov/genetics-glossary/Genetic-Engineering">genetic engineering</a>. And yet, the extent to which quantum effects influence living systems remains barely understood.</p>
<p>Quantum effects are phenomena that occur between atoms and molecules that can’t be explained by classical physics. It has been known for more than a century that the rules of classical mechanics, like Newton’s laws of motion, <a href="https://iopscience.iop.org/book/mono/978-0-7503-1206-6/chapter/bk978-0-7503-1206-6ch1">break down at atomic scales</a>. Instead, tiny objects behave according to a different set of laws known as <a href="https://www.britannica.com/science/quantum-mechanics-physics">quantum mechanics</a>. </p>
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<figcaption><span class="caption">Quantum mechanics describes the properties of atoms and molecules.</span></figcaption>
</figure>
<p>For humans, who can only perceive the macroscopic world, or what’s visible to the naked eye, quantum mechanics can seem counterintuitive and somewhat magical. Things you might not expect happen in the quantum world, like <a href="https://theconversation.com/we-did-a-breakthrough-speed-test-in-quantum-tunnelling-and-heres-why-thats-exciting-113761">electrons “tunneling” through</a> tiny energy barriers and appearing on the other side unscathed, or being in two different places at the same time in a <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">phenomenon called superposition</a>.</p>
<p>I am trained as a <a href="https://scholar.google.com/citations?user=1aqtpo8AAAAJ&hl=en">quantum engineer</a>. Research in quantum mechanics is usually geared toward technology. However, and somewhat surprisingly, there is increasing evidence that nature – an engineer with billions of years of practice – has learned how to <a href="https://royalsociety.org/grants-schemes-awards/book-prizes/science-book-prize/2015/life-on-the-edge/">use quantum mechanics to function optimally</a>. If this is indeed true, it means that our understanding of biology is radically incomplete. It also means that we could possibly control physiological processes by using the quantum properties of biological matter.</p>
<h2>Quantumness in biology is probably real</h2>
<p>Researchers can manipulate quantum phenomena to build better technology. In fact, you already live in a <a href="https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-applications-today">quantum-powered world</a>: from laser pointers to GPS, magnetic resonance imaging and the transistors in your computer – all these technologies rely on quantum effects.</p>
<p>In general, quantum effects only manifest at very small length and mass scales, or when temperatures approach absolute zero. This is because quantum objects like atoms and molecules <a href="https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448/">lose their “quantumness”</a> when they uncontrollably interact with each other and their environment. In other words, a macroscopic collection of quantum objects is better described by the laws of classical mechanics. Everything that starts quantum dies classical. For example, an electron can be manipulated to be in two places at the same time, but it will end up in only one place after a short while – exactly what would be expected classically.</p>
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<figcaption><span class="caption">Electrons can be in two places at the same time, but will end up in one location eventually.</span></figcaption>
</figure>
<p>In a complicated, noisy biological system, it is thus expected that most quantum effects will rapidly disappear, washed out in what the physicist Erwin Schrödinger called the “<a href="https://doi.org/10.1017/CBO9781139644129">warm, wet environment of the cell</a>.” To most physicists, the fact that the living world operates at elevated temperatures and in complex environments implies that biology can be adequately and fully described by classical physics: no funky barrier crossing, no being in multiple locations simultaneously.</p>
<p>Chemists, however, have for a long time begged to differ. Research on basic chemical reactions at room temperature unambiguously shows that <a href="https://doi.org/10.1063/5.0006547">processes occurring within biomolecules</a> like proteins and genetic material are the result of quantum effects. Importantly, such nanoscopic, short-lived quantum effects are consistent with driving some macroscopic physiological processes that biologists have measured in living cells and organisms. Research suggests that quantum effects influence biological functions, including <a href="https://doi.org/10.1146/annurev-biochem-051710-133623">regulating enzyme activity</a>, <a href="https://doi.org/10.1146/annurev-biophys-032116-094545">sensing magnetic fields</a>, <a href="https://doi.org/10.1038/srep38543">cell metabolism</a> and <a href="https://doi.org/10.1038/s41570-019-0087-1">electron transport in biomolecules</a>.</p>
<h2>How to study quantum biology</h2>
<p>The tantalizing possibility that subtle quantum effects can tweak biological processes presents both an exciting frontier and a challenge to scientists. Studying quantum mechanical effects in biology requires tools that can measure the short time scales, small length scales and subtle differences in quantum states that give rise to physiological changes – all integrated within a traditional wet lab environment.</p>
<p><a href="http://www.claricedaiello.com">In my work</a>, I build instruments to study and control the quantum properties of small things like electrons. In the same way that electrons have mass and charge, they also have a <a href="https://www.britannica.com/science/spin-atomic-physics">quantum property called spin</a>. Spin defines how the electrons interact with a magnetic field, in the same way that charge defines how electrons interact with an electric field. The quantum experiments I have been building <a href="https://doi.org/10.1038/ncomms2375">since graduate school</a>, and now in my own lab, aim to apply tailored magnetic fields to change the spins of particular electrons.</p>
<p>Research has demonstrated that many physiological processes are influenced by weak magnetic fields. These processes include <a href="https://doi.org/10.1126/sciadv.aau7201">stem cell development</a> and <a href="https://doi.org/10.1021/nn502923s">maturation</a>, <a href="https://doi.org/10.1371/journal.pone.0054775">cell proliferation rates</a>, <a href="https://doi.org/10.1021/acscentsci.8b00008">genetic material repair</a> and <a href="https://doi.org/10.1371/journal.pone.0179340">countless others</a>. These physiological responses to magnetic fields are consistent with chemical reactions that depend on the spin of particular electrons within molecules. Applying a weak magnetic field to change electron spins can thus effectively control a chemical reaction’s final products, with important physiological consequences.</p>
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<figcaption><span class="caption">Birds use quantum effects in navigation.</span></figcaption>
</figure>
<p>Currently, a lack of understanding of how such processes work at the nanoscale level prevents researchers from determining exactly what strength and frequency of magnetic fields cause specific chemical reactions in cells. Current cellphone, wearable and miniaturization technologies are already sufficient to produce <a href="https://doi.org/10.14814%2Fphy2.15189">tailored, weak magnetic fields that change physiology</a>, both for good and for bad. The missing piece of the puzzle is, hence, a “deterministic codebook” of how to map quantum causes to physiological outcomes.</p>
<p>In the future, fine-tuning nature’s quantum properties could enable researchers to develop therapeutic devices that are noninvasive, remotely controlled and accessible with a mobile phone. Electromagnetic treatments could potentially be used to prevent and treat disease, such as <a href="https://doi.org/10.1038/s41416-020-01136-5">brain tumors</a>, as well as in biomanufacturing, such as <a href="https://doi.org/10.1016/j.biomaterials.2022.121658">increasing lab-grown meat production</a>.</p>
<h2>A whole new way of doing science</h2>
<p>Quantum biology is one of the most interdisciplinary fields to ever emerge. How do you build community and train scientists to work in this area? </p>
<p>Since the pandemic, my lab at the University of California, Los Angeles and the University of Surrey’s Quantum Biology Doctoral Training Centre have organized <a href="https://groups.google.com/u/1/g/bigquantumbiologymeetings">Big Quantum Biology meetings</a> to provide an informal weekly forum for researchers to meet and share their expertise in fields like mainstream quantum physics, biophysics, medicine, chemistry and biology.</p>
<p>Research with potentially transformative implications for biology, medicine and the physical sciences will require working within an equally transformative model of collaboration. Working in one unified lab would allow scientists from disciplines that take very different approaches to research to conduct experiments that meet the breadth of quantum biology from the quantum to the molecular, the cellular and the organismal.</p>
<p>The existence of quantum biology as a discipline implies that traditional understanding of life processes is incomplete. Further research will lead to new insights into the age-old question of what life is, how it can be controlled and how to learn with nature to build better quantum technologies.</p><img src="https://counter.theconversation.com/content/204995/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clarice D. Aiello receives funding from NSF, ONR, IDOR Foundation, Faggin Foundation, Templeton Foundation. </span></em></p>Studying the brief and tiny quantum effects that drive living systems could one day lead to new approaches to treatments and technologies.Clarice D. Aiello, Quantum Biology Tech (QuBiT) Lab, Assistant Professor of Electrical and Computer Engineering, University of California, Los AngelesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2048242023-05-10T12:05:23Z2023-05-10T12:05:23ZStephen Hawking and I created his final theory of the cosmos – here’s what it reveals about the origins of time and life<figure><img src="https://images.theconversation.com/files/525085/original/file-20230509-27-2ly6rr.jpeg?ixlib=rb-1.1.0&rect=38%2C5%2C1230%2C841&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hawking and the author. </span> <span class="attribution"><span class="source">Photograph: Thomas Hertog and Jonathan Wood</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The late physicist Stephen Hawking first asked me to work with him to develop “a new quantum theory of the Big Bang” in 1998. What started out as a doctoral project evolved over some 20 years into an intense collaboration that ended <a href="https://theconversation.com/stephen-hawking-martin-rees-looks-back-on-colleagues-spectacular-success-against-all-odds-93379">only with his passing</a> on March 14 2018. </p>
<p>The enigma at the centre of our research throughout this period was how the Big Bang could have created <a href="https://theconversation.com/the-multiverse-our-universe-is-suspiciously-unlikely-to-exist-unless-it-is-one-of-many-200585">conditions so perfectly hospitable to life</a>. Our answer is being <a href="https://www.penguin.co.uk/books/440139/on-the-origin-of-time-by-hertog-thomas/9781911709084">published in a new book</a>, On the Origin of Time: Stephen Hawking’s Final Theory.</p>
<p>Questions about the ultimate origin of the cosmos, or universe, take physics out of its comfort zone. Yet this was exactly where Hawking liked to venture. The prospect — or hope — to crack the riddle of cosmic design drove much of Hawking’s research in cosmology. “To boldly go where Star Trek fears to tread” was his motto – and also his screen saver. </p>
<p>Our shared scientific quest meant that we inevitably grew close. Being around him, one could not fail to be influenced by his determination and optimism that we could tackle mystifying questions. He made me feel as if we were writing our own creation story, which, in a sense, we did.</p>
<p>In the old days, it was thought that the apparent design of the cosmos meant there had to be a designer – a God. Today, scientists instead point to the laws of physics. These laws have a number of striking life-engendering properties. Take the amount of matter and energy in the universe, the delicate ratios of the forces, or the number of spatial dimensions. </p>
<p>Physicists <a href="https://www.sciencedirect.com/science/article/pii/S0370157319300511">have discovered</a> that if you tweak these properties ever so slightly, it renders the universe lifeless. It almost feels as if the universe is a fix – even a big one. </p>
<p>But where do the laws of physics come from? From Albert Einstein to Hawking in his earlier work, most 20th-century physicists regarded the mathematical relationships that underlie the physical laws as eternal truths. In this view, the apparent design of the cosmos is a matter of mathematical necessity. The universe is the way it is because nature had no choice. </p>
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<p>Around the turn of the 21st century, a different explanation emerged. Perhaps we live in a multiverse, an enormous space that spawns a patchwork of universes, each with its own kind of Big Bang and physics. It would make sense, statistically, for a few of these universes to be life-friendly.</p>
<p>However, soon such multiverse musings got caught in a <a href="https://theconversation.com/the-multiverse-how-were-tackling-the-challenges-facing-the-theory-201729">spiral of paradoxes</a> and no verifiable predictions.</p>
<h2>Turning cosmology inside out</h2>
<p>Can we do better? Yes, Hawking and I found out, but only by relinquishing the idea, inherent in multiverse cosmology, that our physical theories can take a God’s-eye view, as if standing outside the entire cosmos. </p>
<p>It is an obvious and seemingly tautological point: cosmological theory must account for the fact that we exist within the universe. “We are not angels who view the universe from the outside,” Hawking told me. “Our theories are never decoupled from us.”</p>
<p>We set out to rethink cosmology from an observer’s perspective. This required adopting the strange rules of <a href="https://theconversation.com/great-mysteries-of-physics-4-does-objective-reality-exist-202550">quantum mechanics</a>, which governs the microworld of particles and atoms. </p>
<p>According to quantum mechanics, particles can be in several possible locations at the same time – a property called superposition. It is only when a particle is observed that it (randomly) picks a definite position. Quantum mechanics also involves random jumps and fluctuations, such as particles popping out of empty space and disappearing again. </p>
<p>In a quantum universe, therefore, a tangible past and future emerge out of a haze of possibilities by means of a continual process of observing. Such quantum observations don’t need to be carried out by humans. The environment or even a single particle can “observe”. </p>
<p>Countless such quantum acts of observation constantly transform what might be into what does happen, thereby drawing the universe more firmly into existence. And once something has been observed, all other possibilities become irrelevant.</p>
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<img alt="Image of the Carina nebula." src="https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&rect=0%2C32%2C3573%2C2010&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=437&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=437&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473660/original/file-20220712-14-qv200v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=437&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Star-forming region in our galaxy.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, and STScI</span></span>
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<p>We discovered that when looking back at the earliest stages of the universe through a quantum lens, there’s a deeper level of evolution in which even the laws of physics change and evolve, in sync with the universe that is taking shape. What’s more, this meta-evolution has a Darwinian flavor. </p>
<p>Variation enters because random quantum jumps cause frequent excursions from what’s most probable. Selection enters because some of these excursions can be amplified and frozen, thanks to quantum observation. The interplay between these two competing forces – variation and selection – in the primeval universe produced a branching tree of physical laws. </p>
<p>The upshot is a profound revision of the fundamentals of cosmology. Cosmologists usually start by assuming laws and initial conditions that existed at the moment of the Big Bang, then consider how today’s universe evolved from them. But we suggest that these laws are themselves the result of evolution. </p>
<p>Dimensions, forces, and particle species transmute and diversify in the furnace of the hot Big Bang – somewhat analogous to how biological species emerge billions of years later – and acquire their effective form over time. </p>
<p>Moreover, the randomness involved means that the outcome of this evolution – the specific set of physical laws that makes our universe what it is – <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.73.123527">can only be understood in retrospect</a>.</p>
<p>In some sense, the early universe was a superposition of an enormous number of possible worlds. But we are looking at the universe today at a time when humans, galaxies and planets exist. That means we see the history that led to our evolution. </p>
<p>We observe parameters with “lucky values”. But we are wrong to assume they were somehow designed or always like that. </p>
<h2>The trouble with time</h2>
<p>The crux of our hypothesis is that, reasoning backward in time, evolution towards more simplicity and less structure continues all the way. Ultimately, even time and, with it, the physical laws fade away. </p>
<p>This view is especially borne out of the holographic form of our theory. The “<a href="https://www.theguardian.com/science/shortcuts/2017/jan/31/guide-to-holographic-principle-of-universe">holographic principle</a>” in physics predicts that just as a hologram appears to have three dimensions when it is in fact encoded in only two dimensions, the evolution of the entire universe is similarly encoded on an abstract, timeless surface. </p>
