Category: Physics

Nandini Trivedi, The Ohio State University

The 2016 Nobel Prize in physics has been awarded to David Thouless, Duncan Haldane and Michael Kosterlitz, three theoretical physicists whose research used the unexpected mathematical lens of topology to investigate phases of matter and the transitions between them.

Topology is a branch of mathematics that deals with understanding shapes of objects; it’s interested in “invariants” that don’t change when a shape is deformed, like the number of holes an object has. Physics is the study of matter and its properties. The Nobel Prize winners were the first to make the connection between these two worlds.

Everyone is used to the idea that a material can take various familiar forms such as a solid, liquid or gas. But the Nobel Prize recognizes other surprising phases of matter – called topological phases – that the winners proposed theoretically and experimentalists have since explored.

Topology is opening up new platforms for observing and understanding these new states of matter in many branches of physics. I work with theoretical aspects of cold atomic gases, a field which has only developed in the years since Thouless, Haldane and Kosterlitz did their groundbreaking theoretical work. Using lasers and atoms to emulate complex materials, cold atom researchers have begun to realize some of the laureates’ predictions – with the promise of much more to come.

Cold atoms get us to quantum states of matter

All matter is made up of building blocks, such as atoms. When many atoms come together in a material, they start to interact. As the temperature changes, the state of matter starts to change. For instance, water is a liquid until a fixed temperature, when it turns into vapor (373 degrees Kelvin; 212 degrees Fahrenheit; 100 degrees Celsius); and if you cool, solid ice forms at a fixed temperature (273K; 32℉; 0℃). The laws of physics give us a theoretical limit to how low the temperature can get. This lowest possible temperature is called absolute zero (0K) (and equals -460℉ or -273℃).

Classical physics governs our everyday world. Classical physics tells us that if we cool atoms to really low temperatures, they stop their normally constant vibrating and come to a standstill.

But really, as we cool atoms down to temperatures approaching close to 0K, we leave the regime of classical physics – quantum mechanics begins to govern what we see.

In the quantum mechanical world, if an object’s position becomes sharply defined then its momentum becomes highly uncertain, and vice versa. Thus, if we cool atoms down, the momentum of each atom decreases, and the quantum uncertainty of its position grows. Instead of being able to pinpoint where each atom is, we can now only see a blurry space somewhere within which the atom must be. At some point, the neighboring uncertain positions of nearby atoms start overlapping and the atoms lose their individual identities. Surprisingly, the distinct atoms become a single entity, and behave as one coherent unit – a discovery that won a previous Nobel.

This new, amazing way atoms organize themselves at very low temperatures results in new properties of matter; it’s no longer a classical solid in which the atoms occupy periodic well-defined positions, like eggs in a carton.

Instead, the material is now in a new quantum state of matter in which each atom has become a wave with its position no longer identifiable. And yet the atoms are not moving around chaotically. Instead, they are highly coherent, with a new kind of quantum order. Just like laser beams, the coherent matter waves of superfluids, superconductors and magnets can produce interference patterns.

Physicists have known about quantum order in superfluids and magnets in three dimensions since the middle of the last century. We understand that the order is lost at a critical temperature due to thermal fluctuations. But in two dimensions the situation is different. Early theoretical work showed that thermal fluctuations would destroy the quantum order even at very low temperatures.

What Thouless, Haldane and Kosterlitz addressed were two important questions: What is the nature of the quantum ordered state of superfluids, superconductors and magnets in low dimensions? What is the nature of the phase transition from the ordered to the disordered state in two dimensions?

Thinking about defects

Kosterlitz and Thouless’s innovation was to show that topological defects – vortex and anti-vortex whirls and swirls – are crucial to understand the magnetic and superfluid states of matter in two dimensions. These defects are not just local perturbations in the quantum order; they produce a winding or circulation as one goes around it. The vorticity, which measures how many times one winds around, is measured in integer units of the circulation.

Kosterlitz and Thouless showed that at low temperatures, a vortex is bound up with an anti-vortex so the order survives. As the temperature increases, these defects unbind and grow in number and that drives a transition from an ordered to a disordered state.

It’s been possible to visualize the vortices in cold atomic gases that Kosterlitz and Thouless originally proposed, bringing to life the topological defects they theoretically proposed. In my own research, we’ve been able to extend these ideas to quantum phase transitions driven by increasing interactions between the atoms rather than by temperature fluctuations.

Figuring out step-wise changes in materials

The second part of the Nobel Prize went to Thouless and Haldane for discovering new topological states of matter and for showing how to describe them in terms of topological invariants.

