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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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