<p>Hawking and I view time and causality <a href="https://theconversation.com/great-mysteries-of-physics-1-is-time-an-illusion-201026">as “emergent qualities”</a>, having no prior existence but arising from the interactions between countless quantum particles. It’s a bit like how temperature emerges from many atoms moving collectively, even though no single atom has temperature. </p>
<p>One ventures back in time by zooming out and taking a fuzzier look at the hologram. Eventually, however, one loses all information encoded in the hologram. This would be the origin of time - the Big Bang. </p>
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<p>For almost a century, we have studied the origin of the universe against the stable background of immutable laws of nature. But our theory reads the universe’s history from within and as one that includes, in its earliest stages, the genealogy of the physical laws. It isn’t the laws as such but their capacity to transmute that has the final word. </p>
<p>Future cosmological observations may find evidence of this. For instance, precision observations of <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">gravitational waves</a> – ripples in the fabric of spacetime – may reveal signatures of some of the early branches of the universe. If spotted, Hawking’s cosmological finale may well prove to be his greatest scientific legacy.</p><img src="https://counter.theconversation.com/content/204824/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Hertog is professor of theoretical physics at KU Leuven (Belgium). </span></em></p>The enigma at the centre of our 20-year collaboration was how the Big Bang could have created conditions so perfectly hospitable to lifeThomas Hertog, Professor of physics, KU LeuvenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2052322023-05-09T01:03:59Z2023-05-09T01:03:59ZAustralia has a National Quantum Strategy. What does that mean?<figure><img src="https://images.theconversation.com/files/524890/original/file-20230508-197326-ujrjbd.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4080%2C2021&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/ERdTJQTtsbE">Dynamic Wang / Unsplash</a></span></figcaption></figure><p>Imagine a world where computers can solve complex problems in seconds, making our current devices seem like mere typewriters. These supercomputers would revolutionise industries, create new medicines, and even help combat climate change. </p>
<p>Imagine as well we could observe the workings of our own bodies in unprecedented detail, and communicate online without fear of hacking. This may be starting to <a href="https://thequantuminsider.com/2021/07/09/quantum-technology-in-science-fiction-popular-culture/">sound like a sci-fi novel</a>, but quantum technologies have the potential to make it all real.</p>
<p>Australia has just unveiled its first <a href="https://www.industry.gov.au/publications/national-quantum-strategy">National Quantum Strategy</a>. The strategy aims to make Australia “a leader of the global quantum industry” by 2030, by encouraging research, applications and commercialisation. </p>
<p>So what does that actually mean?</p>
<h2>What are quantum technologies?</h2>
<p>Quantum technologies build on the science of quantum mechanics, which studies the behaviour of subatomic particles at a microscopic scale. </p>
<p>At this level, particles behave strangely: they can exist in multiple states simultaneously (called superposition), and be “entangled” with each other. When particles are entangled, their properties are linked together regardless of the distance between them. </p>
<p>Quantum technologies make use of these counterintuitive properties to achieve things that might otherwise be impossible. Three main areas of quantum technology are gaining the most attention: quantum sensing, quantum communications, and quantum computing.</p>
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<a href="https://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">Explainer: quantum computation and communication technology </a>
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<p>Quantum sensing can detect tiny changes in the environment, measuring things like gravity, magnetic fields and temperature with incredible accuracy. This technology could have a huge impact on industries like healthcare, mining and navigation. </p>
<p>For instance, quantum sensors may be able to help us <a href="https://phys.org/news/2020-11-quantum-nanodiamonds-disease-earlier.html">detect early signs of diseases in our bodies</a> and <a href="https://www.australianmining.com.au/breakthrough-technologies-for-mineral-exploration-fetch-billions/">locate valuable minerals hidden deep underground</a>.</p>
<p>Unlike traditional computers, which store and process information using bits (zeroes and ones), quantum computers use “qubits”, which can exist as zeroes, ones, or combinations of both at once. </p>
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<img alt="A photo of the brass coils and circuitry of a quantum computer." src="https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524999/original/file-20230508-195023-bjjc4v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Quantum computers may be able to crack problems that are currently impossible to solve.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>Fully functioning quantum computers don’t exist yet – but scientists believe they will be able to perform certain kinds of calculations at lightning speed, solving <a href="https://www.abc.net.au/news/science/2021-08-14/australian-research-puts-larger-quantum-computers-within-reach/100371544">some problems</a> that would take today’s computers millions of years to crack. This would have <a href="https://hbr.org/2021/07/quantum-computing-is-coming-what-can-it-do">huge implications</a> for fields including cryptography, AI, drug discovery, and climate modelling.</p>
<p>Researchers are also working on <a href="https://www.newscientist.com/article/2253448-secure-quantum-communications-network-is-the-largest-of-its-kind/">super-secure quantum communication networks</a> that are almost impossible to hack or eavesdrop on. On networks like these, attempts to intercept messages would be <a href="https://www.bcg.com/publications/2023/are-you-ready-for-quantum-communications">instantly detectable</a> to the sender and the receiver.</p>
<h2>The quantum race</h2>
<p>Australia’s National Quantum Strategy sees us join other countries and regions, racing to unlock the potential of quantum technology and dominate the market. <a href="https://www.forbes.com/sites/forbestechcouncil/2020/10/05/what-the-us-investment-in-quantum-computing-means-for-security/">The United States</a>, <a href="https://www.newscientist.com/article/mg25233652-000-2021-in-review-jian-wei-pan-leads-chinas-quantum-computing-successes/">China</a>, and <a href="https://digital-strategy.ec.europa.eu/en/policies/quantum-technologies-flagship">Europe</a> are investing billions of dollars in quantum research and development. </p>
<p>If Australia wants to keep up, it needs to act now. But why is keeping up so important?</p>
<p>First, we don’t want to be left behind in the rapidly growing quantum technology industry. <a href="https://www.innovationaus.com/australias-quantum-opportunity-upgraded-to-6-billion/">According to CSIRO projections</a>, the quantum industry could be worth A$4.6 billion by the end of the decade. By 2045, it might employ as many people as the oil and gas sector does today, with revenues of $6 billion and 19,400 direct jobs.</p>
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Read more:
<a href="https://theconversation.com/better-ai-unhackable-communication-spotting-submarines-the-quantum-tech-arms-race-is-heating-up-179482">Better AI, unhackable communication, spotting submarines: the quantum tech arms race is heating up</a>
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<p>As other nations push forward, Australia risks missing out on the potential economic benefits. We could also lose talented workers to countries that are investing more in quantum research. Projects like the ambitious attempt to <a href="https://www.smh.com.au/national/australia-sets-ambitious-goal-to-build-first-complete-quantum-computer-20230502-p5d51r.html">build the world’s first complete quantum computer</a> aim to provide local opportunities and funding alongside their top-line goals.</p>
<p>Moreover, Australia has a responsibility to ensure quantum technologies are developed and used ethically, and their <a href="https://www.weforum.org/agenda/2022/09/organizations-protect-quantum-computing-threat-cybersecurity/">risks</a> managed.</p>
<p>For example, quantum computers could enable hackers to <a href="https://www2.deloitte.com/uk/en/insights/topics/cyber-risk/quantum-computing-ethics-risks.html">break existing encryption protocols</a>, leaving internet services vulnerable. Data harvesting by companies is already a concern, and quantum computing could exacerbate this issue. Even <a href="https://www2.deloitte.com/us/en/insights/industry/public-sector/the-impact-of-quantum-technology-on-national-security.html">national security could be jeopardised</a> by quantum decryption.</p>
<h2>Responsible innovation</h2>
<p>To make the most of the power of quantum technology, we need to be proactive, focus on the public good, and think about it from many perspectives to ensure “<a href="https://research.csiro.au/ri/">responsible innovation</a>”.</p>
<p>Collaboration and broad dialogue will be necessary. Conversations between experts in fields like quantum computing, cybersecurity, ethics and social sciences – perhaps via regular conferences or workshops – will help us tackle the technical and ethical risks.</p>
<p>Engaging with society and focusing on the public good will also be essential. The public must be involved in discussions to ensure new quantum technologies benefit everyone, not just businesses. Town hall meetings, public forums or online chats can help scientists, policymakers and citizens share views.</p>
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Read more:
<a href="https://theconversation.com/the-second-quantum-revolution-is-almost-here-we-need-to-make-sure-it-benefits-the-many-not-the-few-161878">The 'second quantum revolution' is almost here. We need to make sure it benefits the many, not the few</a>
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<p>And we must make sure that “responsibility” always sits right alongside “innovation” in quantum technologies. Organisations working on quantum tech could have “responsible quantum committees” to address risks and involve stakeholders, ensuring responsible innovation in quantum technology.</p>
<p>Success in quantum technology will be all about striking the right balance: encouraging both innovation and responsibility. By investing in quantum technology and working together to ensure its responsible development, Australia can continue to be a leader in scientific innovation while benefiting from these emerging technologies’ transformative potential. </p>
<p>Australia’s National Quantum Strategy is a step in this direction.</p><img src="https://counter.theconversation.com/content/205232/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jarryd Daymond is an associate researcher on a project funded by the Medical Research Future Fund (MRFF) Targeted Translation Research Accelerator (TTRA). </span></em></p>Countries around the world are racing to develop quantum technologies for computing, sensing and communication. Australia is trying not to get left behind.Jarryd Daymond, Lecturer, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2046182023-04-27T05:14:11Z2023-04-27T05:14:11ZNew nanoparticle source generates high-frequency light<figure><img src="https://images.theconversation.com/files/523123/original/file-20230427-26-fls8hc.jpeg?ixlib=rb-1.1.0&rect=8%2C0%2C5982%2C3997&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>High-frequency light is useful. The higher the frequency of light, the shorter its wavelength – and the shorter the wavelength, the smaller the objects and details the light can be used to see.</p>
<p>So violet light can show you smaller details than red light, for example, because it has a shorter wavelength. But to see really, really small things – down to the scale of billionths of a metre, thousands of times less than the width of a human hair – to see those things, you need <em>extreme ultraviolet light</em> (and a good microscope).</p>
<p>Extreme ultraviolet light, with wavelengths between 10 and 120 nanometres, has many applications in medical imaging, studying biological objects, and deciphering the fine details of computer chips during their manufacture. However, producing small and affordable sources of this light has been very challenging.</p>
<p>We have found a way to make nanoparticles of a common semiconductor material emit light with a frequency up to seven times higher than the frequency of light sent to it. We generated blue-violet light from infrared light, and it will be possible to generate extreme ultraviolet light from red light with the same principles. Our research, carried out with colleagues from the University of Brescia, the University of Arizona and Korea University, is <a href="https://www.science.org/doi/10.1126/sciadv.adg2655">published in Science Advances</a>.</p>
<h2>The power of harmonics</h2>
<p>Our system starts out with an ordinary laser that produces long-wavelength infrared light. This is called the pump laser, and there’s nothing special about it – such lasers are commercially available, and they can be compact and affordable.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram illustrating the setup of the light-emitting system" src="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=637&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=637&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523143/original/file-20230427-18-xja1n3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=637&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Incoming laser light hitting a nanoparticle which then emits higher frequency light.</span>
<span class="attribution"><span class="source">Zalogina et al. / Science Advances</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But next we fire short pulses of light from this laser at a specially engineered nanoparticle of a material called aluminium gallium arsenide, and that’s where things get interesting.</p>
<p>The nanoparticle absorbs energy from the laser pulses, and then emits its own burst of light. By carefully engineering the size and shape of the nanoparticle, we can create powerful resonances to amplify certain harmonics of the emitted light.</p>
<p>What does that mean, exactly? Well, we can make a useful analogy with sound.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the first seven harmonics of a guitar string." src="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=666&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=666&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=666&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=837&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=837&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523144/original/file-20230427-28-fgl3ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=837&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Harmonics in a guitar string: in the fundamental frequency, the wavelength is the length of the whole string, but in the higher harmonics multiple shorter wavelengths fit within the length of the string.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Harmonic">Wikimedia / Y Landman</a></span>
</figcaption>
</figure>
<p>When you pluck a string on a guitar, it vibrates with what’s called its <em>fundamental frequency</em> – which makes the main note you hear – plus small amounts of higher frequencies called harmonics, which are multiples of the fundamental frequency. The body of the guitar is designed to produce resonances that amplify some of these harmonics and dampen others, creating the overall sound you hear.</p>
<p>Both light and sound share similarities in their physics – these are both propagating waves (acoustic waves in the case of sound, and electromagnetic waves in the case of light).</p>
<figure class="align-center ">
<img alt="A close up of a hand strumming an acoustic guitar" src="https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523126/original/file-20230427-18-a14ek3.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Just as the body of a guitar dampens some frequencies and amplifies others, carefully designed nanoparticles can boost high-frequency harmonics of laser light.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>In our light source, the pump laser is like the main note of the string, and the nanoparticles are like the guitar body. Except what’s special about the nanoparticles is that they massively amplify those higher harmonics of the pump laser, producing light with a higher frequency (up to seven times higher in our case, and a wavelength correspondingly seven times shorter).</p>
<h2>What it’s good for</h2>
<p>This technology allows us to create new sources of light in parts of the electromagnetic spectrum such as the extreme ultraviolet, where there are no natural sources of light and where current engineered sources are too large or too expensive.</p>
<p>Conventional microscopes using visible light can only study objects down to a size of about a ten-millionth of a metre. The resolution is limited by the wavelength of light: violet light has the wavelength of about 400 nanometres (one nanometre is one billionth of a metre). </p>
<p>But there are plenty of applications, such as biological imaging and electronics manufacturing, where being able to see down to a billionth of a metre or so would be a huge help.</p>
<p>At present, to see at those scales you need “super-resolution” microscopy, which lets you see details smaller than the wavelength of the light you are using, or electron microscopes, which do not use light at all and create image using a flux of electrons. However, such methods are quite slow and expensive.</p>
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Read more:
<a href="https://theconversation.com/a-quantum-hack-for-microscopes-can-reveal-the-undiscovered-details-of-life-161182">A quantum hack for microscopes can reveal the undiscovered details of life</a>
