THE NEW YORK TIMES ON THE WEB   --    March 13, 2001

_Even Without Evidence, String Theory Gains Influence_

By JAMES GLANZ

Scientists have come up with theories in the shower, on barren
mountains, while driving to work and even in their sleep. But what
all theories have in common is that their predictions are eventually
tested in experiments, where nature determines which inspirations
are right and which are wrong.

Then there is string theory, the ambitious, profoundly mathematical
attempt to knit together all of physics =8B from gravity to quantum
mechanics to subatomic forces =8B into a single sublime formalism.
Though string theorists first suspected they might be onto a "theory
of everything" in the mid-1980's, and the field is the hottest area in
theoretical physics, string theorists have yet to devise a
make-or-break laboratory test for their ideas.

In part, that is because the theorized strings cannot be observed
directly; they are thought to be vibrating entities smaller than a
trillionth of a trillionth the size of an atom. Different string
vibrations somehow correspond to different particles in nature,
but scientists have yet to develop more than fragments of
what they presume will ultimately be a complete theory.

Nevertheless, string theorists are already collecting the spoils
that ordinarily go to the experimental victors, including federal
grants, prestigious awards and tenured faculty positions. Less
than a decade ago, there were hardly any jobs for string theorists,
said Dr. David Gross, director of the Institute for Theoretical
Physics at the University of California in Santa Barbara.

"Nowadays," Dr. Gross said, "if you're a hotshot young string
theorist you've got it made."

Dr. Gross has no problems with that success; he was one of string
theory's early developers. But some physicists are dismayed by the
dominance of a theory that has yet to prove itself experimentally.

"I think the whole theory is a long shot," said Sir Roger Penrose, a
physicist at Oxford University. He said he had nothing against an
interesting long shot but that string theory had "taken over at the
expense of all other areas."

Dr. John Baez, a scientist in the mathematics department at the
University of California in Riverside, who studies a different
approach to unification based more directly on relativity theory,
said, "String theorists keep saying that they're succeeding."

"The rest of us can wonder whether they are walking along the
road to triumph," Dr. Baez said, "or whether in 20 years they'll
realize that they were walking into this enormous, beautiful,
mathematically elegant cul-de-sac."

A number of physicists discussed the question at a conference
in Santa Barbara this month to honor Dr. Gross on his 60th birthday.

Their thoughts revealed how in lean experimental times physicists rely
on their aesthetic senses, purely mathematical clues, suggestive
connections with established theories, and a Houdini-like taste for
escaping roadblocks. While physics has always called these tricks into
play, researchers are relying on them as never before in the case of
string theory, simply because it attempts to reach so far into the
unknown.

Still, said Dr. Jeffrey Harvey of the University of Chicago, scientists
in the field are confident their ideas are based in reality; they have,
as he put it, "the feeling that string theory is something we discover
 rather than invent."

String theory has constantly changed since it first emerged several
decades ago, and even its ardent adherents concede that they still
do not understand more than what Dr. Gross called "the tail of the
tiger," or a few suggestive parts of what is believed to be a complete
theory. Until recently the physical crux of the theory was thought to
be vibrating, 10-dimensional loops of string roughly a billion
trillion times smaller than a proton. Different modes of vibration of
the strings (made of what, no one is sure) represented different
particles in nature.

Now physicists believe the ultimate objects are 11-dimensional
membranes. Either way, the extra dimensions beyond the usual
four would be curled up so as to be nearly imperceptible. And
because the vibrations would include the graviton, the particle
thought to transmit gravity, as well as particles involved in the
strong and weak nuclear forces and electromagnetism, string
theory offered the prospect of unifying physics.

But with that aesthetic attraction came deep problems. First,
in the1980's, it seemed that the strings had a basic inability to
cope with known differences between particles and their mirror
images, and other such broad facts of nature. But closer study
showed that, contrary to all expectation, various terms in the
theory canceled each other, fixing the problem.

A decade later, the field again narrowly escaped when what
seemed to be several different string theories all turned out to
be different facets of the same underlying theory =8B a fortunate
development, because physicists would not know what to do
with more than one "ultimate" theory of the universe. Those
episodes tell physicists they are onto something important, said
Dr. Edward Witten, a physicist at the Institute for Advanced
Study in Princeton, N.J.

"If it would turn out that string theory, which has led to so
many miraculous-looking discoveries over so many decades, has
nothing to do with nature, to me this would be remarkable
cosmic conspiracy," Dr. Witten said.

At the same time, string theory's strong influence on several
branches of pure mathematics have provided a good test of the
"intellectual horsepower" of the idea, said Dr. Stephen Shenker,
a Stanford physicist. He said the wider impact suggested both
that physicists had not missed some crucial mathematical error
and that the theory was rich enough to be an encompassing
theory of nature.

All those developments, Dr. Gross said, "do convince people that
there's something here."

But despite these checks, said Dr. Stephen W. Hawking, the
University of Cambridge physicist, who also attended the
conference, physicists should also keep in mind that they have
been wrong before and that string theory still contains many
mysteries.

"For most of the last hundred years, we have thought that
the theory of everything was just 'round the corner," Dr. Hawking
said. "We keep making new discoveries, but I don't think we can
yet say the end is in sight."

Oryginal:
http://www.nytimes.com/2001/03/13/science/13STRI.html?pagewanted=3Dprint