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  • richardmitnick 2:11 pm on December 11, 2017 Permalink | Reply
    Tags: , , Crystal structures, , , , Physics   

    From Notre Dame: “Thirty years of molecular beam epitaxy stimulates international collaborations” 

    Notre Dame bloc

    Notre Dame University

    December 08, 2017
    Tammi Freehling

    1
    Margaret Dobrowolska and Jacek Furdyna in the MBE lab at Notre Dame.

    For nearly thirty years, Professor Jacek Furdyna’s Molecular Beam Epitaxy (MBE) lab at Notre Dame has been providing crystals and materials to students and scientists across the world. In continuous operation since its beginning in 1987, more than 10,000 crystals have been grown in the lab, most in the form of “designer-materials” such as new crystal phases, quantum wells, quantum dots, and other forms that do not occur in nature.

    Growing such crystal structures requires specific combinations of atoms from different elements. Molecular Beam Epitaxy accomplishes this by assembling these atoms into a single crystal on a substrate, atomic layer by atomic layer. Not surprisingly, this must be done under ultra-high vacuum conditions, ensuring ultra-high purity of the resulting material, with no unwanted foreign atoms present.

    “The process of MBE allows us to create materials by assembling the atoms one-by-one, ‘on demand’. Thus we are able to form entirely new crystal phases and, more importantly, to obtain materials with entirely new atomic configurations (such as quantum wells, superlattices, quantum wires, and quantum dots) that perform specific optical, electrical, or magnetic functions that can be applied in solid state devices,” said Margaret Dobrowolska, the Rev. John Cardinal O’Hara, C.S.C. Professor of Physics and associate dean for undergraduate studies, College of Science, who works with Furdyna in the MBE lab (and happens to be his wife). The resulting materials are highly precise films that are widely used in the manufacture of semiconductor devices, such as semiconductor transistors of various forms, light emitting diodes (LEDs), semiconductor lasers, and a myriad other components for modern-day electronics.

    Molecular Beam Epitaxy was invented in the late 1960s at Bell Telephone Laboratories by J. R. Arthur and Alfred Y. Cho. In 1987, Furdyna came to Notre Dame from Purdue and set up the MBE lab in Nieuwland Science Hall. His research interests involve the preparation of new semiconducting compounds and the investigation of their physical properties. Most recently, this activity has focused on three semiconducting systems: quantum well structures for use in blue and blue-green light emitters, including semiconductor lasers; magnetic semiconductors (which combine “traditional” semiconductor phenomena with new magnetic properties, including ferromagnetism); and semiconductor nanostructures, such as self-assembled quantum dots, quantum wires, and their arrays. These systems are investigated by structural, electrical, magnetic, and optical techniques, which provide basic understanding of the electronic and magnetic structures of the new semiconducting materials, as well as the knowledge necessary for constructing electronic and optical devices based on the above materials. One should note here that, because the structures achieved by MBE are controlled at atomic-scale precision, this method provides one of the most effective approaches to the new wave of technology referred to as nanotechnology.

    In addition to the spectroscopic studies carried out at Notre Dame, Furdyna together with his colleagues Dobrowolska and Xinyu Liu, associate research professor of physics, are involved in an extensive program of collaborations with other institutions in the area of structural studies, magnetic measurements, and neutron scattering on the semiconductor systems described above. Materials designed and fabricated in the MBE lab led to collaborations with scientists in more than 100 institutions outside of Notre Dame, including some 35 in foreign countries, resulting in significant worldwide visibility for Notre Dame.

    “One of the most gratifying things about having the MBE lab here at Notre Dame is that it stimulates such extensive international collaborations,” Furdyna said. “As an illustration, in just the past five years alone we’ve had about 10 long-term visiting scientists, including graduate students and postdocs from Ireland, South Korea, Venezuela, Brazil, Poland, and Russia. Apart from getting a great deal of work done, they’ve seriously contributed to broadening our horizons.”

    Furdyna further commented: “More than 40 Notre Dame graduate students carried out their Ph.D. research on materials provided by the MBE lab. Since the MBE lab opened in 1987, the cumulative number of refereed publications by our group is about 700, and the number of citations of these papers in the scientific literature is over 14,000. More than 120 graduate students in institutions other than Notre Dame carried out their Ph.D. research on materials provided by our MBE lab. This includes 90 Ph.D. students in U.S. universities and 30 students in universities abroad. In the area of new semiconductor materials, and particularly in systems involving magnetic semiconductors, our lab has become the ‘go-to place’ in research involving these research fields.”

    See the full article here .

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    Notre Dame Campus

    The University of Notre Dame du Lac (or simply Notre Dame /ˌnoʊtərˈdeɪm/ NOH-tər-DAYM) is a Catholic research university located near South Bend, Indiana, in the United States. In French, Notre Dame du Lac means “Our Lady of the Lake” and refers to the university’s patron saint, the Virgin Mary.

    The school was founded by Father Edward Sorin, CSC, who was also its first president. Today, many Holy Cross priests continue to work for the university, including as its president. It was established as an all-male institution on November 26, 1842, on land donated by the Bishop of Vincennes. The university first enrolled women undergraduates in 1972. As of 2013 about 48 percent of the student body was female.[6] Notre Dame’s Catholic character is reflected in its explicit commitment to the Catholic faith, numerous ministries funded by the school, and the architecture around campus. The university is consistently ranked one of the top universities in the United States and as a major global university.

    The university today is organized into five colleges and one professional school, and its graduate program has 15 master’s and 26 doctoral degree programs.[7][8] Over 80% of the university’s 8,000 undergraduates live on campus in one of 29 single-sex residence halls, each of which fields teams for more than a dozen intramural sports, and the university counts approximately 120,000 alumni.[9]

    The university is globally recognized for its Notre Dame School of Architecture, a faculty that teaches (pre-modernist) traditional and classical architecture and urban planning (e.g. following the principles of New Urbanism and New Classical Architecture).[10] It also awards the renowned annual Driehaus Architecture Prize.

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  • richardmitnick 3:10 pm on December 10, 2017 Permalink | Reply
    Tags: , Physics, ,   

    From IST Austria: “Essential quantum computer component downsized by two orders of magnitude” 

    Institute of Science and Technology Austria

    November 14, 2017

    Researchers at IST Austria have built compact photon directional devices. Their micrometer-scale, nonmagnetic devices route microwave photons and can shield qubits from harmful noise.

