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  • richardmitnick 3:59 pm on May 27, 2016 Permalink | Reply
    Tags: , , Majorana fermions, Physics   

    From Caltech: “Engineering Nanodevices to Store Information the Quantum Way” 

    Caltech Logo

    Caltech

    05/27/2016
    Jessica Stoller-Conrad

    Creating quantum computers which some people believe will be the next generation of computers, with the ability to outperform machines based on conventional technology—depends upon harnessing the principles of quantum mechanics, or the physics that governs the behavior of particles at the subatomic scale. Entanglement—a concept that Albert Einstein once called “spooky action at a distance”—is integral to quantum computing, as it allows two physically separated particles to store and exchange information.

    1
    Stevan Nadj-Perge, assistant professor of applied physics and materials science. Credit: Photo courtesy of S. Nadj-Perge

    Stevan Nadj-Perge, assistant professor of applied physics and materials science, is interested in creating a device that could harness the power of entangled particles within a usable technology. However, one barrier to the development of quantum computing is decoherence, or the tendency of outside noise to destroy the quantum properties of a quantum computing device and ruin its ability to store information.

    Nadj-Perge, who is originally from Serbia, received his undergraduate degree from Belgrade University and his PhD from Delft University of Technology in the Netherlands. He received a Marie Curie Fellowship in 2011, and joined the Caltech Division of Engineering and Applied Science in January after completing postdoctoral appointments at Princeton and Delft.

    He recently talked with us about how his experimental work aims to resolve the problem of decoherence.

    What is the overall goal of your research?

    A large part of my research is focused on finding ways to store and process quantum information. Typically, if you have a quantum system, it loses its coherent properties—and therefore, its ability to store quantum information—very quickly. Quantum information is very fragile and even the smallest amount of external noise messes up quantum states. This is true for all quantum systems. There are various schemes that tackle this problem and postpone decoherence, but the one that I’m most interested in involves Majorana fermions. These particles were proposed to exist in nature almost eighty years ago but interestingly were never found.

    Relatively recently theorists figured out how to engineer these particles in the lab. It turns out that, under certain conditions, when you combine certain materials and apply high magnetic fields at very cold temperatures, electrons will form a state that looks exactly as you would expect from Majorana fermions. Furthermore, such engineered states allow you to store quantum information in a way that postpones decoherence.

    How exactly is quantum information stored using these Majorana fermions?

    The fascinating property of these particles is that they always come in pairs. If you can store information in a pair of Majorana fermions it will be protected against all of the usual environmental noise that affects quantum states of individual objects. The information is protected because it is not stored in a single particle but in the pair itself. My lab is developing ways to engineer nanodevices which host Majorana fermions. Hopefully one day our devices will find applications in quantum computing.

    Why did you want to come to Caltech to do this work?

    The concept of engineered Majorana fermions and topological protection was, to a large degree, conceived here at Caltech by Alexei Kiteav [Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics] who is in the physics department. A couple of physicists here at Caltech, Gil Refeal [professor of theoretical physics and executive officer of physics] and Jason Alicea [professor of theoretical physics], are doing theoretical work that is very relevant for my field.

    Do you have any collaborations planned here?

    Nothing formal, but I’ve been talking a lot with Gil and Jason. A student of mine also uses resources in the lab of Harry Atwater [Howard Hughes Professor of Applied Physics and Materials Science and director of the Joint Center for Artificial Photosynthesis], who has experience with materials that are potentially useful for our research.

    How does that project relate to your lab’s work?

    There are two-dimensional, or 2-D, materials that are basically very thin sheets of atoms. Graphene—a single layer of carbon atoms—is one example, but you can create single layer sheets of atoms with many materials. Harry Atwater’s group is working on solar cells made of a 2-D material. We are thinking of using the same materials and combining them with superconductors—materials that can conduct electricity without releasing heat, sound, or any other form of energy—in order to produce Majorana fermions.

    How do you do that?

    There are several proposed ways of using 2-D materials to create Majorana fermions. The majority of these materials have a strong spin-orbit coupling—an interaction of a particle’s spin with its motion—which is one of the key ingredients for creating Majoranas. Also some of the 2-D materials can become superconductors at low temperatures. One of the ideas that we are seriously considering is using a 2-D material as a substrate on which we could build atomic chains that will host Majorana fermions

    What got you interested in science when you were young?

    I don’t come from a family of scientists; my father is an engineer and my mother is an administrative worker. But my father first got me interested in science. As an engineer, he was always solving something and he brought home some of the problems he was working. I worked with him and picked it up at an early age.

    How are you adjusting to life in California?

    Well, I like being outdoors, and here we have the mountains and the beach and it’s really amazing. The weather here is so much better than the other places I’ve lived. If you want to get the impression of what the weather in the Netherlands is like, you just replace the number of sunny days here with the number of rainy days there.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
    Caltech buildings

     
  • richardmitnick 12:57 pm on May 25, 2016 Permalink | Reply
    Tags: , Has a Hungarian physics lab found a fifth force of nature?, , Physics   

    From Nature: “Has a Hungarian physics lab found a fifth force of nature?” 

    Nature Mag
    Nature

    25 May 2016
    Edwin Cartlidge

    1
    Physicists at the Institute for Nuclear Research in Debrecen, Hungary, say this apparatus — an electron-positron spectrometer — has found evidence for a new particle.

    A laboratory experiment in Hungary has spotted an anomaly in radioactive decay that could be the signature of a previously unknown fifth fundamental force of nature, physicists say – if the finding holds up.

    Attila Krasznahorkay at the Hungarian Academy of Sciences’s Institute for Nuclear Research in Debrecen, Hungary, and his colleagues reported their surprising result* in 2015 on the arXiv preprint server, and this January in the journal Physical Review Letters. But the report – which posited the existence of a new, light boson only 34 times heavier than the electron – was largely overlooked.

    Then, on 25 April, a group of US theoretical physicists brought the finding to wider attention by publishing its own analysis of the result** on arXiv2. The theorists showed that the data didn’t conflict with any previous experiments – and concluded that it could be evidence for a fifth fundamental force. “We brought it out from relative obscurity,” says Jonathan Feng, at the University of California, Irvine, the lead author of the arXiv report.

    Four days later, two of Feng’s colleagues discussed the finding at a workshop at the SLAC National Accelerator Laboratory in Menlo Park, California. Researchers there were sceptical but excited about the idea, says Bogdan Wojtsekhowski, a physicist at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. “Many participants in the workshop are thinking about different ways to check it,” he says. Groups in Europe and the United States say that they should be able to confirm or rebut the Hungarian experimental results within about a year.

    Search for new forces

    Gravity, electromagnetism and the strong and weak nuclear forces are the four fundamental forces known to physics — but researchers have made many as-yet unsubstantiated claims of a fifth. Over the past decade, the search for new forces has ramped up because of the inability of the standard model of particle physics to explain dark matter — an invisible substance thought to make up more than 80% of the Universe’s mass.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Theorists have proposed various exotic-matter particles and force-carriers, including “dark photons”, by analogy to conventional photons that carry the electromagnetic force.

