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  • richardmitnick 2:12 pm on August 27, 2015 Permalink | Reply
    Tags: , , String Theory,   

    From Symmetry: “Looking for strings inside inflation” 

    Symmetry

    August 27, 2015
    Troy Rummler

    1

    Theorists from the Institute for Advanced Study have proposed a way forward in the quest to test string theory.

    Two theorists recently proposed a way to find evidence for an idea famous for being untestable: string theory. It involves looking for particles that were around 14 billion years ago, when a very tiny universe hit a growth spurt that used 15 billion times more energy than a collision in the Large Hadron Collider.

    Scientists can’t crank the LHC up that high, not even close. But they could possibly observe evidence of these particles through cosmological studies, with the right technological advances.
    Unknown particles

    During inflation—the flash of hyperexpansion that happened 10-33 seconds after the big bang— particles were colliding with astronomical power. We see remnants of that time in tiny fluctuations in the haze of leftover energy called the cosmic microwave background [CMB].

    Cosmic Background Radiation Planck
    CMB per Planck

    ESA Planck
    ESA/Planck

    Scientists might be able to find remnants of any prehistoric particles that were around during that time as well.

    “If new particles existed during inflation, they can imprint a signature on the primordial fluctuations, which can be seen through specific patterns,” says theorist Juan Maldacena of the Institute for Advanced Study at Princeton University.

    Maldacena and his IAS collaborator, theorist Nima Arkani-Hamed, have used quantum field theory calculations to figure out what these patterns might look like. The pair presented their findings at an annual string theory conference held this year in Bengaluru, India, in June.

    The probable, impossible string

    String theory is frequently summed up by its basic tenet: that the fundamental units of matter are not particles. They are one-dimensional, vibrating strings of energy.

    The theory’s purpose is to bridge a mathematic conflict between quantum mechanics and [Albert] Einstein’s theory of general relativity. Inside a black hole, for example, quantum mechanics dictates that gravity is impossible. Any attempt to adjust one theory to fit the other causes the whole delicate system to collapse. Instead of trying to do this, string theory creates a new mathematical framework in which both theories are natural results. Out of this framework emerges an astonishingly elegant way to unify the forces of nature, along with a correct qualitative description of all known elementary particles.

    As a system of mathematics, string theory makes a tremendous number of predictions. Testable predictions? None so far.

    Strings are thought to be the smallest objects in the universe, and computing their effects on the relatively enormous scales of particle physics experiments is no easy task. String theorists predict that new particles exist, but they cannot compute their masses.

    To exacerbate the problem, string theory can describe a variety of universes that differ by numbers of forces, particles or dimensions. Predictions at accessible energies depend on these unknown or very difficult details. No experiment can definitively prove a theory that offers so many alternative versions of reality.
    Putting string theory to the test

    But scientists are working out ways that experiments could at least begin to test parts of string theory. One prediction that string theory makes is the existence of particles with a unique property: a spin of greater than two.

    Spin is a property of fundamental particles. Particles that don’t spin decay in symmetric patterns. Particles that do spin decay in asymmetric patterns, and the greater the spin, the more complex those patterns get. Highly complex decay patterns from collisions between these particles would have left signature impressions on the universe as it expanded and cooled.

    Scientists could find the patterns of particles with greater than spin 2 in subtle variations in the distribution of galaxies or in the cosmic microwave background, according to Maldacena and Arkani-Hamed. Observational cosmologists would have to measure the primordial fluctuations over a wide range of length scales to be able to see these small deviations.

    The IAS theorists calculated what those measurements would theoretically be if these massive, high-spin particles existed. Such a particle would be much more massive than anything scientists could find at the LHC.

    A challenging proposition

    Cosmologists are already studying patterns in the cosmic microwave background. Experiments such as Planck, BICEP and POLAR BEAR are searching for polarization, which would be evidence that a nonrandom force acted on it.

    BICEP 2
    BICEP 2 interior
    BICEP

    POLARBEAR McGill Telescope
    PolarBear

    If they rewind the effects of time and mathematically undo all other forces that have interacted with this energy, they hope that what pattern remains will match the predicted twists imbued by inflation.

