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section of a balloon looks flat when viewed close up. This
was the universe long thought to be the most beautiful and
simple. 

But it required, by the logic of Einstein's general
relativity, that there be much more dark matter, or
something, to the universe, enough to "flatten" space-time,
than astronomers had found. 

In fact, this prescription was so hard to reconcile with
other observations, of galaxies and their evolutions, that
by 1991 some astronomers and press reports suggested that
the entire theoretical edifice of inflation to blow up the
universe and cold dark matter to fill it, not to say the
Big Bang itself, might have to be junked. 

So it was with a sigh of relief that cosmologists greeted
the announcement in April 1992 that NASA's Cosmic
Background Explorer, or COBE, satellite had succeeded in
discerning faint blotches in the primordial cosmic radio
glow. 

These were the seeds from which, inflation predicted, large
cosmic structures would eventually grow. 

"If you're religious, it's like seeing God," said Dr.
George Smoot, a physicist from the Lawrence Berkeley
National Laboratory who led the COBE team. 

Astronomers say COBE signaled a transition in which heroic
ideas about the universe began to be replaced by heroic
data, as long-planned new telescopes and other instruments
went into operation. 

A year later, skywalking astronauts corrected the Hubble
telescope's myopic vision. The cosmic background radiation
has come in for particular scrutiny from new radio
telescopes mounted in balloons and on mountaintops. The
news has been good, though not decisive, for inflation. 

For three years, a series of increasingly high-resolution
observations has confirmed that the pattern of blotches
stippling the remnant of the primordial fireball is
consistent with the predictions from inflation and cold
dark matter. The instruments have now mapped details small
enough to have been the seeds of modern clusters of
galaxies. 

"I'm completely snowed by the cosmic background radiation,"
Dr. Guth said. "The signal was so weak it wasn't even
detected until 1965, and now they're measuring fluctuations
of one part in 100,000." 

Perhaps most important, the analysis of the fluctuations
indicates that the universe has a "flat" geometry, as
predicted by inflation. That was a triumph. Although
observations could not prove that inflation was right, a
nonflat universe would have been a blow to the theory, and
to cosmological orthodoxy. 

"Inflation, our boldest and most promising theory of the
earliest moments of creation, passed its first very
important test," Dr. Turner said at the time. 

The most precise measurements of the cosmic background, at
least in the near future, are generally expected to come
late this year from NASA's Microwave Anisotropy Project, or
MAP, satellite, which was launched into space last year on
June 30. MAP will be followed by the European Space
Agency's Planck satellite, in 2006. 

It is highly unlikely that MAP or Planck will be able to
detect what Dr. Turner calls "the smoking gun signature of
inflation." The violent stretching of the universe should
roil space-time with so-called gravitational waves that
would leave a faint imprint on the cosmic fireball. 

Detecting those waves would not only confirm inflation, but
also might help scientists establish what caused the
inflation in the first place, giving science its first look
at the strange physics that prevailed when creation was
only about a trillionth of a trillionth of a trillionth of
a second old. 

The Universe's Fate 

Bleak Implications 
Of `Dark Energy' 

In 1998, two competing teams of
astronomers startled the scientific world with the news
that the expansion of the universe seemed to be speeding up
under the influence of a mysterious antigravity that seems
embedded in space itself and that is hauntingly reminiscent
of Einstein's old, presumably discredited, cosmological
constant. 

"Dark energy," the phenomenon was quickly named. 

If dark
energy is real and the acceleration continues, the galaxies
will eventually speed away from one another so quickly that
they couldn't see one another. The universe would become
cold and empty as the continued acceleration sucked away
the energy needed for life and thought. 

It would be "the worst possible universe," for the quality
and quantity of life, said Dr. Lawrence Krauss, a physicist
at Case Western Reserve University. 

Dr. Edward Witten of the Institute for Advanced Study in
Princeton, called the discovery of dark energy "the
strangest experimental finding since I've been in physics."


The discovery was a surprise to the astronomers involved.
Neither team had expected to find the universe
accelerating. They had each set out to measure by how much
the expansion of the universe was slowing because of the
gravity of its contents and thus settle the question of its
fate.