Physicists knew about the existence of a phenomenon called the quantum Hall effect, first observed in two dimensional electrons in semiconductors. The Hall conductance, which is the ratio of the transverse voltage and the current, was observed to change in very precise integer steps as the magnetic field was increased. This was puzzling because real materials are disordered and messy. How could something so precise be seen in experiments?

It turns out that the current flows only in narrow channels at the edges and not within the bulk of the material. The number of channels is controlled by the magnetic field. Every time an additional channel or lane gets added to the highway, the conductance increase by a very precise integer step, with a precision of one part in billion.

Thouless’ insight was to show that the flow of electrons at the boundaries has a topological character: the flow is not perturbed by defects – the current just bends around them and continues with its onward flow. This is similar to strong water flow in a river that bends around boulders.

Topology is interested in properties that change step-wise, like the number of holes in these
objects. Topology also explains why electrical conductivity inside thin layers changes in integer steps.
Copyright © Johan Jarnestad/The Royal Swedish Academy of Sciences

Thouless figured out that here was a new kind of order, represented by a topological index that counts the number of edge states at the boundary. That’s just like how the number of holes (zero in a sphere, one in a doughnut, two in glasses, three in a pretzel) define the topology of a shape and the robustness of the shape so long as it is deformed smoothly and the number of holes remains unchanged.

Global, not local, properties

Interacting topological states are even more remarkable and truly bizarre in that they harbor fractionalized excitations. We’re used to thinking of an electron, for instance, with its charge of e as being indivisible. But, in the presence of strong interactions, as in the fractional quantum Hall experiments, the electron indeed fractionalizes into three pieces each carrying a third of a charge!

Haldane discovered a whole new paradigm: in a chain of spins with one unit of magnetic moment, the edge spins are fractionalized into units of one-half. Remarkably, the global topological properties of the chain completely determine the unusual behavior at the edges. Haldane’s remarkable predictions have been verified by experiments on solid state materials containing one-dimensional chains of magnetic ions.

Topological states are new additions to the list of phases of matter, such as, solid, liquid, gas, and even superfluids, superconductors and magnets. The laureates’ ideas have opened the floodgates for prizeworthy predictions and observations of topological insulators and topological superconductors. The cold atomic gases present opportunities beyond what can be achieved in materials because of the greater variety of atomic spin states and highly tunable interactions. Beyond the rewards of untangling fascinating aspects of our physical world, this research opens the possibility of using topologically protected states for quantum computing.

Nandini Trivedi, Professor of Physics, The Ohio State University

This article was originally published on The Conversation. Read the original article.

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By Stephen Clark, University of Bath.

The Nobel Prize in Physics for 2016 has been awarded to three British scientists working in the US for their theoretical work explaining strange states of matter, including superconductors, superfluids and thin magnetic films.

The prize was split between David J Thouless of the University of Washington, Duncan M Haldane of Princeton and J Michael Kosterlitz of Brown University. They will share a sum of US$928,000. Their work has helped shape an enormous amount of research over the past three decades and this well-deserved prize reflects the continuing importance of new discoveries that have and will continue to emerge from it.

“Normal” states of matter are ones you’re likely familiar with: solids, liquids and gases. The transition between these states is characterised by what is referred to as “symmetry breaking”.

For example, in a liquid, atoms are arranged uniformly in space and it looks identical no matter how you rotate it. However, when a liquid turns into a solid the atoms are locked into a crystal lattice. This new state of matter is less symmetrical in the sense that it only looks the same if it is rotated at certain angles. However, Thouless, Haldane and Kosterlitz found that matter is a lot more interesting than this. Their work showed how new phases of matter can occur where no symmetry is broken – and they used a mathematical idea to explain this. What distinguished these phases of matter – which display strange behaviour such as unusual patterns of electrical conductivity – were “topological properties”.

Topology is the mathematical study of how surfaces can be deformed continuously and smoothly. A famous example is the surface of an orange, a croissant, a coffee cup and a doughnut. To a mathematician, all these objects are imagined to be made of a malleable material that we are allowed to deform continuously without cutting or tearing. In this way an orange and croissant are identical, since we could mould both of them into a sphere. Likewise the coffee cup and doughnut are also the same to a mathematician because they both have one hole – the cup has a hole in its handle and the doughnut at its centre.

So, in this abstract sense the orange and croissant are in one distinct class, while the coffee cup and doughnut are in another. The difference between them boils down to whether their surface has a hole in it or not. This is the topological property of the object that is robust to any form of moulding we might do. The work of Thouless, Kosterlitz and Haldane made important steps in understanding how the notion of topology plays a role in the phases of matter.