    The patterns proposed by Maldacena and Arkani-Hamed are much subtler and much more susceptible to interference. So any expectation of experimentally finding such signals is still a long way off.

    But this research could point us toward someday finding such signatures and illuminating our understanding of particles that have perhaps left their mark on the entire universe.
    The value of strings

    Whether or not anyone can prove that the world is made of strings, people have proven that the mathematics of string theory can be applied to other fields.

    In 2009, researchers discovered that string theory math could be applied to conventional problems in condensed matter physics. Since then researchers have been applying string theory to study superconductors.

    Fellow IAS theorist Edward Witten, who received the Fields Medal in 1990 for his mathematical contributions to quantum field theory and Supersymmetry, says Maldacena and Arkani-Hamed’s presentation was among the most innovative work he saw at the Strings ‘15 conference.

    Witten and others believe that such successes in other fields indicate that string theory actually underlies all other theories at some deeper level.

    “Physics—like history—does not precisely repeat itself,” Witten says. However, with similar structures appearing at different scales of lengths and energies, “it does rhyme.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:57 pm on January 28, 2015 Permalink | Reply
    Tags: , , , String Theory   

    From NPR: “The Most Dangerous Ideas In Science” 

    NPR

    National Public Radio (NPR)

    January 27, 2015
    Adam Frank, University of Rochester

    1
    Some physicists are pushing back against ideas like string theory and the multiverse. Here, we see a computer-generated image of a black hole, which might, ultimately, be explained by ideas like string theory.

    There’s a battle going on at the edge of the universe, but it’s getting fought right here on Earth. With roots stretching back as far as the ancient Greeks, in the eyes of champions on either side, this fight is a contest over nothing less than the future of science. It’s a conflict over the biggest cosmic questions humans can ask and the methods we use — or can use — to get answers for those questions.

    Cosmology is the study of the universe as a whole: its structure, its origins and its fate. Fundamental physics is the study of reality’s bedrock entities and their interactions. With these job descriptions it’s no surprise that cosmology and fundamental physics share a lot of territory. You can’t understand how the universe evolves after the Big Bang (a cosmology question) without understanding how matter, energy, space and time interact (a fundamental physics question). Recently, however, something remarkable has been happening in both these fields that’s raising hackles with some scientists. As physicists George Ellis and Joseph Silk recently put it in Nature:

    “This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical.”

    The root of the problem rests with two ideas/theories now central for some workers in cosmology (even if they remain problematic for physicists as a whole). The first is string theory, which posits that the world is made up not of point particles but of tiny vibrating strings. String theory only works if the universe has many “extra” dimensions of space other than the three we experience. The second idea is the so-called multiverse which, in its most popular form, claims more than one distinct universe emerged from the Big Bang. Instead, adherents claim, there may be an almost infinite (if not truly infinite) number of parallel “pocket universes,” each with their own version of physics.

    Both string theory and the multiverse are big, bold reformulations of what we mean when we say the words “physical reality.” That is reason enough for them to be contentious topics in scientific circles. But in the pursuit of these ideas, something else — something new — has emerged. Rather than focusing just on questions about the nature of the cosmos, the new developments raise critical questions about the basic rules of science [scientific method] when applied to something like the universe as a whole.

    Here is the problem: Both string theory and the multiverse posit entities that may, in principle or in practice, be unobservable. Evidence for the extra dimensions needed to make string theory work is likely to require a particle accelerator of astronomical proportions. And the other pocket universes making up the multiverse may lie permanently over our “horizon,” such that we will never get direct observations of their existence. It’s this specific aspect of the theories that has scientists like Ellis and Silk so concerned. As they put it:

    “These unprovable hypotheses are quite different from those that relate directly to the real world and that are testable through observations — such as the standard model of particle physics and the existence of dark matter and dark energy. As we see it, theoretical physics risks becoming a no-man’s-land between mathematics, physics and philosophy that does not truly meet the requirements of any.”

