tag:theconversation.com,2011:/us/topics/subatomic-particles-15502/articlesSubatomic particles – The Conversation2023-05-15T12:33:56Ztag: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>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/7kb1VT0J3DE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<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>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/8ROHpZ0A70I?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<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>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0SPD2r0xV8k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<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/1142112019-03-27T12:48:45Z2019-03-27T12:48:45ZExotic particles containing five quarks discovered at the Large Hadron Collider<figure><img src="https://images.theconversation.com/files/265980/original/file-20190326-36270-m9m2v3.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Illustration of the possible layout of the quarks in a pentaquark particle. </span> <span class="attribution"><span class="source">Daniel Dominguez/CERN</span></span></figcaption></figure><p>Everything you see around you is made up of <a href="https://theconversation.com/explainer-what-are-fundamental-particles-38339">elementary particles</a> called quarks and leptons, which can combine to form bigger particles such as protons or atoms. But that doesn’t make them boring – these subatomic particles can also combine in exotic ways we’ve never spotted. Now CERN’s LHCb collaboration <a href="https://home.cern/news/news/physics/lhcb-experiment-discovers-new-pentaquark">has announced the discovery</a> of a clutch of new particles dubbed “pentaquarks”. The results can help unveil many mysteries of the theory of quarks, a key part of the standard model of particle physics.</p>
<p>Quarks were <a href="https://home.cern/news/news/physics/fifty-years-quarks">first proposed</a> to explain the untidy slew of new particles discovered in cosmic ray and collider experiments in the mid 20th century. This growing “zoo” of apparently fundamental particles caused consternation among physicists, who have a natural bias towards simplicity and order – and hate having to remember more than a few basic principles. The famous Italian physicist <a href="https://www.nobelprize.org/prizes/physics/1938/fermi/biographical/">Enrico Fermi</a> captured the mood of his colleagues <a href="https://en.wikiquote.org/wiki/Enrico_Fermi">when he said</a> “Young man, if I could remember the names of all these particles, I would have been a botanist”.</p>
<p>Fortunately, in the 1960s, the American physicist <a href="https://www.nobelprize.org/prizes/physics/1969/gell-mann/biographical/">Murray Gell-Mann</a> noticed patterns in the particle zoo, similar to those spotted by <a href="https://www.chemistryworld.com/features/the-father-of-the-periodic-table/3009828.article">Dimitri Mendeleev</a> when he drew up the periodic table of the chemical elements. Just as the periodic table implied the existence of things smaller than atoms, Gell-Mann’s theory suggested the existence of a new class of fundamental particles. Particle physicists were eventually able to explain the hundreds of particles in the zoo as being made up of a much smaller number of truly fundamental particles called quarks.</p>
<h2>Mystery hadrons</h2>
<p>There are six types of quarks in the standard model – down, up, strange, charm, bottom and top. These also have “antimatter” companions – it is believed that every particle has an antimatter version that is virtually identical to itself, but with the opposite charge. Quarks and antiquarks <a href="https://theconversation.com/cern-study-sheds-light-on-one-of-physics-biggest-mysteries-why-theres-more-matter-than-antimatter-113947">get bound together</a> to make particles known as hadrons. </p>
<p>According to Gell-Mann’s model, there are two broad classes of hadrons. One is particles made of three quarks called <a href="http://www.particleadventure.org/hadrons.html">baryons</a> (which include the protons and neutrons that make up the atomic nucleus) and the other particles made of a quark and an antiquark known as <a href="https://www.britannica.com/science/meson">mesons</a>.</p>
<p>Until recently, baryons and mesons were the only types of hadrons that had been seen in experiments. However, back in the 1960s, Gell-Mann also raised the possibility of more exotic combinations of quarks, such as tetraquarks (two quarks and two antiquarks) and pentaquarks (four quarks and one antiquark). </p>
<p>In 2014, LHCb, which runs one of the four giant experiments at CERN’s Large Hadron Collider, <a href="https://theconversation.com/quirky-quark-combination-creates-exotic-new-particle-25465">published a result</a> showing that the snappily named Z(4430)<sup>+</sup> particle was a tetraquark. This started a flurry of interest in new exotic hadrons. Then, in 2015, LHCb <a href="https://theconversation.com/heres-what-you-need-to-know-about-the-large-hadron-colliders-latest-discovery-pentaquarks-44721">announced the discovery</a> of the first ever pentaquark, adding a brand new class of particle to the hadron family.</p>
<p>The results presented by LHCb today expand upon that first pentaquark discovery by finding additional such particles. This was possible thanks to a big chunk of new data recorded during the second run of the Large Hadron Collider. <a href="https://www.linkedin.com/in/liming-zhang-ab12b73b/">Liming Zhang</a>, an associate professor at Tsinghua University in Beijing and one of the physicists who made the measurement, said that “we now have ten times more data than in 2015, which allows us to see more exciting and finer structures than we could before.” When Liming and his colleagues examined the original pentaquark discovered in 2015, they were surprised to find that it had split in two. The original pentaquark was actually two separate pentaquark particles that had such similar masses that they originally looked like a single particle. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264993/original/file-20190320-93063-r7pdv4.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">LHCb.</span>
<span class="attribution"><span class="source">Maximilien Brice et al./CERN</span></span>
</figcaption>
</figure>
<p>As if two pentaquarks for the price of one wasn’t exciting enough, LHCb also found a third pentaquark with a slightly smaller mass than the other two. All three pentaquarks are made of one down quark, two up quarks, a charm quark and a charm antiquark.</p>
<p>The big question now is: what is the precise internal structure of these pentaquarks? One option is that they are truly made of five quarks, with all of them mixed together evenly within a single hadron. Another possibility is that the pentaquarks are really a baryon and a meson stuck together to form a loosely bound molecule, similar to the way that protons and neutrons bind together inside the atomic nucleus.</p>
<p><a href="http://thecollege.syr.edu/people/faculty/pages/phy/skwarnicki-tomasz.html">Tomasz Skwarnicki</a>, a professor of physics at Syracuse University in New York who also worked on the measurement, told me that the new companion state “is at a mass which offers hints about internal structure of pentaquarks”. The most likely option is that these pentaquarks are baryon-meson molecules, he added. To be absolutely sure, physicists will need more experimental data, as well as further studies from theorists, meaning that the story of these pentaquarks is far from over. </p>
<p>These results complete a week of exciting new announcements from LHCb, which included the discovery of a <a href="https://theconversation.com/cern-study-sheds-light-on-one-of-physics-biggest-mysteries-why-theres-more-matter-than-antimatter-113947">new kind of matter-antimatter asymmetry</a>. The LHC has yet to discover any particles beyond the standard model that could help to explain mysteries like dark matter, an invisible but unknown substance that makes up the majority of matter in the universe. </p>
<p>But these exciting measurements show that there is still lots to learn about the particles and forces of the standard model. It may be that our best chance of finding answers to the big questions facing fundamental physics in the 21st century lies in more detailed studies of the particles we already know about rather than discovering new ones. Either way, we still have a great deal to discover.</p><img src="https://counter.theconversation.com/content/114211/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Harry Cliff is a member of the LHCb Collaboration, though he was not directly involved in the work described in this article.</span></em></p>The LHCb experiment at CERN has discovered three new ‘pentaquark’ particles being created in high energy particle collisions at the Large Hadron Collider.Harry Cliff, Particle physicist, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1062202019-02-07T12:28:21Z2019-02-07T12:28:21ZLise Meitner – the forgotten woman of nuclear physics who deserved a Nobel Prize<figure><img src="https://images.theconversation.com/files/257317/original/file-20190205-86205-ff9763.jpg?ixlib=rb-1.1.0&rect=40%2C4%2C1556%2C1171&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lise Meitner was left off the publication that eventually led to a Nobel Prize for her colleague.</span> </figcaption></figure><p><a href="http://www.atomicarchive.com/Fission/Fission1.shtml">Nuclear fission</a> – the physical process by which very large atoms like uranium split into pairs of smaller atoms – is what makes <a href="https://www.atomicheritage.org/history/science-behind-atom-bomb">nuclear bombs</a> and <a href="http://www.world-nuclear.org/information-library/current-and-future-generation/outline-history-of-nuclear-energy.aspx">nuclear power plants</a> possible. But for many years, physicists believed it energetically impossible for atoms as large as uranium (atomic mass = 235 or 238) to be split into two.</p>
<p>That all changed on Feb. 11, 1939, with a <a href="https://www.nature.com/articles/143239a0">letter to the editor</a> of Nature – a premier international scientific journal – that described exactly how such a thing could occur and even named it fission. In that letter, physicist Lise Meitner, with the assistance of her young nephew <a href="http://www.atomicarchive.com/Bios/Frisch.shtml">Otto Frisch</a>, provided a physical explanation of how nuclear fission could happen.</p>
<p>It was a massive leap forward in nuclear physics, but today Lise Meitner remains obscure and largely forgotten. She was excluded from the victory celebration because she was a Jewish woman. Her story is a sad one.</p>
<h2>What happens when you split an atom</h2>
<p>Meitner based her fission argument on the “<a href="https://socratic.org/questions/how-does-the-liquid-drop-model-account-for-nuclear-fission">liquid droplet model</a>” of nuclear structure – a model that likened the forces that hold the atomic nucleus together to the surface tension that gives a water droplet its structure.</p>