    Krasznahorkay says his group was searching for evidence of just such a dark photon – but Feng’s team think they found something different. The Hungarian team fired protons at thin targets of lithium-7, which created unstable beryllium-8 nuclei that then decayed and spat out pairs of electrons and positrons. According to the standard model, physicists should see that the number of observed pairs drops as the angle separating the trajectory of the electron and positron increases. But the team reported that at about 140º, the number of such emissions jumps — creating a ‘bump’ when the number of pairs are plotted against the angle — before dropping off again at higher angles.

    Bump in confidence

    Krasznahorkay says that the bump is strong evidence that a minute fraction of the unstable beryllium-8 nuclei shed their excess energy in the form of a new particle, which then decays into an electron–positron pair. He and his colleagues calculate the particle’s mass to be about 17 megaelectronvolts (MeV).

    “We are very confident about our experimental results,” says Krasznahorkay. He says that the team has repeated its test several times in the past three years, and that it has eliminated every conceivable source of error. Assuming it has done so, then the odds of seeing such an extreme anomaly if there were nothing unusual going on are about 1 in 200 billion, the team says.

    Feng and colleagues say that the 17-MeV particle is not a dark photon. After analysing the anomaly and looking for properties consistent with previous experimental results, they concluded that the particle could instead be a “protophobic X boson”. Such a particle would carry an extremely short-range force that acts over distances only several times the width of an atomic nucleus. And where a dark photon (like a conventional photon) would couple to electrons and protons, the new boson would couple to electrons and neutrons. Feng says that his group is currently investigating other kinds of particles that could explain the anomaly. But the protophobic boson is “the most straightforward possibility”, he says.

    Unconventional coupling

    Jesse Thaler, a theoretical physicist at the Massachusetts Institute of Technology (MIT) in Cambridge, says that the unconventional coupling proposed by Feng’s team makes him sceptical that the new particle exists. “It certainly isn’t the first thing I would have written down if I were allowed to augment the standard model at will,” he says. But he adds that he is “paying attention” to the proposal. “Perhaps we are seeing our first glimpse into physics beyond the visible Universe,” he says.

    Researchers should not have to wait long to find out whether a 17-MeV particle really does exist. The DarkLight experiment at the Jefferson Laboratory is designed to search for dark photons with masses of 10–100 MeV, by firing electrons at a hydrogen gas target. Now, says collaboration spokesperson Richard Milner of MIT, it will target the 17-MeV region as a priority, and within about a year, could either find the proposed particle or set stringent limits on its coupling with normal matter.

    Also searching for the proposed boson will be the LHCb experiment at CERN, Europe’s particle-physics lab near Geneva, which will study quark–antiquark decays, and two experiments that will fire positrons at a fixed target — one at the INFN Frascati National Laboratory near Rome, due to switch on in 2018, and the other at the Budker Institute of Nuclear Physics in the Siberian town of Novosibirsk, Russia.

    Rouven Essig, a theoretical physicist at Stony Brook University in New York and one of the organizers of the SLAC workshop, thinks that the boson’s “somewhat unexpected” properties make a confirmation unlikely. But he welcomes the tests. “It would be crazy not to do another experiment to check this result,” he says. “Nature has surprised us before!”

    *Science paper:
    Observation of Anomalous Internal Pair Creation in 8Be: A Possible Signature of a Light, Neutral Boson

    **Science paper:
    Evidence for a Protophobic Fifth Force from 8Be Nuclear Transitions

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 9:36 pm on May 24, 2016 Permalink | Reply
    Tags: , , , Physics   

    From Ethan Siegel: “Where Is New Physics Hiding, And How Can We Find It?” 

    From Forbes

    May 24, 2016
    Sabine Hossenfelder

    1
    The particle tracks emanating from a high energy collision at the LHC in 2014. Image credit: Wikimedia Commons user Pcharito, under a c.c.a.-by-s.a.-3.0 license.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN/CMS Detector
    CERN/CMS Detector

    The year is 2016, and physicists are restless. Four years ago, the LHC confirmed the Higgs boson, the last outstanding prediction of the Standard Model. The chances were good, so they thought, that the LHC would also discover other new particles – naturalness seem to demand it. But, so far, given all the data they’ve collected, their greatest hopes appear to be phantasms.

    The Standard Model and General Relativity do a great job, but physicists know this can’t be it. Or at least they think they know: the theories are incomplete, not only disagreeable and staring each other in the face without talking, but inadmissibly wrong, giving rise to paradoxa with no known cure. There has to be more to find, somewhere. But where?

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The hiding places for novel phenomena are getting smaller. But physicists haven’t yet exhausted their options. Here are the most promising areas where they currently search:

    1.) Weak Coupling. Particle collisions at high energies, like those reached at the LHC, can produce all existing particles up to the energy that the colliding particles had.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    The amount of new particles you make, however, depends on the strength by which they couple to the particles that were brought to collision (for the LHC that’s protons, or their constituents quarks and gluons, respectively). A particle that couples very weakly might be produced so rarely that it could have gone unnoticed so far.

    Physicists have proposed many new particles which fall into this category because weakly interacting stuff generally looks a lot like dark matter. Most notably there are the weakly interacting massive particles (WIMPs), sterile neutrinos (that are neutrinos which don’t couple to the known leptons), and axions (proposed to solve the strong CP problem and also a dark matter candidate).

    2
    Limits on the dark matter/nucleon recoil cross-section, including the projected predicted sensitivity of XENON1T. Image credit: Ethan Brown of RPI, via http://ignatz.phys.rpi.edu/site/index.php/the-experiment/.

    These particles are being looked for both by direct detection measurements – monitoring large tanks in underground mines for rare interactions – and by looking out for unexplained astrophysical processes that could make for an indirect signal.

    JUNO Chinese Neutrino Experiment
    JUNO Chinese Neutrino Experiment

    Sudbury Neutrino Observatory
    Sudbury Neutrino Observatory

    Sanford Underground levels
    SURF

    2.) High Energies. If the particles are not of the weakly interacting type, we would have noticed them already, unless their mass is beyond the energy that we have reached so far with particle colliders. In this category we find all the supersymmetric partner particles, which are much heavier than the standard model particles because supersymmetry is broken. Also at high energies could hide excitations of particles that exist in models with compactified extra dimensions. These excitations are similar to higher harmonics of a string and show up at certain discrete energy levels which depend on the size of the extra dimension.

    3
    The supersymmetric particles, next to the (normal) Standard Model ones. Image credit: DESY at Hamburg.

    Strictly speaking, it isn’t the mass that is relevant to the question whether a particle can be discovered, but the energy necessary to produce the particles, which includes binding energy. An interaction like the strong nuclear force, for example, displays “confinement” which means that it takes a lot of energy to tear quarks apart even though their masses are not all that large. Hence, quarks could have constituents – often called “preons” – that have an interaction – dubbed “technicolor” – similar to the strong nuclear force. The most obvious models of technicolor however ran into conflict with data decades ago. The idea however isn’t entirely dead, and though the surviving models aren’t presently particularly popular, some variants are still viable.