    What they, and others, find particularly worrisome is the claim that our attempts to push back frontiers in cosmology and fundamental physics have taken us into a new domain where new rules of science are needed. Some call this domain “post-empirical” science. Recently, for example, the philosopher of physics Richard Dawid has argued that in spite of the fact that no evidence for string theory exists (even after three decades of intense study), it must still be considered the best candidate for a path forward. As Dawid puts it, such arguments include “no-one has found a good alternative to string theory. Another [reason to accept string theory is] one uses the observation that theories without alternatives tended to be viable in the past.”

    Sean Carroll, a highly respected and philosophically astute physicist, takes a different approach from Dawid. For Carroll, it is the concept of falsifiability, which was central to Sir Karl Raimund Popper’s famous philosophy of science, that is too limited for the playing fields we now find ourselves working on. As Carroll writes:

    “Whether or not we can observe [extra dimensions or other universes] directly, the entities involved in these theories are either real or they are not. Refusing to contemplate their possible existence on the grounds of some a priori principle, even though they might play a crucial role in how the world works, is as non-scientific as it gets.”

    Thus, for Carroll, even if a theory predicts entities that can’t be directly observed, if there are indirect consequences of their existence we can confirm, then those theories (and those entities) must be included in our considerations.

    Other scientists, however, are not convinced. High-energy physicist Sabine Hossenfelder called Dawid’s kind of post-empirical science an “oxymoron.” More importantly, for scientists like Paul Steinhardt and collaborators, the new ideas are becoming “post-modern.” They use the term in the sense that without more definitive connections to data, the ideas will not be abandoned because a community exists that continues to support them.

    This is the possibility that troubles Ellis and Silk most of all:

    “In our view, the issue boils down to clarifying one question: What potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory.”

    String theory and the multiverse are exciting ideas in and of themselves. If either one were true, it would have revolutionary consequences for our understanding of the cosmos. But, as debates about post-empirical science and falsifiability demonstrate, critics of these untested theories fear they may be leading the field down a difficult — and ultimately damaging — path. That’s why, one way or another, they may be science’s most dangerous ideas.

    See the full article here.

    My indebtedness to Don Lincoln of FNAL for pointing out this article using a Facebook post. Thanks, Dr Lincoln

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    • s7hummel 1:48 am on January 29, 2015 Permalink | Reply

      was a little empty without YOU! Welcome back!

      Like

    • richardmitnick 3:51 am on January 29, 2015 Permalink | Reply

      I don’t understand your comment. I approved it just to ask you what you mean. I have been posting constantly.

      Like

    • s7hummel 2:03 am on January 30, 2015 Permalink | Reply

      seemed to me that a few days there was no your entries. But maybe i missed something. Indeed, what can YOU expect from a stupid Pole. Sorry!

      Like

    • richardmitnick 4:34 am on January 30, 2015 Permalink | Reply

      Hey, no problem. I am glad to have you aboard. I hope that you continue to find articles interesting.

      Liked by 1 person

  • richardmitnick 9:31 am on January 27, 2015 Permalink | Reply
    Tags: , , , , String Theory,   

    From Huff Post: “The Future of Physics” 

    Huffington Post
    The Huffington Post

    01/26/2015

    Dr. Sten Odenwald, Astronomer, National Institute of Aerospace

    In another few months the Large Hadron Collider. will be powered up to explore its maximum energy range. Many physicists fervently hope we will see definite signs of “new physics,” especially a phenomenon called “supersymmetry.” In the simplest view, the Standard Model souped-up with supersymmetry will offer a massive new partner particle for every known particle (electron, quark, neutrino, etc). One of these, called the neutralino, may even explain dark matter itself!

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

    Supersymmetry standard model
    Standard Model of Supersymmetry

    But Wait, There’s More!

    Supersymmetry is the foundational cornerstone on which string theory rests. That’s why physicists call this “stringy” theory of matter “superstring theory.” If the LHC does not turn up any signs of supersymmetry during the next two or three years, not only will simple modifications to the current Standard Model be ruled out, but the most elegant forms of supersymmetry theory will fall too.

    As an astronomer I am not too worried. The verified Standard Model is now fully capable of accounting for everything we see in the universe since a trillion-trillion-trillionth of a second after the Big Bang to the present time, once you include gravity, and don’t worry too much about dark matter and dark energy.