This connection was exposed by considering the energies that electrons in materials can occupy – which can be plotted as a surface (when presented as a function of their momentum). In the 1980s scientists discovered that electrons in certain two-dimensional thin films move in a strange way when subjected to a strong magnetic field. These electrons order into perfectly conducting channels, located at the edge of the material, based on a quantum mechanical property known as spin.

What’s more, this conductivity increases in discrete steps as the magnetic field increases – an effect called the quantum Hall effect. Thouless and coworkers found that the “energy surface” for these materials could be described as a doughnut in topological terms, and the channels of energy that were seen were effectively the number of holes in that surface. Along with further work by Kosterlitz and Haldane on other systems, like vortices superconductors and hidden ordering in magnetic materials, their work demonstrated that the idea of topology could be used to predict the behaviour of solids.

Great promise

Thouless, Kosterlitz and Haldane’s work has laid the foundations for new emerging fields. In particular they have been crucial to an area of solid state physics called topological insulator materials. These are new three-dimensional materials that carry electricity on the surface but not in their interior. Their energy surface can also be described by topology. These materials have many “spintronic applications”, and heads of hard drives based on this technology are currently used in industry.

Technological applications of materials often rely on how they behave when they are “excited” as a result of some energy transfer. We can imagine an excitation as being a bit like a pulse travelling down a string if we shake it at one end.

One device that is currently being studied is made of topological insulator layered on top of a superconductor (a material with zero electrical resistance at low temperatures). If we poke this system in the right way then it is excited at the interface between the materials. These excitations carry a topological property, like a hole in a doughnut, which is robust to noise and imperfections that might scatter the excitation (which could be some sort of signal).

This effect is potentially very useful for quantum computing. The “bits” of data in a normal computer are 1 or 0. However a quantum computer uses quantum bits, which can be in superpositions of states (according to quantum mechanics) – making calculations super fast. Currently scaling quantum computing up to commercially applicable sizes is hampered by noise from the external environment, such as something shaking. However, by exploiting excitations of topological materials, the information encoded in them could be protected and preserved.

This is an exciting avenue of research that could help revolutionise information processing technologies.

Stephen Clark, Lecturer in Physics, University of Bath

This article was originally published on The Conversation. Read the original article.

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• [Video] Physicist’s New Theory Explains Why Time Travel Is Not Possible

A simple question from his wife—Does physics really allow people to travel back in time?—propelled physicist Richard Muller on a quest to resolve a fundamental problem that had puzzled him throughout his career: Why does the arrow of time flow inexorably toward the future, constantly creating new “nows?”

That quest resulted in a new book called NOW: The Physics of Time (W. W. Norton, 2016), which delves into the history of philosophers’ and scientists’ concepts of time, uncovers a tendency physicists have to be vague about time’s passage, demolishes the popular explanation for the arrow of time,“ and proposes a totally new theory.

His idea: Time is expanding because space is expanding.

“The new physics principle is that space and time are linked; when you create new space, you will create new time,” says Muller, a professor emeritus of the University of California, Berkeley.

In commenting on the theory and Muller’s new book, astrophysicist Neil deGrasse Tyson, host of the 2014 TV miniseries Cosmos: A Spacetime Odyssey, writes, “Maybe it’s right. Maybe it’s wrong. But along the way he’s given you a master class in what time is and how and why we perceive it the way we do.”

“Time has been a stumbling block to our understanding of the universe,” adds Muller. “Over my career, I’ve seen a lot of nonsense published about time, and I started thinking about it and realized I had a lot to say from having taught the subject over many decades, having thought about it, having been annoyed by it, having some really interesting ways of presenting it, and some whole new ideas that have never appeared in the literature.”

The origin of ‘now’

Ever since the Big Bang explosively set off the expansion of the universe 13.8 billion years ago, the cosmos has been growing, something physicists can measure as the Hubble expansion. They don’t think of it as stars flying away from one another, however, but as stars embedded in space and space continually expanding.

Muller takes his lead from Albert Einstein, who built his theory of general relativity—the theory that explains everything from black holes to cosmic evolution—on the idea of a four-dimensional spacetime. Space is not the only thing expanding, Muller says; spacetime is expanding. And we are surfing the crest of that wave, what we call “now.”

“Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as now,” he writes. “The future does not yet exist … it is being created. Now is at the boundary, the shock front, the new time that is coming from nothing, the leading edge of time.”

