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Finding Ripples in Space-Time Sparks Cosmic Research

By Robert C. Cowen / March 3, 1993

A YEAR ago next month, a research team reported finding long-sought ripples in space-time. They reflect the primordial clumpiness from which the main structure of the universe probably has evolved.

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That was a big story at the time. But there's a bigger story yet to come.

Team leader George Smoot says that the new energy this finding has given cosmic research has become one of the discovery's most significant results. It now seems likely that, within this decade, cosmologists will get answers to some fundamental questions.

Is much of the mass in the universe really in the form of presently unseen "dark" matter, as many astronomers suspect? How did galaxies form and how did they group into structures that sometimes span a significant fraction of the universe? What did the universe look like at the moment of the big bang?

Gone are the days of hopeful searching for a phenomenon that might not even exist. Instead, Dr. Smoot says, "everybody feels highly motivated because we now know there is something there." He adds that "we're going from being discoverers to being explorers."

Cosmologists now feel like the old-time geographers who, once a new land was located, faced the challenge of exploring it in detail. Reflecting on this during the recent annual meeting of the American Asso- ciation for the Advancement of Science in Boston, Smoot said cosmologists want to use the new-found space-time ripples to explore backward in time toward the universe's origin and forward to the universe we see today.

Smoot - an astrophysicist at the Lawrence Berkeley Laboratory in Berkeley, Calif. - is principal investigator for the group that uses one of the instruments on the Cosmic Background Explorer Satellite (COBE). It studies the microwave radiation that permeates the cosmos. This "background" radiation is left over from the "big bang" explosive birth of our universe. Its nature reflects the nature of the universe early in its evolution.

Cosmologists expected the radiation to show subtle irregularities. These would reflect underlying ripples in the fabric of space itself - irregularities that would have the gravity to concentrate assemblages of matter. They would be a kind of framework around which groupings of galaxies could form.

But the more scientists probed the background radiation, the smoother it seemed to be. Cosmologists began to wonder if they knew what they were talking about. They felt relieved when the COBE team finally found the irregularities, which show up at a level of less than 1 part in 100,000 in the temperature distribution of the radiation.

Cosmologists now have what Smoot likens to "a baby photograph of the universe at about five hours into a human lifetime." That snapshot contains enough information to work backward and forward in time.

Some of the irregularities - the seeds around which material structures later developed - must have been created at the first instance of the big bang. They are too large to have changed significantly since then, even if their components moved around at the speed of light. Studying them should reveal something of the universe's earliest conditions.

Smaller irregularities should reveal details of how matter assembled itself into galaxies, galaxy clusters, and related structures. These details are too small to show up in the COBE data. Its resolution is only about 7 degrees of angle on the sky.

New studies using ground-based equipment and balloon-borne instruments, however, are sharper "eyed." Smoot is working with a group whose balloon-borne detector may be able to distinguish detail as fine as 1/2 an angular degree. That should pick out space-time ripples small enough to be the seeds of future galaxy clusters.

Stay tuned.