    1
    The new nonreciprocal device acts as a roundabout for photons.
    Here, arrows show the direction of photons propagation.
    Credit: IST Austria/Birgit Rieger

    Qubits, or quantum bits, are the key building blocks that lie at the heart of every quantum computer. In order to perform a computation, signals need to be directed to and from qubits. At the same time, these qubits are extremely sensitive to interference from their environment, and need to be shielded from unwanted signals, in particular from magnetic fields. It is thus a serious problem that the devices built to shield qubits from unwanted signals, known as nonreciprocal devices, are themselves producing magnetic fields. Moreover, they are several centimeters in size, which is problematic, given that a large number of such elements is required in each quantum processor. Now, scientists at the Institute of Science and Technology Austria (IST Austria), simultaneously with competing groups in Switzerland and the United States, have decreased the size of nonreciprocal devices by two orders of magnitude. Their device, whose function they compare to that of a traffic roundabout for photons, is only about a tenth of a millimeter in size, and—maybe even more importantly—it is not magnetic. Their study was published in the open access journal Nature Communications.

    When researchers want to receive a signal, for instance a microwave photon, from a qubit, but also prevent noise and other spurious signals from traveling back the same way towards the qubit, they use nonreciprocal devices, such as isolators or circulators. These devices control the signal traffic, similar to the way traffic is regulated in everyday life. But in the case of a quantum computer, it is not cars that cause the traffic but photons in transmission lines. “Imagine a roundabout in which you can only drive counterclockwise”, explains first author Dr. Shabir Barzanjeh, who is a postdoc in Professor Johannes Fink’s group at IST Austria. “At exit number one, at the bottom, there is our qubit. Its faint signal can go to exit number two at the top. But a signal coming in from exit number two cannot travel the same path back to the qubit. It is forced to travel in a counterclockwise manner, and before it reaches exit one, it encounters exit three. There, we block it and keep it from harming the qubit.”

    The ‘roundabouts’ the group has designed consist of aluminum circuits on a silicon chip and they are the first to be based on micromechanical oscillators: Two small silicon beams oscillate on the chip like the strings of a guitar and interact with the electrical circuit. These devices are tiny in size—only about a tenth of a millimeter in diameter—, one of the major advantages the new component has over its traditional predecessors, which were a few centimeters wide.

    Currently, only a few qubits have been used to test the principles of quantum computers, but in the future, thousands or even millions of qubits will be connected together, and many of these qubits will require their own circulator. “Imagine building a processor that has millions of such centimeter-size components. It would be enormous and impractical,” says Shabir Barzanjeh. “Using our nonmagnetic and very compact on-chip circulators instead makes life a lot easier.” Yet some hurdles need to be overcome before the devices will be used for this specific application. For example, the available signal bandwidth is currently still quite small, and the required drive powers might harm the qubits. However, the researchers are confident that these problems will turn out to be solvable.

    See the full article here.

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    The Institute of Science and Technology Austria (IST Austria) is a young international institute dedicated to basic research and graduate education in the natural and mathematical sciences, located in Klosterneuburg on the outskirts of Vienna. Established jointly by the federal government of Austria and the provincial government of Lower Austria, the Institute was inaugurated in 2009 and will grow to about 90 research groups by 2026.

    The governance and management structures of IST Austria guarantee its independence and freedom from political and commercial influences. The Institute is headed by the President, who is appointed by the Board of Trustees and advised by the Scientific Board. The first President of IST Austria is Thomas A. Henzinger, a leading computer scientist and former professor of the University of California at Berkeley and the EPFL Lausanne in Switzerland.

     
  • richardmitnick 2:05 pm on December 10, 2017 Permalink | Reply
    Tags: , , , New manifestation of magnetic monopoles discovered, Physics,   

    From IST Austria: “New manifestation of magnetic monopoles discovered” 

    Institute of Science and Technology Austria

    December 7, 2017

    Significant effort has gone into engineering the long-sought magnetic monopoles. Now scientists have found them in an unexpected place, and revealed that they have been around for a long time.

    1

    The startling similarity between the physical laws describing electric phenomena and those describing magnetic phenomena has been known since the 19th century. However, one piece that would make the two perfectly symmetric was missing: magnetic monopoles. While magnetic monopoles in the form of elementary particles remain elusive, there have been some recent successes in engineering objects that behave effectively like magnetic monopoles. Now, scientists at the Institute of Science and Technology Austria (IST Austria) have shown that there is a much simpler way to observe such magnetic monopoles: they have demonstrated that superfluid helium droplets act as magnetic monopoles from the perspective of molecules that are immersed inside them. Such droplets have been studied for decades, but until now, this fascinating characteristic had gone entirely unnoticed.

    When working with electric charge, it is easy to separate the positive and negative poles: the negatively charged electron represents a negative pole, the positively charged proton is the opposite (positive) pole, and each one is an individual particle that can be separated from the other. With magnets, it seemed that they always have two poles that are impossible to separate: cut a dipole magnet in half and you will end up with two dipole magnets, cut them again and you will just get even smaller dipole magnets, but you will not be able to separate the north from the south pole. Challenged by this puzzle, scientists put a great deal of effort into constructing systems that effectively act as magnetic monopoles—with success: certain crystal structures were made to behave like magnetic monopoles. But now, an interdisciplinary team comprising theoretical physicists and a mathematician have discovered that this phenomenon also occurs in molecular systems that do not need to be engineered for this purpose but which have been known of for a long time.

    Nanometer-sized drops of superfluid helium with molecules immersed in them have been studied for several decades already, and it is one of the systems that Professor Mikhail Lemeshko and postdoc Enderalp Yakaboylu are particularly interested in. Previously, Professor Lemeshko proposed a new quasiparticle that drastically simplifies the mathematical description of such rotating molecules, and earlier this year he showed that this quasiparticle, the angulon, can explain observations that had been collected over 20 years. Enderalp Yakaboylu moreover used the angulon to predict previously unknown properties of these systems. The property in superfluid helium droplets that they now discovered, however, came unexpectedly—and only after they had exchanged ideas with mathematician Andreas Deuchert, who says: “It was a surprise to all of us to see this characteristic emerge in the equations.” At a strongly interdisciplinary institute like IST Austria, such collaborations are not unusual, and interaction between research groups of different fields is fostered.

    “In the other experiments they engineered a system to become a monopole. Here, it is the other way round,” Enderalp Yakaboylu adds. “The system was well-known. People have been studying rotating molecules for a long time, and only after did we realize that the magnetic monopoles had been there the whole time. This is a completely different viewpoint.”

    According to the researchers, the discovery opens up new possibilities for studying magnetic monopoles. In particular, the appearance of magnetic monopole in superfluid helium droplets is very different from the other, previously studied, systems. “The difference is that we are dealing with a chemical solvent. Our magnetic monopoles form in a fluid rather than in a solid crystal, and you can use this system to study magnetic monopoles more easily,” Professor Mikhail Lemeshko explains.

    Science paper:
    Emergence of Non-Abelian Magnetic Monopoles in a Quantum Impurity Problem
    Physical Review Letters

    See the full article here.