Because the future doesn’t yet exist, we can’t travel into the future, he asserts. He argues, too, that going back in time is equally improbable, since to reverse time you would have to decrease, at least locally, the amount of space in the universe. That does happen, such as when a star explodes or a black hole evaporates. But these reduce time so infinitesimally that the effect would be hidden in the quantum uncertainty of measurement—an instance of what physicists call cosmic censorship.

“The only example I could come up with is black hole evaporation, and in that case it turns out to be censored. So I couldn’t come up with any way to reverse time, and my basic conclusion is that time travel is not possible,” he says.

Merging black holes

Muller’s theory explaining the flow of time led to a collaboration with Caltech theoretician Shaun Maguire and a paper posted online in June that explains the theory in more detail—using mathematics—and proposes a way to test it using LIGO, an experiment that detects gravitational waves created by merging black holes. of time.”

If Muller and Maguire are right, then when two black holes merge and create new space, they should also create new time, which would delay the gravitational wave signal LIGO observes from Earth.

“The coalescing of two black holes creates millions of cubic miles of new space, which means a one-time creation of new time,” Muller says. The black hole merger first reported by LIGO in February 2016 involved two black holes weighing about 29 and 36 times the mass of the sun, producing a final black hole weighing about 62 solar masses. The new space created in the merger would produce about 1 millisecond of new time, which is near the detection level of LIGO. A similar event at one-third the distance would allow LIGO to detect the newly created time.

‘I expect controversy!’

Whether or not the theory pans out, Muller’s book makes a good case.

“[Muller] forges a new path. I expect controversy!” writes UC Berkeley Nobel laureate Saul Perlmutter, who garnered the 2011 Nobel Prize in Physics for discovering the accelerating expansion of the universe. Muller initiated the project that led to that discovery, which involved measuring the distances and velocities of supernovae. The implication of that discovery is that the progression of time is also accelerating, driven by dark energy.

For the book project, Muller explored previous explanations for the arrow of time and discovered that many philosophers and scientists have been flummoxed by the fact that we are always living in the “now:” from Aristotle and Augustine to Paul Dirac—the discoverer of antimatter, which can be thought of as normal matter moving backward in time—and Albert Einstein. While philosophers were not afraid to express an opinion, most physicists basically ignored the issue.

“No physics theories have the flow of time built into them in any way. Time was just the platform on which you did your calculations—there was no ‘now’ mentioned, no flow of time,” Muller says. “The idea of studying time itself did not exist prior to Einstein. Einstein gave physics the gift of time.”

Einstein, however, was unable to explain the flow of time into the future instead of into the past, despite the fact that the theories of physics work equally well going forward or backward in time. And although he could calculate different rates of time, depending on velocity and gravity, he had no idea why time flowed at all. The dominant idea today for the direction of time came from Arthur Eddington, who helped validate Einstein’s general theory of relativity. Eddington put forward the idea that time flows in the direction of increasing disorder in the universe, or entropy. Because the Second Law of Thermodynamics asserts that entropy can never decrease, time always increases.

Was Stephen Hawking wrong?

This idea has been the go-to explanation since. Even Stephen Hawking, in his book A Brief History of Time, doesn’t address the issue of the flow of time, other than to say that it’s “self-evident” that increasing time comes from increasing entropy.

“I don’t see any way that it affects our everyday lives. But it is fascinating.”

Muller argues, however, that it is not self-evident: it is just wrong. Life and everything we do on Earth, whether building houses or making teacups, involves decreasing the local entropy, even though the total entropy of the universe increases. “We are constantly discarding excess entropy like garbage, throwing it off to infinity in the form of heat radiation,” Muller says. “The entropy of the universe does indeed go up, but the local entropy, the entropy of the Earth and life and civilization, is constantly decreasing.

“During my first big experiment, the measurement of the cosmic microwave radiation, I realized there is 10 million times more entropy in that radiation than there is in all of the mass of the universe, and it’s not changing with time. Yet time is progressing,” he says. “The idea that the arrow of time is set by entropy does not make any predictions, it is simply a statement of a correlation. And to claim it is causation makes no sense.”

In his book, Muller explains the various paradoxes that arise from the way the theories of relativity and quantum mechanics treat time, including the Schrodinger’s cat conundrum and spooky action at a distance that quantum entanglement allows. Neither of these theories addresses the flow of time, however. Theories about wormholes that can transport you across the universe or back in time are speculative and, in many cases, wrong.

The discussion eventually leads Muller to explore deep questions about the ability of the past to predict the future and what that says about the existence of free will.