<p>She noted that the surface tension of an atomic nucleus weakens as the charge of the nucleus increases, and could even approach zero tension if the nuclear charge was very high, as is the case for uranium (charge = 92+). The lack of sufficient nuclear surface tension would then allow the nucleus to split into two fragments when struck by a <a href="https://sciencenotes.org/neutron-definition-chemistry/">neutron</a> – a chargeless subatomic particle – with each fragment carrying away very high levels of kinetic energy. Meisner remarked: “The whole ‘fission’ process can thus be described in an essentially classical [physics] way.” Just that simple, right?</p>
<p>Meitner went further to explain how her scientific colleagues had gotten it wrong. When scientists bombarded uranium with neutrons, they believed the uranium nucleus, rather than splitting, captured some neutrons. These captured neutrons were then converted into positively charged protons and thus transformed the uranium into the incrementally larger elements on the <a href="https://www.livescience.com/25300-periodic-table.html">periodic table of elements</a> – the so-called “<a href="https://www.britannica.com/science/transuranium-element">transuranium</a>,” or beyond uranium, elements.</p>
<p>Some people were skeptical that neutron bombardment could produce transuranium elements, including <a href="https://www.atomicheritage.org/profile/irene-joliot-curie">Irene Joliot-Curie</a> – Marie Curie’s daughter – and Meitner. Joliot-Curie had found that one of these new alleged transuranium elements actually behaved chemically just like <a href="https://www.livescience.com/39623-facts-about-radium.html">radium</a>, the element her mother had discovered. Joliot-Curie suggested that it might be just radium (atomic mass = 226) – an element somewhat smaller than uranium – that was coming from the neutron-bombarded uranium.</p>
<p>Meitner had an alternative explanation. She thought that, rather than radium, the element in question might actually be <a href="https://www.livescience.com/37581-barium.html">barium</a> – an element with a chemistry very similar to radium. The issue of radium versus barium was very important to Meitner because barium (atomic mass = 139) was a possible fission product according to her split uranium theory, but radium was not – it was too big (atomic mass = 226).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=460&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=460&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257322/original/file-20190205-86198-76178y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=460&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a neutron bombards a uranium atom, the uranium nucleus splits into two different smaller nuclei.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Kernspaltung.svg">Stefan-Xp/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Meitner urged her chemist colleague <a href="https://www.atomicheritage.org/profile/otto-hahn">Otto Hahn</a> to try to further purify the uranium bombardment samples and assess whether they were, in fact, made up of radium or its chemical cousin barium. Hahn complied, and he found that Meitner was correct: the element in the sample was indeed barium, not radium. Hahn’s finding suggested that the uranium nucleus had split into pieces – becoming two different elements with smaller nuclei – just as Meitner had suspected.</p>
<h2>As a Jewish woman, Meitner was left behind</h2>
<p>Meitner should have been the hero of the day, and the physicists and chemists should have jointly published their findings and waited to receive the world’s accolades for their discovery of nuclear fission. But unfortunately, that’s not what happened.</p>
<p>Meitner had two difficulties: She was a Jew living as an exile in Sweden because of the Jewish persecution going on in Nazi Germany, and she was a woman. She might have overcome either one of these obstacles to scientific success, but both proved insurmountable.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=793&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=793&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=793&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=996&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=996&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257308/original/file-20190205-86195-ggd0rl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=996&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lise Meitner and Otto Hahn in Berlin, 1913.</span>
</figcaption>
</figure>
<p>Meitner had been working as Hahn’s academic equal when they were on the faculty of the Kaiser Wilhelm Institute in Berlin together. By all accounts they were close colleagues and friends for many years. When the Nazis took over, however, Meitner was forced to leave Germany. She took a position in Stockholm, and continued to work on nuclear issues with Hahn and his junior colleague Fritz Strassmann through regular correspondence. This working relationship, though not ideal, was still highly productive. The barium discovery was the latest fruit of that collaboration. </p>
<p>Yet when it came time to publish, Hahn knew that including a Jewish woman on the paper would cost him his career in Germany. So he <a href="https://doi.org/10.1007/BF01488241">published without her</a>, falsely claiming that the discovery was based solely on insights gleaned from his own chemical purification work, and that any physical insight contributed by Meitner played an insignificant role. All this despite the fact he wouldn’t have even thought to isolate barium from his samples had Meitner not directed him to do so.</p>
<p>Hahn had trouble explaining his own findings, though. In his paper, he put forth no plausible mechanism as to how uranium atoms had split into barium atoms. But Meitner had the explanation. So a few weeks later, Meitner wrote her famous fission letter to the editor, ironically explaining the mechanism of “Hahn’s discovery.”</p>
<p>Even that didn’t help her situation. The Nobel Committee awarded the <a href="https://www.nobelprize.org/prizes/chemistry/1944/summary/">1944 Nobel Prize in Chemistry</a> “for the discovery of the fission of heavy nuclei” to Hahn alone. Paradoxically, the word “fission” never appeared in Hahn’s original publication, as Meitner had been the first to coin the term in the letter published afterward. </p>
<p>A controversy has raged about the discovery of nuclear fission ever since, with <a href="https://www.ucpress.edu/book/9780520208605/lise-meitner">critics claiming</a> it represents one of the worst examples of blatant racism and sexism by the Nobel committee. Unlike another prominent female nuclear physicist whose career preceded her – <a href="https://www.nobelprize.org/prizes/chemistry/1911/marie-curie/facts/">Marie Curie</a> – Meitner’s contributions to nuclear physics were never recognized by the Nobel committee. She has been totally left out in the cold, and remains unknown to most of the public.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=561&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=561&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257320/original/file-20190205-86198-1nmuux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=561&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Meitner received the Enrico Fermi Award in 1966. Her nephew Otto Frisch is on the left.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/iaea_imagebank/4311592724">IAEA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>After the war, Meitner remained in Stockholm and became a Swedish citizen. Later in life, she decided to let bygones be bygones. She reconnected with Hahn, and the two octogenarians resumed their friendship. Although the Nobel committee never acknowledged its mistake, the slight to Meitner was partly mitigated in 1966 when the U.S. Department of Energy jointly awarded her, Hahn and Strassmann its prestigious <a href="https://science.energy.gov/fermi/">Enrico Fermi Award</a> “for pioneering research in the naturally occurring radioactivities and extensive experimental studies leading to the discovery of fission.” The two-decade late recognition came just in time for Meitner. She and Hahn died within months of each other in 1968; they were both 89 years old.</p><img src="https://counter.theconversation.com/content/106220/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy J. Jorgensen does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Left off publications due to Nazi prejudice, this Jewish woman lost her rightful place in the scientific pantheon as the discoverer of nuclear fission.Timothy J. Jorgensen, Director of the Health Physics and Radiation Protection Graduate Program and Associate Professor of Radiation Medicine, Georgetown UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/997202018-07-12T15:08:26Z2018-07-12T15:08:26ZThe IceCube observatory detects neutrino and discovers a blazar as its source<figure><img src="https://images.theconversation.com/files/227226/original/file-20180711-27039-129zs7l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">heic a</span> </figcaption></figure><p>About four billion years ago, when the planet Earth was still in its infancy, the axis of a black hole about one billion times more massive than the sun happened to be pointing right to where our planet was going to be on September 22, 2017. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=776&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=776&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=776&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=976&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=976&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227227/original/file-20180711-27015-xp3xne.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=976&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Blazar shoots neutrinos and gamma rays to Earth: Blazars are a type of active galactic nucleus with one of its jets pointing toward us. In this artistic rendering, a blazar emits both neutrinos and gamma rays that could be detected by the IceCube Neutrino Observatory as well as by other telescopes on Earth and in space.</span>
<span class="attribution"><span class="source">IceCube/NASA</span></span>
</figcaption>
</figure>
<p>Along the axis, a high-energy jet of particles sent photons and neutrinos racing in our direction at or near the speed of light. The IceCube Neutrino Observatory at the South Pole detected one of these subatomic particles – the IceCube-170922A neutrino – and traced it back to a small patch of sky in the constellation Orion and pinpointed the cosmic source: a flaring black hole the size of a billion suns, 3.7 billion light years from Earth, known as blazar TXS 0506+056. Blazars have been known about for some time. What wasn’t clear was that they could produce <a href="http://doi.org/10.1126/science.aat2890">high-energy neutrinos</a>. Even more exciting was such neutrinos had never before been traced to its source. </p>