    These phenomena are being looked for at the LHC and also in highly energetic cosmic ray showers.

    3.) High Precision. High precision tests of standard model processes are complementary to high energy measurements. They can be sensitive to tiniest effects stemming from virtual particles with energies too high to be produced at colliders, but still making a contribution at lower energies due to quantum effects. Examples for this are proton decay, neutron-antineutron oscillation, the muon g-2, the neutron electric dipole moment, or Kaon oscillations. There are existing experiments for all of these, searching for deviations from the standard model, and the precision for these measurements is constantly increasing.

    4
    A diagram of neutrinoless double beta decay. The decay time through this pathway is much longer than the age of the Universe. Image credit: public domain image by JabberWok2.

    A somewhat different high precision test is the search for neutrinoless double-beta decay which would demonstrate that neutrinos are Majorana-particles, an entirely new type of particle. (When it comes to fundamental particles that is. Majorana particles have recently been produced as emergent excitations in condensed matter systems.)

    Majorano Demonstrator Experiment
    Majorano Demonstrator Experiment

    4.) Long ago. In the early universe, matter was much denser and hotter than we can hope to ever achieve in our particle colliders. Hence, signatures left over from this time can deliver a bounty of new insights. The temperature fluctuations in the cosmic microwave background (B-modes and non-Gaussianities) may be able to test scenarios of inflation or its alternatives (like phase transitions from a non-geometric phase), whether our universe had a big bounce instead of a big bang, and – with some optimism – even whether gravity was quantized back them.

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck

    5
    A Universe with dark energy: our Universe. Image credit: NASA / WMAP Science Team.

    5.) Far away. Some signatures of new physics appear on long distances rather than of short. An outstanding question is for example what’s the shape of the universe?

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Is it really infinitely large, or does it close back onto itself? And if it does, then how does it do this? One can study these questions by looking for repeating patterns in the temperature fluctuation of the cosmic microwave background (CMB).

    If we live in a multiverse, it might occasionally happen that two universes collide, and this too would leave a signal in the CMB.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/
    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    Another novel phenomenon that would become noticeable on long distances is a fifth force, which would lead to subtle deviations from general relativity. This might have all kinds of effects, from violations of the equivalence principle to a time-dependence of dark energy. Hence, there are experiments testing the equivalence principle and the constancy of dark energy to every higher precision.

    6
    A schematic to explain the polarizations in the double slit quantum eraser experiment of Kim et al. 2007. Image credit: Wikimedia Commons user Patrick Edwin Moran under a c.c.a.-by-s.a. 3.0 license.

    6.) Right here. Not all experiments are huge and expensive. While tabletop discoveries have become increasingly unlikely simply because we’ve pretty much tried all that could be done, there are still areas where small-scale lab experiments reach into unknown territory. This is the case notably in the foundations of quantum mechanics, where nanoscale devices, single photon sources and – detectors, and increasingly sophisticated noise-control techniques have enabled previously impossible experiments. Maybe one day we’ll be able to solve the dispute over the “correct” interpretation of quantum mechanics simply by measuring which one is right.

    Physics is far from over. It has become more difficult to test new fundamental theories, but we are pushing the limits in many currently running experiments. There must be new physics out there; we simply need to look at higher energies, higher precisions, or at more subtle effects. If nature is kind to us, this decade might finally be the one that sees us break through the Standard Model to the novel Universe beyond.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 7:49 am on May 21, 2016 Permalink | Reply
    Tags: Physics, , , Planck scale   

    From Symmetry: “The Planck scale” 

    Symmetry Mag

    Symmetry

    05/19/16
    Rashmi Shivni

    The Planck scale sets the universe’s minimum limit, beyond which the laws of physics break.

    1
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    In the late 1890s, physicist Max Planck proposed a set of units to simplify the expression of physics laws. Using just five constants in nature (including the speed of light and the gravitational constant), you, me and even aliens from Alpha Centauri could arrive at these same Planck units.

    The basic Planck units are length, mass, temperature, time and charge.

    Let’s consider the unit of Planck length for a moment. The proton is about 100 million trillion times larger than the Planck length. To put this into perspective, if we scaled the proton up to the size of the observable universe, the Planck length would be a mere trip from Tokyo to Chicago. The 14-hour flight may seem long to you, but to the universe, it would go completely unnoticed.

    The Planck scale was invented as a set of universal units, so it was a shock when those limits also turned out to be the limits where the known laws of physics applied. For example, a distance smaller than the Planck length just doesn’t make sense—the physics breaks down.

    Physicists don’t know what actually goes on at the Planck scale, but they can speculate. Some theoretical particle physicists predict all four fundamental forces—gravity, the weak force, electromagnetism and the strong force—finally merge into one force at this energy. Quantum gravity and superstrings are also possible phenomena that might dominate at the Planck energy scale.

    The Planck scale is the universal limit, beyond which the currently known laws of physics break. In order to comprehend anything beyond it, we need new, unbreakable physics.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:13 pm on May 19, 2016 Permalink | Reply
    Tags: Alexander Zamolodchikov, , Physics,   

    From Rutgers: “Rutgers Physics Professor Elected to National Academy of Sciences” 

    Rutgers University
    Rutgers University

    May 16, 2016

    Todd Bates
    848-932-0550
    908-208-3422
    tbates@ucm.rutgers.edu

    Alexander Zamolodchikov, a renowned professor of physics at Rutgers University, has been elected to the prestigious National Academy of Sciences.

    He joins 83 other newly elected members and 21 foreign associates from 14 countries. They were named in recognition of their distinguished and ongoing research achievements, according to the academy. New members will be formally inducted into the academy at its annual meeting next year.

    “I am pleased and excited, and I will be greatly honored to become a part of this distinguished institution,” Zamolodchikov said. “I regard this as recognition of the overall importance of the area of theoretical physics which I, along with my colleagues at Rutgers and around the world, have helped to develop.”

    1
    Photo: Alexander Zamolodchikov, professor of physics at Rutgers University. Courtesy of Alexander Zamolodchikov

    Zamolodchikov, known as Sasha, is a native of Dubna in the Moscow Region of Russia. He’s conducted groundbreaking research in theoretical and mathematical physics, focusing on quantum field theories and statistical physics. His most notable research is in the areas of conformal and integrable quantum field theories.

    Zamolodchikov, Board of Governors professor of physics at Rutgers, earned a master’s degree in nuclear physics and engineering at the Moscow Institute of Physics and Technology. He earned a doctorate in theoretical and mathematical physics at the Institute of Theoretical and Experimental Physics in Moscow in 1978.