 

Muller admits that his new theory about time may have observable effects only in the cosmic realm, such as our interpretation of the red shift—the stretching of light waves caused by the expansion of space—which would have to be modified to reflect the simultaneous expansion of time. The two effects may not be distinguishable throughout most of the universe’s history, but the creation of time might be discernible during the rapid cosmic inflation that took place just after the Big Bang, when space and time expanded much, much faster than today.

He is optimistic that in the next few years LIGO will verify or falsify his theory.

“I think my theory is going to have an impact on calculations of the very early universe,” Muller says. “I don’t see any way that it affects our everyday lives. But it is fascinating.”

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by Robert Sanders-UC Berkeley.

Featured Image Credit:   Kjordand via Wikimedia Commons, CC BY-SA 4.0.

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To celebrate the 50th anniversary of the original Star Trek series premiere, physics professor (and sci-fi fan) David Grier offers a look into his New York University lab—the birthplace of the real-life tractor beam.

In this video, Grier explains how the technology works and how it could find practical use in everything from environmental science to space exploration.

“When we were first making the tractor beams in the lab, at first all we could do is move really tiny things very, very small distances—just over a micrometer, a millionth of a meter,” says Grier.

“We’re not lifting up an entire battle cruiser and hauling it across space but then once you’ve got centimeters, then to meters, the next step really is kilometers. And that’s what we’re working towards now.”

Grier’s work also appears in a Smithsonian documentary premiering September 4, 2016 at 7 pm.

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by  Sy Abudu, NYU. 

Featured Image Credit: Elijah van der Giessen/flickr, CC BY 2.0

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Scientists have used a single atom to capture high-resolution images of nanoscale material.

“This is the first tool of its kind,” says physicist Ania Jayich, associate director of the Materials Research Lab at UC Santa Barbara. “It operates from room temperature down to low temperatures where a lot of interesting physics happens. When thermal energy is low enough, the effects of electron interactions, for instance, become observable, leading to new phases of matter. And we can now probe these with unprecedented spatial resolution.”

Members of Jayich’s lab, the Quantum Sensing and Imaging Group, worked for two years to develop the radically new sensor technology, which is capable of nanometer-scale spatial resolution and exquisite sensitivity. Their findings appear in the journal Nature Nanotechnology.

DIAMOND-TIPPED ‘BRISTLES’

Under the microscope, the unique single-spin quantum sensor resembles a toothbrush. Each “bristle” contains a single, solid nanofabricated diamond crystal with a special defect, a nitrogen-vacancy (NV) center, located at the tip. Two adjacent atoms are missing in the diamond’s carbon lattice, and one space has been filled with a nitrogen atom, allowing for the sensing of specific material properties, particularly magnetism. These sensors were manufactured in the clean room of UC Santa Barbara’s Nanofabrication Facility.

The team chose to image a relatively well-studied superconducting material containing magnetic structures called vortices—localized regions of magnetic flux. With their instrument, the researchers were able to image individual vortices.

“Our tool is a quantum sensor because it relies on the bizarreness of quantum mechanics,” Jayich explains. “We put the NV defect into a quantum superposition where it can be one state or another—we don’t know—and then we let the system evolve in the presence of a field and measure it. This superposition uncertainty is what allows that measurement to occur.”

ROOM TEMPERATURE TO -450ºF

Such quantum behavior is often associated with low-temperature environments. However, the group’s specialized quantum instrument operates at room temperature and all the way down to 6 Kelvin (almost minus 450° Fahrenheit), making it very versatile, unique, and capable of studying various phases of matter and the associated phase transitions.

“A lot of other microscopy tools don’t have that temperature range,” Jayich explains. “Further highlights of our tool are its excellent spatial resolution, afforded by the fact that the sensor comprises a single atom. Plus, its size makes it non-invasive, meaning it minimally affects the underlying physics in the materials system.”

The team is currently imaging skyrmions—quasiparticles with magnetic vortex-like configurations—with immense appeal for future data storage and spintronic technologies. Leveraging their instrument’s nanoscale spatial resolution, they aim to determine the relative strengths of competing interactions in the material that give rise to skyrmions. “There are a lot of different interactions between atoms and you need to understand all of them before you can predict how the material will behave,” Jayich says.

“If you can image the size of the material’s magnetic domains and how they evolve on small length scales, that gives you information about the value and strength of these interactions,” she adds. “In the future, this tool will aid in understanding the nature and the strength of interactions in materials that then give rise to interesting new states and phases of matter, which are interesting from a fundamental physics perspective but also for technology.”