<p>Finding the cosmic source of high-energy neutrinos for the first time, announced on July 12, 2018 by the National Science Foundation, marks the dawn of a new era of neutrino astronomy. Pursued in fits and starts since 1976, when pioneering physicists first tried to build a <a href="https://www.phys.hawaii.edu/%7Edumand/">large-scale high-energy neutrino detector off the Hawaiian coast</a>, IceCube’s discovery marks the triumphant conclusion of a long and difficult campaign by many hundreds of scientists and engineers – and simultaneously the birth of a completely new branch of astronomy.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=749&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=749&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=749&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=941&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=941&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227255/original/file-20180711-27015-1t34tjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=941&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The constellation of Orion, with a bullseye on the location of the blazar.</span>
<span class="attribution"><span class="source">Silvia Bravo Gallart/ Project_WIPAC_Communications</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The <a href="http://doi.org/10.1126/science.aat1378">detection of two distinct astronomical messengers</a> -– neutrinos and light –- is a powerful demonstration of how so-called multimessenger astronomy can provide the leverage we need to identify and understand some of the most energetic phenomena in the universe. Since its discovery as a neutrino source less than a year ago, blazar TXS 0506+056 has been the subject of intensive scrutiny. Its associated stream of neutrinos continues to provide deep insights into the physical processes at work near the black hole and its powerful jet of particles and radiation, beamed almost directly toward Earth from its location just off the shoulder of Orion. </p>
<p>As three scientists in a global team of physicists and astronomers involved in this remarkable discovery, we were drawn to participate in this experiment for its sheer audacity, for the physical and emotional challenge of working long shifts at in a brutally cold location while inserting expensive, sensitive equipment into holes drilled 1.5 miles deep in the ice and making it all work. And, of course, for the thrilling opportunity to be the first people to peer into a brand new kind of telescope and see what it reveals about the heavens.</p>
<h2>A remote, frigid neutrino detector</h2>
<p>At an altitude exceeding 9,000 feet and with average summertime temperatures rarely breaking a frigid -30 Celsius, the South Pole may not strike you as the ideal place to do anything, aside from bragging about visiting a place that is so sunny and bright you need sunscreen for your nostrils. On the other hand, once you realize that the altitude is due to a thick coat of ultrapure ice made from several hundred thousand years of pristine snowfall and that the low temperatures have kept it all nicely frozen, then it might not surprise you that for neutrino telescope builders, the scientific advantages outweigh the forbidding environment. The South Pole is now the home of the world’s largest neutrino detector, <a href="https://icecube.wisc.edu">IceCube</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227258/original/file-20180711-27021-mf828x.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"></a>
<figcaption>
<span class="caption">March 2015: The IceCube Laboratory at the Amundsen-Scott South Pole Station, in Antarctica, hosts the computers that collect raw data from the detector. Due to satellite bandwidth allocations, the first level of reconstruction and event filtering happens in near real time in this lab.</span>
<span class="attribution"><a class="source" href="https://icecube.wisc.edu/gallery/press/view/2085">Erik Beiser, IceCube/NSF</a></span>
</figcaption>
</figure>
<p>It may seem odd that we need such an elaborate detector given that about 100 billion of these fundamental particles sashay right through your thumbnail each second and glide effortlessly through the entire Earth without interacting with a single earthly atom. </p>
<p>In fact, neutrinos are the second most ubiquitous particles, second only to the cosmic microwave background photons left over from the Big Bang. They comprise one-quarter of known fundamental particles. Yet, because they barely interact with other matter, they are arguably the least well understood. </p>
<p>To catch a handful of these elusive particles, and to discover their sources, physicists need big – kilometer-wide – detectors made of an optically clear material – like ice. Fortunately Mother Nature provided this pristine slab of clear ice where we could build our detector. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227257/original/file-20180711-27015-15151as.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The IceCube Neutrino Observatory instruments a volume of roughly one cubic kilometer of clear Antarctic ice with 5,160 digital optical modules (DOMs) at depths between 1,450 and 2,450 meters. The observatory includes a densely instrumented subdetector, DeepCore, and a surface air shower array, IceTop.</span>
<span class="attribution"><a class="source" href="http://gallery.icecube.wisc.edu/web/var/albums/WWW_GALLERY/IceCube-Breakthrough/ArrayWSeasonsLabelsAmanda.jpg?m=1386800062">Felipe Pedreros, IceCube/NSF</a></span>
</figcaption>
</figure>
<p>At the South Pole several hundred scientists and engineers have constructed and deployed over 5,000 individual photosensors in 86 separate 1.5-mile-deep holes melted in the polar ice cap with a custom-designed hot-water drill. Over the course of seven austral summer seasons we installed all the sensors. The IceCube array was fully installed in early 2011 and has been taking data continuously since.</p>
<p>This array of ice-bound detectors can sense with great precision when a neutrino flies through and interacts with a few Earthly particles that generate dim patterns of bluish Cherenkov light, given off when charged particles move through a medium like ice at close to light speed.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/OOWNI0iNGo0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Blazar emission reaches Earth: Gamma rays (magenta), the most energetic form of light, and elusive particles called neutrinos (gray) formed in the jet of an active galactic nucleus far, far away. The radiation traveled for about 4 billion years before reaching Earth. The IceCube Neutrino Observatory at the South Pole detected the arrival of neutrino IC170922 entering Antarctica on Sept. 22, 2017. After the interaction with a molecule of ice, a secondary high-energy particle – a muon – enters IceCube, leaving a trace of blue light behind it. Credit: NASA’s Goddard Space Flight Center/CI Lab/Nicolle R. Fuller/NSF/IceCube.</span></figcaption>
</figure>
<h2>Neutrinos from the cosmos</h2>
<p>The Achilles’ heel of neutrino detectors is that other particles, originating in the nearby atmosphere, can also trigger these patterns of bluish Cherenkov light. To eliminate these false signals, the detectors are buried deep in the ice to filter out interference before it can reach the sensitive detector. But in spite of being under nearly a mile of solid ice, IceCube still faces an onslaught of about 2,500 such particles every second, each of which could plausibly have been due to a neutrino. </p>
<p>With the expected rate of interesting, real astrophysical neutrino interactions (like incoming neutrinos from a black hole) hovering at about one per month, we were faced with a daunting needle-in-a-haystack problem.</p>
<p>The IceCube strategy is to look only at events with such high energy that they are exceedingly unlikely to be atmospheric in origin. With these selection criteria and several years of data, IceCube discovered the astrophysical neutrinos it had long been seeking, but it could not identify any individual sources – such as active galactic nuclei or gamma-ray bursts – among the several dozen high-energy neutrinos it had captured. </p>
<p>To tease out actual sources, IceCube began distributing neutrino arrival alerts in April 2016 with help from the <a href="http://www.amon.psu.edu/">Astrophysical Multimessenger Observatory Network</a> at Penn State. Over the course of the next 16 months, 11 IceCube-AMON neutrino alerts were distributed via AMON and the Gamma-ray Coordinates Network, just minutes or seconds after being detected at the South Pole.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227223/original/file-20180711-27042-bxmmo1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On Sept. 22, 2017, IceCube alerted the international astronomy community about the detection of a high-energy neutrino. About 20 observatories on Earth and in space made follow-up observations, which allowed identification of what scientists deem to be a source of very high energy neutrinos and, thus, of cosmic rays. Besides neutrinos, the observations made across the electromagnetic spectrum included gamma-rays, X-rays, and optical and radio radiation. These observatories are run by international teams with a total of more than 1,000 scientists supported by funding agencies in countries around the world.</span>
<span class="attribution"><span class="source">Nicolle R. Fuller/NSF/IceCube</span></span>
</figcaption>
</figure>
<h2>A new window on the universe</h2>
<p>The alerts triggered an automated sequence of X-ray and ultraviolet observations with NASA’s <a href="https://swift.gsfc.nasa.gov">Neil Gehrels Swift Observatory</a> and led to further studies with NASA’s <a href="https://fermi.gsfc.nasa.gov">Fermi Gamma-Ray Space Telescope</a> and <a href="https://www.nasa.gov/mission_pages/nustar/main/index.html">Nuclear Spectroscopic Telescope Array</a>, and 13 other observatories around the world.</p>
<p>Swift was the first facility to identify the flaring blazar TXS 0506+056 as a possible source of the neutrino event. The <a href="https://www-glast.stanford.edu">Fermi Large Area Telescope</a> then reported that the blazar was in a flaring state, emitting many more gamma-rays than it had in the past. As the news spread, other observatories enthusiastically jumped on the bandwagon and a broad range of observations ensued. The MAGIC ground-based telescope noted our neutrino came from a region producing very high-energy gamma-rays (each about ten million times more energetic than an X-ray), the first time such a coincidence has ever been observed. Other optical observations completed the puzzle by measuring the distance to blazar TXS 0506+056: about four billion light years from Earth.</p>
<p>With the first-ever identification of a cosmic source of high-energy neutrinos, a new branch on the astronomy tree has sprouted. As high-energy neutrino astronomy grows with more data, improved inter-observatory coordination, and more sensitive detectors, we will be able to map the neutrino sky with better and better precision. </p>
<p>And we expect exciting new breakthroughs in our understanding of the universe to follow suit, such as: solving the century-old mystery of the origin of astoundingly energetic cosmic rays; testing if spacetime itself is foamy, with quantum fluctuations at very small distance scales, as predicted by certain theories of quantum gravity; and figuring out exactly how cosmic accelerators, like those around the TXS 0506+056 black hole, manage to accelerate particles to such breathtakingly high energies.</p>