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<p>To understand the advantages of a light source like ours, consider computer chips: they are made of very tiny components with feature sizes almost as small as a billionth of a metre. During the production process, it would be useful for manufacturers to use extreme ultraviolet light to monitor the process in real time.</p>
<p>This would save resources and time on bad batches of chips. The scale of the industry is such that even a 1% increase in chip yields could save billions of dollars each year. </p>
<p>In future, nanoparticles like ours could be used to produce tiny, inexpensive sources of extreme ultraviolet light, illuminating the world of extremely small things.</p><img src="https://counter.theconversation.com/content/204618/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sergey Kruk receives funding from the Australian Research Council (DE210100679). </span></em></p><p class="fine-print"><em><span>Anastasiia Zalogina does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new way to make high-frequency light could make it easier to look at things 10 times smaller than conventional microscopes can see.Anastasiia Zalogina, Postdoctoral researcher, Australian National UniversitySergey Kruk, ARC DECRA Fellow, Research School of Physics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2035342023-04-12T10:17:57Z2023-04-12T10:17:57ZGreat Mysteries of Physics: do we really need a theory of everything?<figure><img src="https://images.theconversation.com/files/520260/original/file-20230411-16-7sokyy.jpg?ixlib=rb-1.1.0&rect=57%2C44%2C4173%2C1911&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Particle physics has failed to find some of the evidence physicists were hoping for.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/switzerland-april-2010-cern-european-organization-1287557629">D-Visions/Shutterstock</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/64353c62de066f001110361d" frameborder="0" width="100%" height="190px"></iframe>
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<p>Finding a theory of everything – explaining all the forces and particles in the universe – is arguably the holy grail of physics. While each of its main theories works extraordinarily well, they clash also with each other – leaving physicists to search for a deeper, more fundamental theory.</p>
<p>But do we really need a theory of everything? And are we anywhere near achieving one? That’s what we discuss in the sixth and final episode of our Great Mysteries of Physics podcast – hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute.</p>
<p>Our two best theories of nature are <a href="https://theconversation.com/great-mysteries-of-physics-4-does-objective-reality-exist-202550">quantum mechanics</a> and general relativity, describing the smallest and biggest scales of the universe, respectively. Each is tremendously successful and has been experimentally tested over and over. The trouble is, they are incompatible with one another in many ways – including mathematically.</p>
<p>“General relativity is all about geometry. It’s how space is curved and how space-time – this unified entity that contains three dimensions of space and one dimension of time – is itself also curved,” explains Vlatko Vedral, a professor of physics at Oxford University in the UK. “Quantum physics is actually all about algebra.”</p>
<p>Physicists have already managed to unite quantum theory with Einstein’s other big theory: special relativity (explaining how speed affects mass, time and space). Together, these form a framework called “quantum field theory”, which is the basis for the <a href="https://theconversation.com/the-standard-model-of-particle-physics-may-be-broken-an-expert-explains-182081">Standard Model of Particle Physics</a> – our best framework for describing the most basic building blocks of the universe. </p>
<p>The standard model describes three out of the four fundamental forces in the universe – electromagnetism, and the “strong” and “weak” forces which govern the atomic nucleus – excluding gravity. </p>
<p>While the standard model explains most of what we see in particle physics experiments, there are a few gaps. To bridge these, an extension called “<a href="https://home.cern/science/physics/supersymmetry#:%7E:text=Supersymmetry%20is%20an%20extension%20of,mass%20of%20the%20Higgs%20boson.">supersymmetry</a>”, suggesting particles are connected through a deep relationship, has been proposed. Supersymmetry suggests each particle has a “super partner” with the same mass, but opposite spin. Unfortunately, particle accelerators such as the Large Hadron Collider (LHC) at Cern in Switzerland have failed to find evidence of supersymmetry – despite being explicitly designed to do so.</p>
<p>On the other hand, there are recent hints from both <a href="https://theconversation.com/new-physics-latest-results-from-cern-further-boost-tantalising-evidence-170133">LHC</a> and <a href="https://theconversation.com/how-we-found-hints-of-new-particles-or-forces-of-nature-and-why-it-could-change-physics-158564">Fermilab</a> in the US suggesting that there may be a fifth force of nature. If these results could be replicated and confirmed as actual discoveries, that would have implications for uniting quantum mechanics and gravity.</p>
<p>“I think [the discovery of a new force] would be amazing,” says Vedral. “It would challenge this thing that that has now existed for well over half a century that there are four fundamental forces”. </p>
<p>Vedral argues the first thing to do if we discovered a fifth force would be to establish whether it can be described by quantum mechanics.</p>
<p>If it could, it would indicate that quantum theory might ultimately be more fundamental than general relativity, accounting for four out of five forces – suggesting general relativity ultimately may need to be modified. If it couldn’t, that would shake up physics – suggesting we may need to modify quantum mechanics, too.</p>
<h2>What about other mysterious properties?</h2>
<p>But what should a theory of everything include? Would it be enough to unite gravity and quantum mechanics? And what about other mysterious properties such as dark energy, which causes the universe to expand at an accelerated rate, or dark matter, an invisible substance making up most of the matter in the universe? </p>
<p>As Chanda Prescod-Weinstein, an assistant professor in physics and astronomy at the University of New Hampshire in the US, explains, physicists prefer to use the term “theory of quantum gravity” over “theory of everything”. </p>
<p>“Dark matter and dark energy are most of the matter energy content in the universe. So it’s not really a theory of everything if it’s not accounting for most of the matter energy content in the universe,” she argues. “This is why I’m glad we don’t actually use ‘theory of everything’ in our work.”</p>
<p>Although they might not explain everything, several proposed theories of quantum gravity exist. One is string theory, which suggests the universe is ultimately made up of tiny, vibrating strings. Another is loop quantum gravity, which suggests Einstein’s space-time arises from quantum effects.</p>
<p>“One of the strengths that people will point to with string theory is that string theory built on quantum field theory,” explains Prescod-Weinstein. “It brings the whole standard model with it, which loop quantum gravity doesn’t do in the same way.” But string theory also has its weaknesses, she argues, such as requiring extra dimensions that we’ve never seen any evidence of.</p>
<p>The theories are difficult to test experimentally – requiring much more energy than we can produce in any laboratory. Vedral argues that while we ultimately can’t directly probe the tiny scales needed to find evidence for theories of quantum gravity, it may be possible to amplify such effects so that we could indirectly observe them on larger scales with table-top experiments.</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/203534/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vlatko Vedral has had funding from The Templeton and the Moore Foundations. Chanda Prescod-Weinstein has had funding from the NSF, DoE, NASA, FQxI and Heising-Simons Foundation. She is a member of the American Physical Society, American Astronomical Society, FQxI, NASEM Elementary Particle Physics: Progress and Promise Committee
</span></em></p>Our two best theories of nature, quantum mechanics and general relativity, are incompatible with each other in many ways – leaving physicists to dig deeper.Miriam Frankel, Podcast host, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2031272023-04-05T11:32:05Z2023-04-05T11:32:05ZGreat Mysteries of Physics 5: will we ever have a fundamental theory of life and consciousness?<figure><img src="https://images.theconversation.com/files/518887/original/file-20230402-24-xtaeq6.jpg?ixlib=rb-1.1.0&rect=152%2C0%2C8321%2C3982&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/people-rejoicing-launch-space-rocket-2200754685">metamorworks/Shutterstock</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/642d59ed65d917001197b0cf" frameborder="0" width="100%" height="190px"></iframe>
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<p>What’s the difference between a living collection of matter, such as a tortoise, and an inanimate lump of it, such as a rock? They are, after all, both just made up of non-living atoms. The truth is, we don’t really know yet. Life seems to just somehow emerge from non-living parts.</p>
<p>This is an enigma we’re tackling in the fifth episode of our Great Mysteries of Physics podcast – hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute. </p>
<p>The physics of the living world ultimately seems to contradict the second law of thermodynamics: that a closed system gets more disordered over time, increasing in what physicists call entropy. Living systems have low entropy. A messy lump of tissue in the womb, for example, can grow into a highly ordered state of a foot with five toes. </p>
<p>“We maintain this high sense of order for many, many decades,” explains Jim Al-Khalili, a broadcaster and distinguished professor of physics at the University of Surrey in the UK. “It’s only when we die that entropy and the second law of thermodynamics really kicks in.”</p>
<p>Quantum biology is one approach to understanding how living matter is different from inanimate matter. It is based on the strange world of quantum mechanics, which governs the microworld of particles and atoms. The idea is that living systems may use quantum mechanics to their advantage – promoting or halting quantum processes. </p>
<p>“Evolution has had long enough to fine-tune things or to stop quantum mechanics from doing something that life doesn’t want it to do,” explains Al-Khalili, who carries out research in the area. “It’s a newish area of science.”</p>
<p>One example, albeit still controversial, is photosynthesis, the process in which plants or bacteria absorb particles of sunlight, photons, and convert it to chemical energy. Some physicists believe a quantum property known as superposition – allowing a particle to be in many possible states, such as taking different paths, simultaneously – enables this process. </p>
<p>“A lump of energy [such as a photon] just randomly bouncing around should just be lost as waste heat,” explains Al-Khalili. “There’s a quantum mechanical explanation for how that photon follows multiple paths simultaneously.”</p>
<p>Al-Khalili and his colleagues are now using quantum biology to try to understand DNA mutations – a core part of life – and they’ve made some intriguing discoveries already. And while he isn’t convinced the approach will ever be able to explain consciousness, he argues we cannot rule it out.</p>
<p>Sara Walker, an astrobiologist and theoretical physicist working as a professor at Arizona State University in the US, favours another approach, however. She is trying to create a new physical theory of life based on information theory – which takes information to be real and physical.</p>
<p>Information seems to be crucial to life. Living organisms have an inbuilt set of instructions, DNA, which non-living things simply don’t have. Similarly, when living beings invent things, such as rockets, they rely on information, such as knowledge of the laws of physics, stored in their memory. </p>
<p>We can use the current laws of physics to predict how a planet evolves over time, for example whether and when nearby objects are likely to crash into it. But we can’t use the laws to explain how and when intelligent beings arise and decide to build rockets and satellites which they launch into orbit around the planet. </p>
<p>“I do think that there are laws of physics that are yet undiscovered that explain the phenomena of life, and I think those have to do with how information structures reality in some sense,” explains Walker.</p>
<p>Walker believes that living organisms are more complex and difficult to assemble from fundamental building blocks than inanimate, naturally produced objects, such as simple molecules. And when simple living beings exist, they seem to generate even more complexity – either by evolution or through construction. </p>
<p>So Walker believes life generates a sudden boost in complexity which may have a threshold that could be a fundamental feature in the physics of life. Another central part of her theory is time. “The deeper in time an object is, the more evolution is required to produce it.”</p>
<p>Walker has designed an experiment to look at how molecules are built up by joining smaller pieces together in various ways. She says the team hasn’t found any evidence that molecules with high complexity can be produced by non-living things. The ultimate goal is to pinpoint an origin of life in which a chemical system can generate its own complexity.</p>
<p>Not only could that help us understand how life arises from non-living building blocks, we could also use it to search for life on other worlds in the cosmos.</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/2629/MoP__Ep5_-_Life_TRANSCRIPT.docx.pdf?1681213653">transcript of the episode here</a>.</em></p><img src="https://counter.theconversation.com/content/203127/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Al-Khalili receives funding for his research from various bodies: UK funding agencies (EPSRC, STFC), trusts and charities (Leverhulme Trust, John Templeton Foundation). These funds are used to pay for part of his salary, along with those of colleagues and collaborators, postdoc salaries, travel and subsistence for research and to conferences etc. Sara Walker receives funding from John Templeton Foundation and NASA. She is a fellow at Berggruen Institute and External Faculty at Santa Fe Institute.</span></em></p>Life may be using quantum mechanics to its advantage.Miriam Frankel, Podcast host, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2004872023-03-29T09:57:53Z2023-03-29T09:57:53Z‘QBism’: quantum mechanics is not a description of objective reality – it reveals a world of genuine free will<figure><img src="https://images.theconversation.com/files/517031/original/file-20230322-2124-l9gw62.jpg?ixlib=rb-1.1.0&rect=38%2C16%2C1296%2C1063&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In a cubist painting, reality is more than a single perspective can capture.</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></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/642304b2dd47b5001151d53f" frameborder="0" width="100%" height="190px"></iframe>
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<p>What does quantum mechanics, the most successful theory ever proposed by physics, teach us about reality? The starting point for most philosophers of physics is that quantum mechanics must somehow provide a description of the world as it is independently of us, the users of the theory. </p>
<p>This has led to a large number of incompatible worldviews. Some believe the implication of quantum mechanics is that there are <a href="https://theconversation.com/the-multiverse-how-were-tackling-the-challenges-facing-the-theory-201729">parallel worlds</a> as in the Marvel Comic universe; some believe it implies signals that travel faster than light, contradicting all that Einstein taught us. Some say it implies that <a href="https://theconversation.com/quantum-mechanics-how-the-future-might-influence-the-past-199426">the future affects the past</a>.</p>
<p>According to <a href="https://doi.org/10.1119/1.4874855">QBism</a>, an approach developed by Christopher Fuchs and me, the great lesson of quantum mechanics is that the usual starting point of the philosophers is simply wrong. Quantum mechanics does not describe reality as it is by itself. Instead, it is a tool that helps guide agents immersed in the world when they contemplate taking actions on parts of it external to themselves. </p>
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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>
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<p>The use of the word “agent” rather than the familiar “observer” highlights that quantum mechanics is about <a href="https://doi.org/10.48550/arXiv.1003.5209">actions that participate in creating reality</a>, rather than observations of a reality that exists independently of the agent.</p>
<p>QBism and its homophone, the art movement Cubism, share the understanding that reality is more than what a single agent’s perspective can capture. However, unlike the art movement, QBism does not attempt to represent reality. It does not attempt to bring the different perspectives together in one “third-person” view. QBism is fundamentally anti-representational and first person.</p>
<h2>Rescuing free will</h2>
<p>This puts QBism in direct contradiction with the two pillars of the 19th-century conception of a mechanistic universe. One is that nature is governed by physical laws in the same way that a mechanical toy is governed by its mechanism. The other is that it is, in principle, possible to have an objective view of the universe from the outside – from a God’s eye or third-person standpoint.</p>
<p>This mechanistic vision is still dominant among 21st-century scientists. For instance, in their 2010 book <a href="https://www.goodreads.com/book/show/8520362-the-grand-design">The Grand Design</a>, Stephen Hawking and Leonard Mlodinow write: “It is hard to imagine how free will can operate if our behaviour is determined by physical law, so it seems that we are no more than biological machines and that free will is just an illusion.”</p>
<p>Instead, the QBist vision is that of an unfinished universe, of a world that allows for genuine freedom, a world in which agents matter and participate in the making of reality.</p>