    2
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    But we need some explanation for dark energy and dark matter to complete our understanding of the cosmos, and for that we still need our physicist friends to show the way. Currently their only answers involve supersymmetry theory. If this idea falls, astronomers will be completely stumped to explain what governs our universe on the largest scales.

    Beyond supersymmetry, we also have the huge investment of talent that has pursued superstring theory since the early 1980s. Without supersymmetry, the “super” part of string theory also falls, and you end up with a non-super string theory that is clunky, inelegant and pretty dismal in accounting for the finer details of our physical world, often termed “quantum gravity.” A big part of this is the idea that our universe inhabits more than four dimensions — perhaps as many as 11!

    On April 26, 2006, I had the following exchanges with Stanford theoretical physicist Leonard Susskind, who is widely regarded as one of the fathers of string theory, along with other provocative and foundational ideas such as the “holographic universe.” His comments are still relevant seven years later.

    3

    Odenwald: Why is it so important for physicists to consider the universe having more than four dimensions, as the mathematics of superstring theory seems to require?

    Susskind: Almost all working high-energy theoretical physicists are convinced some sort of extra dimensions are needed to explain the complexity of elementary particles. That particles move in extra dimensions is another way of talking about the fact that they have more complex properties than just position and velocity. It is hard to find a serious paper about particle phenomenology that doesn’t in some way use the tools of superstring theory. Furthermore, we all agree that the origin of elementary particles is most likely at the planck scale and cannot be understood without a good theory of quantum gravity.

    Odenwald: So if superstring theory were found to be an incorrect model for our particular universe, is that like turning the clock back to circa 1978 in physics?

    Susskind: I agree that going back to the ’70s would be turning the clock back in the sense that we would be ignoring the vast amount of mathematical knowledge that has been gained over the subsequent years, mostly from string theory. That is just not going to happen. The changes in our theoretical understanding of quantum field theory, gravity, black holes, are completely irreversible. [String theory mathematics] has even worked its way into nuclear physics and heavy ion collisions as well as into condensed matter physics.

    Odenwald: Kind of a hard place for modern theoreticians to revisit, but for astronomy and cosmology the 1970s seem not such a bad place. Without superstring theory, we would still have cosmological inflation. Without superstring theory, what happened at the instant of the Big Bang would remain unknown, logically indescribable, and still a great puzzle… as it always has.

    Susskind: [Not quite.] Recent cosmology has been completely dominated by studying the cosmic microwave background [CMB] and inflationary theory.

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    Gravitational Wave Background
    Gravitational waves from BICEP2 in support of Inflation theory not yet accepted

    BICEP 2
    BICEP2

    The CMB fluctuation spectrum is widely understood as a quantum effect. Inflation is a gravitational effect. Is there any question that quantum gravity (quantum plus gravity) will be the framework for understanding the early universe? No, there is not. Also I might add that the old inflation that you are referring to was a disaster. It didn’t work. Many inflationary cosmologists like Linde, Vilenkin, and Guth are looking to string theory for possible answers to the puzzles of inflation.

    Odenwald: Is it fair to say that superstring theory is “too big to fail”? I am reminded of the alledged quotation by Einstein as he was awaiting news about a major test of relativity in 1919. A reporter is said to have asked, “Well, what would it mean if your theory is wrong?” to which Einstein allegedly replied, “Then I would feel sorry for the good Lord; the theory is correct!” Is the physics community in the same predicament because superstring theory is a “beautiful” theory that seems to explain so much, and its mathematics is so impeccable that it is used in other theoretical settings in physics?

    Susskind: Exactly right. However, it is fair to say that while theorists were developing powerful tools, they mostly had wrong expectations for what the theory was indicating. Most theorists hoped that string theory would lead to an absolutely unique set of particles, coupling constants, with exactly vanishing cosmological constant. What we have learned from the theory itself is that it is a theory of tremendous diversity. Unexpectedly, string theory is most comfortable with a huge multiverse of tremendous variety instead of the small “knowable” and unique universe we once imagined.