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    The Institute of Science and Technology Austria (IST Austria) is a young international institute dedicated to basic research and graduate education in the natural and mathematical sciences, located in Klosterneuburg on the outskirts of Vienna. Established jointly by the federal government of Austria and the provincial government of Lower Austria, the Institute was inaugurated in 2009 and will grow to about 90 research groups by 2026.

    The governance and management structures of IST Austria guarantee its independence and freedom from political and commercial influences. The Institute is headed by the President, who is appointed by the Board of Trustees and advised by the Scientific Board. The first President of IST Austria is Thomas A. Henzinger, a leading computer scientist and former professor of the University of California at Berkeley and the EPFL Lausanne in Switzerland.

     
  • richardmitnick 1:22 pm on December 10, 2017 Permalink | Reply
    Tags: 8 More Physics Questions Science Hasn’t Answered, , , Physics   

    From Edgy Labs: “8 More Physics Questions Science Hasn’t Answered” 

    Edgy Labs

    December 9, 2017
    Zayan Guedim

    This is the second part of our two-part series on physics mysteries that scientists have yet to solve.

    While our knowledge of the Universe has progressed considerably in recent years, there are still many outstanding questions that need answers.

    And, no, it’s not 42!

    If you haven’t read the first 10 Unanswered Questions, you can check them out here. Then come back for part 2–or you can do it backward, it’ll still be mysterious.

    11. Black Hole Information Paradox

    Black holes are the last stage in the life cycle of massive stars that are much bigger than the Sun. Our home star, which has already used up about half of its fuel, will eventually collapse into a white dwarf.

    The Milky Way alone is riddled with ten million to a billion black holes, including a recently discovered monstrous one.

    As cold relics of giant stars, black hole existence isn’t what puzzles scientists. It’s what’s called the Information Paradox that really gets the gears turning.

    According to the theory of relativity, information (objects) that fall into a black hole are annihilated forever. However, quantum physics says that quantum information can’t be destroyed. Thus, anything that passes a black hole’s event horizon could still be retrieved.

    However, a new type of wormhole could help solve the Information Paradox. Two researchers at Harvard and Stanford University published a study about “Traversable Wormholes” that would allow information to escape black holes.

    12. Naked Singularities

    At the center of a black hole lies what’s called a “singularity”, an infinitesimal point where all the matter of the black hole is concentrated. Around the singularity is a spherical region, known as the event horizon, beyond which no object (information!) can escape, not even light.

    An object that crosses the event horizon is believed to never come out (unless it falls into a traversable wormhole?)

    A “naked singularity” is a gravitational singularity that’s not hidden behind the event horizon, and thus could be observed.

    According to mathematical simulations, naked singularities were thought to exist only in a five-dimensional universe, but it may be that these strange objects do exist in a three-dimensional universe [Physical Review Letters] like ours, as theoretically proved recently by Cambridge researchers.

    13. CP Symmetry Violation

    In particle physics, CP symmetry (charge conjugation parity symmetry) refers to the consistency of physics laws when a particle is inverted to its antiparticle.

    In 1964, James Cronin and Val Fitch found CP violation in some radioactivity reactions, a discovery that earned them the Nobel Prize in Physics in 1980.

    Scientists, however, still don’t understand why and how certain particles violate the CP symmetry.

    14. Sonoluminescence: How Does Sound Create Light?

    Sound and light are two phenomena that involve waves, and which are fundamentally different physically speaking, yet there is another amazing phenomenon that links them in a strange way.

    Sonoluminescence can be demonstrated using simple setup. If you direct sound wave into a container filled with water, bubbles will form then collapse, emitting short bursts of light in the process.

    Where does this light come from? How does the energy of sound waves get converted into light? Tiny nuclear reaction? Gas heating?

    15. What is Gravity Anyway?

    Unlike the other three fundamental forces, gravity can’t be quantized and has been measured until today only at higher scales.

    While the theory of general relativity has succeeded in describing the force of gravity over cosmological distances, it has not been tested in the microscopic realm.

    This is the subject of quantum gravity theory, which suggests the existence of gravitons, massless particles that remain theoretical at the moment, as no one has managed to detect this quantum messenger of gravity.

    Yet, there’s hope. The Higgs-Boson Particle had also only existed theoretically since the 1960s, within the Standard Model, until it was finally detected in 2012 by CERN’s Large Hadron Collider.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    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.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    16. Are we in Trouble Inside the “False Vacuum”?

    The universe is about 14 billion years old, so that might indicate that it’s relatively stable.

    We know that there empty zones in space, but it is not an absolute void because it is unstable. It is constantly stirred by virtual particles that are created and annihilated permanently.

    The Higgs-Boson mentioned above is a particle that gives matter its mass via what’s called the Higgs field–an invisible force that however has a very observable effect.

    So, the vacuum might not be the lowest possible energy state, and some kind of vacuum energy should be at play. Here comes the “false vacuum” theory, which suggests that the universe might not be stable after all.

    Could that mean that a high-energy event could knock this false vacuum into a lower energy state and trigger a “false vacuum bubble” that would annihilate all matter in its way?

    But then again, the universe, as we already said, has been around for a long time, witnessing violent cosmic events, and we’re still here. So, with luck, we might be safe from such a demise.

    17. “Dimensionless” Fundamental Physical Constants

    The mathematical formulas used in physics define relations between physical quantities, which have dimensions, thus can be measured using certain units.

    A physical constant is a physical quantity whose numerical value is fixed, like the speed of light.

    However, dimensionless constants don’t depend on a units system, and so their value is important to describe the nature of the physical world.

    The most known is the fine-structure constant but there are at least 26 dimensionless fundamental physical constants in the Standard Model.

    And that leads us to our last problem.

    18. The Standard Model Limits

    The universe and everything therein seems to be made of fundamental particles obeying is the four fundamental forces: electromagnetism, the weak interaction, the strong interaction, and gravity.

    The Standard Model of particle physics is the current theory that explains all observable phenomena, encompassing all known particles.

    A theory that is both quantum and relativistic, the standard model has helped, since the early 1970s, make precise predictions time and time again. However, this model can’t explain everything.

    For starters, it incorporates only three out of four interactions (fundamental forces) having a particle-scale effect, because gravity is still resisting theoreticians.

    The Standard Model can’t provide definitive answers to the 17 questions we’ve covered in our two-part series and remains in itself an unsolved problem.

    See the full article here .

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  • richardmitnick 12:54 pm on December 10, 2017 Permalink | Reply
    Tags: 10 Physics Questions Science Still Hasn’t Answered, , , Physics   

    From Edgy Labs: “10 Physics Questions Science Still Hasn’t Answered” 

    Edgy Labs

    September 24, 2017
    Zayan Guedim

    EdgyLabs has made an inventory of some of the most important unanswered questions in physics.