<p>A key aspect of quantum mechanics is randomness. Rather than making firm predictions, quantum mechanics is concerned with the probabilities for potential measurement outcomes. The physicist Ed Jaynes famously expressed that to understand quantum mechanics, one has to understand probability first.</p>
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<a href="https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Frank Ramsey, one of the originators of the personalist Bayesian approach." src="https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=693&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=693&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=693&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=871&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=871&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517037/original/file-20230322-182-uoxk0w.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=871&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">Frank Ramsey, one of the originators of the personalist Bayesian approach.</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>In this spirit, QBism’s starting point is the <a href="https://en.wikipedia.org/wiki/Bayesian_probability">personalist Bayesian approach to probability</a> (originally a method of statistical inference and now a fully fledged theory of decision making under uncertainty). In this approach, probabilities are an agent’s personal degrees of belief.</p>
<p>So rather than describing the statistics of some experiment, probabilities provide guidance to agents on how they should act. In other words, probabilities are not descriptive but “normative” – analogous to an instruction manual. It turns out that the standard probability rules can be derived from the (normative) principle that one’s probabilities should fit together in a way that guards against a sure loss when used for making decisions.</p>
<p>QBism’s great insight was that the probabilities that appear in quantum mechanics are no different. They are not, as in the standard view, fixed by physical law, but express an agent’s personal degrees of belief about the consequences of measurement actions the agent is contemplating.</p>
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<p>In QBism, the role of the quantum laws is to provide extra normative principles about how an agent’s probabilities should fit together. Rather than providing a description of the world, the rules of quantum mechanics are an addition to the standard probability rules; to classical (non-quantum) decision theory. They assist physicists in decisions such as how to design a quantum computer in order to minimise the probability of error, or what atoms to use in an atomic clock in order to increase the precision of time measurements. </p>
<h2>Measurements are actions</h2>
<p>Just like “observer”, the term “measurement” can be misleading because it suggests a pre-existing property that is revealed by the measurement. Instead, a measurement should be thought of as an action an agent takes to elicit a response from the world. A measurement is an act of creation that brings something entirely new into the world, an outcome that is shared between the agent and the agent’s external world.</p>
<p>Quantum mechanics is often depicted as “weird” and hard, or indeed impossible, to understand. As a matter of fact, the weirdness of quantum mechanics is an artefact of looking at it the wrong way. Once the two main QBist insights - that the quantum rules are guides to action and that measurements do not reveal pre-existing properties - are taken on board, all quantum paradoxes disappear.</p>
<p>Take Schrödinger’s cat, for example. In the usual formulation, the unfortunate animal is described by a “quantum state” taken to be a part of reality and implying that the cat is neither dead nor alive. </p>
<p>The QBist, by contrast, does not regard the quantum state as a part of reality. The quantum state a QBist agent might assign has no bearing on whether the cat is alive or dead. All it expresses is the agent’s expectations concerning the consequences of possible actions they might take on the cat. Unlike most interpretations of quantum mechanics, QBism respects the fundamental autonomy of the cat.</p>
<p>Or take quantum teleportation. According to a common way of presenting this operation, a particle’s quantum state, again regarded as a part of reality, disappears at one place (A) and mysteriously reappears at another (B) - quite
literally as in a transporter in the Star Trek science fiction series.</p>
<p>For a QBist, however, nothing real is transported from A to B. All that happens in quantum teleportation is that an agent’s belief about the particle at A becomes, after the operation, the same agent’s belief about a particle at B. The quantum state that expresses the agent’s belief about the particle at A initially is mathematically identical to the quantum state that expresses that same agent’s belief about the particle at B after the operation. Quantum teleportation is a powerful tool used in applications such as quantum computing, but in QBism there is nothing counter-intuitive or weird about it.</p>
<p>QBism is an ongoing project. It spells out clearly the meaning of all mathematical objects in the theory and is thus a fully developed interpretation of quantum mechanics. Yet, QBism is also a programme for developing new physics and has already yielded deep insights even if it is still a work in progress.</p>
<p>QBism has also led to a <a href="http://philsci-archive.pitt.edu/id/eprint/20328">fruitful dialogue</a> with the kindred philosophical schools of thought of pragmatism and phenomenology. Its vision of the world is one in which agents possess genuine freedom and respect each other’s autonomy. I like to think that this is what quantum mechanics has been trying to tell us about reality all along.</p><img src="https://counter.theconversation.com/content/200487/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ruediger Schack receives funding from the John Templeton Foundation. </span></em></p>According to a school of thought known as QBism, quantum mechanics is a guide to action.Ruediger Schack, Professor of mathematics, Royal Holloway University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2025502023-03-29T09:56:05Z2023-03-29T09:56:05ZGreat Mysteries of Physics 4: does objective reality exist?<figure><img src="https://images.theconversation.com/files/517677/original/file-20230327-22-x0ycpn.jpg?ixlib=rb-1.1.0&rect=57%2C0%2C3776%2C2149&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/contemplative-young-hispanic-woman-closing-eyes-2214716217">Bricolage/Shutterstock</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/642304b2dd47b5001151d53f" 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>It is hard to shake the intuition that there’s a real and objective physical world out there. If I see an umbrella on top of a shelf, I assume you do too. And if I don’t look at the umbrella, I expect it to remain there as long as nobody steals it. But the theory of quantum mechanics, which governs the micro-world of atoms and particles, threatens this commonsense view. </p>
<p>The fourth episode of our podcast Great Mysteries of Physics – hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute – is all about the strange world of quantum mechanics. </p>
<p>According to quantum theory, each system, such as a particle, can be described by a wave function, which evolves over time. The wave function allows particles to hold multiple contradictory features, such as being in several different places at once – this is called a superposition. But oddly, this is only the case when nobody’s looking.</p>
<p>Although each potential location in a superposition has a certain probability of appearing, the second you observe it, the particle randomly picks one – breaking the superposition. Physicists often refer to this as the wave function collapsing. But why should nature behave differently depending on whether we are looking or not? And why should it be random?</p>
<p>Not everyone is worried. “If you want to explain everything we can observe in our experiments without randomness, you have to go through some really weird and long-winded explanations that I am much more uncomfortable with,” argues Marcus Huber, a professor of quantum information at the Technical University of Vienna. And indeed, you can get rid of randomness if you accept that the <a href="https://theconversation.com/great-mysteries-of-physics-1-is-time-an-illusion-201026">future can influence the past</a>, that there’s more than one outcome to every measurement or that everything in the universe is predetermined since the dawn of time.</p>
<p>Another problem is that quantum mechanics seems to give rise to contradictory facts. Imagine a scientist, Lisa, inside a lab measuring the location of a particle. Before her colleague, Nikhil, knocks on the lab door and asks what outcome she saw, he would measure Lisa as being in a superposition of both branches – one where she sees the particle here and one where she sees the particle there. But at the same time, Lisa herself may be convinced that that she has a definite answer as to where the particle is. </p>
<p>That means that these two people will say that the state of reality is different – they’d have different facts about where the particle is.</p>
<p>There are may other oddities about quantum mechanics, too. Particles can be entangled in a way that enables them to somehow share information instantaneously even if they’re light years apart, for example. This challenges another common intution: that objects need a physical mediator to interact.</p>
<p>Physicists have therefore long debated how to interpret quantum mechanics. Is it a true and objective description of reality? If so, what happens to all the possible outcomes that we don’t measure? The many worlds interpretation argues they do happen – but in parallel universes. </p>
<p>Another set of interpretations, collectively known as the Copenhagen interpretation, suggests quantum mechanics is to some extent a user’s manual rather than a perfect description of reality. “The Copenhagen interpretations what they share is at least a partial step back from the full-blown descriptive aim of physics,” explains Chris Timpson, a philosopher of physics at the University of Oxford. “So the quantum state, this thing which describes these lovely superpositions, that’s just a tool for making predictions about the behaviour of macroscopic measurement scenarios.”</p>
<p>But why don’t we see quantum effect on the scale of humans? Chiara Marletto, a quantum physicist at the University of Oxford, has developed a meta-theory called constructor theory which aims to encompass all of physics based solely on simple principles about which physical transformations in the universe are ultimately possible, which are impossible, and why.</p>
<p>She hopes it can help us understand why we don’t see quantum effects on the macroscopic scale of humans. “There’s nothing [in the laws of physics] that says it’s impossible to have quantum effects at the scale of a human being,” she says. “So either we discover a new principle that says that they really are impossible – which would be interesting – or in the absence of that, it is more a question of trying harder to create conditions in the laboratory to bring these effects about.”</p>
<p>Another problem with quantum mechanics is that it isn’t compatible with general relativity, which describes nature on the largest of scales. Marletto is using constructor theory to try to find ways to combine the two. She has also come up with some experiments which could test such models – and rule out certain interpretations of quantum mechanics.</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/2630/MoP__Ep4_-_Quantum_Mechanics_TRANSCRIPT.docx_%283%29.pdf?1681213764">transcript of the episode here</a>.</em></p><img src="https://counter.theconversation.com/content/202550/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chiara Marletto has received funding from Moore Foundation, John Templeton Foundation, Eutopia Foundation, FQxi, Templeton World Charity Foundation. Marcus Huber has received funding from the Austrian science fund (fwf), the European research council (ERC), the European commission (EC), the fqxi institute, the Templeton foundation and the Austrian academy of sciences. Christopher Timpson has received funding from Arts and Humanities Research Council; John Templeton Foundation; Templeton World Charity Foundation; The Foundational Questions Institute.</span></em></p>Some physicists don’t believe that quantum mechanics is a perfect description of objective reality.Miriam Frankel, Podcast host, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2022022023-03-22T12:06:32Z2023-03-22T12:06:32ZGreat Mysteries of Physics 3: is there a multiverse?<figure><img src="https://images.theconversation.com/files/516427/original/file-20230320-1591-qs31qo.jpg?ixlib=rb-1.1.0&rect=50%2C39%2C1301%2C714&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The light left over from the Big Bang, seen by the Planck satellite.</span> <span class="attribution"><span class="source">ESA/ LFI & HFI Consortia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/6419b6379099ce0011fbbec6" 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>Interest in the multiverse theory, suggesting that our universe is just one of many, spiked following the release of the movie <a href="https://www.imdb.com/title/tt6710474/">Everything Everywhere All At Once</a>. The film follows Evelyn Wang on her journey to connect with versions of herself in parallel universes to ultimately stop the destruction of the multiverse.</p>
<p>The multiverse idea has long been an inspiration for science fiction writers. But does it have any basis in science? And if so, is it a concept we could ever test experimentally? </p>
<p>That’s the topic of the third episode of our podcast Great Mysteries of Physics – hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute.</p>
<p>“One way to think of a multiverse is just to say: ‘Well, the universe might be really, really big – much bigger than our observable universe – and so there could be other regions of the universe that are far beyond our horizon that have different things happening in them’,” explains Katie Mack, Hawking chair in cosmology and science communication at the Perimeter Institute for Theoretical Physics in Canada. “And I think that idea is totally well accepted in cosmology.”</p>
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<p>The idea that there could be other parts of the cosmos with different physical laws, processes and histories is hard to ignore. And the concept is consistent with the theories of quantum mechanics, which governs the micro-world of atoms and particles, string theory (an attempt at a theory of everything) – and also with cosmic inflation, which says the infant universe blew up hugely in size during a brief growth spurt, and then continued to grow at a less frantic pace. These theories each give rise to their own version of the multiverse theory.</p>
<p>For Andrew Pontzen, a professor of cosmology at University College London in the UK, quantum mechanics is the best reason to believe in the multiverse. According to quantum mechanics, particles can be in a mix of different possible states, such as locations, which is known as a “superposition”. But when we measure them, the superposition breaks and each particle randomly “picks” one state.</p>
<p>So what happens to the other possible outcomes? “There’s a brilliant way of understanding this which is to imagine that, actually, the reality we experience is just one kind of facet of a much more complicated multiverse, where pretty much anything that can happen does happen and we just experience one version of events,” explains Pontzen. “Although it sounds crazy, it’s sort of the least crazy option for understanding how quantum mechanics can be right.”</p>
<p>Not all physicists are fans of the multiverse, though. Many argue that if it’s impossible to ever observe other universes, the multiverse can’t be a scientific theory. “I think it’s fine for entertainment,” says Sabine Hossenfelder, a research fellow at the Frankfurt Institute of Advanced Studies, who describes the multiverse as “ascientific”. “You sometimes hear people talk about some kind of mathematical evidence. [But] that’s just not a thing – evidence is something that you actually observe.”</p>
<p>There is currently no observational support for the multiverse theory. However, Mack doesn’t think that necessarily means it is unscientific. “I don’t think that hypothesising the existence of something unobservable is inherently unscientific,” she argues. “The wave function [in quantum mechanics] is unobservable. We have ways to infer the existence of the wave function because the maths all works perfectly. That we never directly observe it is a little beside the point, because it’s such a basic part of the science.”</p>
<p>Pontzen, though, is optimistic that we may one day be able to see signs of a collision with another universe in the cosmic microwave background, which is the light left over from the Big Bang. He is also working on a laboratory experiment trying to shed light on how a baby universe could actually physically be born from a multiverse. </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/2631/MoP__Ep3_-_Multiverse_TRANSCRIPT.docx_%281%29.pdf?1681213830">transcript of the episode here</a>.</em></p><img src="https://counter.theconversation.com/content/202202/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Pontzen has received funding from UK Research and Innovation Quantum Technologies for Fundamental Physics. Katie Mack and Sabine Hossenfelder have nothing to disclose.</span></em></p>Some physicists believe we could one day find evidence of other universes.Miriam Frankel, Podcast host, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1994262023-03-08T11:52:16Z2023-03-08T11:52:16ZQuantum mechanics: how the future might influence the past<figure><img src="https://images.theconversation.com/files/513649/original/file-20230306-16-pbkjv.jpg?ixlib=rb-1.1.0&rect=74%2C89%2C4895%2C2709&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/composition-space-time-flight-spiral-roman-1221181900">FlashMovie/Shutterstock</a></span></figcaption></figure><iframe src="https://embed.acast.com/638f4b009a65b10011b94c5e/63ff7a9ec60fff0011bc8567" frameborder="0" width="100%" height="190px"></iframe>