    Odenwald: So what would our theoretical explanations for our universe look like without added dimensions, quantum gravity or string theory?

    Susskind: Without these things the world as we know it couldn’t exist. Giving up quantum gravity means giving up either the ideas of quantum [mechanics] or of gravity [and general relativity]. In a cosmological context quantum gravity is responsible for the primordial density fluctuations [we directly observe in the CMB] that ultimately condensed to form stars, galaxies, planets, etc. Without string theory we should not have the diversity of possibilites that allow pocket universes [Alan Guth’s term] with the ultra-fine tuning needed to insure conditions for our kind of life.

    Odenwald: If string theory loses its experimental support at the LHC, wouldn’t it be far worse than merely going back to cosmology circa 1975 or even 1965? We would have to question the very mathematical tools we have been using for the last 50 years!

    Susskind: I agree with your analysis, except that I would add: Expect the unexpected. Unforseen surprises are the rule in science, not the exception. Remember: Stuff happens.

    Odenwald: If superstring theory falls, are there any competing theories out there that could hold out some hope?

    Susskind: Not as far as I know.

    • * * * *

    So there you have it. The Large Hadron Collider absolutely has to find some clue about supersymmetry, or superstring theory is compromised, we will have no good idea about dark matter, and we will definitely be in a bad place until the super-LHC is built in the 2030s.

    Patience, however, is a still a necessary virtue. Physicists were in this same quandary before the Higgs boson was finally discovered after 50 years of increasingly panicked searching.

    See the full article here.

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  • richardmitnick 7:21 am on January 10, 2015 Permalink | Reply
    Tags: , , , , String Theory   

    From Byron Jennings at Quantum Diaries: “String Theory and the Scientific Method” 

    Jan 9, 2015

    b
    Byron Jennings, Triumf Lab

    It seems some disagreements are interminable: the Anabaptists versus the Calvinists, capitalism versus communism, the Hatfields versus the McCoys, or string theorists versus their detractors. It is the latter I will discuss here although the former may be more interesting. This essay is motivated by a comment in the December 16, 2014 issue of Nature by George Ellis and Joe Silk. The comment takes issue with attempts by some string theorists and cosmologists to redefine the scientific method by eliminating the need for experimental testing and relying on elegance or similar criteria instead. I have a lot of sympathy with Ellis and Silk’s point of view but believe that it is up to scientists to define what science is and that hoping for deliverance by outside people, like philosophers, is doomed to failure.

    To understand what science is and what science is not, we need a well-defined model for how science behaves. Providing that well-defined model is the motivation behind each of my essays. The scientific method is quite simple: build models of how the universe works based on observation and simplicity. Then test them by comparing their predictions against new observation. Simplicity is needed since observations underdetermine the models (see for example: Willard Quine’s (1908 –2000) essay: The Two Dogmas of Empiricism). Note also that what we do is build models: the standard model of particle physics, the nuclear shell model, string theory, etc. Quine refers to the internals of the models as myths and fictions. Henri Poincaré (1854 – 1912) talks of conventions and Hans Vaihinger (1852 –1933) of the philosophy of as if otherwise known as fictionalism. Thus it is important to remember that our models, even the so-called theory of everything, are only models and not reality.

    s
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    v
    Partly filled valence orbitals for both neutrons and protons appear at energies over the filled inert core orbitals, in the shell model of the atomic nucleus

    It is the feedback loop of observation, model building and testing against new observation that define science and give it its successes. Let me repeat: The feedback loop is essential. To see why, consider example of astrology and why scientists reject it. Its practitioners consider it to be the very essence of elegance. Astrology uses careful measurements of current planetary locations and mathematics to predict their future locations, but it is based on an epistemology that places more reliance on the eloquence of ancient wisdom than on observation. Hence there is no attempt to test astrological predictions against observations. That would go against their fundamental principles of eloquence and the superiority of received knowledge to observation. Just as well, since astrological predictions routinely fail. Astrology’s failures provide a warning to those who wish to replace prediction and simplicity with other criteria. The testing of predictions against observation and simplicity are hard taskmasters and it would be nice to escape their tyranny but that path is fraught with danger, as astrology illustrates. The feedback loop from science has even been picked up by the business management community and has been built into the very structure of the management standards (see ISO Annex SL for example). It would be shame if management became more scientific than physics.

