From: Terry W. Colvin <fortean1.nul>
Date: Wed, 04 Aug 2004 22:32:38 -0700
Fwd Date: Thu, 05 Aug 2004 09:56:11 -0400
Subject: The Truth Is Still Out There


Source: THe New York Times

http://www.nytimes.com/2004/08/03/opinion/03ginsparg.html?ex=1092667003&ei=1&en=98090d78a6197c56

08-03-04

The Truth Is Still Out There
By Paul Ginsparg

Ithaca, N.Y.

Stephen Hawking's recent concession that black holes do not
irretrievably eradicate information after all has garnered much
attention. It is refreshing to see the public focused, if just
for a moment, on an important conundrum that has fascinated
theoretical physicists for three decades, and prompted much
conceptual progress. The scientific issues, however, remain much
less settled than Dr. Hawking's celebrated wager on the
question. He most recently pronounced: "If you jump into a black
hole, your mass energy will be returned to our universe, but in
a mangled form, which contains information about what you were
like but in an unrecognizable state."

To appreciate why this is different from awakening after any
night's sleep requires a brief reprise of 20th century physics.
Einstein's theory of general relativity in 1915 was the
culmination of centuries of classical physics, and Einstein and
others soon found solutions to his gravitational field
equations. One of these solutions was later termed a "black
hole" in the 1960's, since it describes the gravitational field
produced by an object so dense that nothing can escape, not even
light. Indeed, the existence of black holes is inferred only
through their gravitational effects on other astronomical
bodies. Stars recently detected orbiting very close to the
center of our own Milky Way galaxy, for example, suggest the
existence of a supermassive black hole at the center, almost
three million times the mass of our sun and about five million
miles in radius. If the mass of the entire Earth were compressed
into a black hole, it would be a little ball only a third of an
inch in radius. Fortunately, the Earth is in no imminent danger
of collapse because of the electrostatic repulsion of its
constituent atoms.

Quantum mechanics, which describes the behavior of very small
objects like atoms, blossomed a decade after general relativity,
and the two are notoriously difficult to reconcile. Thirty years
ago, Dr. Hawking published a calculation incorporating some
quantum mechanical effects into black hole physics, and showed
that matter or energy could leak from a black hole. While
surprising, this was not paradoxical since there are examples of
processes forbidden by classical physics but allowed by quantum
mechanics. Shortly afterward, however, Dr. Hawking articulated a
more shocking consequence of his calculation.


One of the central tenets of relativity theory, termed
causality, is that nothing, not even information, can travel
faster than the speed of light. This means that as long as a
black hole exists, no information about objects that had fallen
into it can ever emerge. Therefore, according to Dr. Hawking's
original calculation, the radiation emitted quantum mechanically
from a black hole is generic, in the sense that it conveys no
information. Further, if a black hole were permitted to
evaporate entirely, then the information content of any objects
previously ingested by it would vanish from the universe,
without a trace. By contrast, if you throw your diary into a
fireplace, then the information contained therein could be
reconstructed, at least in principle, from subtle properties of
the resulting smoke and flames. A permanent loss of information
because of black hole evaporation, on the other hand, is in
contradiction with one of the central tenets of quantum
mechanics, termed unitarity, which permits tracking information
flow in all such processes and forbids its disappearance.

In the early 1980's, I was fortunate to attend some of Dr.
Hawking's lectures in which he speculated on ways to modify
quantum mechanics to accommodate this potential loss of
information. He stimulated much debate among quantum field
theorists, who in turn enjoyed working to rebut his arguments.
The black hole information paradox thereby emerged as an
important catalyst toward further theoretical progress in
reconciling gravitational and quantum effects. Despite many new
ideas and progress on other fronts, no definitive resolution
emerged.

Near the end of a small meeting I attended in 1993, the question
of "What happens to information that falls into a black hole?"
arose, and a democratic method was chosen to address it. The
vote proceeded more or less along party lines, with the general
relativists firm in their adherence to causality, and the
quantum field theorists equally adamant in their faith in
unitarity. Of the 77 participants, 25 voted for the category
"It's lost;'' and 39, a slight majority, voted for "It comes
out,'' (that it re-emerges). Seven voted that the black hole
would not evaporate entirely, and the remaining six voted for an
unspecified "Something else." I voted with the majority,
anticipating progress and hoping that one of us would soon
perform a calculation to help Dr. Hawking and the relativists
see the light. But with the question still unresolved four years
later, three of the protagonists eschewed the old political
duel-to-the-death methodology for a variety of practical
reasons, settling instead on a simple wager whose unsatisfying
outcome was announced last month.

It once was that important scientific results were presented to
the general public only after they were subjected to peer review
and accepted for publication in an edited journal. Some
professional journals, particularly in medicine, still refuse to
publish results that have already been announced via press
release. Since the early 1990's, articles in many fields have
nonetheless been publicly available in "prepublication" form
through organized Internet repositories, a type of instant
communication frequently concurrent with peer review.

The recent "resolution" of the information puzzle, however, has
neither supporting publication nor calculation, peer-reviewed or
otherwise. While a press release may be sufficient in some
realms of human endeavor, one of the joys of scientific research
is that it is subject to more objective measures of progress. It
is possible that some new revolutionary mechanism to avoid
information loss will yet emerge from the latest spectacle. But
without even a hint yet as to what might have been missing from
Dr. Hawking's original calculation, it is more likely that
theoretical physicists will continue to view the information
paradox as a profound puzzle whose resolution will provide clues
to understanding the basic laws of physics.

String theory, a parallel quantum gravitational effort over the
past 30 years, offers many tantalizing hints toward possible
resolution of the puzzle. Perhaps some of its ideas have
subconsciously persuaded Dr. Hawking to join the quantum
conservation of information camp. But should we ultimately be
more inclined to trust Dr. Hawking's past youthful intuition?
Physicists, particularly eminent British ones, have a historical
tendency to stray in excessively speculative directions in their
later years. A bigger surprise may yet await us, and those who
voted for "Something else'' may prove the most prescient.
Perhaps the real winners of this bet will be some middle-school
students who, inspired by the current hoopla, will help provide
a more substantive answer a decade from now.

Paul Ginsparg, professor of physics and information science
at Cornell University, was named aMacArthur fellow in 2002.


Copyright 2004 The New York Times Company