    As physicist Brian Cox said:

    “I’m comfortable with the unknown – that’s the point of science… I don’t need answers to everything. I want to have answers to find.”

    With all of the discoveries and all the progress that has been made and advanced scientific tools at their disposal, physicists have yet to find answers to many of the most prominent questions that pertain to our physical universe.

    We looked at 18 of the most compelling enigmas to see more precisely what we know and do not know about our universe. Far from being exhaustive, this list is a representative sample of the major issues facing physics today–and we’d love your input to help round out this list.

    1. Why There’s Less Antimatter Than Matter?

    To each type of particle there’s a twin antiparticle with identical properties, but opposite charge. If a particle meets its antiparticle, the two immediately annihilate one another.

    If antimatter and matter have the same properties, why doesn’t the universe contain equal amounts of the two?

    Of course, if that was the case, it’s possible that we wouldn’t be here to ask about it!

    2. What is Dark Matter?

    Cosmologists think that only about 5% of the universe is visible, made up of ordinary matter that forms billions of galaxies, stars, and planets, including us and everything else.

    So what exactly is this “dark matter” that emits no light and makes up roughly 25% of the universe?

    3. What is Dark Energy?

    The largest majority of the universe’s content (70%) is in the form of an unknown energy that has earned the name of “dark energy”.

    What is this mysterious, gravity-repellent, dark energy that may suggest new physical laws beyond the standard model?

    4. Is There a Multiverse?

    Some astrophysicists think that the visible universe is but one among an infinite number of universes.

    And, according to quantum physics, there’s only a finite number of possible particle arrangements, which are forced to repeat themselves in the multiverse over and over again.

    That means that there are parallel universes that are exact copies of our realm (including you!), another that differs with only one particle configuration, or two… infinitely!

    But we have yet to detect the presence of our parallel selves.

    5. What Will be the Universe’s Grand Finale?

    If the widely-accepted theory of the beginning of the universe (Big Bang) is yet to be proven, the ultimate fate of the universe may be a tougher nut to crack.

    There are scenarios aplenty: try the Big Crunch, Big Freeze, Big Rip–many theories with the word “big” in them try to predict what destiny awaits our universe, with no definitive answer.

    But hey, as far as us mortals are concerned, the human civilization (and any intelligent alien life!) will probably be long gone before the end of time.

    But time doesn’t end, does it?

    6. Why Time Appears to be Linear?

    Time, as defined by Newton, remains a constant in physics. Newtonian mechanics organizes sequences of moments or events in chronological order.

    But mounting scientific evidence suggests that time is cyclic and non-linear; in theory, it can be slowed down, stopped or reversed.

    Why does time give the illusion of flowing as a linear and irreversible arrow?

    7. How Consciousness Affects Reality?

    If you want to put a quantum physicist or a philosopher of science on the spot, just bring up “The Measurement Problem”.

    Simply put, a particle only takes a particular position if there’s an observer measuring it; that’s the ‘Measurement’ or ‘Observation’ Problem.

    That means that a particle is all over the place until one decides to observe it in their own space-time. In other words, the very act of observation affects or creates, reality.

    But how could a particle decide its position and momentum? Does this mean that objects, time, and locality are mere tools of our consciousness, projected out as “reality”?

    8. Does the String Theory Hold up?

    An active area of research, String Theory is touted as “the theory of everything”, one that can reconcile Relativity with Quantum physics and describe the universe as a whole.

    Michio Kaku explains it in this video.

    For the equations of String Theory to work, they require 10 to 11 dimensions, and the vibrating “strings” it describes are so small (a billionth of a trillionth the size of an atomic nucleus).

    That makes this theory very difficult to verify or debunk.

    9. Is it an Orderly Chaos or a Chaotic Order?

    What is the nature of chaos in the universe? For example, with all the math knowledge, data, and processing power we have, we still can’t accurately predict the weather.

    Perhaps under the apparent disorder hides a very strict order, a chaotic system that obeys the physical principles but nonetheless unpredictable over the long term.

    Perhaps we just don’t have the right math.

    10. Is There a Super-Force Behind the 4 Fundamental Forces?

    There are four fundamental forces that govern the universe: gravity, electromagnetism, strong nuclear, and weak nuclear.

    Maybe these universal forces operate in a similar way to Marvel’s Infinity Stones: each stone has its own purpose but their six powers can be harvested collectively using the Infinity Gauntlet.

    Physicist think that the 4 forces would’ve resulted from a single and even more fundamental force and, because of that, may unite into one super-force.

    They also postulate that they could unify at least three of them (except gravity) using a particle accelerator, but all the available energy in the world wouldn’t be enough.

    See the full article here .

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  • richardmitnick 10:56 am on December 10, 2017 Permalink | Reply
    Tags: , , Physics, Volumetric 3D printing builds on need for speed   

    From LLNL: “Volumetric 3D printing builds on need for speed” 


    Lawrence Livermore National Laboratory

    Dec. 8, 2017
    Jeremy Thomas
    thomas244@llnl.gov
    925-422-5539

    1
    By using laser-generated, hologram-like 3D images flashed into photosensitive resin, researchers at Lawrence Livermore National Laboratory, along with academic collaborators, have discovered they can build complex 3D parts in a fraction of the time of traditional layer-by-layer printing. With this process, researchers have printed beams, planes, struts at arbitrary angles, lattices and complex and uniquely curved objects in a matter of seconds.

    While additive manufacturing (AM), commonly known as 3D printing, is enabling engineers and scientists to build parts in configurations and designs never before possible, the impact of the technology has been limited by layer-based printing methods, which can take up to hours or days to build three-dimensional parts, depending on their complexity.

    However, by using laser-generated, hologram-like 3D images flashed into photosensitive resin, researchers at Lawrence Livermore National Laboratory (LLNL), along with collaborators at UC Berkeley (link is external), the University of Rochester (link is external) and the Massachusetts Institute of Technology (link is external) (MIT), have discovered they can build complex 3D parts in a fraction of the time of traditional layer-by-layer printing. The novel approach is called “volumetric” 3D printing, and is described in the journal Science Advances.

    “The fact that you can do fully 3D parts all in one step really does overcome an important problem in additive manufacturing,” said LLNL researcher Maxim Shusteff, the paper’s lead author. “We’re trying to print a 3D shape all at the same time. The real aim of this paper was to ask, ‘Can we make arbitrary 3D shapes all at once, instead of putting the parts together gradually layer by layer?’ It turns out we can.”