    But back to string theory. Gravity has always been a tough nut to crack. [Sir] Isaac Newton (1643 – 1727) proposed the decidedly inelegant idea of instantaneous action at a distance and it served well until 1905 and the development of special theory of relativity. Newton’s theory of gravity and special relativity are inconsistent since the latter rules out instantaneous action at a distance. In 1916, Albert Einstein (1879 – 1955) with an honorable mention to David Hilbert (1862 – 1943) proposed the general theory of relativity to solve the problem. In 1919, the prediction of the general theory of relativity for the bending of light by the sun was confirmed by an observation by [Sir] Arthur Eddington (1882 – 1944). Notice the progression: conflict between two models, proposed solution, confirmed prediction, and then acceptance.

    Like special relativity and Newtonian gravity, general relativity and quantum mechanics are incompatible with one another. This has led to attempts to generate a combined theory. Currently string theory is the most popular candidate, but it seems to be stuck at the stage general relativity was in 1917 or maybe even 1915: a complicated (some would say elegant, others messy) mathematical theory but unconfirmed by experiment. Although progress is definitely being made, string theory may stay where it is for a long time. The problem is that the natural scale of quantum gravity is the Planck mass and this scale is beyond what we can explore directly by experiment. However, there is one place that quantum gravity may have left observable traces and that is in its role in the early Universe. There are experimental hints that may indicate a signature in the cosmic microwave background radiation but we must await further experimental results. In the meantime, we must accept that current theories of quantum gravity are doubly uncertain. Uncertain, in the first instance, because, like all scientific models, they may be rendered obsolete by new a understanding and uncertain, in the second instance, because they have not been experimentally verified through testable predictions.

    Cosmic Background Radiation Planck
    Cosmic Microwave Background per ESA/Planck

    ESA Planck
    ESA/Planck

    Let’s now turn to the question of multiverses. This is an even worse dog’s breakfast than quantum gravity. The underlying problem is the fine tuning of the fundamental constants needed in order for life as we know it to exist. What is needed for life, as we do not know it, to exist is unknown. There are two popular ideas for why the Universe is fined tuned. One is that the constants were fine-tuned by an intelligent designer to allow for life as we know it. This explanation has the problem that by itself it can explain anything but predict nothing. An alternate is that there are many possible universes, all existing, and we are simply in the one where we can exist. This explanation has the problem that by itself it can explain anything but predict nothing. It is ironic that to avoid an intelligent designer, a solution based on an equally dubious just so story is proposed. Since we are into just so stories, perhaps we can compromise by having the intelligent designer choosing one of the multiverses as the one true Universe. This leaves the question of who the one true intelligent designer is. As an old farm boy, I find the idea that Audhumbla, the cow of the Norse creation myth, is the intelligent designer to be the most elegant. Besides the idea of elegance, as a deciding criterion in science, has a certain bovine aspect to it. Who decides what constitutes elegance? Everyone thinks their own creation is the most elegant. This is only possible in Lake Wobegon, where all the women are strong, all the men are good-looking, and all the children are above average (A PRAIRIE HOME COMPANION – Garrison Keillor (b. 1942)). Not being in Lake Wobegon, we need objective criteria for what constitutes elegance. Good luck with that one.

    Some may think the discussion in the last paragraph is frivolous, and quite by design it is. This is to illustrate the point that once we allow the quest for knowledge to escape from the rigors of the scientific method’s feedback loop all bets are off and we have no objective reason to rule out astrology or even the very elegant Audhumbla. However, the idea of an intelligent designer or multiverses can still be saved if they are an essential part of a model with a track record of successful predictions. For example, if that animal I see in my lane is Fenrir, the great gray wolf, and not just a passing coyote, then the odds swing in favor of Audhumbla as the intelligent designer and Ragnarok is not far off. More likely, evidence will eventually be found in the cosmic microwave background or elsewhere for some variant of quantum gravity. Until then, patience (on both sides) is a virtue.

