From: Larry Klaes (firstname.lastname@example.org)
Date: Wed Jun 13 2001 - 08:08:02 PDT
Theorists of Inner Space Look to Observers of Outer Space
By DENNIS OVERBYE
The Big Bang, David Schramm, the University of Chicago cosmologist,
liked to say, is the poor man's particle accelerator: in its
detritus, which after all includes the whole universe, are the
effects of energies and processes unattainable on Earth. If
astronomers looked closely enough at the sky, he maintained, they
could test theories and phenomena that were beyond the power and
the budgets of physicists to recreate in their laboratories.
That's a notion that seems to have caught fire lately among the
practitioners of string theory, the daunting "theory of everything"
that describes nature as comprising tiny strings and membranes
vibrating in 10 or 11 dimensions.
Since its inception, string theory has been criticized for
producing ideas that seem as experimentally untestable as they are
mathematically elegant. But in the last couple of years string
theorists have began turning out new models of the universe
designed to show that so-called stringy physics "can have an
observable effect on precision cosmological measurements," as one
recent paper put it. In some of these, for example, cosmic history
begins with a pair of island universes slapping together in the
fifth dimension like wet leaves. If the string theorists are right,
they say, tangible support for such notions may come from detailed
measurements of faint radio waves from the Big Bang or from studies
of so- called gravitational waves crisscrossing space-time, making
it expand and contract like an accordion.
Emboldened by the prospect of their newfound empiricism, the
theorists have even ventured out to cosmological conferences — to
the delight of astronomers eager for some new observing challenge.
During a recent meeting in Baltimore, for example, Dr. Gia Dvali,
a physicist at New York University, was besieged by astronomers
eager for more details and precise astronomical predictions after
he offered a string-based explanation of the so- called dark energy
that seems to be accelerating the expansion of the universe.
In romancing the cosmologists, string theorists are following a
well trodden path. In the last half century — as astronomers have
found quasars, pulsars and a faint radio hiss alleged to be the
primordial fireball itself — physicists looking for fresh fields to
conquer have migrated in waves into cosmology.
Dr. Saul Perlmutter, a physicist at Lawrence Berkeley National
Laboratory who led one of two teams of astronomers that discovered
that the expansion of the universe is apparently speeding up,
admitted that he sidled into astronomy in part to avoid being a cog
in a giant particle accelerator experiment.
"Astronomers ought to be able to ask fundamental questions without
accelerators," Dr. Perlmutter said.
But the marriage of inner space and outer space has not always
gone smoothly. Astronomers are traditionally solitary, sometimes
spending years following a single star. Physicists are sociable and
like to tackle problems in gangs. Each group is capable of
defending its turf.
Physicists were amused when Dr. Schramm, a burly and
self-confident crusader who died in an airplane crash in 1997,
claimed in the 1970's that measurements of the abundance of helium
produced in the Big Bang could be used to conclude that there were
only three or four kinds of neutrinos, mysterious lightweight
elementary particles, in the universe. Experiments at CERN — the
leading European particle physics laboratory — and at Stanford in
1989 proved him and his colleagues right.
More than a few physicists have recalled being taken aback at the
apparent simplicity of the standard models of the Big Bang, in
which only three parameters, or numbers, control the history and
destiny of the universe.
Einstein was a cagey and early exploiter of the connection between
inner space and outer space. Even before he was finished
formulating his general theory of relativity, which explains
gravity as the warping of space-time by matter and energy, he began
to lobby astronomers to measure the effect of light bending during
a total solar eclipse, when light rays from a distant star would
graze the sun's disk and — he predicted — bend enough to cause the
star to appear to be displaced outward. In 1919, three years after
the theory was published, the English astronomer Arthur Eddington
announced with great fanfare that he had confirmed the effect
(although some historians have criticized his handling of the
data), anointing Einstein the new Copernicus.
In the meantime Einstein had fudged his equations so that they
would not lead inexorably to the conclusion that the universe was
expanding, having been convinced by common astronomical lore that
it was static. He unfudged them in 1931 after the astronomer Edwin
Hubble discovered that the cosmos was indeed expanding.
Nevertheless, despite its obvious relevance to the universe at
large and its mathematical elegance, general relativity soon became
a kind of backwater in physics, regarded as a beautiful theory that
didn't seem to have much to do with the real world. Lacking a way
to test some of the more bizarre consequences of the theory, such
as the notion that stars collapsing under their own weight could
wrap space around them like a cloak and literally disappear into
what were later dubbed "black holes," not even Einstein knew what
ideas to take seriously.
All this changed in the 1960's when astronomers discovered
quasars, distant starlike objects that seemed to radiate baffling
amounts of energy. Black holes —- although the name had not yet
been invented — were the best way to explain them. Suddenly it
seemed that "the relativists with their sophisticated work were not
only magnificent cultural ornaments but might actually be useful to
science," as the British astrophysicist Thomas Gold put it during a
meeting in 1963. "What a shame it would be," he added, "if we had
to go and dismiss all the relativists again."
The string theorists, who would lay claim to Einstein's mantle,
have not had their light-bending moment yet. The question is
whether they ever will. The standard form of the theory holds that
the energies at which the forces are supposed to be unified and the
effects of string physics show up are thousands of trillions of
times the expected capacity of the largest particle accelerator now
envisioned, CERN's Large Hadron Collider, which will shoot protons
around an electromagnetic racetrack 18 miles around in Geneva and
collide them at energies of 14 trillion electron volts. (In a
string theory variant proposed a few years ago, interference from a
neighboring universe could produce effects at the low energies in
Fortunately, however, as Dr. Schramm would have pointed out,
nature has already done the experiment using the poor man's
particle accelerator. And the results may be written on the sky —
in ripples inscribed on the primordial fireball, astronomers say,
when it was only a billionth of a trillionth of a trillionth of a
second old, or in gravitational waves fluttering the fabric of
The job of reading those cosmic ripples, with delicate radio
telescopes lofted on balloons and satellites, has just begun and is
expected to take the rest of the decade. Likewise the quest to
unravel the history of the strange acceleration of the universe.
The serious study of gravitational waves — which have not been
directly detected yet — is even further in the future.
String theorists must hope that in the ranks of the astronomers
carrying out those investigations there dwells their own Eddington.
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