<p>For 20 years, the IceCube Collaboration had a dream to identify the sources of high-energy cosmic neutrinos – and this dream is now a reality.</p><img src="https://counter.theconversation.com/content/99720/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Doug Cowen receives funding from the National Science Foundation, which also supports the IceCube experiment. </span></em></p><p class="fine-print"><em><span>Derek Fox receives funding from the National Science Foundation, which also supports the IceCube experiment. </span></em></p><p class="fine-print"><em><span>Azadeh Keivani does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A detector buried under more than a mile of ice in Antarctica has detected a high-energy subatomic neutrino and traced it to its origin, a blazar – a gargantuan black hole more than a billion times more massive than the sun.Doug Cowen, Professor of Physics and Professor of Astronomy & Astrophysics, Penn StateAzadeh Keivani, Frontiers of Science Fellow, Columbia UniversityDerek Fox, Associate Professor of Astronomy and Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/580062016-04-29T10:06:06Z2016-04-29T10:06:06ZA new state of matter: quantum spin liquids explained<figure><img src="https://images.theconversation.com/files/120548/original/image-20160428-28040-ojld52.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Spin, liquid – just add quantum.</span> <span class="attribution"><span class="source">Panom Pensawang/shutterstock.com</span></span></figcaption></figure><p>Magnetism is one of the oldest recognised material properties. Known since antiquity, records from the 3rd century BC describe how <a href="http://www.oceannavigator.com/January-February-2003/Lodestone-and-needle-the-rise-of-the-magnetic-compass/">lodestone</a>, a naturally occurring magnetised ore of iron, was used in primitive magnetic compasses. Today, thanks to the theory of quantum mechanics we now understand the nature of magnetism, too, with the concept of spin explaining the behaviour of elementary particles such as electrons in the material that make it magnetic.</p>
<p>Spin, a property of sub-atomic particles such as electrons and quarks, makes each individual electron behave as if it were a tiny magnetic compass needle. The millions or billions of electron spins in a piece of material interact with each other in various ways and stabilise to form the different possible magnetic states found in solid matter. Taken together in such large numbers, the spin of the material’s electrons grants the same magnetic properties to the material itself.</p>
<p>Magnetism is essential for the basic trappings of modernity: magnetic materials form the basis of modern electronics and information storage. With this in mind, scientists have pursued the discovery of materials with entirely new magnetic behaviours or new states of matter with unprecedented and potentially beneficial properties. </p>
<p>One is that of a <a href="http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Quantum%20Spin%20Liquids">quantum spin liquid</a>, first proposed by the Nobel Prize-winning theoretical physicist PW Anderson in the early 1970s. In a paper published in the journal Nature Materials, a research team led by Professor Stephen Nagler at the Oak Ridge National Laboratory in the US has <a href="http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4604.html">demonstrated the quantum spin liquid nature</a> of the magnetic material ruthenium trichloride (α-RuCl₃).</p>
<h2>How do quantum spin liquids form?</h2>
<p>Quantum spin liquids are frequently found in a class of materials known as <a href="http://phys.org/news/2015-04-frustrated-magnets-reveals-clues-discontent.html">frustrated magnets</a>. In a conventional magnet, the interactions between spins result in stable formations, known as their <a href="http://www.britannica.com/science/long-range-order">long-range order</a>, in which the magnetic directions of each individual electron is aligned.</p>
<p>In a frustrated magnet, the arrangement of electron spins prevents them from forming an ordered alignment, and so they collapse into a fluctuating, liquid-like state. In a true quantum spin liquid, the electron spins never align, and continue to fluctuate even at the very lowest temperatures of absolute zero, at which the spins in other magnetic states of matter would have already frozen.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Herbertsmithite, a candidate quantum spin liquid source.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Herbertsmithite-herb03a.jpg">Rob Lavinsky/iRocks.com</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The conditions required for a quantum spin liquid to form are often found in nature. The most famous example is the copper-based mineral <a href="http://www.mindat.org/min-26600.html">Herbertsmithite</a>, for which there is significant evidence to suggest that a quantum spin liquid state exists within the frustrated magnetic layers of copper ions that make up its structure. </p>
<h2>Where do we find quantum spin liquids?</h2>
<p>A challenge for scientists is to recreate the conditions required to synthetically grow candidate quantum spin liquid materials in the laboratory to allow for a complete understanding of their properties.</p>
<p>Quantum spin liquids’ evasive character make it notoriously difficult to confirm their existence and pinpoint their exact nature. The presence of a quantum spin liquid can be inferred from a lack of alignment of electron spins, but definitive confirmation is tricky: absence of evidence is not evidence of absence, as the adage goes. A more sophisticated approach is to uncover the more distinctive and unique characteristics of the quantum spin liquid to allow for a positive confirmation.</p>
<p>This is why Nagler’s study is particularly noteworthy. In experiments using <a href="http://www.spectroscopyonline.com/neutron-spectroscopy">neutron spectroscopy</a>, the team revealed that α-RuCl₃ realises something extremely close to a special flavour of quantum spin liquid called a <a href="http://www.esrf.eu/home/news/spotlight/content-news/spotlight/spotlight236.html">Kitaev spin liquid</a>. A prerequisite for this particular quantum spin liquid state is that the spins of the magnetic ruthenium ions form a frustrated honeycomb network: a layered, two-dimensional hexagonal structure, similar to that assumed by carbon atoms in graphite.</p>
<p>In their experiment, a beam of neutron particles created by a particle accelerator was scattered from the sample of α-RuCl₃ transferring energy between the neutrons and the sample in the process. This energy transfer was quantified by a set of detectors surrounding the sample, and the response observed fits that described by the theory developed for the Kitaev quantum spin liquid in particular.</p>
<h2>What can we do with quantum spin liquids?</h2>
<p>We now recognise that the quantum spin liquid comes in several different varieties with subtly different properties, but that they all share the ability to support peculiar quantum mechanical phenomena. This is exciting, and not just from a purely scientific perspective: these states could be used in the development of quantum computers and other transformative quantum technologies that are expected to provide revolutionary changes to how we process and store data throughout the 21st century. </p>
<p>In the age of quantum computing, we will be able to perform calculations that are currently unsolvable on even the most powerful supercomputers of today. This will allow for breakthroughs in a vast array of fields in which we are tackling some of the biggest challenges of our time, from drug discovery to the design of smarter materials for a whole host of applications. As we discover more candidate quantum state liquid materials and better understand their behaviour, we will unravel ever more exotic physics and discover ways to manipulate and control this novel state of matter to our advantage.</p><img src="https://counter.theconversation.com/content/58006/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucy Clark receives funding from The Leverhulme Trust. </span></em></p>Here’s how they could revolutionise science.Lucy Clark, Research Fellow, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/499792015-11-13T10:52:30Z2015-11-13T10:52:30ZScientist at work: searching for tiny neutrinos in the South Pole’s thick ice<figure><img src="https://images.theconversation.com/files/101719/original/image-20151112-9362-1al7h43.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice cold physics: hunting for neutrinos in Antarctica.</span> <span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/press/view/1336">Sven Lidström, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Standing at the South Pole is the next-best thing to being on another planet. If you walk a few hundred yards away from the buildings that make up the National Science Foundation’s <a href="https://www.nsf.gov/news/special_reports/livingsouthpole/intro.jsp">research station</a>, you see a featureless plain of snow and ice, most likely empty of living creatures larger than microbes for hundreds of miles. With nothing but snow for sound waves to echo off, there’s an eerie silence. It’s easy to get lost in reverie, contemplating the stark landscape. But then you remember that you’re here for a reason: to work on what may be the world’s weirdest telescope, searching for some of nature’s most mysterious subatomic particles.</p>
<p>Every second, more than <a href="http://pdg.lbl.gov/2015/reviews/rpp2014-rev-cosmic-rays.pdf">10,000 high-energy particles</a> – protons and atomic nuclei – rain down on every square meter of the Earth’s atmosphere. Some of them carry more than a million times the energy of the protons at the most powerful particle accelerator, CERN’s <a href="http://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>. Fortunately, the atmosphere absorbs most of them, but a few stray particles pass through your body every second – they’re the reason intercontinental airline crews are classified as <a href="http://www.cdc.gov/niosh/topics/aircrew/cosmicionizingradiation.html">radiation workers</a>.</p>
<p>Scientists discovered these particles, known as cosmic rays, more than a century ago, before <a href="https://theconversation.com/from-newton-to-einstein-the-origins-of-general-relativity-50013">Einstein’s theory of general relativity</a> or <a href="http://www.nbi.ku.dk/english/www/niels/bohr/bohratomet/">Bohr’s quantum mechanical model</a> of the atom. But even today, despite half a dozen Nobel Prizes awarded for research related to cosmic rays, we’re not sure where these particles come from. The magnetic fields that fill the universe deflect cosmic rays on their way to Earth, so the direction they’re traveling when they reach us doesn’t tell us where they were originally produced. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Constructing the support tower for the hot water ‘drill’ used to melt holes 1.5 miles deep in the Antarctic ice to install IceCube sensors.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/view/170">Jeff Cherwinka, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Neutrinos hint at where cosmic rays come from</h2>
