String theory hints at explanation for superconductivity

Nature News ^ | 19 July 2009 | Eric Hand

[neverdem]

Baroque field gets fresh lease of life in condensed-matter physics.

String theory - more than just a 'theory of everything'?Alamy

Until recently, string theory — long heralded as a 'theory of everything' — hadn't been particularly good at explaining anything.

But at a workshop this month at the Kavli Institute for Theoretical Physics in Santa Barbara, California, scientists have been using the theory to make progress in tackling one of the biggest puzzles in condensed-matter physics: the origin of high-temperature superconductivity.

String theory suggests that vibrating strings that exist in 10 dimensions underpin the observable Universe. Although that basic premise is still very much in doubt — and as yet impossible to test experimentally — some of the mathematical tools used in string theory have in the past few years been applied to describe the behaviour of hot particle plasmas and supercooled lattices of atoms.

The latest claim for string theory is that it is a key tool in explaining the normal behaviour of materials that conduct electricity without any resistance at relatively high temperatures. The theory that explains conventional superconductivity at temperatures close to absolute zero is well-developed — but the theory that explains the behaviour of a second class of materials, which can superconduct at temperatures as high as 70 K, remains something of a mystery. By explaining the normal behaviour of these materials just above their superconducting temperature, string theorists hope to get a better handle on high-temperature superconductivity itself.

"It suggests that we are on the verge of understanding a new state of matter using a string-theory description," says Subir Sachdev, a condensed-matter theorist at Harvard University in Cambridge, Massachusetts, who co-organized the workshop. At the workshop, Sachdev and his collaborators circulated a paper, as yet not even a preprint, in which they stake their claim to a string-theory model for high-temperature superconductors.

Finding new applications for the mathematics of string theory is reinvigorating the field, says Harvard University postdoctoral researcher Sean Hartnoll, another workshop co-organizer. "It now has the feeling of being a melting pot of ideas."

Baroque complexity

String theory started out in the late 1960s as a tool to explain the strong forces between nuclear atomic particles, but was replaced in the 1970s by the more successful quantum chromodynamics (QCD) theory. String theory went off in its own direction, acquiring ever more baroque layers of mathematical complexity. Some physicists found it anathema that the only way the resulting theories could be tested required energies far higher than those achievable in particle accelerators.

But in 2005, string theory did find its way, albeit indirectly, into one accelerator: the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York. Scientists discovered that string theory could be as useful as QCD in explaining the strong nuclear forces involved in a quark–gluon plasma. This new state of matter, comprising the basic constituents of protons and neutrons, was created in the hot mash-ups of gold ions generated at the RHIC. The key to this discovery was a mathematical technique in string theory that embodies the principles of holography, in which information contained in a higher dimension can be embedded in one fewer dimensions — just as a three-dimensional image can be stored within a flat, two-dimensional hologram.

Since then, researchers such as Sachdev and Hartnoll have extended the holographic techniques to the cooler regimes of condensed matter. The same string-theory tools have helped to explain the behaviour of quantum critical points — the changes in matter cooled close to absolute zero when quantum mechanical effects start to dominate its behaviour.

That in turn has allowed physicists to describe the quantum behaviour of a variety of systems, including laser-induced lattices of supercooled atoms, and now high-temperature superconductivity.

Noted string theory critic Peter Woit, a mathematician at Columbia University in New York City, says that using string theory as a tool in these ways could be useful, but they are not tests of string theory itself. "Just because a model works in one context, doesn't mean you can unify physics and get a fundamental theory of reality," he says.

Joseph Polchinski, a string theorist at the Kavli Institute and the third conference organizer, argues that if the same string-theory tools used to describe black holes can help explain the behaviour of electrons in a metal, the crossover will enable string theory applications in one area to benefit other fields

The excitement is catching on, he adds. The institute received 110 applications for just 30 spots at the workshop — the toughest workshop to get into in his memory. Quite a feat given that when it was organized 18 months ago there were fewer than a dozen papers published on the topic. "It was clearly a good gamble," says Polchinski. "It's clear there's interesting new science here."

[UCANSEE2]

I wasn’t aware that superconductivity needed an explanation.