An Air Force Office of Scientific Research Presidential Early Career Award for Scientists and Engineers award, the Defense Advanced Research Projects Agency’s Quantum-Assisted Sensing and Readout program, and the Materials Research Science and Engineering Center program of the National Science Foundation supported the research.

Additional coauthors are from UC Santa Barbara and UCLA. Their findings appear in the journal Nature Nanotechnology.

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by Julie Cohen-UC Santa Barbara.

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The NoVA Neutrino Experiment is the largest neutrino detector in the world at this time, and includes the largest plastic block structure ever built, known as the “Far Detector.” The 260 members of the NOvA Neutrino Experiment recently reported their initial findings in two papers. The team is trying get a clearer picture of the role neutrinos, mysterious subatomic particles, played in the evolution of the cosmos.

The first paper, in Physical Review Letters, describes the first appearance of electron neutrinos in the NOvA experiment. A second paper, in Physical Review D, describes the disappearance of muon neutrinos in the experiment.

Taken together, the papers offer insights into fundamental neutrino properties such as mass, the way neutrinos oscillate from one type to another, and whether neutrinos are a key to the dominance of matter in the universe.

“THESE ARE ABSOLUTELY STUNNING ELECTRON NEUTRINO EVENTS. WE’VE LOOKED AT THEM AND THEY’RE TEXTBOOK PERFECT—ALL 11 OF THEM SO FAR.”

In a presentation describing the results, physicist Mayly Sanchez clicked to a slide showing the telltale track of an electron neutrino racing through the 14,000-ton Far Detector of the experiment.

Since that detector started full operations in November 2014, two analyses of data from the long-distance experiment have made the first experimental observations of muon neutrinos changing to electron neutrinos.

One analysis found 11 such transitions. Sanchez wrote on her slide, “All 11 of them are absolutely gorgeous.”

HOW THE EXPERIMENT WORKS

NOνA scientists use a 300-ton particle detector at US Department of Energy’s Fermilab near Chicago (the Near Detector) and a 14,000-ton detector in northern Minnesota (the Far Detector) to study neutrino oscillations. The Near Detector sits in a cavern 350 feet underground and measures the composition of the neutrino beam as it leaves the Fermilab site. As they travel straight through the earth, the neutrinos oscillate. The Far Detector records what types of neutrino arrive in Minnesota.

Sanchez, an Iowa State University associate professor of physics and astronomy who is also an Intensity Frontier Fellow at Fermilab, is one of the leaders of the NOvA experiment. She serves on the experiment’s executive committee and co-leads the analysis of electron neutrino appearance in the Far Detector.

The paper about electron neutrino appearance reports two, independent analyses of detector data: One found six cases of the muon neutrinos sent to the Far Detector oscillating into electron neutrinos. The other found 11 oscillations. If there were no oscillations, researchers predicted there would be one electron neutrino observed in the Far Detector.

Sanchez says the flickering electron neutrino tracks she helped analyze prove the experiment can do what it was designed to do—spotting and measuring neutrinos after they make the 500-mile, 3-millisecond journey from Fermilab to the Far Detector in northern Minnesota.

The detector is huge: 344,000 plastic cells within a structure 200 feet long, 50 feet high, and 50 feet wide, making it the world’s largest freestanding plastic structure.

“The big news here is we observed electron neutrino appearance,” Sanchez says.

If the calibrations and parameters had been just a little off, “we might not have seen anything,” she says. “When you design an experiment like this, you hope that nature is kind to you and allows you to do a measurement.”

In this case, physicists are detecting and measuring mysterious and lightweight neutrinos. They’re subatomic particles that are among the most abundant in the universe but almost never interact with matter. They’re created in nature by the sun, by collapsing stars, and by cosmic rays interacting with the atmosphere. They’re also created by nuclear reactors and particle accelerators.

There are three types of neutrinos: electron, muon, and tau. As they travel at almost the speed of light, they oscillate from one type to another. Takaaki Kajita of Japan and Arthur B. McDonald of Canada won the 2015 Nobel Prize in Physics for their contributions to the independent, experimental discoveries of neutrino oscillation.

3 GOALS OF NOVA

The NOvA experiment has three main physics goals: make the first observations of muon neutrinos changing to electron neutrinos, determine the tiny masses of the three neutrino types, and look for clues that help explain how matter came to dominate antimatter in the universe.

At the beginning of the universe, physicists believe there were equal amounts of matter and antimatter. That’s actually a problem because matter and antimatter annihilate each other when they touch.

But the universe still exists. So something happened to throw off that balance and create a universe full of matter. Could it be that neutrinos decayed asymmetrically and tipped the scales toward matter?

The NOvA experiment, as it takes more and more neutrino data, could provide some answers.