    The way it works, Shusteff explained, is by overlapping three laser beams that define an object’s geometry from three different directions, creating a 3D image suspended in the vat of resin. The laser light, which is at a higher intensity where the beams intersect, is kept on for about 10 seconds, enough time to cure the part. The excess resin is drained out of the vat, and, seemingly like magic, researchers are left with a fully formed 3D part.

    The approach, the scientists concluded, results in parts built many times faster than other polymer-based methods, and most, if not all, commercial AM methods used today. Due to its low cost, flexibility, speed and geometric versatility, the researchers expect the framework to open a major new direction of research in rapid 3D printing.

    2
    Volumetric 3D printing creates parts by overlapping three laser beams that define an object’s geometry from three different directions, creating a hologram-like 3D image suspended in the vat of resin. The laser light, which is at a higher intensity where the beams intersect, is kept on for about 10 seconds, enough time to cure the object. No image credit.

    “It’s a demonstration of what the next generation of additive manufacturing may be,” said LLNL engineer Chris Spadaccini, who heads Livermore Lab’s 3D printing effort. “Most 3D printing and additive manufacturing technologies consist of either a one-dimensional or two-dimensional unit operation. This moves fabrication to a fully 3D operation, which has not been done before. The potential impact on throughput could be enormous and if you can do it well, you can still have a lot of complexity.”

    With this process, Shusteff and his team printed beams, planes, struts at arbitrary angles, lattices and complex and uniquely curved objects. While conventional 3D printing has difficulty with spanning structures that might sag without support, Shusteff said, volumetric printing has no such constraints; many curved surfaces can be produced without layering artifacts.

    “This might be the only way to do AM that doesn’t require layering,” Shusteff said. “If you can get away from layering, you have a chance to get rid of ridges and directional properties. Because all features within the parts are formed at the same time, they don’t have surface issues.

    “I’m hoping what this will do is inspire other researchers to find other ways to do this with other materials,” he added. “It would be a paradigm shift.”
    Shusteff believes volumetric printing could be made even faster with a higher power light source. Extra-soft materials such as hydrogels could be wholly fabricated, he said, which would otherwise be damaged or destroyed by fluid motion. Volumetric 3D printing also is the only additive manufacturing technique that works better in zero gravity, he said, expanding the possibility of space-based production.

    3
    The LLNL logo in 3D printed technology.

    The technique does have limitations, researchers said. Because each beam propagates through space without changing, there are restrictions on part resolution and on the kinds of geometries that can be formed. Extremely complex structures would require lots of intersecting laser beams and would limit the process, they explained.

    Spadaccini added that additional polymer chemistry and engineering also would be needed to improve the resin properties and fine tune them to make better structures.

    “If you leave the light on too long it will start to cure everywhere, so there’s a timing game,” Spadaccini said. “A lot of the science and engineering is figuring out how long you can keep it on and at what intensity, and how that couples with the chemistry.”

    The work received Laboratory Directed Research and Development (LDRD) program funding. Additional LLNL researchers who contributed to the project were Todd Weisgraber and Robert Panas, Lawrence Graduate Scholar and University of Rochester Ph.D. student Allison Browar, UC Berkeley graduate students Brett Kelly and Johannes Henriksson, along with Nicholas Fang at MIT.

    See the full article here .

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  • richardmitnick 1:09 pm on December 9, 2017 Permalink | Reply
    Tags: , Atom interferometry, Blackbody radiation, Hot bodies are attractive, Optical tweezers, Physics,   

    From UC Berkeley: “Hot bodies are attractive” 

    UC Berkeley

    UC Berkeley

    December 8, 2017
    Robert Sanders
    rlsanders@berkeley.edu

    Our physical attraction to hot bodies is real, according to UC Berkeley physicists.

    To be clear, they’re not talking about sexual attraction to a “hot” human body.

    1
    The blackbody attraction between a hot tungsten cylinder and a cesium atom is 20 times stronger than the gravitational attraction between them. (Holger Müller graphic)

    But the researchers have shown that a glowing object actually attracts atoms, contrary to what most people – physicists included – would guess.

    The tiny effect is much like the effect a laser has on an atom in a device called optical tweezers, which are used to trap and study atoms, a discovery that led to the 1997 Nobel Prize in Physics shared by former UC Berkeley professor Steven Chu, now at Stanford, Claude Cohen-Tannoudji and William D. Phillips.

    Until three years ago, when a group of Austrian physicists predicted it, no one thought that regular light, or even just the heat given off by a warm object – the infrared glow you see when looking through night-vision goggles – could affect atoms in the same way.

    UC Berkeley physicists, who are expert at measuring minute forces using atom interferometry, designed an experiment to check it out. When they measured the force exerted by the so-called blackbody radiation from a warm tungsten cylinder on a cesium atom, the prediction was confirmed.

    The attraction is actually 20 times the gravitational attraction between the two objects, but since gravity is the weakest of all the forces, the effect on cesium atoms – or any atom, molecule or larger object – is usually too small to worry about.

    “It’s hard to find a scenario where this force would stand out,” said co-author Victoria Xu, a graduate student in the physics department at UC Berkeley. “It is not clear it makes a significant effect anywhere. Yet.”

    As gravity measurements become more precise, though, effects this small need to be taken into account. The next generation of experiments to detect gravitational waves from space may use lab-bench atom interferometers instead of the kilometer-long interferometers now in operation. Interferometers typically combine two light waves to detect tiny changes in the distance they’ve traveled; atom interferometers combine two matter waves to detect tiny changes in the gravitational field they’ve experienced.

    3
    Thermal images like this record blackbody radiation, essentially the infrared light given off as a body cools. (iStock image)

    For very precise inertial navigation using atom interferometers, this force would also have to be taken into account.

    “This blackbody attraction has an impact wherever forces are measured precisely, including precision measurements of fundamental constants, tests of general relativity, measurements of gravity and so on,” said senior author Holger Müller, an associate professor of physics. Xu, Müller and their UC Berkeley colleagues published their study in the December issue of the journal Nature Physics.

    Optical tweezers

    Optical tweezers work because light is a superposition of magnetic and electric fields – an electromagnetic wave. The electric field in a light beam makes charged particles move. In an atom or a small sphere, this can separate positive charges, like the nucleus, from negative charges, like the electrons. This creates a dipole, allowing the atom or sphere to act like a tiny bar magnet.
    The electric field in the light wave can then move this induced electric dipole around, just as you can use a bar magnet to shove a piece of iron around.

    Using more than one laser beam, scientists can levitate an atom or bead to conduct experiments.

    With weak, incoherent light, like blackbody radiation from a hot object, the effect is much weaker, but still there, Müller’s team found.

    4
    The shiny tungsten cylinder can be seen at top through a window into the vacuum chamber of the atom interferometer The cesium atoms are launched upwards through the circular opening below the cylinder. (Holger Müller photo)

    They measured the effect by placing a dilute gas of cold cesium atoms – cooled to three-millionths of a degree above absolute zero (300 nanoKelvin) – in a vacuum chamber and launching them upward with a quick pulse of laser light.