<p>I’m part of an international team of scientists who built an unusual type of telescope to look for the sources of the cosmic rays. Since the cosmic rays themselves don’t point back to their sources, we look instead for neutrinos, a type of subatomic particle that should be produced as a byproduct of cosmic ray acceleration, wherever it’s happening. (The same process occurs when cosmic rays hit our atmosphere; these “atmospheric” neutrinos were used to discover neutrino oscillations by one of the two experiments that won <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/">2015’s Nobel Prize in Physics</a>.)</p>
<p><a href="https://theconversation.com/how-neutrinos-which-barely-exist-just-ran-off-with-another-nobel-prize-48726">Neutrinos are very strange</a> – they’ve been called ghost particles. They very rarely interact with other matter, so to see them, you need a very large detector. Our telescope is called <a href="http://icecube.wisc.edu">IceCube</a>, because we use a cubic kilometer – a billion tons – of the Antarctic ice cap to catch neutrinos.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of IceCube’s 86 strings of sensors, called DOMs (digital optical modules), being lowered into the ice. They’re vertically spaced about 17 meters apart and meant to catch the visual repercussions of a neutrino collision.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/press/view/1336">Jim Haugen, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Most neutrinos pass invisibly through IceCube, but by chance a few of them will smash into a proton or neutron in the ice, releasing a shower of relativistic particles we <em>can</em> see. By measuring the number and direction of these visible particles, we can determine the direction the original neutrino came from, its energy, and its type or “flavor.” One by one, we build up a picture of the sky as it shines in neutrinos, rather than starlight.</p>
<p>Antarctica may not sound like the obvious place to build such a telescope, but in fact it’s the easiest and cheapest place to do it. The US maintains a <a href="https://www.nsf.gov/geo/plr/support/southp.jsp">scientific facility at the South Pole</a>, home to several other experiments besides IceCube. Most importantly for us, the South Pole station sits on top of nearly three kilometers of the purest, clearest ice in the world – a perfect neutrino target just waiting to be used.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Planes need skis to land and take off at the South Pole.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/view/211">Mark Krasberg, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Good for science, tough for people</h2>
<p>But “easiest” is not the same as “easy” – the South Pole is a challenging place to work. Traveling to the pole from the US can take a week or more. The last leg of the trip is on a special ski-equipped C-130 cargo aircraft operated by the Air National Guard, which lands on a runway made of compressed snow. These aircraft can only reach the pole for four months of the year: at midsummer (January, in the southern hemisphere), the average temperature is a balmy -15 degrees Fahrenheit (-26 degrees Celsius), but by March temperatures have fallen to -50F (-45C), too cold for C-130s to operate. We pack our work into those summer months, then hand IceCube off to two hardy “winter-over” scientists. Our winter-overs are part of a team of 45 people who stay at the station for the rest of the year, cut off from the rest of the world for eight months except for internet and radio communications. </p>
<p>In the summer, the station population expands to about 150. The South Pole is a high-altitude desert, so the air is thin and very, very dry. But the cold isn’t the toughest part of working at the South Pole – at least in the summer. The strangest thing, at least for me, is the constant daylight. At the South Pole, the sun stays up for six months, circling along the horizon and slowly spiraling down until it sets at the autumn equinox. Then our winter-overs get six months of constant darkness until sunrise in the spring. This plays havoc with circadian rhythms; I’ve awoken to see the clock read 3:00, not knowing whether it’s am or pm, whether I’ve slept for four hours or 16.</p>
<p>Despite being one of the most isolated places on Earth, the station is also very crowded in the summer. It takes a lot of expensive fuel to heat buildings, so space is at a premium, and needless to say most of us work indoors. It also takes fuel to melt water, so showers are rationed to two minutes of running water twice a week, contributing to the unique working atmosphere at the South Pole. </p>
<h2>Results starting to roll in</h2>
<p>After seven years of work, IceCube was fully commissioned in 2011, on schedule and on budget. Coordinating the efforts of around 250 scientists around the world was another challenge, and that was only the beginning. Most new telescopes are validated by observing known sources: stars, pulsars, radio galaxies. But there are no known high-energy neutrino sources – IceCube is opening an entirely new window on the universe – so we had to convince ourselves and the rest of the scientific community that we know what we are seeing.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3PZgfPHULHw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A neutrino interacting with the ice inside the IceCube telescope produces electrically charged secondary particles that are detected thanks to a process called Cherenkov radiation. The Cherenkov light, a blue light emitted by charged particles passing through a medium at a speed greater than the speed of light in that medium, will spread through the ice over hundreds of meters.</span></figcaption>
</figure>
<p>Two years after IceCube was completed, we <a href="http://inspirehep.net/record/1265461">announced</a> that we had identified our first two neutrinos from outside the solar system – the first entries in our map of the neutrino sky. (We named them Bert and Ernie.) Last year we recorded the <a href="http://www.astronomerstelegram.org/?read=7856">highest-energy neutrino ever seen</a>: 1,000 times the energy of the protons accelerated at CERN.</p>
<p>There’s a wonderful debate in the scientific community over where these neutrinos come from, whether any of them might be produced in our own galaxy or even be related to exotic new particles like dark matter. As we take more data, we hope more exciting new discoveries are in store.</p><img src="https://counter.theconversation.com/content/49979/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tyce DeYoung receives funding from the US National Science Foundation. </span></em></p>A cubic kilometer of clear, stable ice could help physicists answer big questions about cosmic rays and neutrinos. Hardy scientists collect data via a unique telescope at the frozen bottom of the world.Tyce DeYoung, Associate Professor of Physics and Astronomy, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/487262015-10-07T01:55:44Z2015-10-07T01:55:44ZHow neutrinos, which barely exist, just ran off with another Nobel Prize<figure><img src="https://images.theconversation.com/files/97519/original/image-20151007-7358-1860y5z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Neutrinos, we're looking for you! Japan's Super-Kamiokande detector.</span> <span class="attribution"><a class="source" href="http://www-sk.icrr.u-tokyo.ac.jp/sk/detector/image-e.html">Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo</a></span></figcaption></figure><p>Neutrinos take patience. They’re worth it, and the announcement of the <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/">2015 Nobel Prize in Physics</a> recognizes that, following related prizes in <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1988/">1988</a>, <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1995/">1995</a> and <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2002/">2002</a>. Ironically, these near-undetectable particles can reveal things that cannot be seen any other way.</p>
<p>I could begin by telling you that neutrinos are elementary particles, but that sounds condescending. They’re not called elementary because they’re easy to understand – they aren’t – but because they are seemingly point-like in size, and we can’t break them down into smaller constituents. There’s no such thing as half a neutrino.</p>
<h2>The smallest things in the universe</h2>
<p>Atoms, despite the Greek name (“cannot be cut”), are not elementary particles, meaning they can be disassembled. An atom is a diffuse cloud of electrons surrounding a tiny, dense nucleus composed of protons and neutrons, which can be broken into up and down quarks.</p>
<p>Particle colliders, which accelerate particles to near the speed of light and smash them together, help us discover new elementary particles. First, because of E = mc<sup>2,</sup> the energy in the collision can be converted into the mass of particles. Second, the higher the accelerator’s beam energy, the more finely we can resolve composite structures, just as we can see smaller things with X-rays than with visible light.</p>
<p>We haven’t been able to take apart electrons or quarks. These are elementary particles, forming the basic constituents of ordinary matter: the Lego bricks of the universe. Interestingly, there are many heavy cousins of familiar particles that exist only for fractions of a second, and thus are not part of ordinary matter. For example, for electrons these are the muon and tauon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97521/original/image-20151007-7371-c493pr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Elementary particles, of which neutrinos are one kind.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg">MissMJ</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>What’s a neutrino?</h2>
<p>How is this elementary particle – the neutrino – different from all other elementary particles? It’s unique in that it’s both almost massless and almost noninteracting. Those features are different, though often conflated (don’t take advice about neutrinos from a poet, even it is <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1995/illpres/cosmic-call.html">John Updike</a>).</p>
<p>It’s a mystery why neutrinos are almost, but not quite, massless. We do know why they’re almost noninteracting, though: They don’t feel the electromagnetic or strong forces that bind nuclei and atoms, only the aptly named <a href="http://www.livescience.com/49254-weak-force.html">weak force</a> (and gravity, but barely, because their masses are small). </p>
<p>Though neutrinos are not constituents of ordinary matter, they are everywhere around us – a trillion from the sun pass through your eyes every second. There are hundreds per every cubic centimeter left over from the Big Bang. Because they so rarely interact, it’s almost impossible to observe them, and you certainly don’t feel them.</p>
<p>Neutrinos have other weird aspects. They come in three types, called flavors – electron, muon and tauon neutrinos, corresponding to the three charged particles they pair with – and all of these seem to be stable, unlike the heavy cousins of the electron.</p>