Sanchez likes the data she’s seen: “These are absolutely stunning electron neutrino events. We’ve looked at them and they’re textbook perfect—all 11 of them so far.”

For the details on how the NoVA experiment works the visit Fermilab’s NOvA Neutrino Experiment page, and you can also click here to view live data from the experiment.

Click here to view a time lapse video of Far Detector’s construction.

The experimental findings were published in Physical Review Letters, and  Physical Review D. 

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by Mike Krapfl-Iowa State.

Featured Photo Credit:  Reidar Hahn/Fermilab, the NoVA Near Detector.

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By Roger Jones, Lancaster University.

Antimatter was one of the most exciting physics discoveries of the 20th century. Picked up by fiction writers such as Dan Brown, many people think of it as an “out there” theoretical idea – unaware that it is actually being produced every day. What’s more, research on antimatter is actually helping us to understand how the universe works.

Antimatter is a material composed of so-called antiparticles. It is believed that every particle we know of has an antimatter companion that is virtually identical to itself, but with the opposite charge. For example, an electron has a negative charge. But its antiparticle, called a positron, has the same mass but a positive charge. When a particle and its antiparticle meet, they annihilate each other – disappearing in a burst of light.

Such particles were first predicted by British physicist Paul Dirac when he was trying to combine the two great ideas of early modern physics: relativity and quantum mechanics. Previously, scientists were stumped by the fact that it seemed to predict that particles could have energies lower than when they were at “rest” (ie pretty much doing nothing). This seemed impossible at the time, as it meant that energies could be negative.

Dirac, however, accepted that the equations were telling him that particles are really filling a whole “sea” of these lower energies – a sea that had so far been invisible to physicists as they were only looking “above the surface”. He envisioned that all of the “normal” energy levels that exist are accounted for by “normal” particles. However, when a particle jumps up from a lower energy state, it appears as a normal particle but leaves a “hole”, which appears to us as a strange, mirror-image particle – antimatter.

Despite initial scepticism, examples of these particle-antiparticle pairs were soon found. For example, they are produced when cosmic rays hit the Earth’s atmosphere. There is even evidence that the energy in thunderstorms produces anti-electrons, called positrons. These are also produced in some radioactive decays, a process used in many hospitals in Positron Emission Tomography (PET) scanners, which allow precise imaging within human bodies. Nowadays, experiments at the Large Hadron Collider (LHC) can produce matter and antimatter, too.

Matter-antimatter mystery

Physics predicts that matter and antimatter must be created in almost equal quantities, and that this would have been the case during the Big Bang. What’s more, it is predicted that the laws of physics should be the same if a particle is interchanged with its antiparticle – a relationship known as CP symmetry. However, the universe we see doesn’t seem to obey these rules. It is almost entirely made of matter, so where did all the antimatter go? It is one of the biggest mysteries in physics to date.

Experiments have shown that some radioactive decay processes do not produce an equal amount of antiparticles and particles. But it is not enough to explain the disparity between amounts of matter and antimatter in the universe. Consequently, physicists such as myself at the LHC, on ATLAS, CMS and LHCb, and others doing experiments with neutrinos such as T2K in Japan, are looking for other processes that could explain the puzzle.

Other groups of physicists such as the Alpha Collaboration at CERN are working at much lower energies to see if the properties of antimatter really are the mirror of their matter partners. Their latest results show that an anti-hydrogen atom (made up of an anti-proton and an anti-electron, or positron) is electrically neutral to an accuracy of less than one billionth of the charge of an electron. Combined with other measurements, this implies that the positron is equal and opposite to the charge of the electron to better than one part in a billion – confirming what is expected of antimatter.

However, a great many mysteries remain. Experiments are also investigating whether gravity affects antimatter in the same way that it affects matter. If these exact symmetries are shown to be broken, it will require a fundamental revision of our ideas about physics, affecting not only particle physics but also our understanding of gravity and relativity.

In this way, antimatter experiments are allowing us to put our understanding of the fundamental workings of the universe to new and exciting tests. Who knows what we will find?

Roger Jones, Professor of Physics, Head of Department, Lancaster University

This article was originally published on The Conversation. Read the original article.

Featured Photo Credit: Thomas Bresson/Flickr, CC BY-SA

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Scientists have determined that two-dimensional boron is a natural low-temperature superconductor. In fact, it may be the only 2D material with such potential.

Theoretical physicist Boris Yakobson and colleagues at Rice University published their calculations that show atomically flat boron is metallic and will transmit electrons with no resistance. The work appears in journal Nano Letters.