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<p>In 2022, the <a href="https://theconversation.com/nobel-prize-physicists-share-prize-for-insights-into-the-spooky-world-of-quantum-mechanics-191884">physics Nobel prize</a> was awarded for experimental work showing that the quantum world must break some of our fundamental intuitions about how the universe works. </p>
<p>Many look at those experiments and conclude that they challenge “locality” — the intuition that distant objects need a physical mediator to interact. And indeed, a mysterious connection between distant particles would be one way to explain these experimental results. </p>
<p>Others instead think the experiments challenge “realism” — the intuition that there’s an objective state of affairs underlying our experience. After all, the experiments are only difficult to explain if our measurements are thought to correspond to something real. Either way, many physicists agree about what’s been <a href="https://doi.org/10.1038/nature15631">called</a> “the death by experiment” of local realism.</p>
<p>But what if both of these intuitions can be saved, at the expense of a third? A growing group of experts think that we should abandon instead the assumption that present actions can’t affect past events. Called “retrocausality”, this option claims to rescue both locality and realism.</p>
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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>
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<h2>Causation</h2>
<p>What is causation anyway? Let’s start with the line everyone knows: correlation is not causation. Some correlations are causation, but not all. What’s the difference? </p>
<p>Consider two examples. (1) There’s a correlation between a barometer needle and the weather – that’s why we learn about the weather by looking at the barometer. But no one thinks that the barometer needle is causing the weather. (2) Drinking strong coffee is correlated with a raised heart rate. Here it seems right to say that the first is causing the second. </p>
<p>The difference is that if we “wiggle” the barometer needle, we won’t change the weather. The weather and the barometer needle are both controlled by a third thing, the atmospheric pressure – that’s why they are correlated. When we control the needle ourselves, we break the link to the air pressure, and the correlation goes away. </p>
<p>But if we intervene to change someone’s coffee consumption, we’ll usually change their heart rate, too. Causal correlations are those that still hold when we wiggle one of the variables. </p>
<p>These days, the science of looking for these robust correlations is called “causal discovery”. It’s a big name for a simple idea: finding out what else changes when we wiggle things around us. </p>
<p>In ordinary life, we usually take for granted that the effects of a wiggle are going to show up later than the wiggle itself. This is such a natural assumption that we don’t notice that we’re making it.</p>
<p>But nothing in the scientific method requires this to happen, and it is easily abandoned in fantasy fiction. Similarly in some religions, we pray that our loved ones are among the survivors of yesterday’s shipwreck, say. We’re imagining that something we do now can affect something in the past. That’s retrocausality.</p>
<h2>Quantum retrocausality</h2>
<figure class="align-right ">
<img alt="John Stewart Bell." src="https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=604&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=604&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=604&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=759&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=759&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513622/original/file-20230306-16-94jie1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=759&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">John Bell.</span>
<span class="attribution"><span class="source">wikipedia/cern</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>The quantum threat to locality (that distant objects need a physical mediator to interact) stems from an argument by the Northern Ireland <a href="https://mathshistory.st-andrews.ac.uk/Biographies/Bell_John/">physicist John Bell</a> in the 1960s. Bell considered experiments in which two hypothetical physicists, Alice and Bob, each receive particles from a common source. Each chooses one of several measurement settings, and then records a measurement outcome. Repeated many times, the experiment generates a list of results.</p>
<p>Bell realised that quantum mechanics predicts that there will be strange correlations (now confirmed) in this data. They seemed to imply that Alice’s choice of setting has a subtle “nonlocal” influence on Bob’s outcome, and vice versa – even though Alice and Bob might be light years apart. Bell’s argument is <a href="https://www.scientificamerican.com/article/a-quantum-threat-to-special-relativity-extreme-physics-special/">said</a> to pose a threat to Albert Einstein’s theory of special relativity, which is an essential part of modern physics.</p>
<p>But that’s because Bell assumed that quantum particles don’t know what measurements they are going to encounter in the future. <a href="https://plato.stanford.edu/entries/qm-retrocausality/">Retrocausal models</a> propose that Alice’s and Bob’s measurement choices affect the particles back at the source. This can explain the strange correlations, without breaking special relativity. </p>
<p>In recent work, <a href="https://link.springer.com/article/10.1007/s10701-021-00511-3">we’ve proposed</a> a simple mechanism for the strange correlation – it involves a familiar statistical phenomenon called <a href="https://slate.com/human-interest/2014/06/berksons-fallacy-why-are-handsome-men-such-jerks.html">Berkson’s bias</a> (see our popular summary <a href="https://arxiv.org/abs/2212.06986">here</a>). </p>
<p>There’s now a thriving group of scholars who work on quantum retrocausality. But it’s still invisible to some experts in the wider field. It gets confused for a different view called “superdeterminism”.</p>
<h2>Superdeterminism</h2>
<p><a href="https://www.newscientist.com/article/mg25033340-700-is-everything-predetermined-why-physicists-are-reviving-a-taboo-idea/">Superdeterminism</a> agrees with retrocausality that measurement choices and the underlying properties of the particles are somehow correlated.</p>
<p>But superdeterminism treats it like the correlation between the weather and the barometer needle. It assumes there’s some mysterious third thing – a “superdeterminer” – that controls and correlates both our choices and the particles, the way atmospheric pressure controls both the weather and the barometer.</p>
<p>So superdeterminism denies that measurement choices are things we are free to wiggle at will, they are predetermined. Free wiggles would break the correlation, just as in the barometer case. Critics <a href="https://www.tandfonline.com/doi/abs/10.1080/00107510600581011">object</a> that superdeterminism thus undercuts core assumptions necessary to undertake scientific experiments. They also say that it means denying free will, because <a href="https://www.forbes.com/sites/chadorzel/2017/02/08/quantum-loopholes-and-the-problem-of-free-will/">something is controlling</a> both the measurement choices and particles.</p>
<p>These objections don’t apply to retrocausality. Retrocausalists do scientific causal discovery in the usual free, wiggly way. We say it is folk who dismiss retrocausality who are forgetting the scientific method, if they refuse to follow the evidence where it leads.</p>
<h2>Evidence</h2>
<p>What is the evidence for retrocausality? Critics ask for experimental evidence, but that’s the easy bit: the relevant experiments just won a Nobel Prize. The tricky part is showing that retrocausality gives the best explanation of these results.</p>
<p>We’ve mentioned the potential to remove the threat to Einstein’s special relativity. That’s a pretty big hint, in our view, and it’s surprising it has taken so long to explore it. The confusion with superdeterminism seems mainly to blame.</p>
<p>In addition, <a href="https://www.mdpi.com/1099-4300/17/11/7752">we</a> and <a href="https://phys.org/news/2017-07-physicists-retrocausal-quantum-theory-future.html">others</a> have argued that retrocausality makes better sense of the fact that the microworld of particles doesn’t care about the difference between past and future. </p>
<p>We don’t mean that it is all plain sailing. The biggest worry about retrocausation is the possibility of sending signals to the past, opening the door to the paradoxes of time travel. But to make a paradox, the effect in the past has to be measured. If our young grandmother can’t read our advice to avoid marrying grandpa, meaning we wouldn’t come to exist, there’s no paradox. And in the quantum case, it’s well known that we can never measure everything at once. </p>
<p>Still, there’s work to do in devising concrete retrocausal models that enforce this restriction that you can’t measure everything at once. So we’ll close with a cautious conclusion. At this stage, it’s retrocausality that has the wind in its sails, so hull down towards the biggest prize of all: saving locality and realism from “death by experiment”.</p><img src="https://counter.theconversation.com/content/199426/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Huw Price has received funding from the Australian Research Council and the Leverhulme Trust.</span></em></p><p class="fine-print"><em><span>Ken Wharton 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>If we accepted that the future could influence the past, we could get rid of many counter-intuitive aspects of quantum mechanics.Huw Price, Emeritus Fellow, Trinity College, University of CambridgeKen Wharton, Professor of Physics and Astronomy, San José State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1977122023-01-17T00:16:42Z2023-01-17T00:16:42ZPhysicists have used entanglement to ‘stretch’ the uncertainty principle, improving quantum measurements<figure><img src="https://images.theconversation.com/files/504370/original/file-20230113-14-rc7nuw.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C7000%2C4191&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Almost a century ago, German physicist Werner Heisenberg realised the laws of quantum mechanics placed some fundamental limits on how accurately we can measure certain properties of microscopic objects. </p>
<p>However, the laws of quantum mechanics can also offer ways to make measurements more accurate than would otherwise be possible.</p>
<p>In new research <a href="https://www.nature.com/articles/s41567-022-01875-7">published in Nature Physics</a>, we have outlined a way to achieve more accurate measurements of microscopic objects using quantum computers. This could prove useful in a huge range of next-generation technologies, including biomedical sensing, laser ranging and quantum communications. </p>
<p>We were also able to push beyond the limits of a variation of Heisenberg’s “uncertainty principle” in certain circumstances, suggesting different uncertainty principles may be necessary in different scenarios.</p>
<h2>Quantum uncertainties</h2>
<p>If you want to examine the properties of a large everyday object like a car, it’s a simple process. </p>
<p>For example, a car has a well-defined position, colour and speed. You can measure them one after another or all at once with no issues. Measuring the position of your car will not change its colour or speed.</p>
<p>However, this becomes much trickier if you’re trying to examine microscopic quantum objects like electrons or photons (which are tiny little particles of light). </p>
<p>Certain properties of quantum objects are connected to each other. Measuring one property can influence another property. </p>
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Read more:
<a href="https://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">Explainer: Heisenberg’s Uncertainty Principle</a>
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<p>For example, measuring the position of an electron will affect its speed and vice versa. </p>
<p>These properties are called “conjugate” properties. </p>
<p>The link between these properties is a direct manifestation of Heisenberg’s uncertainty principle. It is not possible to simultaneously measure two conjugate properties of a quantum object to whatever degree of accuracy you like: the more you know about one, the less you know about the other.</p>
<p>While the uncertainty principle imposes a limit on how accurate some measurements can be, reaching that limit in practice can be very challenging. However, measuring quantum objects in the greatest amount of detail possible is important for advancing fundamental science as well as developing new technologies. </p>
<h2>Entangled objects</h2>
<p>In our new research, we designed a way to determine conjugate properties of quantum objects more accurately. Our collaborators were then able to carry out this measurement in various labs around the world.</p>
<p>The new technique revolves around a strange quirk of quantum systems, known as entanglement. When two objects are entangled, we can measure them more accurately than if they weren’t entangled.</p>
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<strong>
Read more:
<a href="https://theconversation.com/what-is-quantum-entanglement-a-physicist-explains-the-science-of-einsteins-spooky-action-at-a-distance-191927">What is quantum entanglement? A physicist explains the science of Einstein’s ‘spooky action at a distance’</a>
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<p>We realised we could use quantum computers, which can precisely control the state of quantum objects, to create two identical quantum objects and entangle them. By measuring the entangled objects together, we could determine their properties more precisely than if they were measured individually. </p>
<p>Measuring the two entangled identical quantum objects reduces the noise in the measurement, making it more accurate.</p>
<h2>A less noisy future</h2>
<p>In theory, it is also possible to entangle and measure three or more quantum systems to achieve even better precision. However, we haven’t been able to make this work experimentally as yet. </p>
<p>The results of measuring three identical entangled objects together were very noisy. However, as quantum computers improve and become more accurate, it may be possible to faithfully measure three copies of a quantum system simultaneously in the future.</p>
<figure class="align-center ">
<img alt="An elaborate cooling rig for a quantum computer, against a black background." src="https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504371/original/file-20230113-20-t7ufet.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Quantum computers of the future may be less noisy.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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</figure>
<p>One of the key strengths of this work is that a quantum enhancement can still be observed in very noisy scenarios. This bodes well for future practical applications, such as in biomedical measurements, which will inevitably occur in noisy real-world environments.</p>
<h2>What about the uncertainty principle?</h2>
<p>This research also has implications for the aforementioned uncertainty principle. </p>
<p>One interpretation of the uncertainty principle is that it is impossible to measure conjugate properties of quantum objects with unlimited accuracy. But another interpretation is that measuring one conjugate property of a quantum object must necessarily disturb the second conjugate property by some minimum amount. </p>
<p>In this research, we were able to violate an uncertainty principle based on the second interpretation. This suggests that, depending on what physical setting is considered, different uncertainty principles may be necessary for different scenarios. </p>
<h2>A global collaboration</h2>
<p>We tested our theory on a total of 19 different quantum computers, which used three different quantum computing technologies: superconductors, trapped ions and photonics. These devices are located across Europe and America and can be accessed via the internet, allowing researchers from across the globe to connect and carry out important research.</p>
<p>We carried out the study with colleagues at the ARC Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), in collaboration with researchers from the Institute of Materials Research and Engineering at A*STAR in Singapore, the University of Jena, the University of Innsbruck, Macquarie University and Amazon Web Services.</p><img src="https://counter.theconversation.com/content/197712/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>Examining microscopic quantum objects is exceedingly tricky, because their properties are connected to each other. But there could be a new method to measure them as accurately as possible.Lorcan Conlon, PhD student, Quantum Science & Technology, Australian National UniversitySyed Assad, Research Associate, Quantum Science & Technology, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1920622022-11-08T11:50:20Z2022-11-08T11:50:20ZFour common misconceptions about quantum physics<figure><img src="https://images.theconversation.com/files/489048/original/file-20221010-12-vbbj25.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4578%2C3095&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Shrödinger's cat is world famous, but what does it really mean?</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/29233640@N07/8132455446">Robert Couse-Baker/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Quantum mechanics, the theory which rules the microworld of atoms and particles, certainly has the X factor. Unlike many other areas of physics, it is bizarre and counter-intuitive, which makes it dazzling and intriguing. When the 2022 Nobel prize in physics was <a href="https://theconversation.com/nobel-prize-physicists-share-prize-for-insights-into-the-spooky-world-of-quantum-mechanics-191884">awarded to Alain Aspect, John Clauser and Anton Zeilinger</a> for research shedding light on quantum mechanics, <a href="https://twitter.com/skdh/status/1577870071526998016?s=20&t=Vqj_K2asXmLTO2ezwN3jyw">it sparked excitement and discussion</a>.</p>
<p>But debates about quantum mechanics – be they on chat forums, in the media or in science fiction – can often get muddled thanks to a number of persistent myths and misconceptions. Here are four.</p>
<h2>1. A cat can be dead and alive</h2>