[muawiyah]

BTW, the fundamental thesis propounded by the Leftwingtards when it comes to medicine or drugs is that if safety and efficacy studies were done by private parties they must necessarily be invalid ~ because those studies were paid for with private funds.

Now, flip that on its head and we find that grants frequently come from private sources (foundations are private), and even if they come from the government the money used to be in private hands.

Just following Leftwingtard logic anything requiring work which is paid for is invalid because it's not free.

Not saying the Leftwingtard logic is valid or useful, just that it is what it is.

As I was just noting to another Freeper into "tp" (Theoretical Physics or Toilet Papering?) many folks in that field are ignorant of current events, and the ebb and flow of criticism of scientific studies due to the source of the funding paying the scientists (or grad students) to do the work is definitely current events.

Gotta' keep up on this stuff you know, particularly when everyone of every political orientation thinks scientists should be independent of coercive thought due to funding!

[neverdem]

Brain Surgery Using Sound Waves

The Grail Searchers (science shows that an embryo is a human being)

Induced Pluripotent Stem Cells Repair Heart

Jupiter Hit by an Astronomical Object

FReepmail me if you want on or off my health and science ping list.

[AFPhys]

I’ve read a lot of explanations of ‘string theory’ and for the most part my feeble noggin can’t quite grasp it. I wish it could, because this stuff does interest me. But at the same time, the more I read up on it the more I find it hard to believe that these same folks think we’re nuts because we believe in God. ; )

-—<>-—<>-—<>-—<>-—<>-—

WONDERFUL comment!

This scientist, who believes in ALL OF THE ABOVE (well, following:) - God, Jesus, Big Bang, Creationism, Evolution, Genesis and many other supposed items that “Clash with reality” agrees whole heartedly with your comment! It always amazes me that people, and especially ANY physicist, can possibly eliminate God from their concept of the universe.

[Fractal Trader]

string theory ping

[GOPJ]

Thanks for the ping.

[SunkenCiv]

Wow! Easily the best recent string theory list topic -- not least because it's actually a string theory topic (as opposed to just being more generally about physics). Thanks Fractal Trader! Another possible topic is here:

• An Iron Key to High-Temperature Superconductivity? · Graham P. Collins · Scientific American · August 2009

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· List topics · post a topic · FR page layout · Google ·

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[SunkenCiv]

Whoops, and thanks AdmSmith for the ping.

[Paradox]

Something sort of suggesting a hope for string theory. I am certainly hopeful that things like this will allow us to "test" the validity of string theory.

Too bad the Luddites come out in these threads though.

[bmwcyle]

[ozark hilljilly]

Well, “somebody” had to pull the trigger for The Big Bang, right?
; )
Just finished reading “Can a Smart Person Believe in God?” The author makes some surprising comparisons between the nature of God and what we know of physics and science. Like fr’instance, how the concept of God “being everywhere at once” squares with quantum mechanics. It was a quick, but edifying and entertaining read!

[AFPhys]

I am not sure that this is really a test of string theory, from my reading. The article more properly discusses that this application is using the mathematics developed for string theory, and that the math seems to work for this limited case. Whether that is useful for validating string theory seems to be a bridge too far, but maybe it is a case of something like Quantum Chromodynamics, where it there is not really any definitive single way to “prove” or disprove it, but that many coordinated experiments picking out various parts have been useful.

Einstein developed a whole new branch of mathematical notation in order to handle the way he worked with general relativity, and Newton developed calculus. The accuracy and utility of those mathematical tools didn’t prove their respective theories of gravitation, but they have proven very useful to many other scientists over time. Some comments in these articles suggest that a similar “spin-off” of string theory may be what is going on here, rather than a fundamental breakthrough that argues FOR string theory itself.

[Paradox]

Some comments in these articles suggest that a similar “spin-off” of string theory may be what is going on here, rather than a fundamental breakthrough that argues FOR string theory itself.

Thanks for interpreting the article and your insights. I must admit, that I actually value the technical and scientific commentary on FR more than the political.

[AFPhys]

Agreed. I consider the ‘purge’ of FR to have severely damaged FR for that reason. Many good commentators are no longer here.