    Zamolodchikov was a researcher at the L.D. Landau Institute for Theoretical Physics in Moscow from 1978 to 1990, when he became a professor of physics at Rutgers. He became a Board of Governor’s professor of physics at Rutgers in 2005.

    Zamolodchikov has won numerous awards and honors, including: the Lenin Komsomol Prize; American Physical Society Dannie Heineman Prize for Mathematical Physics; Alexander von Humboldt Research Award; Chair Blaise Pascal; American Physical Society Lars Onsager Prize; ICTP Dirac Medal; and Pomeranchuk Prize. He is a fellow of the American Physical Society and a member of the American Academy of Arts and Sciences. He also won a John Simon Guggenheim Memorial Foundation Fellowship.

    With its recent announcement, the National Academy of Sciences now has 2,291 active members, along with 465 foreign associates. Foreign associates are nonvoting members who are not U.S. citizens.

    The National Academy of Sciences – a private, nonprofit institution established in 1863 under a congressional charter signed by President Abraham Lincoln – recognizes achievement in science. It provides science, technology and health policy advice to the federal government and other organizations through the National Academy of Engineering, Institute of Medicine and National Research Council.

    See the full article here .

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    Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

    Founded in 1766, Rutgers teaches across the full educational spectrum: preschool to precollege; undergraduate to graduate; postdoctoral fellowships to residencies; and continuing education for professional and personal advancement.

    Rutgers Original seal

     
  • richardmitnick 12:05 pm on May 14, 2016 Permalink | Reply
    Tags: , , Physics, Six physics equations that changed the course of history   

    From COSMOS: “Six physics equations that changed the course of history” 

    Cosmos Magazine bloc

    COSMOS

    3 May 2016 [this just appeared in social media]
    Cathal O’Connell

    1
    Illustration: Alison Mackey/Discover, Apple: Thinkstock

    Physics equations are forms of magic. They allow us to explain the past, such as why Halley’s comet visits every 76 years, and predict the future – as far as the ultimate fate of the Universe.

    They place limits on the possible, as in the efficiency of an engine, and they reveal possibilities we could never have imagined, such as the energy inside an atom.

    Occasionally over the past few centuries, a new equation endowed the next generation with a new magical tool, and so changed the course of history. Here are some of the most pivotal.

    1. Newton’s second law of motion (1687)

    What does it say?

    Force equals mass times acceleration.

    In other words …

    It’s easier to push an empty shopping cart than a full one.

    What did it teach us?

    Together with Isaac Newton’s other two laws of motion (the first says you need a force to move something, the third says every action has an equal and opposite reaction), this equation forms the foundation of classical mechanics.

    F=ma allowed physicists and engineers to calculate the value of a force. For instance, your weight (measured in newtons) is your mass (in kilograms) multiplied by acceleration due to gravity (on Earth, about 10 metres per second squared).

    Saying you “weigh” 60 kilograms is incorrect in physics terms – your actual weight is about 600 newtons. This is the force pushing down on your bathroom scales.

    But was it practical?

    This equation was crucial to the arrival of the mechanical age. It’s used in almost every calculation which involves using force to cause movement.

    It tells you how powerful an engine needs to be to power a car, how much lift an aircraft needs to take-off, how much thrust to lift a rocket, how far a cannonball flies.

    2. Newton’s law of universal gravitation (1687)
    What does it say?

    Any two massive objects pull on one another across space. But the force decreases rapidly the further apart they are.

    In other words …

    We’re stuck to the Earth’s surface because our planet is comparatively big with lots more mass.

    What did it teach us?

    For centuries, the Universe had been divided into two realms – the earthly and the celestial. But Newton’s law of gravitation applied to everything. The same tug that causes an apple to fall from a tree keeps the Moon orbiting the Earth. Newton gave us the first direct connection between everyday life and the movement of the heavens.

    But was it practical?

    For a long time, the equation’s main use was to calculate the orbits of planets. The space-age of the 1950s and 60s saw it used in practice – to send satellites into orbit and astronauts to the Moon.

    One failing, which Newton himself admitted, was that he did not know “why” gravity operated. It took nearly 230 years for Albert Einstein to come along and explain gravity as arising from the warping of spacetime by massive objects in his theory of general relativity.

    Even so, general relativity is only used in extreme situations, such as when gravity is very strong, or when great precision is required, such as for GPS satellites. In most cases Newton’s 330-year-old equation is still good enough.

    4. The Maxwell-Faraday equation (1831 and 1865)
    What does it say?

    You can create a changing electric field (left side of the equation) from a changing magnetic field (on the right) and vice versa.

    In other words …

    Electricity and magnetism are related!

    What did it teach us?

    In 1831, Michael Faraday discovered the connection between two natural forces, electricity and magnetism, when he found a changing magnetic field induced a current in a nearby wire.

    Later, James Clark Maxwell generalised Faraday’s observation as one of his four fundamental equations of electromagnetism.

    But was it practical?

    This is the equation that powers the world. Most electric generators (whether in a wind turbine, coal-fired plant or a hydroelectric dam) work by converting mechanical energy (from steam or water) to rotate a magnet. By running this process in reverse, you get the electric motor.

    More generally, Maxwell’s equations are still used in almost every application of electrical engineering, communications technology and optics.

    5. Einstein’s mass-energy equivalence (1905)
    What does it say?

    Energy equals mass multiplied by the speed of light squared.
    In other words …

    Mass is really just a super-condensed form of energy.

    What did it teach us?

    Because of the size of the constant in the equation (the speed of light squared, an unimaginably huge number) a colossal amount of energy can be released through converting a tiny amount of mass.

    But was it practical?

    Einstein’s most famous equation hinted at the potential for the huge amounts of energy released in nuclear fission, when a large unstable nucleus breaks into two smaller ones. This is because the mass of the two smaller nuclei together is always less than the mass of the original big nucleus – and the missing mass is converted into energy.

    The “Fat Man” atomic bomb dropped over Nagasaki in Japan on 9 August 1945 converted just one gram of mass to energy, but produced an explosion the equivalent around 20,000 tonnes of TNT.

    Einstein himself had signed a letter to US president at the time Franklin Roosevelt recommending the atom bomb be developed – a decision he later regarded as the “one great mistake” of his life.

    6. The Schrödinger wavefunction (1925)
    What does it say?

    It describes how the change of a particle’s wavefunction (represented by psi, the candlestick shaped symbol) can be calculated from its kinetic energy (movement) and its potential energy (the interactions on it).

    In other words …

    It’s the quantum version of F=ma.

    What did it teach us?

    When Erwin Schrödinger formulated his equation in 1925, it placed the new theory of quantum mechanics on firm footing by allowing physicists to calculate how quantum particles move and interact.

    The equation looks a bit weird because it uses the mathematics of waves. (Subatomic particles are “wavy”, so their interaction is described as interference of waves, rather than like billiard balls.)

    But was it practical?

    In one of its simplest forms, it describes the structure of the atom, such as the arrangement of electrons around the nucleus, and all chemical bonding.

