SETI bioastro: FW: update.539

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From: Larry Klaes (larry.klaes@incent.com)
Date: Mon May 21 2001 - 12:04:01 PDT


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Sent: Tuesday, May 15, 2001 2:28 PM
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Subject: update.539

PHYSICS NEWS UPDATE
                      
The American Institute of Physics Bulletin of Physics News
Number 539 May 15, 2001 by Phillip F. Schewe, Ben Stein, and
James Riordon

(DE)CONSTRUCTING DIMENSIONS. What is space? We
generally take space for granted. We exist within it, we move
about, make measurements of it. It's there before anything else and
it seems to be continuous. Furthermore, extra dimensions, beyond
the three spatial dimensions we perceive, are mandated by modern
string theories in the process of bringing quantum mechanics and
general relativity together in a single theoretical framework. That
we can't see these dimensions is usually explained by saying that
they are curled up in some way. The customary prescription for
discovering such dimensions is to study particle interactions at ever
higher energies, which is equivalent to studying matter at ever
smaller size scales. Now, three physicists want to re-examine the
whole concept of space by coming from the other direction. As
higher energies are probed, say Nima Arkani-Hamed (LBL, 617-
496-8188) Andrew Cohen (Boston Univ, 617-495-1988) and
Howard Georgi (Harvard, 617-496-8293) dimensions may actually
disappear, revealing themselves as only a property of particle forces
at low energies. Imagine, for the moment, a number of copies of
our four-dimensional (three space plus time) universe. Without
interactions between them, these universes are inaccessible---we are
ignorant of their existence. But further imagine a new set of forces,
linking pairs of these universes. If these forces are similar to the
strong nuclear (hadronic) force, which is strong at low energies but
gets weak at high energies, relatively low energy experiments
(although still high energy in the TeV range by today's standards)
would detect these alternate universes while high energy ones would
not. This connection between different universes at low energies, the
ability to transfer information, and even travel among them, appears
as a new dimension. This dimension was not present beforehand,
but appeared dynamically. In other words, the new dimension
comes into existence only through interactions among particles. At
high energies these forces "melt" away, and the extra dimension
disappears. The theorists suggest that even our familiar three spatial
dimensions might come about in this way. Evidence for this kind of
dynamical dimension would be the discovery, amid high energy
collisions, of a finite series of new particles with a very specific
spectrum of masses. (Physical Review Letters, 21 May 2001)

COMPUTING WITH WAVES. Conventional computers do their
jobs by using electrons as billiard-ball like particles to move
around circuits and carry out the desired tasks. At last week's
CLEO/QELS lasers/optics conference in Baltimore, a University
of Rochester group (Ian Walmsley, 716-275-0312,
walmsley@optics.rochester.edu) presented a simple optical system
that performs a database search of 50 items in a way that cannot be
duplicated in any particle-powered computer. To do the search,
the researchers use wave interference, the patterns that are created
when two waves, such as light waves, combine. While their
demonstration is not any more efficient than traditional database
searches, it is the largest search performed with wave interference.
It is a follow-up to a similar demonstration in an atom (Ahn et al.,
Science, 21 January 2000) and expands possibilities for "wave
computing" which would be intermediate in power between
classical computing and quantum computing. In addition, the
Rochester group uses light, which is much easier to prepare and
transport than atoms. In their demonstration, the researchers
produce a single pulse of light carrying a spectrum of different
colors, each containing a different bit of information. They split
the pulse into two identical pulses each with half the intensity. One
travels to an "Oracle," an optical element (an acousto-optic
modulator) which for certain colors shifts their phase, the relative
position of the peaks of the wave compared to other colors. Then
they combine the Oracle pulse with the other, untreated pulse at a
beamsplitter, which produces two output beams, each going in
different direction. Only the components of the beam which have
their phases changed travel toward a spectrometer and detector,
enabling the researchers to read out the information and determine
the location of the desired item in the database. (Paper QWB3;
http://www.osa.org/mtg_conf/CLEO/)


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