Fw: Scientists study black holes created in laboratory.
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From: "Do Wah Ditty" <DoWahDitty@...>
Sent: Monday, February 04, 2002 4:57 PM
Subject: Scientists study black holes created in laboratory.
Scientists study black holes created in laboratory
Copyright © 2002
United Press International
By MIKE MARTIN, United Press International
ST. LOUIS (February 2, 2002 4:45 p.m. EST) - Lab-generated "dumb
the acoustic, or sound wave analogs of black holes - may provide
experimental evidence for quantum gravity, a theory that unifies
Black holes have massive, ultra-dense collapsed stars at their
gravitational force surrounding the star is so strong that
nothing - not
even light - can escape. The point of no return for light
entering a black
hole, the point at which it is too close to escape the
is called the "event horizon."
Dumb holes arise when fluids flowing faster than the speed of
regions that trap sound waves. They too have a surface of no
return - the
"acoustic horizon". While black holes remain interstellar
researchers can create dumb holes in a laboratory.
"By reproducing the most important qualities of black holes in a
system, some of the predictions of quantum gravity can be tested
paradoxes of the theory understood," University of Maryland
Stefano Liberati told United Press International from College
chief paradox is so-called "Hawking radiation."
In a discovery that stunned the scientific community, renowned
Stephen Hawking found that black holes slowly evaporate by
radiating, quantum particles. "Hawking radiation" presented a
can certain kinds of sub-atomic particles somehow escape the
strong gravitational fields that trap even light.
"In a black hole, Hawking radiation is a process where the
gravity near the
event horizon pulls apart particle-antiparticle pairs that exist
deep-space vacuum," Liberati said. The black hole captures one of
partners while the other escapes to freedom, making it appear as
black hole is radiating particles.
Researchers have long hoped Hawking radiation would yield clues
quantum forces that hold atoms together and the gravitational
guide planets and collapse stars.
"We are interested in black hole analogues because we would like
to find the
analog of the Hawking radiation process," Liberati said.
Dumb holes that trap sound waves may yield experimental evidence
understand quantum gravity because these acoustic black holes
the characteristics -- paradoxes included -- of their light-wave
"It turns out that the equations for sound waves in a continuous
exactly the same as the equations for certain kinds of radiation
gravitational field," said physicist William Unruh, from the
Institute for Physics and Astronom, in Vancouver, British
surface at which the fluid exceeds the velocity of sound acts in
same way as the horizon of a black hole, including the Hawking
Using a special kind of matter called a "Bose-Einstein
Liberati's team hopes to recreate the most important features of
"The Bose-Einstein condensate is a peculiar state of matter which
realized at very low temperatures," Liberati said. "A collective
of atoms in a condensed matter system such as this Bose-Einstein
forms a wave composed of quantum particles called 'phonons,' just
is a wave composed of particles called photons."
A phonon is "the equivalent of the photon for sound," said Unruh.
are the particle you get when you treat sound as a quantum
field," just as
photons are quantised, or particulate, light.
Supersonic flow of a Bose-Einstein condensate will form a dumb
inescapably traps phonons the same way gravitational collapse
forms a black
hole that traps photons, Liberati told UPI.
"Phonons travel at the speed of sound, so if we think of a flow
fluid speed is increasing, then once it reaches and overtakes the
sound, it generates a region where phonons cannot escape,"
explained. "The phonons would have to climb up the flow-as
salmons against a
stream-but the flow is too fast for them, so the region of
is a 'trap.' "
Hawking radiation can occur in both dumb holes and black holes.
that at the acoustic horizon phonon pairs are generated and
Liberati said. "The phonons falling in the supersonic region are
their partners are seen as a radiation of sound waves emitted
from the dumb
Using dumb holes to study black holes is an example of a common
technique-substituting a well - understood system for its
"We understand the physics of fluids completely, unlike our
quantum gravity," Unruh said.
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