update.532 (fwd)

[Jim Choate]

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Date: Thu, 29 Mar 2001 12:04:36 -0500 (EST)
From: AIP listserver <physnews at aip.org>
To: physnews-mailing at aip.org
Subject: update.532

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 532  March 28, 2001   by Phillip F. Schewe, Ben Stein,
and James Riordon

PROGRAMMABLE BLACK HOLE COMPUTERS.  One usually
thinks of a black hole as an omnivorous object swallowing energy
and spitting some of it back in the form of Hawking evaporation
radiation, consisting of particles created in pairs out of the vacuum
near the edge of the black hole.  In principle, a tiny black hole can
be formed in a way that encodes instructions for performing
calculations.  Correspondingly, the answers could be read out from
the escaping Hawking radiation.  Why use a black hole at all? 
Because of the presumed  tremendous density of information and
potential processing speed implicit in the extreme black hole
environment.  Seth Lloyd of MIT has previously addressed himself
to calculating the conceivable limits on the computing power of
such a black hole computer (Nature, 31 August 2000) and arrives
at a maximum processing speed of about 10^51 operations/sec for
a 1-kg black hole.  Now Jack Ng of the University of North
Carolina yjng at physics.unc.edu, 919-962-7208) extends this study
by asking whether the very foaminess of spacetime, thought to
arise at the level of 10^-35 m, provides an alternative way to limit
theoretical computation.  Ng not only finds that it does but that the
foaminess of spacetime leads to an uncertainty in timekeeping (the
more accurate the clock, the shorter its
lifetime) which in turn leads to a bound on information processing
(speed and memory simultaneously) analogous to the Heisenberg
bound on simultaneous measurement of momentum and position. 
These limits are so generous that they normally pose little problem
for ordinary physical measurements, but in the case of black hole
computer the limits would apply immediately.  Ng adds, apropos
of detecting gravity waves with LIGO and other interferometric
devices, that in addition to accounting for various forms of noise,
such as seismic disturbances or thermal noise in the detectors, the
faint gurgle of spacetime foam will eventually have to be  included
as an additional and unavoidable source of noise in the
measurement of very short displacements (the movement of
mirrors owing to the flexings of spacetime brought about by
passing gravity waves).    If Ng is right, the noise sensitivity
achievable by the prospective advanced phase of LIGO will only
need a further hundredfold enhancement in order to detect the
quantum foam, which is to say the very fabric of spacetime.   Thus
the Planck scale, so far only a hypothetical extreme regime, might
eventually become a realm that can be approached and measured.
(Physical Review Letters, 2 April 2001.)

A BOSE EINSTEIN CONDENSATE (BEC) IN HELIUM has
[SSZ: text deleted]

FUSION AVALANCHES.  Providing more than child's play,
[SSZ: text deleted]

CORRECTION:  Researchers at IBM have not yet made an
integrated circuit of carbon nanotubes (Update 531).  Rather,
Phaedon Avouris and Philip Collins of IBM have announced a
scheme for the fabrication of large arrays of nanotubes.  They also
put together one p-type nanotube transistor and one n-type
transistor to form a working logic NOT gate.


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