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String Theory Predicts Behavior of Superfluids
schrodingers_rabbit writes "Despite formidable odds, condensed matter physicists have made a breakthrough most thought impossible — finding a practical use for string theory. The initial breakthrough was made by physicist and cosmologist Juan Maldacena. His theory states that the known universe is only a 2D construct in anti-de-Sitter space, projected into 3 dimensions. This theory manages to model black holes and quantum theory congruently, a feat that has eluded scientists for decades; but it fails to correspond to the shape of space-time in the known universe. However, it does predict thermodynamic properties of black holes, including higher-dimensional viscosity — the equations for which elegantly and almost exactly calculate the behavior of quark-gluon plasma and other superfluids. According to Jan Zaanen at the University of Leiden, 'The theory is calculating precisely what we are seeing in experiments.' Unfortunately, the correspondence cannot prove or disprove string theory, although it is a positive step." Not an easy path to follow: one condensed matter theorist said, "It took two years and two 1000-page books of dense mathematics, but I learned string theory and got kind of enchanted by it. [When the string-theory related] thing began to... make predictions about high-temperature superconductors, my traditional mainstay, I was one of the few condensed matter physicists with the preparation to take it up."
That is to say, if you view that the proving of string theory to be true a positive step.
I'm always amazed that theoretical physicists can manipulate such immensely complex abstract objects in their heads and still be able to breathe and maintain bladder control. It really makes software engineering look like a piece of piss. Much respect.
I would also say that having worked with academic medics, chemists, mathematicians, computer scientists and biologists, physicists are almost always the coolest, most down to earth and least douchey scientists out there.
String theory works because the math works. There isn't anything special about the string theorists' model of humming cosmic strings that makes it work. All particle behavior is explainable using mathematics.
What makes this interesting is that the model allowed for the construction of mathematical constructs that explain the behavior correctly. But it still doesn't say anything about the predictions that the model completely blows.
What String Theory has, more than anything else, is a great set of marketeers behind it. Michio Kaku is a smart and articulate guy. It's not the steak, it's the sizzle.
The main criticism of string theory is that it is too flexible. It can be contorted to generate any prediction, so it predicts nothing. This problem is not unique to physics; I saw it in economics too. Add more parameters to your model and you can fit historical data better, but your predictions of the future get worse. TFA seems to be just a string of examples of contorting string theory to fit past experimental results.
The holographic principle doesn't mean that the universe has only 2 spatial dimensions, but rather that the universe can be modeled using one less degree of freedom than our view of spacetime would imply. Again, these kinds of theories are not suggesting that our space is two-dimensional, rather they are saying that the 3 dimensions we observe are emergent from a lower-dimensional description. All of the 'information' in a given region of space can be described as being encoded in the surface of said region.
This remarkable, if bizarre, conclusion gains considerable support from the fact that black-hole entropy (and entropy is a measure of information content) is related only to the surface area of the black hole. So this is a case where we know with some confidence that we can indeed reduce all the information about a 3D region of space (the black hole) to an expression that only relies on 2 dimensions (the surface of the black hole). The holographic principle appears in numerous theories that imply that this holds generally for any region of space, not just black holes.
Now, whether you view this is 'just a mathematical trick' or 'a deep insight into the actual structure of the universe' is in some sense a matter of taste. (The same goes for all other physical theories: e.g. do electrons exist or are they just mathematically-useful constructs? How about photons? Gravity waves? Spacetime?) If you take the math seriously then this may mean that our universe is in some sense 'actually' 2-dimensional, with the three spatial dimensions we see being emergent instead of fundamental.
But in no case is the theory saying that there are not 3 spatial dimensions. The predictions it makes are for particles moving through a 3+1 spacetime.