<p>Erwin Schrödinger could probably never have predicted that his <a href="https://www.nationalgeographic.com/science/article/130812-physics-schrodinger-erwin-google-doodle-cat-paradox-science">thought experiment</a>, Schrödinger’s cat, would attain <a href="https://knowyourmeme.com/memes/schrodingers-cat">internet meme status</a> in the 21st century.</p>
<p>It suggests that an unlucky feline stuck in a box with a kill switch triggered by a random quantum event – radioactive decay, for example – could be alive and dead at the same time, as long as we don’t open the box to check.</p>
<p>We’ve long known that quantum particles can be in two states – for example in two locations – at the same time. We call this a superposition. </p>
<p>Scientists have been able to show this in the famous double-slit experiment, where a single quantum particle, such as a photon or electron, can go through two different slits in a wall simultaneously. How do we know that? </p>
<p>In quantum physics, each particle’s state is also a wave. But when we send a stream of photons – one by one – through the slits, it creates a pattern of two waves interfering with each other on a screen behind the slit. As each photon didn’t have any other photons to interfere with when it went through the slits, it means it must simultaneously have gone through both slits – interfering with itself (image below).</p>
<figure class="align-center ">
<img alt="Image of a light interference pattern." src="https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489003/original/file-20221010-22-dbq37n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&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">Interference pattern.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/diffraction-light-double-slit-experiment-test-1842566269">grayjay</a></span>
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<p>For this to work, however, the states (waves) in the superposition of the particle going through both slits need to be “<a href="https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448">coherent</a>” – having a well defined relationship with each other.</p>
<p>These superposition experiments can be done with objects of ever increasing size and complexity. One <a href="https://www.nature.com/articles/44348">famous experiment</a> by Anton Zeilinger in 1999 demonstrated quantum superposition with large molecules of <a href="https://www.forbes.com/sites/rebeccasuhrawardi/2021/04/30/this-nobel-prize-winning-molecule-could-be-the-best-thing-for-anti-aging/?sh=60c6e0036ada">Carbon-60</a> known as “buckyballs”.</p>
<p>So what does this mean for our poor cat? Is it really both alive and dead as long as we don’t open the box? Obviously, a cat is nothing like an individual photon in a controlled lab environment, it is much bigger and more complex. Any coherence that the trillions upon trillions of atoms that make up the cat might have with each other is extremely shortlived.</p>
<p>This does not mean that quantum coherence is impossible in biological systems, just that it generally won’t apply to big creatures such as cats or a human.</p>
<h2>2. Simple analogies can explain entanglement</h2>
<p>Entanglement is a quantum property which links two different particles so that if you measure one, you automatically and instantly know the state of the other – no matter how far apart they are.</p>
<p>Common explanations for it <a href="https://hackaday.com/2015/11/11/what-do-bertlmanns-socks-mean-to-the-nature-of-reality/">typically involve everyday objects</a> from our classical macroscopic world, such as dice, cards or even pairs of odd-coloured socks. For example, imagine you tell your friend you have placed a blue card in one envelope and an orange card in another. If your friend takes away and opens one of the envelopes and finds the blue card, they will know you have the orange card.</p>
<p>But to understand quantum mechanics, you have to imagine the two cards inside the envelopes are in a joint superposition, meaning they are both orange and blue at the same time (specifically orange/blue and blue/orange). Opening one envelope reveals one colour determined at random. But opening the second still always reveals the opposite colour because it is “spookily” linked to the first card.</p>
<p>One could force the cards to appear in a different set of colours, akin to doing another type of measurement. We could open an envelope asking the question: “Are you a green or a red card?”. The answer would again be random: green or red. But crucially, if the cards were entangled, the other card would still always yield the opposite outcome when asked the same question.</p>
<p>Albert Einstein attempted to explain this with classical intuition, suggesting the cards could have been provided with a <a href="https://www.nature.com/articles/news011129-15">hidden, internal instruction set</a> which told them in what colour to appear given a certain question. He also rejected the apparent “spooky” action between the cards that seemingly allows them to instantly influence each other, which would mean communication faster than the speed of light, something forbidden by Einstein’s theories.</p>
<p>However, Einstein’s explanation was subsequently ruled out by <a href="https://www.quantamagazine.org/how-bells-theorem-proved-spooky-action-at-a-distance-is-real-20210720/">Bell’s theorem</a> (a theoretical test created by the physicist John Stewart Bell) and experiments by 2022’s Nobel laureates. The idea that measuring one entangled card changes the state of the other is not true. Quantum particles are just mysteriously correlated in ways we can’t describe with everyday logic or language – they don’t communicate while also containing a hidden code, as Einstein had thought. So forget about everyday objects when you think about entanglement. </p>
<h2>3. Nature is unreal and ‘non-local’</h2>
<p>Bell’s theorem is often said to prove that nature isn’t “local”, that an object isn’t just directly influenced by its immediate surroundings. Another common interpretation is that it implies properties of quantum objects aren’t “real”, that they do not exist prior to measurement.</p>
<p>But Bell’s theorem <a href="https://twitter.com/ericcavalcanti/status/1578319993673986049">only allows us to say</a> that quantum physics means nature isn’t both real and local if we assume a few other things at the same time. These assumptions include the idea that measurements only have a single outcome (and not multiple, perhaps in parallel worlds), that cause and effect flow forward in time and that we do not live in a “clockwork universe” in which everything has been predetermined since the dawn of time. </p>
<figure class="align-center ">
<img alt="Entanglement concept." src="https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489006/original/file-20221010-22-964bew.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Entanglement concept.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/particle-quantum-entanglement-correlation-mechanics-3d-1457191784">Jurik Peter/Shuttestock</a></span>
</figcaption>
</figure>
<p>Despite Bell’s theorem, nature may well be real and local, <a href="https://link.springer.com/chapter/10.1007/978-3-319-38987-5_6">if you allowed for breaking some other things</a> we consider common sense, such as time moving forward. And further research will hopefully narrow down the great number of potential interpretations of quantum mechanics. However, most options on the table — for example, time flowing backwards, or the absence of free will — are at least as absurd as giving up on the concept of local reality. </p>
<h2>4. Nobody understands quantum mechanics</h2>
<p>A <a href="https://www.ornl.gov/media/76081#:%7E:text=DEAN%3A%20The%20one%20of%20the,theory%20my%20entire%20professional%20career.">classic quote</a> (attributed to physicist <a href="https://www.nobelprize.org/prizes/physics/1965/feynman/biographical/">Richard Feynman</a>, but in this form also paraphrasing <a href="https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/">Niels Bohr</a>) surmises: “If you think you understand quantum mechanics, you don’t understand it.”</p>
<p>This view is widely held in public. Quantum physics is supposedly impossible to understand, including by physicists. But from a 21st-century perspective, quantum physics is neither mathematically nor conceptually particularly difficult for scientists. We understand it extremely well, to a point where we can predict quantum phenomena with high precision, simulate highly complex quantum systems and even start to <a href="https://theconversation.com/how-we-created-the-first-ever-blueprint-for-a-real-quantum-computer-72290">build quantum computers</a>.</p>
<p>Superposition and entanglement, when explained in the language of quantum information, requires no more than high-school mathematics. Bell’s theorem doesn’t require any quantum physics at all. It can be derived in a few lines using probability theory and linear algebra. </p>
<p>Where the true difficulty lies, perhaps, is in how to reconcile quantum physics with our intuitive reality. Not having all the answers won’t stop us from making further progress with quantum technology. We can simply just <a href="https://aeon.co/essays/shut-up-and-calculate-does-a-disservice-to-quantum-mechanics">shut up and calculate</a>.</p>
<p>Fortunately for humanity, Nobel winners Aspect, Clauser, and Zeilinger refused to shut up and kept asking why. Others like them may one day help reconcile quantum weirdness with our experience of reality.</p><img src="https://counter.theconversation.com/content/192062/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alessandro Fedrizzi receives funding from the UK Engineering and Physical Sciences Research Council (EPSRC) (EP/T001011/1). </span></em></p><p class="fine-print"><em><span>Mehul Malik receives funding from the UK Engineering and Physical Sciences Research Council (EPSRC) (EP/P024114/1) and the European Research Council (ERC) Starting Grant PIQUaNT (950402). </span></em></p>Nope, ‘entangled’ particles don’t communicate.Alessandro Fedrizzi, Professor of Physics, Heriot-Watt UniversityMehul Malik, Professor of Physics, Heriot-Watt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1896742022-10-31T18:35:43Z2022-10-31T18:35:43ZWhat quantum technology means for Canada’s future<figure><img src="https://images.theconversation.com/files/492191/original/file-20221027-23824-csb3yk.png?ixlib=rb-1.1.0&rect=23%2C23%2C3970%2C2622&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A look inside the quantum computing process. Quantum technology is a $142 billion opportunity that could employ 229,000 Canadians by 2040.</span> <span class="attribution"><span class="source">(Photonic)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Canada is a world leader in developing quantum technologies and is well-positioned to secure its place in the emerging quantum industry. </p>
<p><a href="https://qt.eu/discover-quantum/quantum-technologies-in-a-nutshell/">Quantum technologies</a> are new and emerging technologies based on the unique properties of <a href="https://scholar.harvard.edu/files/david-morin/files/waves_quantum.pdf">quantum mechanics</a> — the science that deals with the physical properties of nature on an atomic and subatomic level.</p>
<p>In the future, we’ll see quantum technology transforming computing, communications, cryptography and much more. They will be incredibly powerful, offering capabilities that reach beyond today’s technologies. </p>
<p>The potential impact of these technologies on the Canadian economy will be transformative: the <a href="https://policyoptions.irpp.org/magazines/august-2021/how-to-ensure-canadas-quantum-computing-strategy-is-a-success/">National Research Council of Canada</a> has identified quantum technology as a $142 billion opportunity that could employ 229,000 Canadians by 2040.</p>
<p>Canada could gain far-reaching economic and social benefits from the rapidly developing quantum industry, but it must act now to secure them — before someone else delivers the first large-scale quantum computer, which will likely be sooner than expected.</p>
<h2>Quantum technology is the future</h2>
<p>Quantum computing is a <a href="https://theconversation.com/in-the-future-everyone-might-use-quantum-computers-112063">rapidly-developing type of quantum technology</a> that combines concepts from quantum physics with classical computation. The result is quantum computers, which can accomplish tasks that classical computers can’t.</p>
<p>While quantum computers will be revolutionary, they will also introduce new problems by breaking the public key cryptography that secures today’s internet and corporate networks. <a href="https://doi.org/10.1038/nature23461">Public key cryptography</a> is a method of encrypting data with pairs of keys. Anyone with a public key can encrypt a message, but only those holding the matching private key can decrypt it. </p>
<p>The keys are generated by computers running complex mathematical problems that can’t be broken by today’s most powerful computers, but can be broken by quantum computers. Data intercepted and stored today <a href="https://www.factbasedinsight.com/quantum-crypto-trust-me-ive-come-to-save-the-world">is already vulnerable to this future threat</a>. </p>
<p>This presents an opportunity for Canada to invest in new technologies to secure communications, starting with “post-quantum” encryption algorithms, then layering on
<a href="https://www.techtarget.com/searchsecurity/definition/quantum-key-distribution-QKD">quantum key distribution</a>, a type of provably secure quantum encryption based on quantum mechanics. </p>
<p>To use quantum key distribution over vast distances, we’ll need to develop <a href="https://doi.org/10.1088/1367-2630/abfa63">satellite-based quantum repeaters</a> that function similarly to repeaters in today’s telecommunications fibre networks. They allow quantum signal transmission over long distances. <a href="https://www.asc-csa.gc.ca/eng/satellites/qeyssat.asp">Canadian researchers are well on their way to developing them</a>.</p>
<p>Unless we defend our cybersecurity infrastructure now, the advent of a quantum computer could be the information-security equivalent of the nuclear bomb: almost no information or computing systems would be secure against a future quantum attack. Canada needs to seize the opportunity to lead the world in building, deploying and exporting technology to enable the global quantum internet and protect itself.</p>
<h2>Preparing for the future</h2>
<p>Truly predicting the impact of <a href="https://hbr.org/2021/07/quantum-computing-is-coming-what-can-it-do">large-scale quantum computers</a> is as hard as predicting the changes that followed the commercialization of semiconductor physics. </p>
<p>When the crown jewel of semiconductor microchip technology — transistors — were first commercialized, they were expected to be most helpful in the development of hearing aids. They drove a <a href="https://www.semiconductors.org/semiconductors-101/what-is-a-semiconductor/">computation and communications revolution</a>; <a href="https://www.bbc.com/future/bespoke/made-on-earth/how-the-chip-changed-everything/">today we find the physics of semiconductors inside everything</a> from laptops and phones to cars and medical devices.</p>
<p>Once large-scale quantum physics is commercialized, it will similarly impact almost every field, industry and aspect of our lives. Scientists and engineers will be able to solve all sorts of problems with quantum computers, including simulating and designing drug targets, making better batteries and <a href="https://www.bcg.com/publications/2020/quantum-advantage-fighting-climate-change">creating more efficient ways to produce green hydrogen and synthetic gas</a>.</p>
<h2>Maintaining the lead</h2>
<p>To maintain its leadership, Canada needs to move beyond research and development and accelerate a quantum ecosystem that includes a strong talent pipeline, businesses supported by supply chains and governments and industry involvement. There are a few things Canada can do to drive this leadership: </p>
<p><strong>Continue to fund quantum research:</strong> Canada has <a href="https://www.univcan.ca/media-room/media-releases/how-canadian-universities-are-propelling-us-towards-a-quantum-future/">more than a dozen quantum research institutes and labs</a>, including my <a href="https://www.sfu.ca/physics/siliconquantum/">Silicon Quantum Technologies Lab</a> at Simon Fraser University. The Canadian government has invested more than $1 billion since 2005 in quantum research and will likely announce a national quantum strategy soon. Canada must continue funding quantum research or risk losing its talent base and current competitive advantage.</p>
<p><strong>Build our talent pipeline with more open immigration</strong>: Even though quantum experts are trained in every major university in Canada, the demand for them is <a href="https://thebusinesscouncil.ca/publication/closing-the-quantum-computing-skills-gap-could-make-all-the-difference-in-tackling-climate-change/">three times the number of new graduates</a>. Canada needs the kind of <a href="https://www.ictc-ctic.ca/wp-content/uploads/2012/06/ICTC_IEP_SA_National_EN_03-12.pdf">fast-track immigration programs that fuelled the telecom boom in the 1990s</a>.</p>
<figure class="align-center ">
<img alt="Someone wearing a mask and protective goggles holding a computer microchip in front of their face" src="https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/492194/original/file-20221027-24414-egb33q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Transistors are one of the building blocks of modern electronic technology, including computer chips.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p><strong>Be our own best customers</strong>: Canadian companies are leading the way, but they need support. <a href="https://www.quantumindustrycanada.ca/">Quantum Industry Canada</a> boasts of more than 30 member companies. Vancouver is home to <a href="https://www.dwavesys.com/company/about-d-wave/">the pioneering D-Wave</a> and <a href="https://photonic.com/about-photonic/">Photonic Inc.</a>, the company I founded to commercialize silicon quantum technologies. More than <a href="https://www.mckinsey.com/%7E/media/mckinsey/featured%20insights/the%20rise%20of%20quantum%20computing/quantum%20technology%20monitor/2021/mckinsey-quantum-technology-monitor-202109.pdf">$650 million was invested in Canadian startups between 2001 and 2021</a>. On a per capita basis, this is far beyond the $2.1 billion invested in U.S. companies over the same period.</p>