<p>Because the three flavors of neutrinos are almost identical, there is the theoretical possibility that they could change into each other, which is another unusual aspect of these particles, one that can reveal new physics. This transformation requires three things: that neutrino masses are nonzero, are different for different types, and that neutrinos of definite flavor are quantum combinations of neutrinos of definite mass (this is called “neutrino mixing”).</p>
<p>For decades, it was generally expected that none of these conditions would be met. Not by neutrino physicists, though – we held out hope.</p>
<h2>Doing astronomy with invisible particles</h2>
<p>In the end, nature provided, and experimentalists discovered, supported by calculations from theorists. First came decades of searching by many experiments, with important hints to encourage the chase.</p>
<p>Then, in <a href="http://inspirehep.net/record/472711?ln=en">1998</a>, the <a href="http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html">Super-Kamiokande experiment</a> in Japan announced strong evidence that muon neutrinos produced in Earth’s atmosphere change to another type (now thought to be tauon neutrinos). The proof was seeing this happen for neutrinos that came from “below,” having traveled a long distance through Earth, but not for those from “above,” having traveled just the short distance through the atmosphere. Because the neutrino flux is (nearly) the same at different places on Earth, this allowed a “before” and “after” measurement.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=610&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=610&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=610&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=767&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=767&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97516/original/image-20151007-7333-1oswd4y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=767&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">View from the bottom of the Sudbury Neutrino Observatory acrylic vessel and PMT array.</span>
<span class="attribution"><a class="source" href="http://www.sno.phy.queensu.ca/sno/images/publicity_photos/index.html">Ernest Orlando Lawrence Berkeley National Laboratory</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In <a href="http://inspirehep.net/record/558620?ln=en">2001</a> and <a href="http://inspirehep.net/record/585723?ln=en">2002</a>, the <a href="http://www.sno.phy.queensu.ca">Sudbury Neutrino Observatory</a> in Canada announced strong evidence that electron neutrinos produced in the core of the sun also change flavors. This time the proof was seeing that electron flavor neutrinos that disappeared then reappeared as other types (now thought to be a mix of muon and tauon neutrinos).</p>
<p>Each of those experiments saw about half as many neutrinos as expected from theoretical predictions. And, perhaps fittingly, Takaaki Kajita and Arthur McDonald each got half a Nobel Prize. </p>
<p>In both cases, quantum-mechanical effects, which normally operate only at microscopic distances, were observed on terrestrial and astronomical distance scales.</p>
<p>As the front page of The New York Times <a href="http://www.nytimes.com/1998/06/05/us/mass-found-in-elusive-particle-universe-may-never-be-the-same.html?pagewanted=all">said</a> in 1998, “Mass Found in Elusive Particle; Universe May Never Be the Same.” These clear indications of neutrino flavor change, since confirmed and measured in detail in laboratory experiments, show that neutrinos have mass and that these masses are different for different types of neutrino. Interestingly, we don’t yet know what the values of the masses are, though other experiments show that they must be about a million times smaller than the mass of an electron, and perhaps smaller.</p>
<p>That’s the headline. The rest of the story is that the mixing between different neutrino flavors is in fact quite large. You might think it’s bad news when predictions fail – for example, that we would never be able to observe neutrino flavor change – but this kind of failure is good, because we learn something new.</p>
<h2>International society of neutrino hunters</h2>
<p>I’m delighted to see this recognition for my friends Taka and Art. I wish that several key people, both experimentalists and theorists, who contributed in essential ways had been similarly recognized. It took many years to construct and operate those experiments, which themselves built on slow, difficult and largely unrewarding work going back decades, requiring the effort of hundreds of people. That includes major US participation in both Super-Kamiokande and the Sudbury Neutrino Observatory. So, congratulations to neutrinos, to Taka and Art, and to the many others who made this possible! </p>
<p>When I first started working on neutrinos, over 20 years ago, many people, including prominent scientists, told me I was wasting my time. Later, others urged me to work on something else, because “people who worked on neutrinos don’t get jobs.” And, even now, plenty of physicists and astronomers think we’re chasing something almost imaginary.</p>
<p>But we’re not. Neutrinos are real. They’re an essential part of physics, shedding light on the origin of mass, the <a href="http://press.web.cern.ch/backgrounders/matterantimatter-asymmetry">particle-antiparticle asymmetry</a> of the universe, and perhaps the existence of new forces that are too feeble to test with other particles. And they are an essential part of astronomy, revealing the highest-energy accelerators in the Universe, what’s inside the densest stars, and perhaps new and otherwise unseen astrophysical objects.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/d6eMdixkoRI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The author describes how the facts we learn about the universe shape our sense of meaning.</span></figcaption>
</figure>
<h2>Tiny particles, big mysteries</h2>
<p>Why should you care, beyond sharing our curiosity about revealing some of the weirdest things in the universe? </p>
<p>The weak force that neutrinos feel is what changes protons to neutrons, powering nuclear fusion reactions in the sun and other stars, and creating the elements that make planets and life itself possible.</p>
<p>Neutrinos are the only component of dark matter that we understand, and figuring out the rest will help us understand the structure and evolution of the universe. If the neutrino masses had been much larger, the universe would look much different, and perhaps we wouldn’t be here to see.</p>
<p>Finally, if you are purely practical, neutrino physics and astrophysics is one of the most difficult jobs, requiring us to invent incredibly sensitive detectors and techniques. This knowledge has other uses; for example, using a neutrino detector, we could tell if a purported nuclear reactor is on, what its power level is and even if it is producing plutonium. This may have some real-world applications.</p>
<p>The past decades in neutrino physics and astronomy have been great, but some of the most exciting things are just starting to happen. The <a href="http://icecube.wisc.edu">IceCube Neutrino Observatory</a> at the South Pole is now seeing high-energy neutrinos from outside our galaxy. Super-Kamiokande has announced a plan, based on a <a href="http://inspirehep.net/search?p=find+eprint+HEP-PH/0309300">proposal</a> from me and Mark Vagins, to improve their sensitivity to antineutrinos compared to neutrinos. And the international community hopes to build a major new neutrino facility, in which a powerful beam of neutrinos will be sent from Fermilab in Illinois to a detector deep underground in the Homestake mine in South Dakota. Who knows what we’ll find?</p>
<p>And that’s what I’ve really been waiting for.</p><img src="https://counter.theconversation.com/content/48726/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Beacom receives funding from the National Science Foundation.</span></em></p>They’re beyond tiny and super mysterious. Neutrinos are an elemental particle that might just help us understand the structure and evolution of the universe.John Beacom, Professor of Physics, Professor of Astronomy, and Director of the Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/447212015-07-15T12:57:00Z2015-07-15T12:57:00ZHere’s what you need to know about the Large Hadron Collider’s latest discovery: pentaquarks<figure><img src="https://images.theconversation.com/files/88494/original/image-20150715-17815-1pe2ckw.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">CERN</span></span></figcaption></figure><p>The Large Hadron Collider, famous for finding the Higgs boson, has now revealed another new and rather unusual particle. Teams at the LHC, the world’s largest particle accelerator, <a href="https://theconversation.com/large-hadron-collider-is-back-to-change-our-understanding-of-the-universe-again-42775">recently began</a> a second <a href="https://theconversation.com/explainer-how-does-an-experiment-at-the-large-hadron-collider-work-42846">run of experiments</a> using far more energy than the ones that found the Higgs particle <a href="https://theconversation.com/cern-discovers-a-higgs-like-particle-let-the-party-and-head-scratching-begin-8036">back in 2012</a>. But another of the groups, LHCb, have also been sifting through its data from the billions of particle collisions of the first run of the LHC, and now think they’ve <a href="http://arxiv.org/abs/1507.03414">spotted something new</a>: pentaquarks.</p>
<p>Pentaquarks are an exotic form of matter first predicted <a href="http://journals.aps.org/prd/abstract/10.1103/PhysRevD.20.748">back in 1979</a>. Everything around us is made of atoms, which are mode of a cloud of electrons orbiting a heavy nucleus made of protons and neutrons. But <a href="http://www.sciencedirect.com/science/article/pii/S0031916364920013">since the 1960s</a>, we’ve also known that protons and neutrons are made up of even smaller <a href="https://theconversation.com/explainer-quarks-12003">particles named “quarks</a>”, held together by something called the “strong force”, the strongest known force in nature in fact.</p>
<p><a href="http://wwwphy.princeton.edu/%7Ekirkmcd/examples/EP/breidenbach_prl_23_935_69.pdf">Experiments in 1968</a> provided the evidence for the quark model. If protons are hit hard enough, the strong force can be overcome and the proton smashed apart. The quark model actually explains the existence of more than 100 particles, all known as “hadrons” (as in Large Hadron Collider) and made up of different combinations of quarks. For example the proton is made of three quarks.</p>
<p>All hadrons seem to be made up of combinations of either two or three quarks, but there is no obvious reason more quarks could not stick together to form other types of hadron. <a href="https://inis.iaea.org/search/search.aspx?orig_q=RN:190196">Enter the pentaquark</a>: five quarks bound together to form a new type of particle. But until now, nobody knew for sure if pentaquarks actually existed – and, although there have been several discoveries claimed in the last 20 years, none has stood the test of time.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88496/original/image-20150715-17785-klc9jf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The intricate dance of the J/psi and the proton.</span>
