[EAS]Science and Ultimate Realit

[pjk]

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A fascinating recent conference.  --PJK

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Date: 4/1/02 7:37 PM
From: AIP listserver
PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 583  April 1, 2002   by Phillip F. Schewe, Ben Stein, and
James Riordon

"SCIENCE AND ULTIMATE REALITY," a meeting about forefront theoretical
and experimental physics, was held at Princeton 15-18 March in honor
of John Wheeler's 90th birthday and his many contributions to quantum
mechanics, cosmology, and information science.  Such a meeting is
especially timely because these fields have enjoyed a burst of
fruitful research in recent years.  New experiments demonstrating
nonlocality, the idea that an event in one place can affect an event
at another place more quickly than it would take a light pulse to pass
from the one place to the other, and the pursuit of robust systems
which could perform extended "quantum computing," have energized the
study of quantum reality.  In the celestial realm the advent of
automated redshift surveys of the galaxies and compilation of sharp
maps of the cosmic microwave background are making possible an era of
"high precision cosmology."

     The Princeton meeting served up an impressive menu of hot topics
and notable speakers
(http://www.metanexus.net/ultimate_reality/agenda.htm).  Examples
include the subject of decoherence (Wojciech Zurek, Los Alamos), the
process by which a quantum system (one whose whereabouts and movements
can only be described in terms of likelihood, using a complex wave
function) converts to a classical system (with  definite observable
coordinates) by subtle but often swift interactions with the
surrounding environment; the many- worlds interpretation of quantum
mechanics (Bryce DeWitt, Texas), according to which a quantum system
does not suffer a "collapse of probability" rather the universe itself
continues to bifurcate into multiple versions corresponding to the
many possible histories available to the quantum system as it moves
through space-time; the entanglement of ions in an atom trap (i.e.,
putting them into a special quantum state in which properties of the
participating particles, such as spin or movement, are correlated) for
the purpose of forming logic gates for a future quantum computer
(Chris Monroe, Michigan).

      Several speakers addressed the persistent problem of bringing
quantum mechanics and general relativity into a single framework. 
Prominent issues here include the fate of information supposedly lost
inside black holes (Juan Maldacena, Institute for Advanced Study);
comparisons of string theory with the rival quantum loop gravity
theory, which holds that space is not a mere platform for interactions
but is itself a sort of dynamical thing; how gravity behaves in extra
dimensions (Lisa Randall, Harvard); and the effort to detect gravity
waves.  Raymond Chiao(UC Berkeley) described an experiment in which he
will try to convert electromagnetic waves into controlled
gravitational waves inside a device in which a circuit is poised to go
from a normally conducting state into a superconducting state.  Using
a second such device he hopes to convert gravity radiation back into
electromagnetic radiation.  Robert Laughlin (Stanford), who won the
Nobel Prize for his studies of how patterns emerge in two-dimensional
electron gases by way of the quantum hall effect, spoke about how
general relativity might "emerge" at the edge of a black hole (for
background see the online paper arXiv:gr-qu/0012094).

     One purpose of the meeting was to promote freewheeling debate on
all of the above issues, including the role of human consciousness in
the measurement process.  Young scientists were especially encouraged
to engage in this debate, for which scholarships were given for
attending the meeting.  In fact a Young Researchers Competition was
held for papers on quantum reality.  The joint winners, from among 64
entries, were Raphael Bousso from UC Santa Barbara and Fotini
Markopoulou-Kalamara from the University of Waterloo in Canada.

     At the heart of the meeting was the keynote speech by the always
interesting Anton Zeilinger (Vienna), who paid tribute to John
Wheeler's many  physics insights.  One of those ideas was a proposal
for a "delayed choice" experiment in which the dissipation of wavelike
interference effects brought about by the experimenter's efforts to
determine which of several possible paths a particle took in going
toward a detector might be avoided by delaying the observation of the
path until the particle (or wave) had made its mark.  Zeilinger has
carried out just such an experiment with entangled photons in a setup
he referred to as a "Heisenberg microscope."

     Zeilinger mentioned another of his recent experiments, one in
which carbon-70 molecules, in wavelike form, passed through a series
of slits to form an interference pattern.  The C-70 molecules,
however, were produced in an oven at 900 K, and this warm birth
imparted a diversity of vibrations to the molecule, prompting it to
shed an average of four or five photons on its way through the
apparatus.  Why did this communication between the molecule wave and
its environment not result in decoherence and loss of interference
effects?  Answer: the "size" of the photons was much larger than slit
spacing or the deBroglie (quantum) wavelength of the molecule itself,
and so the photons did not betray any "which- path" information. 
Apparently a quantum system doesn't decohere if useful information is
not being passed along.

      Zeilinger holds that quantum reality needn't seem so weird if
only students were exposed to the subject at an earlier stage.  After
all, we teach youngsters that the Earth goes around the sun and not
vice versa, even though the sun seems to "rise" each morning.  Could
early instruction in wave mechanics reduce schoolkids' (and adults')
alienation from "quantum weirdness"?  Zeilinger thought that the time
to start was in kindergarten.  He said someday he wanted to devise a
game with slits and counters which would show what happens when you
turn interference off and on.  He hadn't thought of the details for
the game but he knew there would be no math, no equations, just
demonstration.

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