Fun_People Archive
19 Dec
Amazing Bits from PHYSICS NEWS UPDATE #462 12/17/99

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From: Peter Langston <psl>
Date: Sun, 19 Dec 99 19:27:45 -0800
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Subject: Amazing Bits from PHYSICS NEWS UPDATE #462 12/17/99

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The American Institute of Physics Bulletin of Physics News
Number 462 December 17, 1999   by Phillip F. Schewe and Ben Stein

COMPETING ARROWS OF TIME. Lawrence S. Schulman of Clarkson University has
found that time might actually flow backwards in certain regions of space.
This time reversal has nothing to do with quantum fluctuations or the
spacetime-warping effects of a black hole.  It's just ordinary matter
obeying the ordinary and mostly time- symmetric laws of physics. The
difference lies in its statistics. If the laws of physics have no preferred
direction then why do we never see a shattered wineglass jump back up on
the table and reassemble itself? The "arrow of time" concept enshrines this
domestic disaster in the form of a law, the second law of thermodynamics.
The arrow describes the tendency for macroscopic systems consisting of many
particles (the falling wineglass) to evolve in time in such a way that
disorder grows and information decreases. This tendency is statistical and
does not prevail at the microscopic level, where a movie of two atoms
colliding would seem credible if run in the forward or reverse direction.
The wineglass, however, consists of zillions of atoms.  The reason we never
see the glass re-assemble and lift itself (courtesy of the warmth of the
original breakage returning from the floor and air) back onto the table is
that this highly specialized (and, as we would say, unlikely) scenario is
but one of a myriad of possible configurations, in most of which the glass
shards stay on the floor.  This statistical explanation leads to two
   First, why does this arrow point the way it does? Why not the other way?
And second, why should it point at all? On the first question, Schulman
subscribes to the view that the "thermodynamic" arrow of time is a
consequence of the "cosmological" arrow reflected in the one- way expansion
of the universe, a theory advanced some years ago by Thomas Gold of Cornell.
As to the second question, that's exactly where Schulman's
( new results have their impact. The prevailing view
holds that if opposite-arrow systems came into even the mildest of contact,
the order in at least one of them would be destroyed. This is because from
the perspective of one observer the coordination needed to reassemble the
other's wineglass would be so fantastic that even a single photon could
disrupt it. Not so, says Schulman who, in his computer modeling of the
universe, specifies not one boundary condition in time (the big bang) but
two, the other being a supposed "big crunch" when the universe would
contract (or so it would seem to us; from the perspective of that arrow,
the universe would be expanding).  In his model the two arrows of time (one
growing out of either end of the "timeline"; see the figure at can be mildly in contact and nevertheless
each have its wineglasses break and its rain fall appropriately. Observers
associated with either arrow might even watch the other grow young---from
a distance.
   Some relatively-isolated relics of matter subject to the opposite arrow
might be found in our vicinity. By its own clock such a region would be very
old and no longer luminous, although gravitationally it would not be
anomalous, exactly the hallmark of dark matter.  Or we might see an
opposite-arrow black hole giving matter back to an accretion disk, which in
turn would feed it back to a companion star which would seem (to us) to be
coming into existence.   Schulman concedes that recent observations may rule
out a final crunch in our actual universe but argues that there is still a
lot we don't understand about our thermodynamic arrow, and that a competing
time arrow might arise from another, as yet unknown, cause. (Physical Review
Letters, 27 Dec.)

University of St. Andrews astronomers.  Roughly 30 planets have been
detected around nearby stars through an indirect method which monitors
fluctuations in the stars' positions.  More recently the shadow of an
extrasolar planet was observed to transit across the face of its star
(Update 458).  Now light has been detected which apparently comes to us
directly from a planet circling the star tau Bootis, some 50 light years
away.  The main difficulty was of course discerning the reflected light
while blocking out the  glare of the star itself.   The planet seems to be
blue-green in color, is twice the size of Jupiter, and 8 times as massive.
(Cameron et al., Nature, 16 December 1999.)

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