<span class="attribution"><span class="source">CERN</span></span>
</figcaption>
</figure>
<p>Pentaquarks are incredibly difficult to see; they are very rare and very unstable. This means that if it is possible to stick five quarks together, they won’t stay together for very long. The team on the LHCb experiment made their discovery by looking in detail at other exotic hadrons produced in the collisions and they way these break apart. In particular, they looked for the Lambda<sub>b</sub> particle, which can decay into thee other hadrons: a Kaon, a J/psi, and a proton.</p>
<p>The J/psi is made of two quarks and the proton is made of three. The scientists discovered that for a short period of time these five quarks were bound together in a single particle: a pentaquark. In fact, through detailed analysis of the data, they actually discovered two pentaquarks and have given them the catchy names Pc(4450)+ and Pc(4380)+.</p>
<h2>Why is this important?</h2>
<p>The discovery answers a decades-old question in particle physics and highlights another part of the mission of the LHC. Discoveries of new fundamental particles such as the Higgs boson tell us something completely new about the universe. But discoveries like pentaquarks give us a more complete understanding of the rich possibilities that lie in the universe we already know.</p>
<p>By developing this understanding, we may get some hints about how the universe developed after the Big Bang and how we’ve ended up with protons and neutrons instead of pentaquarks making up everyday matter. </p>
<p>With the LHC now colliding protons at almost twice the energy, scientists are ready to tackle some of the <a href="https://theconversation.com/large-hadron-collider-is-back-to-change-our-understanding-of-the-universe-again-42775">other open questions</a> in <a href="https://theconversation.com/beyond-the-higgs-boson-five-reasons-physics-is-still-interesting-20380">particle physics</a>. One of the main targets with the new data is <a href="https://theconversation.com/shedding-new-light-on-the-search-for-the-invisible-dark-matter-40083">Dark Matter</a>, a strange particle which seems to be all around the universe, but has never been seen. Testing the current understanding of quarks, the strong force and all the known particles at this new energy is an essential step towards making such discoveries.</p><img src="https://counter.theconversation.com/content/44721/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gavin Hesketh is a lecturer in particle physics at University College London, and a member of the ATLAS Collaboration at CERN. He receives funding from the Science and Technology Facilities Council, and the Royal Society.</span></em></p>The latest data from the particle accelerator that found the Higgs Boson has confirmed another of our theories about how the universe works.Gavin Hesketh, Lecturer in Particle Physics, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/427752015-06-03T14:14:14Z2015-06-03T14:14:14ZLarge Hadron Collider is back to change our understanding of the universe … again<p>The Large Hadron Collider (LHC) has just begun smashing particles together at higher energies than ever before. This marks the start of the second run of the world’s largest physics experiment, the huge particle accelerator that sits beneath the Alps and in 2012 was used to prove the existence of the <a href="https://theconversation.com/definitely-maybe-evidence-grows-for-positive-id-of-higgs-boson-12790">Higgs boson</a>.</p>
<p>Now, after more than two years’ work <a href="https://theconversation.com/goodbye-for-a-while-to-the-large-hadron-collider-12238">upgrading the accelerator</a> systems and the particle detectors (and more years of preparation before that), the team at research group CERN are ready to start using the LHC to answer more questions about how the universe works.</p>
<p>The goal is to explain the missing pieces in our understanding of fundamental physics. One example is the nature of the so-called <a href="http://home.web.cern.ch/about/physics/dark-matter">dark matter</a> that scientists say we can’t see directly but that dominates the universe. Another is the imbalance between matter and antimatter in the present-day universe. Our current theories suggest there would have been almost exactly equal amounts of matter and antimatter in the early universe. But somehow the antimatter decayed, allowing the universe that we know made entirely of matter to emerge.</p>
<p>Physicists have proposed a range of theories, <a href="http://home.web.cern.ch/about/physics/supersymmetry">such as “supersymmetry”</a>, to answer these questions and that also predict the existence of new particles and subtle changes to the behaviour of known particles. By colliding particles at energies measured at 13 teraelectronvolts, researchers may also find evidence of the hidden extra dimensions that feature in many theories. Or it could show that the Higgs boson, the particle associated with giving mass to the other particles that make up matter, is one of a whole family of related particles.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83813/original/image-20150603-2963-6ok9uw.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">Energy levels up.</span>
<span class="attribution"><span class="source">M Brice/CERN</span></span>
</figcaption>
</figure>
<p>The significance of almost doubling the energy at which particles are fired around the LHC is that the resulting collisions should produce new particles that were inaccessible before. Rarer processes should also become more frequent and so easier to distinguish from the approximately 600m “ordinary” collisions that occur in each experiment each second. And the rate at which Higgs bosons are produced should increase, allowing researchers to determine their true nature.</p>
<p>There are several different experiments scheduled for the higher-energy LHC. My team at the University of Lancaster is part of the <a href="http://atlas.ch">ATLAS experiment</a> and we will be looking studying how the Higgs boson decays into a particle called the tau, a heavier version of the electron. We will be seeing if the decay exhibits what is called <a href="http://cerncourier.com/cws/article/cern/28092">CP violation</a>, a process that distinguishes between matter and antimatter and might help explain the matter-antimatter imbalance.</p>
<p>The improvements to the ATLAS detector for measuring the paths of the particles produced by collisions and the points where they decay mean we in Lancaster will be able to make really precise measurements of CP violation and particle lifetimes in more conventional particles. The extremely large samples of the relevant decays will also contribute to the high precision required to see the influence of any new physics effects such as supersymmetry.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=309&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=309&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=309&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=388&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=388&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83812/original/image-20150603-2966-1rs9yi0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=388&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Smashing job.</span>
<span class="attribution"><span class="source">CMS/CERN</span></span>
</figcaption>
</figure>
<p>We will also be looking for other new particles, particularly those that decay into two “jets” of ordinary particles. This is really important for understanding how often you get double collisions between the particles inside the protons. The energy signature from these double collisions can mimic some of the effects predicted by new theories. So we need to understand the collisions before we can claim them as evidence for those theories. </p>
<p>The two year period during which the LHC was offline was an intensely busy time for the accelerator and detector teams. But the work will now intensify at major analysis centres such as Lancaster to extract the relevant results from the large volumes of data the LHC is producing. For the young physicists doing their PhD studies or in their first research positions and the older hands directing them, this is the most exciting time when the work all comes together.</p>
<p>What will be found is unknown – and an unexpected finding could transform our whole programme of work. Whatever nature reveals, it will be interesting and potentially could profoundly change our view of the fundamental workings of the universe.</p><img src="https://counter.theconversation.com/content/42775/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Jones receives funding from STFC.</span></em></p>CERN’s huge particle accelerator has been switched back on after a two-year upgrade to continue its search for answers.Roger Jones, Professor of Physics, Head of Department, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/383392015-03-20T06:32:22Z2015-03-20T06:32:22ZExplainer: what are fundamental particles?<figure><img src="https://images.theconversation.com/files/75089/original/image-20150317-22277-fpy7cs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The epoch of the leptons existed for nine seconds after the Big Bang. </span> <span class="attribution"><span class="source">Big Bang by Shutterstock</span></span></figcaption></figure><p>It is often <a href="http://phys.org/news/2013-10-ancient-greece-nobel-prize-higgs.html">claimed that the Ancient Greeks</a> were the first to identify objects that have no size, yet are able to build up the world around us through their interactions. And as we are able to observe the world in tinier and tinier detail through <a href="https://theconversation.com/nobel-prize-in-chemistry-beating-natures-limits-to-build-super-microscopes-32444">microscopes of increasing power</a>, it is natural to wonder what these objects are made of. </p>
<p>We believe we have found some of these objects: subatomic particles, or fundamental particles, which having no size can have no substructure. We are now seeking to explain the properties of these particles and working to show how these can be used to explain the contents of the universe. </p>
<p>There are two types of fundamental particles: matter particles, some of which combine to produce the world about us, and force particles – one of which, the photon, is responsible for electromagnetic radiation. These are classified in <a href="http://home.web.cern.ch/about/physics/standard-model">the standard model of particle physics</a>, which theorises how the basic building blocks of matter interact, governed by fundamental forces. Matter particles are fermions while force particles are bosons.</p>
<h2>Matter particles: quarks and leptons</h2>
<p>Matter particles are split into two groups: quarks and leptons – there are six of these, each with a corresponding partner. </p>
<p>Leptons are divided into three pairs. Each pair has an elementary particle with a charge and one with no charge – one that is much lighter and extremely difficult to detect. The lightest of these pairs is the electron and electron-neutrino. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=942&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=942&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75083/original/image-20150317-22294-qb87ml.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=942&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">And then some.</span>