    Half are given an extra kick up towards an inch-long tungsten cylinder glowing at 185 degrees Celsius (365 degrees Fahrenheit), while the other half remain unkicked. When the two groups of cesium atoms fall and meet again, their matter waves interfere, allowing the researchers to measure the phase shift caused by the tungsten-cesium interaction, and thus calculate the attractive force of the blackbody radiation.

    “People think blackbody radiation is a classic concept in physics – it was a catalyst for starting the quantum mechanical revolution 100 years ago – but there are still cool things to learn about it,” Xu said.

    The research was funded by the David and Lucile Packard Foundation, National Science Foundation (037166), Defense Advanced Research Projects Agency (033504) and National Aeronautics and Space Administration (041060-002, 041542, 039088, 038706, and 036803). Other co-authors are Philipp Haslinger, Matt Jaffe and Osip Schwartz of UC Berkeley, Matthias Sonnleitner of the University of Glasgow, Monika Ritsch-Marte of the Medical University of Innsbruck in Austria and Helmut Ritsch of the University of Innsbruck.

    See the full article here .

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    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

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  • richardmitnick 9:47 am on December 8, 2017 Permalink | Reply
    Tags: , , , ESRF-European Synchrotron Radiation Facility, , Physics, RIXS-resonant inelastic x-ray scattering, Scientists found that as superconductivity vanishes at higher temperatures powerful waves of electrons begin to curiously uncouple and behave independently—like ocean waves splitting and rippling in, Superconductors carry electricity with perfect efficiency, The puzzling interplay between two key quantum properties of electrons: spin and charge   

    From BNL: “Breaking Electron Waves Provide New Clues to High-Temperature Superconductivity” 

    Brookhaven Lab

    December 5, 2017
    Justin Eure
    jeure@bnl.gov

    Scientists tracked elusive waves of charge and spin that precede and follow the mysterious emergence of superconductivity.

    1
    Brookhaven’s Robert Konik, Genda Gu, Mark Dean, and Hu Miao

    Superconductors carry electricity with perfect efficiency, unlike the inevitable waste inherent in traditional conductors like copper. But that perfection comes at the price of extreme cold—even so-called high-temperature superconductivity (HTS) only emerges well below zero degrees Fahrenheit. Discovering the ever-elusive mechanism behind HTS could revolutionize everything from regional power grids to wind turbines.

    Now, a collaboration led by the U.S. Department of Energy’s Brookhaven National Laboratory has discovered a surprising breakdown in the electron interactions that may underpin HTS. The scientists found that as superconductivity vanishes at higher temperatures, powerful waves of electrons begin to curiously uncouple and behave independently—like ocean waves splitting and rippling in different directions.

    “For the first time, we pinpointed these key electron interactions happening after superconductivity subsides,” said first author and Brookhaven Lab research associate Hu Miao. “The portrait is both stranger and more exciting than we expected, and it offers new ways to understand and potentially exploit these remarkable materials.”

    The new study, published November 7 in the journal PNAS, explores the puzzling interplay between two key quantum properties of electrons: spin and charge.

    “We know charge and spin lock together and form waves in copper-oxides cooled down to superconducting temperatures,” said study senior author and Brookhaven Lab physicist Mark Dean. “But we didn’t realize that these electron waves persist but seem to uncouple at higher temperatures.”

    Electronic stripes and waves

    2
    In the RIXS technique, intense x-rays deposit energy into the electron waves of atomically thin layers of high-temperature superconductors. The difference in x-ray energy before and after interaction reveals key information about the fundamental behavior of these exciting and mysterious materials.

    Scientists at Brookhaven Lab discovered in 1995 that spin and charge can lock together and form spatially modulated “stripes” at low temperatures in some HTS materials. Other materials, however, feature correlated electron charges rolling through as charge-density waves that appear to ignore spin entirely. Deepening the HTS mystery, charge and spin can also abandon independence and link together.

    “The role of these ‘stripes’ and correlated waves in high-temperature superconductivity is hotly debated,” Miao said. “Some elements may be essential or just a small piece of the larger puzzle. We needed a clearer picture of electron activity across temperatures, particularly the fleeting signals at warmer temperatures.”

    Imagine knowing the precise chemical structure of ice, for example, but having no idea what happens as it transforms into liquid or vapor. With these copper-oxide superconductors, or cuprates, there is comparable mystery, but hidden within much more complex materials. Still, the scientists essentially needed to take a freezing-cold sample and meticulously warm it to track exactly how its properties change.

    Subtle signals in custom-made materials

    The team turned to a well-established HTS material, lanthanum-barium copper-oxides (LBCO) known for strong stripe formations. Brookhaven Lab scientist Genda Gu painstakingly prepared the samples and customized the electron configurations.

    “We can’t have any structural abnormalities or errant atoms in these cuprates—they must be perfect,” Dean said. “Genda is among the best in the world at creating these materials, and we’re fortunate to have his talent so close at hand.”

    At low temperatures, the electron signals are powerful and easily detected, which is part of why their discovery happened decades ago. To tease out the more elusive signals at higher temperatures, the team needed unprecedented sensitivity.

    “We turned to the European Synchrotron Radiation Facility (ESRF) in France for the key experimental work,” Miao said.


    ESRF. Grenoble, France

    “Our colleagues operate a beamline that carefully tunes the x-ray energy to resonate with specific electrons and detect tiny changes in their behavior.”

    The team used a technique called resonant inelastic x-ray scattering (RIXS) to track position and charge of the electrons. A focused beam of x-rays strikes the material, deposits some energy, and then bounces off into detectors. Those scattered x-rays carry the signature of the electrons they hit along the way.

    As the temperature rose in the samples, causing superconductivity to fade, the coupled waves of charge and spin began to unlock and move independently.

    “This indicates that their coupling may bolster the stripe formation, or through some unknown mechanism empower high-temperature superconductivity,” Miao said. “It certainly warrants further exploration across other materials to see how prevalent this phenomenon is. It’s a key insight, certainly, but it’s too soon to say how it may unlock the HTS mechanism.”

    That further exploration will include additional HTS materials as well as other synchrotron facilities, notably Brookhaven Lab’s National Synchrotron Light Source II (NSLS-II), a DOE Office of Science User Facility.

    BNL NSLS-II

    BNL NSLS II

    “Using new beamlines at NSLS-II, we will have the freedom to rotate the sample and take advantage of significantly better energy resolution,” Dean said. “This will give us a more complete picture of electron correlations throughout the sample. There’s much more discovery to come.”