    More generally it’s used for many calculations in quantum mechanics and is fundamental to much of modern technology from lasers to transistors, and the future development of quantum computers

    See the full article here .

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    • clearskies2016 5:29 am on May 15, 2016 Permalink | Reply

      You really explained it so I can understand! Thank you. I will be referring to this article a lot this week as I go into more detail on them. Thank you!

      Like

    • richardmitnick 7:30 am on May 15, 2016 Permalink | Reply

      Thanks, But it was Cathal O’Connell at COSMOS who explained it, I just presented it here.
      Thanks for reading and “liking” my stuff.

      Like

  • richardmitnick 10:15 am on May 13, 2016 Permalink | Reply
    Tags: , Brane theory and testing, Physics,   

    From physicsworld: “Parallel-universe search focuses on neutrons” 

    physicsworld
    physicsworld.com

    May 10, 2016
    Edwin Cartlidge

    1
    No braner: there is no evidence that ILL neutrons venture into an adjacent universe. No image credit.

    The first results* from a detector designed to look for evidence of particles reaching us from a parallel universe have been unveiled by physicists in France and Belgium. Although they drew a blank, the researchers say that their experiment provides a simple, low-cost way of testing theories beyond the Standard Model of particle physics, and that the detector could be made significantly more sensitive in the future.

    Standard Model
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    A number of quantum theories of gravity predict the existence of dimensions beyond the three of space and one of time that we are familiar with. Those theories envisage our universe as a 4D surface or “brane” in a higher-dimensional space–time “bulk”, just as a 2D sheet of paper exists as a surface within our normal three spatial dimensions. The bulk could contain multiple branes separated from one another by a certain distance within the higher dimensions.

    Physicists have found no empirical evidence for the existence of other branes. However, in 2010, Michaël Sarrazin of the University of Namur in Belgium and Fabrice Petit of the Belgian Ceramic Research Centre put forward a model showing that particles normally trapped within one brane should occasionally be able to tunnel quantum mechanically into an adjacent brane. They said that neutrons should be more affected than charged particles because the tunnelling would be hindered by electromagnetic interactions.

    Nearest neighbour

    The researchers have now teamed up with physicists at the University of Grenoble in France and others at the University of Namur to put their model to the test. This involved setting up a helium-3 detector a few metres from the nuclear reactor at the Institut Laue-Langevin (ILL) in Grenoble and then recording how many neutrons it intercepted. The idea is that neutrons emitted by the reactor would exist in a quantum superposition of being in our brane and being in an adjacent brane (leaving aside the effect of more distant branes). The neutrons’ wavefunctions would then collapse into one or other of the two states when colliding with nuclei within the heavy-water moderator that surrounds the reactor core.

    Most neutrons would end up in our brane, but a small fraction would enter the adjacent one. Those neutrons, so the reasoning goes, would – unlike the neutrons in our brane – escape the reactor, because they would interact extremely weakly with the water and concrete shielding around it. However, because a tiny part of those neutrons’ wavefunction would still exist within our brane even after the initial collapse, they could return to our world by colliding with helium nuclei in the detector. In other words, there would be a small but finite chance that some neutrons emitted by the reactor would disappear into another universe before reappearing in our own – so registering events in the detector.

    Sarrazin says that the biggest challenge in carrying out the experiment was minimizing the considerable background flux of neutrons caused by leakage from neighbouring instruments within the reactor hall. He and his colleagues did this by enclosing the detector in a multilayer shield – a 20 cm-thick polyethylene box on the outside to convert fast neutrons into thermal ones and then a boron box on the inside to capture thermal neutrons. This shielding reduced the background by about a factor of a million.

    Stringent upper limit

    Operating their detector over five days in July last year, Sarrazin and colleagues recorded a small but still significant number of events. The fact that these events could be residual background means they do not constitute evidence for hidden neutrons, say the researchers. But they do allow for a new upper limit on the probability that a neutron enters a parallel universe when colliding with a nucleus – one in two billion, which is about 15,000 times more stringent than a limit the researchers had previously arrived at by studying stored ultra-cold neutrons. This new limit, they say, implies that the distance between branes must be more than 87 times the Planck length (about 1.6 × 10–35 m).

    To try and establish whether any of the residual events could indeed be due to hidden neutrons, Sarrazin and colleagues plan to carry out further, and longer, tests at ILL in about a year’s time. Sarrazin points out that because their model doesn’t predict the strength of inter-brane coupling, these tests cannot be used to completely rule out the existence of hidden branes. Conversely, he says, they could provide “clear evidence” in support of branes, which, he adds, could probably not be obtained using the LHC at CERN. “If the brane energy scale corresponds to the Planck energy scale, there is no hope to observe this kind of new physics in a collider,” he says.

    Axel Lindner of DESY, who carries out similar “shining-particles-through-a-wall” experiments (but using photons rather than neutrons), supports the latest research. He believes it is “very important” to probe such “crazy” ideas experimentally, given presently limited indications about what might supersede the Standard Model. “It would be highly desirable to clarify whether the detected neutron signals can really be attributed to background or whether there is something else behind it,” he says.

    The research is described in Physics Letters B.

    *Science paper:
    Search for passing-through-walls neutrons constrains hidden braneworlds

    See the full article here .

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    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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  • richardmitnick 3:10 pm on May 10, 2016 Permalink | Reply
    Tags: , Physics, , Tiny Tests Seek the Universe’s Big Mysteries   

    From Quanta: “Tiny Tests Seek the Universe’s Big Mysteries” 

    Quanta Magazine
    Quanta Magazine

    May 3, 2016
    Joshua Sokol

    Huge supercolliders aren’t the only way to search for new physical phenomena. A new generation of experiments that can fit on a tabletop are probing the nature of dark matter and dark energy and searching for evidence of extra dimensions.


    Access mp4 video here .
    Video: David Moore of Stanford University describes how, inside this chamber, silica spheres probe for distortions of gravity. Peter DaSilva for Quanta Magazine

    To answer some of the biggest unsolved questions in the cosmos, you might not need a supercollider. For decades, theorists have been dreaming up a Wild West of exotic physics that could be visible at scales just below the thickness of a dollar bill — provided you build a clever-enough experiment, one small enough to fit on a tabletop. Over distances of a few dozen microns — a little thinner than that dollar — known forces like gravity could get weird, or, even more exciting, previously unknown forces could pop up. Now a new generation of tabletop experiments is coming online to look into these phenomena.

    One such experiment uses levitated spheres of silica — “basically a glass bead that we hold up using light,” according to Andrew Geraci, the lead investigator — to search for hidden forces far weaker than anything we can imagine. In a paper* uploaded to the scientific preprint site arxiv.org in early March, his team announced that they had detected sensitivities of a few zeptonewtons — a level of force 21 orders of magnitude below a newton, which is about what is needed to depress a computer key.