    See the full article here.

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  • richardmitnick 11:54 am on January 10, 2014 Permalink | Reply
    Tags: , , , String Theory   

    From Fermilab: “Physics in a Nutshell – Superstrings” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, Jan. 10, 2014
    Don Lincoln

    Fermilab Don Lincoln
    Dr. Don Lincoln

    One of the oldest scientific questions in history is “What are the ultimate building blocks of the universe?” Today’s article talks about a cool idea called “superstrings,” tiny subatomic strings that play a cosmic and subatomic symphony. Superstrings are a possible answer to the ancient question surrounding the identity of the universe’s smallest components. Understanding this answer requires some historical context.

    fuzzball
    Fuzzball of String Theory from Wikipedia

    The first recorded debate on the subject was written down about 2,500 years ago in Greece, with a philosopher named Democritus making the most accurate guess when he postulated discrete units he called atomos. The question was left to the realm of the philosophers for millennia until the 1700s, when modern chemistry began to shed light on the topic using empirical techniques. With the identification of the atoms of the chemical elements, central features of Democritus’ model were validated.

    Over the next two-plus centuries, scientists proposed and discovered increasingly smaller components that make up our universe. They discovered the familiar proton, neutron and electron that make up atoms. Then they learned that the proton and neutron contained even smaller components called quarks. They also discovered that the two types of quarks that make up protons and neutrons, called the up and down quarks, weren’t the only quarks out there.

    Today we know the building blocks of matter can be classified into two types called quarks and leptons, each of which consists of six examples. The six quarks are called up, down, charm, strange, top and bottom. The six leptons are called electron, electron neutrino, muon, muon neutrino, tau and tau neutrino. With so many fundamental particles, a new organizing principle is needed to make sense of what was understood to be the universe’s building blocks.

    So what the heck is the story with these particles of the Standard Model, the modern-day atomos of Democritus? What role do they play in our understanding of the subatomic world?

    sm
    Standard Model of Particle Physics

    Well, we don’t know the answer to that in detail. We do know of patterns. Up, charm and top quarks all have the same electrical charge but rather different masses, with up being the lightest and top the heaviest. Down, strange and bottom also have identical electric charge and increasing mass. The electron, muon and tau lepton exhibit the same behavior. Naturally, when we see recurring patterns like this, we go looking for an explanation. One such explanation is superstrings.

    Unlike what we’ve seen before, with each particle being composed of an even smaller one, superstrings break the pattern. Superstring theory postulates that the ultimate building block of matter consists of tiny, tiny “strings” that vibrate. Strings that vibrate the least are the quarks and leptons with the smallest mass, while the heavier particles have more energetic vibrations. Employing a musical metaphor, it’s as if the electron might be a B-flat, while the bottom quark might be an F-sharp above that.

    There are some bizarre consequences to this idea. Early calculations using superstring theory yielded nonsense. For example, when adding up all the things that could happen when two strings interacted, physicists found that there was more than a 100 percent chance something would happen. Since 100 percent is the maximum, that was a very bad outcome. These calculations were done in ordinary three dimensional space.

    Then a curious soul played around with the same calculation, but using more than three spatial dimensions. Scientists found that when four dimensions were invoked, the answer was more sensible, but still above 100 percent. By adding more and more dimensions, the answer became more and more reasonable. When 10 dimensions were invoked, the result gave the expected 100 percent. This is the reason people talk about 10 dimensions of space and time.

    Physicists put forward five different versions of superstring theory, but it turned out that by invoking one additional dimension, all the five versions turned out to be the same. This is the reason you might have heard that there are 11 dimensions of space and time.

    It is important to note that the idea of superstrings has not been proven empirically. It could well be wrong. However, the idea that the universe could have a single building block (the string) and that all the observed particles of nature are just different vibrations is a very attractive idea. Another benefit of superstring theory is that it incorporates gravity very easily. Other ideas unifying the various forces have a tough time with gravity. This isn’t a reason to believe in superstrings, but it is a reason to find the theory to be attractive.

