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in string theory, the singularity disappears - a comforting
realization for physicists who have a strong distaste for any
infinite quantity. In addition, black holes have no empty
space; the strings are extremely compressed, but they fill the
entire space from the singularity out to the outer boundary.
And because a black hole made of strings lacks a perfect outer
boundary, it behaves like any other scrunched-up ball of
matter. Just as matter and energy can escape a compact,
high-density object like a neutron star, matter and energy can
gradually escape a black hole despite the intense
gravitational forces. "This solves the information paradox,
because black holes radiate energy like any other body," says
Mathur.

In the relativist view, two black holes with the same mass and
spin are identical. But in the string theory view, no two
black holes are exactly alike, because they form from
different material. "We find many different kinds of black
holes, with many different internal states," says Mathur.

Mathur points to these calculations as one more indicator that
string theorists are on the right track in developing a
quantum theory of gravity - a "theory of everything" that
reconciles the two seemingly disparate pillars of 20th-century
physics: quantum mechanics and general relativity. Amazingly,
both string theory and general relativity predict the exact
same diameter for a black hole of any given mass - even though
the two calculations are entirely independent. In addition,
the calculated radiation from a black hole made of strings
exactly matches the properties that quantum mechanics predicts
for the Hawking radiation.

"String theory is so miraculous that whenever it comes up to a
problem, it always gives us the right numbers," says Mathur.
It is for reasons like this, and the internal self-consistency
of string theory, that its adherents feel confident they are
hot on the trail of nature's deepest secrets.

"The black hole information paradox is crucial," says Mathur.
"If we can't resolve it, quantum mechanics and general
relativity cannot be put together."

If some of the extra dimensions in string theory are larger
than a certain size, physicists might soon be able to test
these ideas in the laboratory. Starting around 2007, the Large
Hadron Collider (LHC) in Switzerland will smash subatomic
particles into one another at extremely high energies. Some
theorists have hypothesized that if the extra dimensions are
as large as a few millimeters in diameter, these particle
collisions will create miniature black holes, which will
almost instantaneously evaporate in bursts of Hawking
radiation. By analyzing the particles in the Hawking
radiation, physicists might be able to determine the
fundamental nature of black holes and whether the Hawking
radiation carries information about the material that formed
them. "I bet if mini-black holes are produced at the LHC or
future colliders, we will be able to study Hawking radiation
to death and answer all of these impending questions," says
Landsberg.

But many physicists, Mathur included, remain skeptical that
the extra dimensions in string theory are large enough to
enable black holes to be created at the LHC. If so, it might
be centuries before experiments shed light on the information
paradox.

Press Center
Copyright 2004 Sky Publishing Corp.







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