    “A bathroom scale might be able to tell your weight to maybe 0.1 newtons if it was very accurate,” said Geraci, a physicist at the University of Nevada, Reno. “If you had a single virus land on you, that would be about 10^–19 newtons, so we’re about two orders of magnitude below that.”

    The targets of these searches feature in some of the most compelling questions in physics, including those that center on the nature of gravity, dark matter and dark energy. “There’s a whole panoply of things these experiments could look for,” said Nima Arkani-Hamed, a physicist at the Institute for Advanced Study in Princeton, N.J. For example, dark matter, the massive stuff whose existence has been inferred only on astronomical scales, might leave faint electric charges behind when it interacts with ordinary particles. Dark energy, the pressure powering the accelerating expansion of the universe, might make itself felt through so-called “chameleon” particles that a tabletop experiment could theoretically be able to spot. And certain theories predict that gravity will be much weaker than expected at short range, while others predict that it will be stronger. If the extra dimensions posited by string theory exist, the tug of gravity between objects separated by a micron might exceed what Isaac Newton’s law predicts by a factor of 10 billion.

    Janet Conrad, a physicist at the Massachusetts Institute of Technology who is not directly involved with any of these small-scale searches, thinks that they complement the work done at massive accelerators such as the Large Hadron Collider.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    “We are like dinosaurs. We have gotten bigger, and bigger, and bigger,” she said. But experiments like these offer the chance for a more agile kind of fundamental physics, in which individual researchers with small devices can make a big impact. “I really do believe that this is a new field,” she said.

    For theorists like Arkani-Hamed, what happens just beyond the limits of our vision is interesting because of a curious numerical connection. The Planck scale, the infinitesimal size scale in which quantum gravity is thought to rule, is 16 orders of magnitude smaller than the weak scale, the neighborhood of particle physics explored in the Large Hadron Collider.

    Theories that blend these length scales often compare the two. (Physicists will take the length of the weak scale, square it, then divide this number by the length of the Planck scale.) The result of the comparison yields a range of distances matching what may be another fundamental scale: one that runs between a micron and a millimeter. Here, Arkani-Hamed suspects, new forces and particles may arise.

    Similar sizes arise when physicists consider the dark energy that fills empty space throughout the universe. When that energy density is associated with a length scale on which particles may be acting, it turns out to be about 100 microns — again suggesting this neighborhood would be an auspicious place to look for signs of new physics.

    One such search started in the late 1990s, after Arkani-Hamed and two colleagues suggested that gravity may be leaking into extra dimensions of space, a process that would explain why gravity is far weaker than the other forces known to physics. At scales smaller than the extra dimensions, before gravity had a chance to leak away, its attraction would be stronger than expected. The researchers calculated that these dimensions could be as big as a millimeter in size.

    This inspired Eric Adelberger and his colleagues to search for those dimensions. They already had the device to do it. In the 1980s, Adelberger and the so-called Eöt-Wash group at the University of Washington had built a device called a “torsion balance” that would twist in response to small forces. At first the group used the balance to search for a “fifth force” that had been proposed based on century-old experimental results. They failed to find it. “We built an apparatus, and we found that this thing wasn’t true,” Adelberger said. “It was so much fun, and it was much easier than we thought it would be.”

    Now they set out to work on Arkani-Hamed’s prediction that gravity would be much stronger at small distances — before it has a chance to leak into extra dimensions — than when objects are farther away.

    Since 2001, the team has published results from four torsion balances, each more sensitive than the last. So far, any diminutive dimensions haven’t revealed themselves. The team first reported that gravity acts normally at a distance of 218 microns. Then they reduced this number to 197 microns, then 56, and finally 42, as reported in a 2013 study. Today, their data come from two different instruments with pendulums. One pendulum twists at a rate determined by the strength of gravity; the other should stay still unless gravity behaves unexpectedly.

    But they haven’t been able to shrink their measurements much beyond 42 microns. Currently, they’re tweaking the 2013 analysis, and they hope to publish updated numbers soon. While Adelberger is hesitant to cite the new limit they’re pushing for, he said it’s unlikely to be under 20 microns. “When you first do something, the bar is relatively low,” he said. “It gets so much harder when you make the distances shorter.”

    Techniques borrowed from atomic physics may indicate another way down the ladder, even to nanoscopic scales.

    In 2010, Geraci, then a physicist at the National Institute of Standards and Technology in Boulder, Colo., suggested a scheme****to probe hidden forces at tiny scales. Instead of using the pendulums at Washington, small-force hunters could use spheres of silica levitated by lasers. By measuring how nearby objects change the position of a floating bead, this kind of experiment can look at the forces spanning just a few microns.

    The experiment is able to probe scales of smaller lengths, but there’s a catch. Gravity is most easily measured using massive objects. Geraci’s design, now built, uses spheres just 0.3 microns in size. David Moore, a physicist at Stanford University who works in the lab of Giorgio Gratta, has his own working version that uses larger silica spheres about five microns in diameter. Compared to the Eöt-Wash team, which uses torsion balances that are a few centimeters wide, both experiments trade away the larger gravitational signals for more precision at close range.

    Geraci’s and Moore’s masses are so light that the teams are not yet able to directly measure the gravitational pull of nearby objects; they can only see it if it turns out stronger than predicted by Newton’s law. That may make it harder to determine if gravity or something else is behind anything strange they might see. “One thing we always like to point out about gravity is that having the force sensitivity to see gravity is basically table stakes to play the game,” said Charlie Hagedorn, a postdoc at Washington. Adelberger adds, “If you want to know what gravity does, you’ve got to be able to see it.

    But to Geraci and Moore, the levitated beads are a general platform they can use to investigate small physics beyond just gravity. “The vision here is that once you’re able to measure these tiny forces, there’s a lot you can do,” Moore said. At the end of 2014, Moore conducted a search for particles with electric charges much smaller than one electron. Some models of dark matter suggest these “millicharged” particles could have formed in the early universe, and could still be lurking in ordinary matter.

    To try to find these particles, Moore held positively charged spheres between a pair of electrodes. He then zapped the entire apparatus with flashes of ultraviolet light to knock electrons off the electrodes. These electrons then attached to the positively charged spheres, turning them neutral. Then he applied an electric field. If any millicharged particles were still stuck on the spheres, they would impart a small force. Moore didn’t see any effects, which means that any millicharged particles must have an exceedingly small charge, or the particles themselves must be rare, or both.

    In a more recent test published** in April, Moore, working with his colleagues Alex Rider and Charles Blakemore, also used the microspheres to look for so-called “chameleon” particles that may explain dark energy. They didn’t find any, a result that echoed one published*** last year in the journal Science by a team at the University of California, Berkeley.

    “These small-scale experiments are — I don’t know what it’s called in English — ‘wild goose chase’?” said Savas Dimopoulos, a physicist at Stanford who was a co-author of the paper with Arkani-Hamed that proposed the search for millimeter-size extra dimensions. “You don’t really know where to look, but you look wherever you can.”