<span class="attribution"><a class="source" href="http://www.flickr.com/photos/51324729@N06/8521699366/in/photolist-dZ2U5E-4QfW8W-dZ2SkS-dZ2Wk9-dYWf14-dYWapc-dZ2PyU-fHXxg3-dYWare-dYWbv8-dYWdWZ-dZ2Vub-dYWeSi-dYW8Yz-dYWfqM-dZ2WJ1-dYWeTc-dYWfhD-dYWf3k-dYWdRg-dZ2VHQ-dYWvqV-dYWq3i-dZ2Wxy-dYWf8K-dZ2T5Y-dYW9tg-dZ2mGC-dZ2ooS-bmSrT4-dyhNrD-3fCzD8-aueBhN-wTpD-dYVETe-eiwixk-boDzCD-eiwkS6-8tbk55-dYWekV-dZ2jNG-eiC5SU-ijUZn-A7Tvu-7sR4E3-6qTSH-8eodca-b7w3ZR-82Ur7X-82Uqgk">James Childs</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The charged electron is responsible for electric currents. Its uncharged partner, known as the electron-neutrino, is produced copiously in the sun and these interact so weakly with their surroundings that they pass unhindered through the Earth. A million of them pass through every square centimetre of your body every second, day and night. </p>
<p>Electron-neutrinos are produced in unimaginable numbers <a href="http://hep.bu.edu/%7Esuperk/gc.html">during supernova explosions</a> and it is these particles that disperse elements produced by nuclear burning into the universe. These elements include the carbon from which we are made, the oxygen we breathe, and almost everything else on earth. Therefore, in spite of the reluctance of neutrinos to interact with other fundamental particles, they are vital for our existence. The other two neutrino pairs (called muon and muon neutrino, tau and tau neutrino) appear to be just heavier versions of the electron. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75082/original/image-20150317-22297-1qfduuz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">J J Thomson’s 1897 cathode ray tube with magnet coils – used to discover the electron.</span>
<span class="attribution"><a class="source" href="http://www.flickr.com/photos/sciencemuseum/9663807404/in/photolist-fHXxg3-dZ2U5E-4QfW8W-dZ2SkS-dZ2Wk9-dYWf14-dYWapc-dZ2PyU-dYWare-dYWbv8-dYWdWZ-dZ2Vub-dYWeSi-dYW8Yz-dYWfqM-dZ2WJ1-dYWeTc-dYWfhD-dYWf3k-dYWdRg-dZ2mGC-dyhNrD-3fCzD8-aueBhN-wTpD-eiwixk-boDzCD-eiwkS6-8tbk55-eiC5SU-ijUZn-6qTSH-8eodca-b7w3ZR-82Uqgk-dZ2VHQ-dYWvqV-dYWq3i-dZ2Wxy-dYWf8K-dZ2T5Y-dYW9tg-dZ2ooS-bmSrT4-dYVETe-dYWekV-dZ2jNG-A7Tvu-7sR4E3-82Ur7X">Science Museum London</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Since normal matter does not contain these particles it may seem that they are an unnecessary complication. However <a href="http://historyoftheuniverse.com/index.php?p=leptonEpoch.htm">during the first one to ten seconds</a> of the universe following the Big Bang, they had a crucial role to play in establishing the structure of the universe in which we live – known as the Lepton Epoch.</p>
<p>The six quarks are also split into three pairs with whimsical names: “up” with “down”, “charm” with “strange”, and “top” with “bottom” (previously called “truth” and “beauty” though regrettably changed). The up and down quarks stick together to form the protons and neutrons which lie at the heart of every atom. Again only the lightest pair of quarks are found in normal matter, the charm/strange and top/bottom pairs seem to play no role in the universe as it now exists, but, like the heavier leptons, played a role in the early moments of the universe and helped to create one that is amenable to our existence.</p>
<h2>Force particles</h2>
<p>There are six force particles in the standard model, <a href="http://www.particleadventure.org/unseen.html">which create the interactions</a> between matter particles. They are divided into <a href="https://theconversation.com/what-will-we-find-next-inside-the-large-hadron-collider-38664">four fundamental forces</a>: gravitational, electromagnetic, strong and weak forces.</p>
<p>A photon is a particle of light and <a href="https://van.physics.illinois.edu/qa/listing.php?id=414">is responsible for electric and magnetic fields</a>, created by the exchange of photons from one charged object to another. </p>
<p>The gluon produces the force responsible for holding quarks together to form protons and neutrons, and for holding those protons and neutrons together to form heavier nuclei. </p>
<p>Three particles named the “W plus”, the “W minus” and the “Z zero” – referred to as intermediate vector bosons – are responsible for the process of radioactive decay and for <a href="http://www.damtp.cam.ac.uk/user/db275/concepts/Particles.pdf">the processes in the sun which cause it to shine</a>. A sixth force particle, the graviton, is believed to be responsible for gravitation, but <a href="http://io9.com/what-are-gravitons-and-why-cant-we-see-them-1643904640">has not yet been observed</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/w-41gAPmUG0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>Anti-matter: the science fiction reality</h2>
<p>We also know of the existence of anti-matter. This is a concept much beloved by science fiction writers, but it really does exist. Anti-matter particles have been frequently observed. For example, the positron (the anti-particle of the electron) is used in medicine to map our internal organs <a href="https://theconversation.com/the-science-of-medical-imaging-spect-and-pet-14086">using positron emission tomography</a> (PET). Famously when a particle meets its anti-particle they both annihilate each other and a burst of energy is produced. A PET scanner is used to detect this. </p>
<p>Each of the matter particles above has a partner particle which has the same mass, but opposite electric charge, so we can double the number of matter particles (six quarks and six leptons) to arrive at a final number of 24.</p>
<p>We give matter quarks a number of +1 and anti-matter quarks a value of -1. If we add up the number of matter quarks plus the number of anti-matter quarks then we get the net number of quarks in the universe, this never varies. If we have enough energy we can create any of the matter quarks as long as we create an anti-matter quark at the same time. In the early moments of the universe these particles were being created continuously – now they are only created in the collisions of cosmic rays with the atmosphere of planets and stars.</p>
<h2>The famous Higgs boson</h2>
<p>There is a final particle which completes the roll call of particles in what is referred as the standard model of particle physics so far described. It is the Higgs, predicted by Peter Higgs 50 years ago, and whose <a href="http://home.web.cern.ch/topics/higgs-boson">discovery at CERN</a> in 2012 led to a Nobel Prize for Higgs and Francois Englert. </p>
<p>The Higgs boson is an odd particle: it is the second heaviest of the standard model particles and it resists a simple explanation. It is often said to be the origin of mass, which is true, but misleading. It gives mass to the quarks, and quarks make up the protons and neutrons, but only 2% of the mass of protons and neutrons is provided by the quarks, and the rest is from the energy in the gluons.</p>
<p>At this point we have accounted for all the particles required by the standard model: six force particles, 24 matter particles and one Higgs particle – a total of 31 fundamental particles. Despite what we know about them, their properties have not been measured well enough to allow us to say definitively that these particles are all that is needed to build the universe we see around us, and we certainly <a href="https://theconversation.com/beyond-the-higgs-boson-five-reasons-physics-is-still-interesting-20380">don’t have all the answers</a>. The next run of the <a href="http://home.web.cern.ch/topics/large-hadron-collider">Large Hadron Collider</a> will allow us to refine our measurements of some of these properties – but there is something else. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=392&fit=crop&dpr=1 600w, https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=392&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=392&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=492&fit=crop&dpr=1 754w, https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=492&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/75091/original/image-20150317-22288-1mp6qat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=492&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The great collider.</span>
<span class="attribution"><a class="source" href="http://www.flickr.com/photos/11304375@N07/2046228644/in/photolist-5pdeiQ-5m4QNL-4qZaVM-4roqPb-4ropM1-5s3JdT-47Psud-fZeRQ5-815XEw-812Vo6-812NhM-815Xib-815XQ1-815WVo-815Xy7-815WNo-812PAF-812P3F-A7Tuj-4rjnLp">Image Editor</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Yet the theory is still wrong</h2>
<p>The beautiful theory, the standard model, has been tested and re-tested over two decades and more; and we have not yet made a measurement that is in contradiction with our predictions. But we know that the standard model must be wrong. When we collide two fundamental particles together a number of outcomes are possible. Our theory allows us to calculate the probability that any particular outcome can occur, but at energies beyond which we have so far achieved it predicts that some of these outcomes occur with a probability of greater than 100% – clearly nonsense. </p>
<p>Theoretical physicists have spent much effort in trying to construct a theory which gives sensible answers at all energies, while giving the same answer as the standard model in every circumstance in which the standard model has been tested. </p>
<p>The most common modification implies that there are very heavy undiscovered particles. The fact they are heavy means lots of energy will be needed to produce them. The properties of these extra particles can be chosen to make sure that the resulting theory gives sensible answers at all energies, but they have no effect on the measurements that agree so well with the standard model. </p>
<p>The number of these undiscovered and as-yet-unseen particles depends on which theory you choose to believe. The most popular class of these theories are called <a href="http://home.web.cern.ch/about/physics/supersymmetry">supersymmetric</a> theories and they imply that all the particles which we have seen have a much heavier counterpart. However, if they are too heavy, problems will arise at energies we can produce before these particles are found. But the energies that will be reached in <a href="https://theconversation.com/what-will-we-find-next-inside-the-large-hadron-collider-38664">the next run of the LHC</a> are high enough that an absence of new particles will be a blow to all supersymmetric theories.</p><img src="https://counter.theconversation.com/content/38339/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Kyberd works on Compact Muon Solenoid, an experiment at the LHC collider at CERN</span></em></p>Subatomic particles have shaped and continue to shape our universe but despite perfect predictions by physicists, the theory about unseen particles is still wrong.Paul Kyberd, Senior Lecturer in Particle Physics Informatics, Brunel University LondonLicensed as Creative Commons – attribution, no derivatives.