--- In physical_sciences@yahoogroups.com, "Robert Karl Stonjek" <stonjek@...>
wrote:

A "theory of everything" is said to solve its first real-world problem

July 8, 2009
Courtesy University of Leiden
and World Science staff

For the first time, researchers say they have solved a real-world problem using
a very abstract "theory of everything" that often has been criticized as
untestable.

Now, the scientists claim, the critics may have to rethink their position.

The scientists attempted to use the controversial doctrine, known as string
theory, to explain an aspect of super-conductivity-a phenomenon in which
electric current zooms through an object without meeting any of the normal
resistance.




'AdS/CFT' correspondence that relates a gravity-determined world in a
higher dimension to 'quantum-critical' worlds formed, for example, by electrons
in a lower-dimensional world on the 'outside' of the first world. (Courtesy
Science)


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String theory is a bid to resolve almost all the mysteries of physics at a blow
by bridging the gap between the two most successful theories of the 20th
century, general relativity and quantum mechanics. Each has been successful at
explaining how the universe behaves over vast distances and in tiny spaces,
respectively. But they conflict in some ways; both can't be right.

String theory claims all the particles of nature are actually different
vibrations of unseen, tiny loops called "strings." The theory mathematically
fixes the major inconsistencies between the other two. In the process, if it's
correct, it would show the underlying unity of nature's forces.

But it only works if the strings have several extra dimensions in which to
vibrate beyond the dimensions we see. Different versions of string theory
propose 10 or 26 dimensions, some of which are invisible because they are rolled
up into tiny balls.

Scientists at the University of Leiden in the Netherlands used the mathematics
of string theory to understand so-called high-temperature superconductivity. The
effortless shooting of current through "superconducting" materials was once
believed to occur only at temperatures so absurdly cold as to make practical
applications of the phenomenon unlikely. But more and more examples are coming
up where it also occurs at higher temperatures, according to the Leiden
physicists.

Electrons, the subatomic particles that carry electric current, can form a
special kind of state, a so-called quantum critical state, that plays a role in
this high-temperature super-conductivity.

"It has always been assumed that once you understand this quantum-critical
state, you can also understand high temperature super-conductivity. But,
although the experiments produced a lot of information, we hadn't the faintest
idea of how to describe this phenomenon," said Leiden physicist Jan Zaanen.

String theory now offers a solution, he added. "This is superb. I have never
experienced such euphoria," he remarked, explaining that the numbers fit so
precisely that he was astonished. The finding is reported this week in the
research journal Science.

Zaanen describes the quantum-critical state as a "quantum soup," whereby the
electrons form a collective independent of distances, and show the same
behaviour at tiny scales or at the roughly human scale.

Because of Zaanen's interest in string theory, he and string theoreticist
Koenraad Schalm became acquainted after Schalm's arrival at Leiden University.
Zaanen had an unsolved problem and Schalm was an expert in the field of string
theory. Their common interest brought them together, and they decided to work
jointly.

The pair used the aspect of string theory known as AdS/CFT correspondence. This
allows situations in a large, so-called relativistic, world to be translated
into a description at minuscule, so-called quantum physics level. This
correspondence bridges the gap between these two different worlds. By applying
the correspondence to the theoretical situation where a black hole vibrates when
an electron falls into it, they arrived at a description of electrons that move
in and out of a quantum-critical state.

This is the first time a calculation based on string theory has been published
in Science, even though the theory is widely known, Zaanen said.

"There have always been a lot of expectations surrounding string theory," Zaanen
explained, having himself studied the theory to satisfy his own curiosity.
"String theory is often seen as a child of Einstein that aims to devise a
revolutionary and comprehensive theory, a kind of 'theory of everything.' Ten
years ago, researchers even said: 'Give us two weeks and we'll be able to tell
you where the Big Bang came from.' The problem of string theory was that, in
spite of its excellent maths, it was never able to make a concrete link with the
physical reality-the world around us."

"AdS/CFT correspondence now explains things that colleagues who have been
beavering away for ages were unable to resolve, in spite of their enormous
efforts," he went on. "There are a lot of things that can be done with it. We
don't fully understand it yet, but I see it as a gateway to much more."

Source: WorldScience
http://www.world-science.net/othernews/090707_string

Posted by
Robert Karl Stonjek

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