    For Dimopoulos, these tabletop searches are an appealing cottage industry. They offer a cheap alternative way to study provocative theories. “These ideas have been proposed over the last 40 years, but they’ve been staying on the back burner, because the main focus of fundamental physics has been accelerators,” he said.

    It’s a pitch Dimopoulos has been honing in talks over the last three years. Several experiments like those aimed at short-range forces are in the works, but they’re underfunded and underappreciated. “The field doesn’t even have a proper name,” he said.

    What might help is what Dimopoulos calls a “super lab” — a facility that would bring many such tabletop experiments together under one roof, like the research communities that have built up around high-energy projects like the Large Hadron Collider. Conrad, for her part, would like these endeavors to be better supported while still remaining at universities.

    Either way, both argue that more effort is warranted in the search for lower-energy particles, especially those predicted to lurk at scales only a little smaller than the width of a human hair. “There is a whole zoo of these things,” Dimopoulos said. “High energy is not the only frontier that exists.”

    *Science paper:
    Zeptonewton force sensing with nanospheres in an optical lattice

    **Science paper:
    Search for Screened Interactions Below the Dark Energy Length Scale Using Optically Levitated Microspheres

    ***Science paper
    Atom-interferometry constraints on dark energy

    ****Science paper:
    Short-range force detection using optically-cooled levitated microspheres

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 7:02 pm on May 9, 2016 Permalink | Reply
    Tags: , , Physics, Researchers find unexpected magnetic effect of two thin films   

    From MIT: “Researchers find unexpected magnetic effect” 

    MIT News
    MIT News
    MIT Widget

    May 9, 2016
    David L. Chandler

    1
    Arrows indicate the spin direction in the ferromagnetic insulator (EuS, shown in red) and topological insulator (Bi2Se3, shown in blue) at the interface between the two materials. Image: Ferhat Katmis

    A new and unexpected magnetic effect has taken researchers by surprise, and could open up a new pathway to advanced electronic devices and even robust quantum computer architecture.

    The finding is based on a family of materials called topological insulators (TIs) that has drawn much interest in recent years. The novel electronic properties of TIs might ultimately lead to new generations of electronic, spintronic, or quantum computing devices. The materials behave like ordinary insulators throughout their interiors, blocking electrons from flowing, but their outermost surfaces are nearly perfect conductors, allowing electrons to move freely. The confinement of electrons to this vanishingly thin surface makes then behave in unique ways.

    But harnessing the materials’ promise still faces numerous obstacles, one of which is to find a way of combining a TI with a material that has controllable magnetic properties. Now, researchers at MIT and elsewhere say they have found a way to overcome that hurdle.

    The team at MIT, led by Jagadeesh Moodera of the Department of Physics and postdoc Ferhat Katmis, was able to bond together several molecular layers of a topological insulator material called bismuth selenide (Bi2Se3) with an ultrathin layer of a magnetic material, europium sulfide (EuS). The resulting bilayer material retains all the exotic electronic properties of a TI and the full magnetization capabilities of the EuS.

    But the big surprise was the stability of that effect. While EuS itself is known to retain its ability to hold a magnetic state only at extremely low temperatures, just 17 degrees above absolute zero (17 Kelvin), the combined material keeps those characteristics all the way up to ordinary room temperature. That could make all the difference for developing devices that are practical to operate, and could open up new avenues of device design as well as research into a new area of basic physical phenomena.

    The findings are being reported* in the journal Nature, in a paper by Katmis, Moodera, and 10 others at MIT, and a multinational, multidisciplinary team from Oak Ridge, Argonne National Laboratories, and institutions in Germany, France, and India.

    The room-temperature magnetic effect seen in this work, Moodera says, was something that “wasn’t in anybody’s wildest expectations. This is what astonished us.” Research like this, he says, is still so near the frontiers of scientific knowledge that the phenomena are impossible to predict. “You can’t tell what you’re going to see next week or what’s going to happen” in the next experiment, he says.

    In particular, novel combinations of two materials with very different properties “is an area with very little depth of research.” And getting clear and repeatable results depends on a high degree of precision in the preparation of the surfaces and joining of the two materials; any contamination or imperfections at the interface between the two – even down to the level of individual atomic layer – can throw off the results, Moodera says. “What happens, happens where they meet,” he says, and the careful and persistent effort of Katmis in making these materials was key to the new discovery.

    The finding could be a step toward new kinds of magnetic interactions at the interfaces between materials, with stability that could result in magnetic memory devices which could store information at the level of individual molecules, the team says.

    The effect, which the researchers call proximity-induced magnetism, could also enable a new variety of “spintronic” devices based on a property of electrons called spin, rather than on their electrical charge. It might also provide the first practical way of producing a kind of particle called Majorana fermions, predicted by physicists but not yet observed convincingly. That in turn could help in the development of quantum computers, they say.

    “A nice thing about this is that it shows both very fundamental physics and also takes us forward to many possible applications,” Katmis says. He says the effect is somewhat similar to unexpected findings a decade ago in the interfaces between some oxide materials, which has triggered a decade of intensive research.

    This new finding, coupled with other recent quantum behavior observed in TIs, can lead to many possibilities for future electronics and spintronics, the team says.

    “This beautiful work from Moodera’s group is a very exciting demonstration that the whole is greater than the sum of its parts,” says Philip Kim, a professor of physics at Harvard University, who was not involved in this work. “Topological insulators and magnetic insulators are two completely dissimilar materials. Yet they produce very unusual emergent effects at their atomically clean interface,” he adds. “The enhanced interfacial magnetism shown in this work can be very relevant to building up novel spintronics devices that can process information with low energy consumption.”

    The team also included associate professor of physics Pablo Jarillo-Herrero and postdoc Peng Wei at MIT, and researchers at the Institute for Theoretical Physics in Bochum and the Institute for Theoretical Solid State Physics in Dresden, both in Germany; the Ecole Normale Superieure in Paris; and the Institute of Nuclear Physics, in Kolkata, India. The work was supported by the National Science Foundation, Office of Naval Research, and the U.S. Department of Energy.

    *Science paper:
    A high-temperature ferromagnetic topological insulating phase by proximity coupling

    See the full article here .

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  • richardmitnick 4:47 pm on May 9, 2016 Permalink | Reply
    Tags: , , Physics,   

    From COSMOS: “Particle physics: a primer to the theory of (almost) everything” 

    Cosmos Magazine bloc

    COSMOS

    9 May 2016
    Cathal O’Connell

    Are you a boson bozo? Do quarks leave you quizzical? Do gluons get you unstuck? Cathal O’Connell has a guide to the zoo of particles, known as the Standard Model of particle physics.

    1
    Graphic of a transverse section through a detector showing one of the numerous particle collision events recorded during the search for the Higgs boson.Credit: ATLAS COLLABORATION/CERN

    CERN ATLAS Higgs Event
    CERN/ATLAS
    ATLAS

    Around the turn of the 4th century BC, the Greek philosopher Democritus caught the smell of baking and thought that little bits of bread must be floating through the air and into his nose. He called the little bits “atoms” (meaning “uncuttable”) and imagined them as tiny spherical balls.