    Additional collaborators on the study include Yingying Peng, Giacomo Ghiringhelli, and Lucio Braicovich of the Politecnico di Milano, who contributed to the x-ray scattering, as well as José Lorenzana of the University of Rome, Götz Seibold of the Institute for Physics in Cottbus, Germany, and Robert Konik of Brookhaven Lab, who all contributed to the theory work.

    This research was funded by DOE’s Office of Science through Brookhaven Lab’s Center for Emergent Superconductivity.

    See the full article here .

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 2:39 pm on December 7, 2017 Permalink | Reply
    Tags: A space mission to test how objects fall in a vacuum has released its first results providing an improved foundation for Einstein's famous theory, , , , , , , , Physics, , The theory is fundamentally incompatible with another well-tested theory: quantum mechanics which describes the physics of the extremely small, The theory of general relativity and the conclusions it draws about gravity have been shown to be true wherever tested, This first result is going to shake the world of physics and will certainly lead to a revision of alternative theories to general relativity   

    From ICL: “European satellite confirms general relativity with unprecedented precision” 

    Imperial College London
    Imperial College London

    07 December 2017
    Hayley Dunning

    A space mission to test how objects fall in a vacuum has released its first results, providing an improved foundation for Einstein’s famous theory.

    The first results of the ‘Microscope’ satellite mission were announced this week by a group of researchers led by the French space agency CNES and including Imperial scientists. The findings are published in the journal Physical Review Letters.

    CNES Microscope satellite

    Launched in April 2016, the mission set out to test the ‘equivalence principle’, the founding assumption of Einstein’s theory of general relativity. The theory poses that gravity is not a ‘pulling’ force, but is the result of large bodies, like the Earth, bending spacetime.

    As a result, when two objects are dropped in a vacuum under the same force of gravity, they fall at the same rate, no matter what their difference in weight or composition. This principle was demonstrated by Apollo 15 astronaut David Scott, who dropped a hammer and a feather on the Moon and showed them both reaching the ground at the same time.

    However, dropping household objects on the lunar surface does not allow very precise measurements – it could be that they reach the ground fractions of a second apart. This is important for scientists to know, because if the equivalence principle does not hold absolutely, then it could provide clues to a unifying theory of physics.

    Finding a single theory

    The theory of general relativity, and the conclusions it draws about gravity, have been shown to be true wherever tested. However, the theory is fundamentally incompatible with another well-tested theory: quantum mechanics, which describes the physics of the extremely small.

    The major goal for 21st Century physics is a single theory that ties them all together neatly. Certain candidate theories predict that the equivalence principle may be violated at very weak levels.

    The new results have measured the equivalence principle with ten times the precision of any previous experiment, and show that objects in a vacuum fall with the same acceleration.

    Professor Timothy Sumner, from the Department of Physics at Imperial was involved in the early discussions for the project thirty years ago, which led to the current mission. He more recently joined the Science Working Team. Commenting on the latest results, he said: “The equivalence principle has proven unshakeable yet again.

    “This result is the first new measurement for several years and demonstrates the possibility of taking such difficult ‘laboratory’ experiments into the quiet and interference-free space environment. There will more results from this impressive experiment.”

    1,900 orbits of the Earth

    To test the principle, the Microscope satellite contains a series of ‘test masses’: blocks of metals of different weights with very precisely measured properties. These masses are isolated from any other influence and are monitored as they freefall in space while orbiting the Earth.

    This means their acceleration due to the freefall can be measured and compared to test the equivalence principle. If two test masses of equal size but different composition are accelerated differently during the freefall, then the equivalence principle is violated.

    The science phase of the mission began in December 2016 and has already collected data from 1,900 orbits of the Earth. This means that altogether the objects have been freefalling in space for the equivalent of 85 million kilometres, or half the Earth-Sun distance.

    The mission’s principle investigator, Pierre Touboul from France’s national aerospace research centre, ONERA, said: “The satellite’s performance is far exceeding expectations. Data from more than 1,900 additional orbits are already available and more are to come.

    “This first result is going to shake the world of physics and will certainly lead to a revision of alternative theories to general relativity.”

    The Microscope experiment is continuing to collect data, and the team hope that the final analysis will have a precision within a tenth of a trillionth of a percent.

    See the full article here .

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    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

     
  • richardmitnick 11:26 am on December 6, 2017 Permalink | Reply
    Tags: , , George Uhlenbeck and Samuel Goudsmit came up with the idea of quantum spin in the mid-1920s, How a quantum number that made no physical sense turned out to be real… and irreplaceable, Physics,   

    From Ethan Siegel: “Spin: The Quantum Property That Should Have Been Impossible” 

    Ethan Siegel

    Dec 5, 2017
    Paul Halpern

    1
    George Uhlenbeck (L) and Samuel Goudsmit (R) came up with the idea of quantum spin in the mid-1920s. This photo was taken with Hendrik Kramers (center) in 1928 (Public Domain)

    How a quantum number that made no physical sense turned out to be real… and irreplaceable.

    In the early 1920s, physicists were first working out the mysteries of the quantum Universe. Particles sometimes behaved as waves, with indeterminate positions, momenta, energies, and other properties. There was an inherent uncertainty to a great many properties that we could measure, and physicists raced to work out the rules.

    Amidst this frenzy, a young Dutch researcher named George Uhlenbeck implored Paul Ehrenfest, his research supervisor at the University of Leiden, not to submit the paper he wrote with Samuel “Sam” Goudsmit about a new quantum number called spin. It was not correct, Uhlenbeck told him in a frenzy. Let’s just drop it and start over, he implored.

    Uhlenbeck and Goudsmit, both then in their mid-20s, had just showed their joint result to the great Dutch physicist Hendrik Lorentz who had found what seemed like a major error. Electrons, he pointed out, couldn’t possibly rotate fast enough to generate the magnetic moment (interaction strength between a particle and an external magnetic field) that the duo had predicted. The particles would need to whirl faster than the sacred speed limit of light. How could they? The spin paper is unphysical, Uhlenbeck told Ehrenfest, and should not be published.

    1
    Electrons, like all spin-1/2 fermions, have two possible spin orientations when placed in a magnetic field (CK-12 Foundation / Wikimedia Commons).

    Ehrenfest’s reply was curt. “It is too late,” he told Uhlenbeck. “I have already submitted the paper. It will be published in two weeks.” Then he added, “Both of you are young and can afford to do something stupid.”

    Ehrenfest’s words certainly weren’t comforting. Surely, Uhlenbeck didn’t want to start off his career with a foolish error. Luckily, however, the spin quantum number, interpreted abstractly and having nothing whatsoever to do with rotation despite its name, has become an essential feature of modern physics. Electrons somehow acted in a magnetic field as if they were whirling, even thought they really couldn’t be. Uhlenbeck and Goudsmit’s roulette wheel bet on a weird new concept had paid off handsomely.