The hitch, as with most superconducting materials, is that it loses its resistivity only when very cold, in this case between 10 and 20 kelvins (roughly, minus-430 degrees Fahrenheit). But for making very small superconducting circuits, it might be the only game in town.

The basic phenomenon of superconductivity has been known for more than 100 years, said Evgeni Penev, a research scientist in the Yakobson group, but had not been tested for its presence in atomically flat boron.

“It’s well-known that the material is pretty light because the atomic mass is small,” Penev says. “If it’s metallic too, these are two major prerequisites for superconductivity. That means at low temperatures, electrons can pair up in a kind of dance in the crystal.”

“Lower dimensionality is also helpful,” Yakobson says. “It may be the only, or one of very few, two-dimensional metals. So there are three factors that gave the initial motivation for us to pursue the research. Then we just got more and more excited as we got into it.”

Electrons with opposite momenta and spins effectively become Cooper pairs; they attract each other at low temperatures with the help of lattice vibrations, the so-called “phonons,” and give the material its superconducting properties, Penev explains.

“Superconductivity becomes a manifestation of the macroscopic wave function that describes the whole sample. It’s an amazing phenomenon,” he says.

THE FIRST SAMPLES OF BORON

It wasn’t entirely by chance that the first theoretical paper establishing conductivity in a 2D material appeared at roughly the same time the first samples of the material were made by laboratories in the United States and China. In fact, an earlier paper by the Yakobson group had offered a road map for doing so.

That 2D boron has now been produced is a good thing, according to Yakobson and lead authors Penev and Alex Kutana, a postdoctoral researcher at Rice.

“We’ve been working to characterize boron for years, from cage clusters to nanotubes to planer sheets, but the fact that these papers appeared so close together means these labs can now test our theories,” Yakobson says.

“In principle, this work could have been done three years ago as well,” he adds. “So why didn’t we? Because the material remained hypothetical; okay, theoretically possible, but we didn’t have a good reason to carry it too far.

“But then last fall it became clear from professional meetings and interactions that it can be made. Now those papers are published. When you think it’s coming for real, the next level of exploration becomes more justifiable,” Yakobson says.

Boron atoms can make more than one pattern when coming together as a 2D material, another characteristic predicted by Yakobson and his team that has now come to fruition. These patterns, known as polymorphs, may allow researchers to tune the material’s conductivity “just by picking a selective arrangement of the hexagonal holes,” Penev says.

He also notes boron’s qualities were hinted at when researchers discovered more than a decade ago that magnesium diborite is a high-temperature electron-phonon superconductor.

“People realized a long time ago the superconductivity is due to the boron layer,” Penev says. “The magnesium acts to dope the material by spilling some electrons into the boron layer. In this case, we don’t need them because the 2D boron is already metallic.”

Penev suggests that isolating 2D boron between layers of inert hexagonal boron nitride (aka “white graphene”) might help stabilize its superconducting nature.

The Office of Naval Research and the Department of Energy Office of Basic Energy Sciences supported the research, which was published in the journal Nano Letters.

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by Mike Williams-Rice.

Featured Image Credit: Evgeni Penev/Rice University

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Theoretical physicists have used a super computer to simulate Einstein’s theory of general relativity in more than 4 dimensions, and in the process have discovered a special type of black hole that would cause the general relativity concepts to break down completely if one formed.  It’s an interesting proposition, because only four dimensions have been proven to exist, although theoretical physicists have proposed up to 11 total dimensions in order to describe the behavior of the universe.

This new simulation, completed by researchers from University of Cambridge and Queen Mary University of London, found that in 5 dimensions, a special form of ring-shaped black hole could break down and create a “naked singularity,” violating the predictions of general relativity.

An excellent press release on the EurekAlert website provides the fascinating details of this novel research:

Researchers have shown how a bizarrely shaped black hole could cause Einstein’s general theory of relativity, a foundation of modern physics, to break down. However, such an object could only exist in a universe with five or more dimensions.

The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of ‘bulges’ connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.

Ring-shaped black holes were ‘discovered’ by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a ‘naked singularity’, which would cause the equations behind general relativity to break down. The results are published in the journal Physical Review Letters.

General relativity underpins our current understanding of gravity: everything from the estimation of the age of the stars in the universe, to the GPS signals we rely on to help us navigate, is based on Einstein’s equations. In part, the theory tells us that matter warps its surrounding spacetime, and what we call gravity is the effect of that warp. In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities.

Continue reading to learn why singularities are an Achilles heel for general relativity and how a “naked singularity” might form.

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