TIME: Almanac 1993/TIME Almanac 1993.iso/time/050492/0504300.000

Text File | 1992-09-10 | 6.4 KB | 133 lines

                                                                                SCIENCE, Page 62

Echoes of the Big Bang


By peering back into the beginning of time, a satellite finds
the largest and oldest structures ever observed -- evidence
of how the universe took shape 15 billion years ago

By MICHAEL D. LEMONICK/WASHINGTON


    They were, by far, the largest and most distant objects
that scientists had ever detected: a swath of gargantuan cosmic
clouds some 15 billion light-years from earth. But even more
important, it was the farthest that scientists had ever been
able to peer into the past, for what they were seeing were the
patterns and structures that existed 15 billion years ago. That
was just about the moment -- or more precisely, an infinitesimal
300,000 years after the moment -- that the universe was born.
What the researchers found was at once both amazing and
expected: NASA'S Cosmic Background Explorer satellite -- COBE
-- had discovered landmark evidence that the universe did in
fact begin with the primeval explosion that has become known as
the Big Bang.

    In anticipation of the announcement, an overflow crowd had
crammed into the meeting of the American Physical Society in
Washington last week, and they were not disappointed. "If you're
religious, it's like looking at God," proclaimed the leader of
the research team, George Smoot, an astrophysicist at the
University of California, Berkeley. Princeton astrophysicist
David Spergel, who had recently co-authored a theory that was
demolished by the COBE results, cheerily admitted, "We're dead.
But this is great stuff . . . It's the most important discovery
in cosmology in the past 20 years."

    The existence of the giant clouds was virtually required
for the Big Bang, first postulated in the 1920s, to maintain
its reign as the dominant explanation of the cosmos. According
to the theory, the universe burst into being as a
submicroscopic, unimaginably dense knot of pure energy that flew
outward in all directions, spewing radiation as it went,
congealing into particles and then into atoms of gas. Over
billions of years, the gas was compressed by gravity into
galaxies, stars, planets and, eventually, even humans.

    The first evidence of this scenario was established in
1964, when astronomers discovered the cosmic microwave
background, the original radiation from the Big Bang. The second
part, though, was much trickier. In order for gravity to make
galaxies out of atoms, it needed something to work with -- some
chunks of space in which the atoms were closer together, a
region of greater than average density, so that they could draw
surrounding matter in. The excess densities need not have been
very large, but they had to be there if matter was to congeal.
And if they were present, they should be visible to a sensitive
enough probe in the form of warm and cool spots mottling the
microwave background.

    The COBE satellite was designed to be sensitive enough,
but the first maps of the microwave sky it beamed down showed
nothing. That was not a big problem. The research team knew that
the cosmic microwaves are polluted with local microwaves from
the Milky Way galaxy and that it would take months of computer
analysis to weed out the unwanted signals.

    In the end, it took more than a year. What finally
appeared on the computer screens at the Goddard Space Flight
Center in Maryland was a map with blotches of all sizes
indicating regions of the sky where the microwaves are a
minuscule 30 millionths of a degree warmer or cooler than
average -- almost imperceptible, but enough to save the Big Bang
theory. Says University of California, Berkeley, astronomer
Joseph Silk: "They've found the missing link. This removes the
biggest remaining objection to the Big Bang."

    Because the microwaves have been traveling for 15 billion
years to get to the COBE sensors, the warm patches have long
since evolved into groups of galaxies. Even the smallest patch
observed by COBE is by far the largest area ever surveyed. The
structures dwarf the "great wall" of galaxies discovered in
1990. The largest spans one-third of the known universe, or 10
billion light-years, which is 60 billion trillion (60 followed
by 21 zeros) miles.

    COBE is designed to see just the biggest structures, but
astronomers would like to see much smaller hot spots as well,
the seeds of local objects like clusters and superclusters of
galaxies. They shouldn't have long to wait. Astrophysicists
working with ground-based detectors at the South Pole and
balloon-borne instruments in the stratosphere are closing in on
such structures, and may report their findings soon.

    If the small hot spots look as expected, that will be a
triumph for yet another scientific idea, a refinement of the Big
Bang called the inflationary universe theory. Inflation says
that very early on, the universe expanded in size by more than
a trillion trillion trillion trillionfold in much less than a
second, propelled by a sort of antigravity. Bizarre though it
sounds, cosmic inflation is a scientifically plausible
consequence of some respected ideas in elementary-particle
physics, and many astrophysicists have been convinced for the
better part of a decade that it is true.

    One prediction that comes out of the theory of inflation
is that the mix of big and small hot spots in the early
universe should follow a characteristic pattern. The spots COBE
found conform to that pattern, and scientists like Smoot expect
that the smaller hot spots will too. Another prediction of
inflation is the surprising notion that everything astronomers
can see, including all the stars and galaxies, constitutes just
1% of existing matter. The other 99% of the universe is dark and
invisible.

    There is already strong evidence that at least some dark
matter must exist. The Milky Way and virtually all other
galaxies rotate so fast that they should literally fly apart --
unless the gravity from invisible halos of dark matter is
holding them together. The halos still fall short of what
inflation requires, but bolstered by the latest results,
theorists are sure the rest will be found. Says Paul Steinhardt,
a University of Pennsylvania physicist who helped develop
inflation: "We were confident in our theory, of course, but it's
always nice to know that Nature is cooperating."