    3
    Thomas precession demonstrated with a gyroscope in space, as in the Gravity Probe B experiment (NASA).

    One of the harshest critics of spin was the acerbic physicist Wolfgang Pauli. Pauli, like Ehrenfest was born in Vienna, and moved elsewhere for his career. Like Lorentz, Pauli believed at first that spin was unphysical. (In January 1925, German American researcher Ralph Kronig had made a similar suggestion to Pauli, which he had immediately rejected and was never published.) He changed his mind only after Llewellyn Thomas demonstrated a phenomenon called “Thomas precession” that examined spin using special relativity.

    4
    Wolfgang Pauli (L) and Paul Ehrenfest (R), only a few years before Ehrenfest would tragically commit suicide (CERN photo archives)

    Pauli and Ehrenfest shared a blunt demeanor and willingness to criticize others in matters of science. They had first met in 1922 at the “Bohrfestspiele” (celebration of Niels Bohr’s work around the time of his Nobel Prize ) in Göttingen, Germany. Pauli, then in his early 20s, was already famous as a “wunderkind” for an excellent article about general relativity that appeared in a scientific encyclopedia edited by German physicist Arnold Sommerfeld. Ehrenfest and his wife had contributed a piece on statistical mechanics for the same volume. Pauli and Ehrenfest’s initial conversation centered on those respective works.

    As physicist Oskar Klein reported: “On that occasion Ehrenfest stood a little away from Pauli, looked at him mockingly and said: ‘Herr Pauli, I like your article better than I like you! To which Pauli very calmly replied: ‘That is funny, with me it is just the opposite!’”

    5
    In an atom, each s orbital (red), each of the p orbitals (yellow), the d orbitals (blue) and the f orbitals (green) can contain only two electrons apiece: one spin up and one spin down in each one (Libretexts Library / NSF / UC Davis).

    It was ironic that Pauli was initially opposed to spin, given that one of his key proposals — the exclusion principle — was one of the main motivators for its development. Introduced in early 1925, it stated that no two electrons (later extended to an entire class of particles called fermions) could occupy exactly the same quantum state. (Other types of particles, such as photons, that don’t obey that law are called bosons.)

    Quantum states in atoms (such as hydrogen) can be characterized by quantum numbers denoting the properties of an electron occupying such a state. The principal quantum number, introduced by Bohr, described the energy of an electron due to its electric interaction with the nucleus. The second and third quantum numbers, introduced by Sommerfeld, pertained to aspects of an electron’s angular momentum (a measure of the shape and configuration of its orbit). Traditionally, each of those quantum numbers were integers — counting numbers denoting a finite set of possibilities, such as the seat and row numbers in an arena. In tandem, those three quantum numbers determine how the probability clouds representing the electrons position themselves in the “stadium” surrounding the nucleus. That intricate pattern, well known by chemists, helps explain the periodic table.

    6
    Periodic Table 2017. Wikipedia

    7
    Hydrogen density plots for an electron in a variety of quantum states. While the three quantum numbers of charge and angular momentum in two different dimensions could explain a great deal, ‘spin’ must be added to explain the periodic table and the number of electrons in orbitals for each atom (PoorLeno / Wikimedia Commons).

    However, as Goudsmit realized in May 1925, there was a problem with using pure integers to characterize the quantum states. If you did, the exclusion principle couldn’t be maintained. Two electrons in the ground state (lowest energy level) of an atom would have identical set of those three quantum numbers. Goudsmit found that by introducing a fourth quantum number, representing a kind of intrinsic or extra angular momentum, that could take on only one of two possible values — either +½ or -½ — he could preserve the Pauli exclusion principle. The ground state could still have two electrons, but their fourth quantum numbers would be opposite: if one was +½, the other would be -½.

    8
    In the absence of a magnetic field, the energy levels of various states within an atomic orbital are identical (L). If a magnetic field is applied, however (R), the states split according to the Zeeman effect. Here we see the Zeeman splitting of a P-S doublet transition (Evgeny at English Wikipedia).

    Introducing a half-integer quantum number without physical justification was a rather audacious move. In a stadium concert, if an agency issued two tickets for the same seat A11 by labeling them A10½ & A11½ that would seem like chicanery. In hindsight, Goudsmit freely admitted that his physical understanding was not developed enough to justify such a move. He was working part time with Pieter Zeeman on atomic spectral lines, but had yet to see the connection. Zeeman had found extra spectral lines when an atom was placed in a magnetic field for which there was no explanation. Luckily Ehrenfest paired Goudsmit with Uhlenbeck, who knew a greater deal of foundational physics.

    9
    Graph showing the Zeeman splitting in Rb-87, the energy levels of the 5s orbitals, including fine structure and hyperfine structure (Danski14 / Wikimedia Commons).

    As Goudsmit recalled, “Ehrenfest said: ‘You should work together with him for a while, then he may learn something about the new atomic structure and all that spectral business.’ What he clearly thought, of course, was: ‘Perhaps I might learn a little bit of real physics from Uhlenbeck.’”

    Uhlenbeck learned from Goudsmit about the anomalous spectral lines as well as his theory of a half-integer quantum number and brilliantly connected the two ideas. The fourth quantum number, Uhlenbeck pointed out, made sense if the electron generated its own magnetic field like a spinning ball of charge. If it was a mini-magnet that could spin either clockwise or counterclockwise, it would have two different energy states in the presence of an external magnet — either aligned or anti-aligned — which would explain the split in spectral lines. Goudsmit was convinced. They wrote up their results and gave them to Ehrenfest, who promptly submitted them to a journal.

    10
    The visualization of an electron’s spin on the exterior wall of a building in Leiden (Vysotsky: Wikimedia)

    The young physicists were lucky that Ehrenfest could be impulsive. If he had discussed the spin idea with others, probably few in the physics community (except, potentially, for Werner Heisenberg, who was also thinking about half-integer quantum numbers) would have supported it. But once it was published, and the spin idea was re-interpreted as an abstract quantum number, it seemed the perfect way of understanding Pauli’s exclusion principle. Integer “stadium seating” for electrons was out, half-integer was in.

    When they left Leiden, Uhlenbeck and Goudsmit conducted a different kind of experiment, dubbed the “Michigan experiment,” when they both took on roles as Assistant Professors at the University of Michigan at the same time. They even collaborated on training graduate students, including Dutch physicist Max Dresden (who would become the research supervisor of this author and carry on the pedagogical tradition handed down by Ehrenfest, Uhlenbeck, and Goudsmit.) Open-minded inquiry was the hallmark of that school of thought — which splendidly led to the important concept of spin.

    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

     
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