<p>What early quantum companies need most is customers: early, major procurement contracts, or <a href="https://www.darpa.mil/about-us/what-darpa-does">DARPA-like moonshot contracts</a>. Without these contracts, the entire Canadian quantum industry will slip away into other jurisdictions that focus investment and procurement on domestic bidders, like what is happening in <a href="https://doi.org/10.1088/2058-9565/ab042d">the European Union</a> and <a href="https://www.whitehouse.gov/briefing-room/statements-releases/2022/05/04/fact-sheet-president-biden-announces-two-presidential-directives-advancing-quantum-technologies/">the U.S.</a></p>
<h2>Learning from the past</h2>
<p>Canada has an opportunity to break out of its pattern of inventing transformative technology, but not reaping the rewards. This is what happened with the invention of the transistor.</p>
<p>The <a href="https://hackaday.com/2018/12/11/julius-lilienfeld-and-the-first-transistor/">first transistor patent was actually filed in Canada</a> by Canadian-Hungarian physicist Julius Edgar Lilienfeld, 20 years before the Bell Labs demonstration. Canada was also one of the places where <a href="https://www.bce.ca/about-bce/history/timeline">Alexander Graham Bell</a> worked to develop and patent the telephone. </p>
<p>Despite this, the transistor was commercialized in the U.S. and led to the country’s <a href="https://www.ibisworld.com/industry-statistics/market-size/semiconductor-circuit-manufacturing-united-states">US$63 billion semiconductor industry</a>. Bell commercialized the telephone through <a href="https://www.nytimes.com/interactive/2016/02/12/technology/att-history.html">The Bell Telephone Company, which eventually became AT&T</a>.</p>
<p>Canada is poised to make even greater contributions to quantum technology. Much existing technology has been invented here in Canada — including quantum cryptography, <a href="https://sciencebusiness.net/news/canada-lays-groundwork-become-powerhouse-quantum-technology">which was co-invented by University of Montreal professor Gilles Brassard</a>. Instead of repeating its past mistakes, Canada should act now to secure the success of the quantum technology industry.</p><img src="https://counter.theconversation.com/content/189674/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephanie Simmons is the founder and Chief Quantum Officer at Photonic Inc. She is an Associate Professor, Canada Research Chair, and CIFAR Fellow, based out of the Department of Physics at Simon Fraser University (SFU). </span></em></p>Canada is well positioned to gain far-reaching economic and social benefits from the rapidly developing quantum industry, but it must act now to secure its success.Stephanie Simmons, Associate Professor, SFU and Tier 2 Canada Research Chair in Silicon Quantum Technologies, Simon Fraser UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1919402022-10-07T01:46:53Z2022-10-07T01:46:53ZHow philosophy turned into physics – and reality turned into information<figure><img src="https://images.theconversation.com/files/488677/original/file-20221007-21010-xxbv1k.jpg?ixlib=rb-1.1.0&rect=19%2C25%2C4229%2C2783&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/-SmCKTIcH5E">Daniels Joffe / Unsplash</a></span></figcaption></figure><p>The Nobel Prize in physics this year has been <a href="https://www.nobelprize.org/prizes/physics/2022/summary/">awarded</a> “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”.</p>
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<p>
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<strong>
Read more:
<a href="https://theconversation.com/nobel-prize-physicists-share-prize-for-insights-into-the-spooky-world-of-quantum-mechanics-191884">Nobel prize: physicists share prize for insights into the spooky world of quantum mechanics</a>
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<p>To understand what this means, and why this work is important, we need to understand how these experiments settled a long-running debate among physicists. And a key player in that debate was an Irish physicist named <a href="https://en.wikipedia.org/wiki/John_Stewart_Bell">John Bell</a>.</p>
<p>In the 1960s, Bell figured out how to translate a philosophical question about the nature of reality into a physical question that could be answered by science – and along the way broke down the distinction between <em>what we know</em> about the world and how the world <em>really is</em>.</p>
<h2>Quantum entanglement</h2>
<p>We know that quantum objects have properties we don’t usually ascribe to the objects of our ordinary lives. Sometimes light is a wave, sometimes it’s a particle. Our fridge never does this.</p>
<p>When attempting to explain this sort of unusual behaviour, there are two broad types of explanation we can imagine. One possibility is that we perceive the quantum world clearly, just as it is, and it just so happens to be unusual. Another possibility is that the quantum world is just like the ordinary world we know and love, but our view of it is distorted, so we can’t see quantum reality clearly, as it is.</p>
<p>In the early decades of the 20th century, physicists were divided about which explanation was right. Among those who thought the quantum world just is unusual were figures such as <a href="https://en.wikipedia.org/wiki/Werner_Heisenberg">Werner Heisenberg</a> and <a href="https://en.wikipedia.org/wiki/Niels_Bohr">Niels Bohr</a>. Among those who thought the quantum world must be just like the ordinary world, and our view of it is simply foggy, were <a href="https://en.wikipedia.org/wiki/Albert_Einstein">Albert Einstein</a> and <a href="https://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinger">Erwin Schrödinger</a>.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-quantum-entanglement-a-physicist-explains-the-science-of-einsteins-spooky-action-at-a-distance-191927">What is quantum entanglement? A physicist explains the science of Einstein’s ‘spooky action at a distance’</a>
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<p>At the heart of this division is an unusual prediction of quantum theory. According to the theory, the properties of certain quantum systems that interact remain dependent on each other – even when the systems have been moved a great distance apart.</p>
<p>In 1935, the same year he devised his <a href="https://www.jstor.org/stable/986572">famous thought experiment</a> involving a cat trapped in a box, Schrödinger coined the term “entanglement” for this phenomenon. He argued it is absurd to believe the world works this way.</p>
<h2>The problem with entanglement</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=868&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=868&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=868&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1091&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1091&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488669/original/file-20221006-12631-77ng4x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1091&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Niels Bohr (left) and Albert Einstein (right) argued for many years over whether the world was really as fuzzy and strange as quantum mechanics suggested.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Albert_Einstein#/media/File:Niels_Bohr_Albert_Einstein_by_Ehrenfest.jpg">Paul Ehrenfest</a></span>
</figcaption>
</figure>
<p>If entangled quantum systems really remain connected even when they are separated by large distances, it would seem they are somehow communicating with each other instantaneously. But this sort of connection is not allowed, according to Einstein’s theory of relativity. Einstein called this idea “spooky action at a distance”.</p>
<p>Again in 1935, Einstein, along with two colleagues, devised <a href="https://journals.aps.org/pr/abstract/10.1103/PhysRev.47.777">a thought experiment</a> that showed quantum mechanics can’t be giving us the whole story on entanglement. They thought there must be something more to the world that we can’t yet see.</p>
<p>But as time passed, the question of how to interpret quantum theory became an academic footnote. The question seemed too philosophical, and in the 1940s many of the brightest minds in quantum physics were busy using the theory for a very practical project: building the atomic bomb.</p>
<p>It wasn’t until the 1960s, when Irish physicist John Bell turned his mind to the problem of entanglement, that the scientific community realised this seemingly philosophical question could have a tangible answer.</p>
<h2>Bell’s theorem</h2>
<p>Using a simple entangled system, Bell <a href="https://journals.aps.org/ppf/abstract/10.1103/PhysicsPhysiqueFizika.1.195">extended</a> Einstein’s 1935 thought experiment. He showed there was no way the quantum description could be incomplete while prohibiting “spooky action at a distance” and still matching the predictions of quantum theory.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=748&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=748&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488670/original/file-20221006-18-ox9h0a.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=748&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 in his office at CERN in Switzerland.</span>
<span class="attribution"><a class="source" href="https://cds.cern.ch/record/1823944">CERN</a></span>
</figcaption>
</figure>
<p>Not great news for Einstein, it seems. But this was not an instant win for his opponents. </p>
<p>This is because it was not evident in the 1960s whether the predictions of quantum theory were indeed correct. To really prove Bell’s point, someone had to put this philosophical argument about reality, transformed into a real physical system, to an experimental test.</p>
<p>And this, of course, is where two of this year’s Nobel laureates enter the story. First <a href="https://www.caltech.edu/about/news/proving-that-quantum-entanglement-is-real">John Clauser</a>, and then <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.47.460">Alain Aspect</a>, performed the experiments on Bell’s proposed system that ultimately showed the predictions of quantum mechanics to be accurate. As a result, unless we accept “spooky action at a distance”, there is no further account of entangled quantum systems that can describe the observed quantum world.</p>
<h2>So, Einstein was wrong?</h2>
<p>It is perhaps a surprise, but these advances in quantum theory appear to have shown Einstein to be wrong on this point. That is, it seems we do not have a foggy view of a quantum world that is just like our ordinary world.</p>
<p>But the idea that we perceive clearly an inherently unusual quantum world is likewise too simplistic. And this provides one of the key philosophical lessons of this episode in quantum physics.</p>
<p>It is no longer clear we can reasonably talk about the quantum world beyond our scientific description of it – that is, beyond the <em>information</em> we have about it.</p>
<p>As this year’s third Nobel laureate, <a href="https://www.nature.com/articles/438743a">Anton Zeilinger</a>, put it:</p>
<blockquote>
<p>the distinction between reality and our knowledge of reality, between reality and information, cannot be made. There is no way to refer to reality without using the information we have about it.</p>
</blockquote>
<p>This distinction, which we commonly assume to underpin our ordinary picture of the world, is now irretrievably blurry. And we have John Bell to thank.</p>
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Read more:
<a href="https://theconversation.com/better-ai-unhackable-communication-spotting-submarines-the-quantum-tech-arms-race-is-heating-up-179482">Better AI, unhackable communication, spotting submarines: the quantum tech arms race is heating up</a>
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<img src="https://counter.theconversation.com/content/191940/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Evans receives funding from the Australian Research Council and the Foundational Questions Institute.</span></em></p>Quantum mechanics raised tough philosophical questions about the nature of the world – and a physicist named John Bell figured out how experiments could answer them.Peter Evans, Lecturer, The University of QueenslandLicensed 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/1918842022-10-04T13:15:46Z2022-10-04T13:15:46ZNobel prize: physicists share prize for insights into the spooky world of quantum mechanics<figure><img src="https://images.theconversation.com/files/488060/original/file-20221004-16-nzmxg7.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6386%2C4260&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Members of the Nobel Committee for Physics announce the winners of the 2022 Nobel Prize in Physics (L-R on the screen) Alain Aspect, John F. Clauser and Anton Zeilinger</span> <span class="attribution"><a class="source" href="https://www.alamy.com/secretary-general-of-the-royal-swedish-academy-of-sciences-hans-ellegren-c-eva-olsson-l-and-thors-hans-hansson-r-members-of-the-nobel-committee-for-physics-announce-the-winners-of-the-2022-nobel-prize-in-physics-l-r-on-the-screen-alain-aspect-john-f-clauser-and-anton-zeilinger-during-a-press-conference-at-the-royal-swedish-academy-of-sciences-in-stockholm-sweden-on-october-4-2022photo-jonas-ekstromer-tt-code-10030-image484884852.html?imageid=AD349CFE-58DF-4ECA-8C06-D7FFAB83D939&p=0&pn=1&searchId=eb5f38dd260158c9c72eaeb3929f9ed1&searchtype=0">TT News Agency / Alamy Stock Photo</a></span></figcaption></figure><p>The 2022 Nobel prize in physics <a href="https://www.nobelprize.org/prizes/physics/2022/press-release/">has been awarded</a> to a trio of scientists for pioneering experiments in quantum mechanics, the theory covering the micro-world of atoms and particles. </p>
<p>Alain Aspect from Université Paris-Saclay in France, John Clauser from J.F. Clauser & Associates in the US, and Anton Zeilinger from University of Vienna in Austria, will share the prize sum of 10 million Swedish kronor (US$915,000) “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”.</p>
<p>The world of quantum mechanics appears very odd indeed. In school, we are taught that we can use equations in physics to predict exactly how things will behave in the future – where a ball will go if we roll it down a hill, for example. </p>
<p>Quantum mechanics is different from this. Rather than predicting individual outcomes, it tells us the probability of finding subatomic particles in particular places. A particle can actually be in several places at the same time, before “picking” one location at random when we measure it.</p>
<p>Even the great Albert Einstein himself was unsettled by this – to the point where he was <a href="https://theconversation.com/einsteins-two-mistakes-139003">convinced that it was wrong</a>. Rather than outcomes being random, he thought there must be some “hidden variables” – forces or laws that we can’t see – which predictably influence the results of our measurements.</p>
<p>Some physicists, however, embraced the consequences of quantum mechanics. John Bell, a physicist from Northern Ireland, made an important breakthrough in 1964, <a href="https://theconversation.com/quantum-weirdness-passes-the-atomic-walk-test-37495">devising a theoretical test</a> to show that the hidden variables Einstein had in mind don’t exist. </p>
<p>According to quantum mechanics, particles can be “entangled”, spookily connected so that if you manipulate one then you automatically and immediately also manipulate the other. If this spookiness – particles far apart mysteriously influencing each other instantaneously – were to be explained by the particles communicating with each other through hidden variables, it would require faster-than-light communication between the two, which Einstein’s theories forbid.</p>
<p>Quantum entanglement is a challenging concept to understand, essentially linking the properties of particles no matter how far apart they are. Imagine a light bulb that emits two photons (light particles) that travel in opposite directions away from it. </p>
<p>If these photons are entangled, then they can share a property, such as their polarisation, no matter their distance. Bell imagined doing experiments on these two photons separately and comparing the results of them to prove that they were entangled (truly and mysteriously linked).</p>
<p>Clauser put Bell’s theory into practice at a time when doing experiments on single photons was almost unthinkable. In 1972, just eight years after Bell’s famous thought experiment, Clauser showed that light could indeed be entangled. </p>
<p>While <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.28.938">Clauser’s results</a> were groundbreaking, there were a few alternative, more exotic explanations for the results <a href="https://www.sciencedirect.com/science/article/abs/pii/0375960175906556?via%3Dihub">he obtained</a>. </p>
<p>If light didn’t behave quite as the physicists thought, perhaps his results could be explained without entanglement. These explanations are known as loopholes in Bell’s test, and Aspect was the first to challenge this.</p>
<p>Aspect came up with an ingenious experiment to rule out one of the most important potential loopholes in Bell’s test. He showed that the entangled photons in the experiment aren’t actually communicating with each other through hidden variables to decide the outcome of Bell’s test. This means <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.49.91">they really are spookily linked</a>.</p>
<p>In science it is incredibly important to test the concepts that we believe to be correct. And few have played a more important role in doing this than Aspect. Quantum mechanics has been tested time and again over the past century and survived unscathed.</p>
<h2>Quantum technology</h2>
<p>At this point, you may be forgiven for wondering why it matters how the microscopic world behaves, or that photons can be entangled. This is where the vision of Zeilinger really shines.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488063/original/file-20221004-18-4r0onq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Austrian quantum physicist Anton Zeilinger stands in his office at the Institute of Quantum Optics and Quantum Information (IQOQI)</span>