    The story of superstrings is much bigger than I can describe here. I’ve only given the quickest possible description. If the idea of the entire universe being a cosmic melody played by tiny strings interests you, you might be interested in reading Brian Greene’s book The Elegant Universe.

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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  • richardmitnick 2:54 pm on July 25, 2013 Permalink | Reply
    Tags: , , , , , , String Theory, Superfluids   

    From M.I.T.: “Superfluid turbulence through the lens of black holes” 

    Study finds behavior of the turbulent flow of superfluids is opposite that of ordinary fluids.

    July 25, 2013
    Jennifer Chu, MIT News Office

    “A superfluid moves like a completely frictionless liquid, seemingly able to propel itself without any hindrance from gravity or surface tension. The physics underlying these materials — which appear to defy the conventional laws of physics — has fascinated scientists for decades.

    fluid
    Black hole physics shows that superfluids in turbulence behave much like cigarette smoke. Image: Christine Daniloff

    Think of the assassin T-1000 in the movie “Terminator 2: Judgment Day” — a robotic shape-shifter made of liquid metal. Or better yet, consider a real-world example: liquid helium. When cooled to extremely low temperatures, helium exhibits behavior that is otherwise impossible in ordinary fluids. For instance, the superfluid can squeeze through pores as small as a molecule, and climb up and over the walls of a glass. It can even remain in motion years after a centrifuge containing it has stopped spinning.

    Now physicists at MIT have come up with a method to mathematically describe the behavior of superfluids — in particular, the turbulent flows within superfluids. They publish their results this week in the journal Science.

    ‘Turbulence provides a fascinating window into the dynamics of a superfluid,’ says Allan Adams, an associate professor of physics at MIT. ‘Imagine pouring milk into a cup of tea. As soon as the milk hits the tea, it flares out into whirls and eddies, which stretch and split into filigree. Understanding this complicated, roiling turbulent state is one of the great challenges of fluid dynamics. When it comes to superfluids, whose detailed dynamics depend on quantum mechanics, the problem of turbulence is an even tougher nut to crack.’

    To describe the underlying physics of a superfluid’s turbulence, Adams and his colleagues drew comparisons with the physics governing black holes. At first glance, black holes — extremely dense, gravitationally intense objects that pull in surrounding matter and light — may not appear to behave like a fluid. But the MIT researchers translated the physics of black holes to that of superfluid turbulence, using a technique called holographic duality.

    Consider, for example, a holographic image on a magazine cover. The data, or pixels, in the image exist on a flat surface, but can appear three-dimensional when viewed from certain angles. An engineer could conceivably build an actual 3-D replica based on the information, or dimensions, found in the 2-D hologram.

    ‘If you take that analogy one step further, in a certain sense you can regard various quantum theories as being a holographic image of a world with one extra dimension,’ says Paul Chesler, a postdoc in MIT’s Department of Physics.

    Taking this cosmic line of reasoning, Adams, Chesler and colleagues used holographic duality as a ‘dictionary’ to translate the very well-characterized physics of black holes to the physics of superfluid turbulence.

    To the researchers’ surprise, their calculations showed that turbulent flows of a class of superfluids on a flat surface behave not like those of ordinary fluids in 2-D, but more like 3-D fluids, which morph from relatively uniform, large structures to smaller and smaller structures. The result is much like cigarette smoke: From a burning tip, smoke unfurls in a single stream that quickly disperses into smaller and smaller eddies. Physicists refer to this phenomenon as an “energy cascade.”

    ‘For superfluids, whether such energy cascades exist is an open question,’ says Hong Liu, an associate professor of physics at MIT. ‘People have been making all kinds of claims, but there hasn’t been any smoking-gun type of evidence that such a cascade exists. In a class of superfluids, we produced very convincing evidence for the direction of this kind of flow, which would otherwise be very hard to obtain.’”

    See the full article here.


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  • richardmitnick 11:33 am on October 28, 2012 Permalink | Reply
    Tags: , , String Theory   

    From SETI Institute: “String Theory Landscape – Alexander Westphal (SETI Talks)” Video 

    A very good video on the subject.

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