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  • Joe McGonagle
    From the NG s ... From: Do Wah Ditty Newsgroups: alt.alien.research,alt.ufo.reports,uk.rec.ufo Sent: Monday, February 04, 2002 4:57 PM
    Message 1 of 1 , Feb 4, 2002
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      From the NG's
      ----- Original Message -----
      From: "Do Wah Ditty" <DoWahDitty@...>
      Newsgroups: alt.alien.research,alt.ufo.reports,uk.rec.ufo
      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
      holes" -
      the acoustic, or sound wave analogs of black holes - may provide
      important
      experimental evidence for quantum gravity, a theory that unifies
      atomic and
      gravitational forces.
      Black holes have massive, ultra-dense collapsed stars at their
      centers. The
      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
      gravitational pull,
      is called the "event horizon."

      Dumb holes arise when fluids flowing faster than the speed of
      sound form
      regions that trap sound waves. They too have a surface of no
      return - the
      "acoustic horizon". While black holes remain interstellar
      objects,
      researchers can create dumb holes in a laboratory.

      "By reproducing the most important qualities of black holes in a
      fluid
      system, some of the predictions of quantum gravity can be tested
      and some
      paradoxes of the theory understood," University of Maryland
      physicist
      Stefano Liberati told United Press International from College
      Park,Md. The
      chief paradox is so-called "Hawking radiation."

      In a discovery that stunned the scientific community, renowned
      physicist
      Stephen Hawking found that black holes slowly evaporate by
      emitting, or
      radiating, quantum particles. "Hawking radiation" presented a
      puzzle: how
      can certain kinds of sub-atomic particles somehow escape the
      inescapably
      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
      in a
      deep-space vacuum," Liberati said. The black hole captures one of
      the
      partners while the other escapes to freedom, making it appear as
      though the
      black hole is radiating particles.

      Researchers have long hoped Hawking radiation would yield clues
      about the
      quantum forces that hold atoms together and the gravitational
      forces that
      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
      used to
      understand quantum gravity because these acoustic black holes
      exhibit all
      the characteristics -- paradoxes included -- of their light-wave
      brethren.

      "It turns out that the equations for sound waves in a continuous
      fluid are
      exactly the same as the equations for certain kinds of radiation
      in a
      gravitational field," said physicist William Unruh, from the
      Canadian
      Institute for Physics and Astronom, in Vancouver, British
      Columbia. "The
      surface at which the fluid exceeds the velocity of sound acts in
      exactly the
      same way as the horizon of a black hole, including the Hawking
      effect."

      Using a special kind of matter called a "Bose-Einstein
      condensate,"
      Liberati's team hopes to recreate the most important features of
      black holes
      using sound.

      "The Bose-Einstein condensate is a peculiar state of matter which
      is
      realized at very low temperatures," Liberati said. "A collective
      vibration
      of atoms in a condensed matter system such as this Bose-Einstein
      condensate
      forms a wave composed of quantum particles called 'phonons,' just
      as light
      is a wave composed of particles called photons."

      A phonon is "the equivalent of the photon for sound," said Unruh.
      "Phonons
      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
      hole that
      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
      where the
      fluid speed is increasing, then once it reaches and overtakes the
      speed of
      sound, it generates a region where phonons cannot escape,"
      Liberati
      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
      supersonic flow
      is a 'trap.' "

      Hawking radiation can occur in both dumb holes and black holes.
      "We expect
      that at the acoustic horizon phonon pairs are generated and
      pulled apart,"
      Liberati said. "The phonons falling in the supersonic region are
      lost while
      their partners are seen as a radiation of sound waves emitted
      from the dumb
      hole."

      Using dumb holes to study black holes is an example of a common
      technique-substituting a well - understood system for its
      poorly -
      understood counterpart.

      "We understand the physics of fluids completely, unlike our
      understanding of
      quantum gravity," Unruh said.
      --
      _____________
      Dum Ditty Do
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