<span class="attribution"><a class="source" href="https://www.alamy.com/viena-austria-02nd-july-2018-02072018-austria-vienna-the-austrian-quantum-physicist-anton-zeilinger-stands-in-his-office-at-the-institute-of-quantum-optics-and-quantum-information-iqoqi-of-the-austrian-academy-of-sciences-aw-zeilinger-is-one-of-the-worlds-leading-minds-working-on-a-completely-new-way-of-transmitting-information-by-means-of-a-spooky-remote-effect-0-credit-matthias-rderdpaalamy-live-news-image217025930.html?imageid=5A336ADB-5DA5-4356-B202-AAEDE6046061&p=173981&pn=1&searchId=926a8f4a3b6a4b4af978223e04b94dc0&searchtype=0">dpa picture alliance / Alamy Stock Photo</a></span>
</figcaption>
</figure>
<p>We once harnessed our knowledge of classical mechanics to build machines, to make factories, leading to the industrial revolution. Knowledge of the behaviour of electronics and semiconductors has driven the digital revolution. </p>
<p>But understanding quantum mechanics allows us to exploit it, to build devices that are capable of doing new things. Indeed, many believe that it will drive the next revolution, of quantum technology.</p>
<p>Quantum entanglement <a href="https://theconversation.com/scientists-discover-how-to-harness-the-power-of-quantum-spookiness-by-entangling-clouds-of-atoms-95612">can be harnessed in computing</a> to process information in ways that were not possible before. Detecting small changes in entanglement can allow sensors to detect things with greater precision than ever before. Communicating with entangled light can also guarantee security, as measurements of quantum systems can reveal the presence of the eavesdropper.</p>
<p>Zeilinger’s work paved the way for the quantum technological revolution by showing how it is possible to link a series of entangled systems together, to build the quantum equivalent of a network. </p>
<p>In 2022, these applications of quantum mechanics are not science fiction. We have the first <a href="https://www.ibm.com/quantum">quantum computers</a>. The Micius satellite <a href="https://www.scientificamerican.com/article/china-reaches-new-milestone-in-space-based-quantum-communications/">uses entanglement</a> to enable secure communications across the world. And <a href="https://theconversation.com/better-ai-unhackable-communication-spotting-submarines-the-quantum-tech-arms-race-is-heating-up-179482">quantum sensors</a> are being used in applications from medical imaging to detecting submarines.</p>
<p>Ultimately, the 2022 Nobel panel have recognised the importance of the practical foundations producing, manipulating and testing quantum entanglement and the revolution it is helping to drive.</p>
<p>I am pleased to see this trio receiving the award. In 2002, I started a PhD at the University of Cambridge that was inspired by their work. The aim of my project was to make a simple semiconductor device to generate entangled light. </p>
<p>This was to greatly simplify the equipment needed to do quantum experiments and to allow practical devices for real-world applications to be built. Our <a href="https://www.nature.com/articles/nature04446">work was successful</a> and it amazes and excites me to see the leaps and bounds that have been made in the field since.</p><img src="https://counter.theconversation.com/content/191884/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Young does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The discovery that particles can be spookily connected has lead to a technological revolution.Robert Young, Professor of Physics and Director of the Lancaster Quantum Technology Centre, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1812682022-04-14T05:55:33Z2022-04-14T05:55:33ZTime might not exist, according to physicists and philosophers – but that’s okay<figure><img src="https://images.theconversation.com/files/458074/original/file-20220414-12-s9hvgo.jpg?ixlib=rb-1.1.0&rect=17%2C2%2C1979%2C1119&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/composition-space-time-flight-spiral-roman-1221181900">Shutterstock</a></span></figcaption></figure><p>Does time exist? The answer to this question may seem obvious: of course it does! Just look at a calendar or a clock.</p>
<p>But developments in physics suggest the non-existence of time is an open possibility, and one that we should take seriously.</p>
<p>How can that be, and what would it mean? It’ll take a little while to explain, but don’t worry: even if time doesn’t exist, our lives will go on as usual.</p>
<h2>A crisis in physics</h2>
<p>Physics is in crisis. For the past century or so, we have explained the universe with two wildly successful physical theories: general relativity and quantum mechanics.</p>
<p>Quantum mechanics describes how things work in the incredibly tiny world of particles and particle interactions. <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">General relativity</a> describes the big picture of gravity and how objects move.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">How Einstein's general theory of relativity killed off common-sense physics</a>
</strong>
</em>
</p>
<hr>
<p>Both theories work extremely well in their own right, but the two are thought to conflict with one another. Though the exact nature of the conflict is controversial, scientists generally agree both theories need to be replaced with a new, more general theory. </p>
<p>Physicists want to produce a theory of “quantum gravity” that <em>replaces</em> general relativity and quantum mechanics, while capturing the extraordinary success of both. Such a theory would explain how gravity’s big picture works at the miniature scale of particles.</p>
<h2>Time in quantum gravity</h2>
<p>It turns out that producing a theory of quantum gravity is extraordinarily difficult. </p>
<p>One attempt to overcome the conflict between the two theories is <a href="https://theconversation.com/explainer-string-theory-2983">string theory</a>. String theory replaces particles with strings vibrating in as many as 11 dimensions. </p>
<p>However, string theory faces a further difficulty. String theories provide a range of models that describe a universe broadly like our own, and they don’t really make any clear predictions that can be tested by experiments to figure out which model is the right one. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-string-theory-2983">Explainer: String theory</a>
</strong>
</em>
</p>
<hr>
<p>In the 1980s and 1990s, many physicists became dissatisfied with string theory and came up with a range of new mathematical approaches to quantum gravity. </p>
<p>One of the most prominent of these is <a href="https://www.space.com/loop-quantum-gravity-space-time-quantized">loop quantum gravity</a>, which proposes that the fabric of space and time is made of a network of extremely small discrete chunks, or “loops”.</p>
<p>One of the remarkable aspects of loop quantum gravity is that it appears to eliminate time entirely. </p>
<p>Loop quantum gravity is not alone in abolishing time: a number of other approaches also seem to remove time as a fundamental aspect of reality. </p>
<h2>Emergent time</h2>
<p>So we know we need a new physical theory to explain the universe, and that this theory might not feature time.</p>
<p>Suppose such a theory turns out to be correct. Would it follow that time <em>does not exist</em>? </p>
<p>It’s complicated, and it depends what we mean by <em>exist</em>.</p>
<p>Theories of physics don’t include any tables, chairs, or people, and yet we still accept that tables, chairs and people exist.</p>
<figure class="align-center ">
<img alt="A person walking beneath a large clock swinging from a rope." src="https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/458075/original/file-20220414-24-y990i8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If time isn’t a fundamental property of the universe, it may still ‘emerge’ from something more basic.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/surreal-view-man-walking-on-pavement-1097947538">Shutterstock</a></span>
</figcaption>
</figure>
<p>Why? Because we assume that such things exist at a higher level than the level described by physics. </p>
<p>We say that tables, for example, “emerge” from an underlying physics of particles whizzing around the universe. </p>
<p>But while we have a pretty good sense of how a table might be made out of fundamental particles, we have no idea how time might be “made out of” something more fundamental.</p>
<p>So unless we can come up with a good account of how <a href="https://www.preposterousuniverse.com/blog/2013/10/18/is-time-real/">time emerges</a>, it is not clear we can simply assume time exists. </p>
<p>Time might not exist at any level.</p>
<h2>Time and agency</h2>
<p>Saying that time does not exist at any level is like saying that there are no tables at all.</p>
<p>Trying to get by in a world without tables might be tough, but managing in a world without time seems positively disastrous.</p>
<p>Our entire lives are built around time. We plan for the future, in light of what we know about the past. We hold people morally accountable for their past actions, with an eye to reprimanding them later on.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/time-is-but-a-dream-or-is-it-928">Time is but a dream ... or is it?</a>
</strong>
</em>
</p>
<hr>
<p>We believe ourselves to be <em>agents</em> (entities that can <em>take action</em>) in part because we can plan to act in a way that will bring about changes in the future. </p>
<p>But what’s the point of acting to bring about a change in the future when, in a very real sense, there is no future to act for?</p>
<p>What’s the point of punishing someone for a past action, when there is no past and so, apparently, no such action?</p>
<p>The discovery that time does not exist would seem to bring the entire world to a grinding halt. We would have no reason to get out of bed. </p>
<h2>Business as usual</h2>
<p>There is a way out of the mess. </p>
<p>While physics might eliminate time, it seems to leave <em>causation</em> intact: the sense in which one thing can bring about another. </p>
<p>Perhaps what physics is telling us, then, is that causation and not time is the basic feature of our universe. </p>
<p>If that’s right, then agency can still survive. For it is possible to reconstruct a sense of agency entirely in causal terms. </p>
<p>At least, that’s what Kristie Miller, Jonathan Tallant and I argue in <a href="https://global.oup.com/academic/product/out-of-time-9780192864888?facet_narrowbypubdate_facet=Next%203%20months&lang=en&cc=kw">our new book</a>.</p>
<p>We suggest the discovery that time does not exist may have no direct impact on our lives, even while it propels physics into a new era.</p><img src="https://counter.theconversation.com/content/181268/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>Cutting-edge theories of physics suggest time may not be real – but even if they’re right, life can still go on as usual.Sam Baron, Associate Professor, Philosophy of Science, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1780812022-04-06T13:31:53Z2022-04-06T13:31:53ZCurious Kids: how likely is it that there are parallel universes and other Earths?<figure><img src="https://images.theconversation.com/files/456084/original/file-20220404-17-sni8rd.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C3714%2C2383&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/parallel-universe-view-above-shanghai-1118702738">MingzhePhoton/Shutterstock</a></span></figcaption></figure><p><strong>How likely is it that there are other Earths or that the multiverse exists? – Tasneem, aged 16, Indore, India</strong></p>
<p>In fiction and in films such as <a href="https://edition.cnn.com/2019/01/20/opinions/science-behind-spider-man-into-the-spider-verse-lincoln/index.html">Spiderman: Into the Spider-Verse</a>, parallel universes – also called <a href="https://www.space.com/32728-parallel-universes.html">the multiverse</a> – exist alongside our own, with anything from small differences in events to entirely different rules of physics. It is an exciting and fascinating idea. </p>
<p>Physicists have given the question of whether parallel universes could exist a lot of thought – and have come up with quite <a href="https://space.mit.edu/home/tegmark/multiverse.pdf">a few theories</a>. </p>
<h2>Infinite expanse</h2>
<p>One popular theory relies on something physicists already know about. The universe is expanding. This means galaxies far from Earth are moving away from us. This process is called <a href="https://www.bbc.co.uk/news/av/science-environment-26623114">cosmic inflation</a>.</p>
<hr>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series by <a href="https://theconversation.com/uk">The Conversation</a> that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskids@theconversation.com">curiouskids@theconversation.com</a> and make sure you include the asker’s first name, age and town or city. We won’t be able to answer every question, but we’ll do our very best.</em></p>
<hr>
<p>What’s more, the further away from Earth you get, the faster the universe is expanding. At some point the universe is expanding too fast for light to ever reach us from some very far away galaxies. This means there is a point in the universe that we cannot see past.</p>
<p>That doesn’t mean there is nothing there, though. There are still more galaxies beyond this edge – but we will never be able to see them. Some physicists describe the parts of the universe beyond this edge as a separate, parallel universe. This theory is popular, as it doesn’t require any special physics or changes in our current understanding of the universe.</p>
<h2>Universe bubbles</h2>
<p>Another theory about parallel universes relies on cosmic inflation happening more than once. The idea goes that when inflation occurred immediately after the Big Bang, it happened in multiple places. This caused <a href="https://www.wired.com/story/how-universes-might-bubble-up-and-collide/">separate universe bubbles</a> to inflate, and in some cases certain types of matter ended up in one bubble rather than another. This means in some bubbles the physical rules which affect how things work might be different. </p>
<figure class="align-center ">
<img alt="Pink and blue bubbles" src="https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/456090/original/file-20220404-13-o5vu5o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In the universe bubbles theory, each bubble contains a separate universe.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/abstract-background-about-water-space-multicolored-1879344409">Miramiska/Shutterstock</a></span>
</figcaption>
</figure>
<p>Each bubble is still infinite in size, yet separate from our universe. Physicists find this theory interesting, as it could explain why we haven’t found certain things that, scientifically, we would expect to see in our universe. This includes <a href="https://www.youtube.com/watch?v=dw1sekg6SUY">magnetic monopoles</a> – one-sided magnetic fields which only have a negative or positive side. They might exist in another universe bubble instead.</p>
<h2>Many worlds</h2>
<p>The last theory requires us to think about a type of science called <a href="https://scienceissimple.com/quantum-mechanics/">quantum mechanics</a>. Quantum mechanics is all about the probability of tiny particles doing something. If a tiny particle is fired at a wall, it might bounce off it – or travel right through it. Quantum mechanics tells us which event is more likely. However, there is nothing in the maths that says that only one of the events must occur. Both of these things might happen at once.</p>
<p>But we would only see one of these things happen. So, if saw the particle bounce off the wall, it might have also, at the same time, tunnelled through the wall – just in another universe, not our one.</p>
<figure class="align-center ">
<img alt="Multiple Earths in space" src="https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/456089/original/file-20220404-19-9kqhw7.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">
<figcaption>
<span class="caption">In the many worlds theory, lots of other Earths could exist. Earth textures provided by Nasa.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/alignment-array-many-earth-planet-outer-1799052499">MattLphotography/Shutterstock</a></span>
</figcaption>
</figure>
<p>In this parallel universe, everything would be exactly the same as in our universe, except for one tiny change. In that universe, the particle travelled through the wall, instead of bouncing off it. The many worlds theory suggests that this happens every time a quantum mechanical reaction occurs, creating <a href="https://www.sciencefocus.com/science/the-parallel-worlds-of-quantum-mechanics/">a separate parallel universe</a> each time.</p>
<p>Once the parallel universe is created, however, we have no way of interacting with it. So while this theory is exciting, we have no way to test it.</p>
<h2>So is there another Earth?</h2>
<p>In the many worlds theory, there is plenty of room for another Earth. Each quantum reaction on our planet would create another parallel universe with another Earth. </p>
<p>Things get trickier in the other theories – of the universe bubbles and the infinite expanse. If there are infinite universe bubbles and infinite space, that means there is a chance that exactly the same kinds of events repeated themselves in another bubble or elsewhere in the expanse of space to create another Earth. </p>
<p>When you do the maths, though, it quickly becomes unlikely. For just 1,000 particles to interact in <a href="https://www.forbes.com/sites/startswithabang/2016/11/18/is-there-another-you-out-there-in-a-parallel-universe/">exactly the same way twice</a>, the chance would be 1 in 10<sup>2477.</sup> The number 10<sup>2477</sup> is a 10 followed by 2477 zeros, which is an incredibly big number. There are far more particles in the universe than 1,000, so the chances for another Earth are not in our favour.</p>
<p>Unfortunately, we don’t know if these parallel universes exist. Or at least, we don’t at the moment. Physicists are trying to find ways to <a href="https://theconversation.com/the-theory-of-parallel-universes-is-not-just-maths-it-is-science-that-can-be-tested-46497">test these theories</a>, but it is very difficult. For now, they remain just theories. But who knows – perhaps scientists in another universe have already figured it out.</p><img src="https://counter.theconversation.com/content/178081/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brianna Smart 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>Scientists have come up with a number of theories about the multiverse.Brianna Smart, Research Associate in the Department of Physics, Astronomy and Mathematics, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.