    But atoms are not little solid spheres. They are made of even smaller bits, called particles.

    Scientists’ best description of those particles and the forces that govern their behaviour is called the Standard Model of particle physics, or just “The Standard Model”.

    The Standard Model categorises all of the particles of nature, in the same way that the periodic table categorises the elements. The theory is called the Standard Model because it is so successful it has become “standard”.

    And no, there is no Economy Model, nor a Deluxe one.

    There are, however, still a few kinks to be ironed out (as well as a couple of whopping omissions). That’s why it is sometimes called the “Theory of Almost Everything”.

    How did it all kick off?

    Back in the early 20th century, scientists thought there were only three fundamental particles in nature: protons and neutrons, which make up the nucleus of an atom, and electrons that whizz round it.

    But in the 1950s and 1960s physicists started smashing these particles together and some of them broke. It turned out the protons and neutrons had even smaller particles inside them.

    Many dozens of new particles were discovered – and for a while, nobody could explain them. Physicists called it the “particle zoo”.

    In the 1970s, physicists such as Murray Gell-Mann found an order amongst the chaos. The step they took was similar to the one Russian chemist Dmitri Mendeleev took to find an order to the chemical elements in his periodic table.

    The new ordering of the particles explained many of the properties of the newly discovered particles, as well as correctly predicting some new ones.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Meet the family

    The particles of the Standard Model make up one big family. Your first introduction can be daunting, a bit like attending a gathering with a lot of distant cousins you’ve never heard of. No matter how strange these cousins are, it is important to remember that they are all related.
    The basics

    Gell-Mann and others placed the particles in two main categories: fermions and bosons.

    Fermions, such as the electron, make up the stuff we call matter. Bosons, such as the photon, transmit forces.

    Fermions are subdivided again into two kinds of particles, depending on the forces they feel. These are the quarks and the leptons (see below).
    Forces of nature

    Particles communicate with one another via four forces: electromagnetism, the strong force, the weak force and gravity.

    The Standard Model describes the first three (gravity does not feature in the Standard Model, as explained below).

    Different particles communicate through different forces, similar to the way people can communicate in different languages. For example, only the quarks speak “gluon”. While electrons can speak “photon” as well as “W boson” and “Z boson”.

    Electromagnetism is the force that holds electrons in an atom. It is communicated by photons.

    The strong force keeps the nuclei of atoms together. Without it, every atom in the universe would spontaneously explode. It is communicated by gluons.

    The weak force causes radioactive decay. It’s transmitted by W and Z bosons.

    The fundamental particles

    All matter is made of two types of particles known as quarks and leptons.

    Quarks: (the purple particles in the figure) come in six “flavours”, all with weird names. It’s useful to see them as coming in pairs to make three generations. These are “up” and “down” (first generation), “charmed” and “strange” (second generation) and “top” and “bottom” (third generation).

    Only the up and down quarks are important in day-to-day life because they make protons and neutrons.

    The others make only “exotic” matter, which is too unstable to form atoms. Physicists can create exotic matter in particle accelerators, but it usually only lasts a fraction of a second before decaying.

    Leptons: there are six leptons, the best known of which is the electron, a tiny fundamental particle with a negative charge.

    The muon (second generation) and tau (third generation) particles are like fatter versions of the electron. They also have negative electric charge, but they are too unstable to feature in ordinary matter.

    And each of these particles has a corresponding neutrino, with no charge.

    Neutrinos deserve a special mention because they are perhaps the least understood of all the particles in the Standard Model.

    They are fast but interact only through the weak force, which means they can easily zip straight through a planet. They are created in nuclear reactions, such as those powering the Sun’s core.

    Hadrons: the composite particles

    Now that we know the fundamental particles of nature, we can begin to stack them together in different ways to make bigger particles.

    The most important composite particles are the baryons, made of three quarks. Protons and neutrons are both kinds of baryon.

    The European Organisation for Nuclear Research’s (CERN) biggest particle collider smashes protons together. Because protons are a kind of hadron, it’s called the Large Hadron Collider, or LHC.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Antimatter: double or nothing?

    As far as we know, all quarks and leptons have twin particles of antimatter. Antimatter is like matter except it has the opposite charge. For example, the electron has a counterpart that’s exactly the same mass, except with positive charge instead of negative. When a particle of matter meets its antimatter twin, they both annihilate in a burst of pure energy.

    Antimatter is incredibly rare in the Universe, although it does have some important roles in technology. Positron emission tomography (PET) scanners, for instance, use the annihilation of positrons to see inside the body.

    One of the great mysteries of physics is why the Universe is made almost entirely of matter. Many particle physicists are striving to answer it.

    Atoms: composites of composites

    The bread that Democritus sniffed is made of only the first generation of fundamental particles.

    Up and down quarks bind together through the strong force to make protons and neutrons, and the strong force also sticks them together to form the nucleus of an atom.

    Electrons orbit the nucleus in arrangements determined by quantum mechanics (see our primer Quantum physics for the terminally confused).
    The Higgs: the god particle

    You probably noticed the loner off to the right side of particle table – the Higgs boson. The Higgs is a special kind of particle that gives the other fundamental particles their mass.

    The idea is that there is a field existing everywhere in space. And when particles move through space, they tend to bump into this field, and this interaction slows them down (similar to how it’s more difficult to move through water than air). This interaction is what gives fundamental particles their mass.

    Some particles such as photons and gluons don’t interact with the Higgs field, so are massless.

    Just as photons communicate the electromagnetic force, the Higgs Boson communicates the Higgs Field.

    The Higgs Boson was a theoretical particle until 2013 when CERN announced it had been discovered at last, although scientists are still uncovering its properties.
    What’s missing?

    Gravity

    The biggest hole in the Standard Model is the lack of gravity. The fourth force of nature just does not fit into the current picture.

    Gravity is also incredibly weak compared to the other forces (the strong force is 100,000,000,000,000,000,000,000,000,000,000,000,000 times stronger than gravity, for example).

    Some physicists think gravity is also transmitted by a kind of particle, called a graviton, but so far there is no evidence that this particle exists.

    Neutrino mass

    The neutrino is so tiny compared to all the other particles that it really begs an explanation. It’s possible that the neutrino doesn’t get its mass from the Higgs in the same way other particles do.

    Dark matter: For observing the Universe, it looks like a huge portion of it is made of Dark Matter – a new kind of stuff that doesn’t interact with regular matter and so is probably missing from the Standard Model entirely.

    Supersymmetry

    Some physicists are looking for extensions to the Standard Model to explain these mysteries. Supersymmetry is one extension where every particle has another twin with higher mass.

    Some of these particles would interact very weakly with ordinary stuff and so could be good candidates for Dark Matter.

    See the full article here .

    Please help promote STEM in your local schools.

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