Can man know what happened before Big Bang?

Like baseball, in which three strikes make an out, three outs on a side make an inning, nine innings make a typical game, the universe makes its own time. There is no outside timekeeper. Space and time are part of the universe, not the other way around, thinkers since Augustine have said, and that is one of the central and haunting lessons of Einstein's general theory of relativity.

In explaining gravity as the "bending" of space-time geometry, Einstein's theory predicted the expansion of the universe, the primal fact of 20th-century astronomy. By imagining the expansion going backward, like a film in reverse, cosmologists have traced the history of the universe credibly back to a millionth of a second after the Big Bang that began it all.

But to ask what happened before the Big Bang is a little bit like asking who was on base before the first pitch was thrown out in a game, say between the Yankees and the Red Sox. There was no "then" then.

Still, this has not stopped some theorists with infinity in their eyes from trying to imagine how the universe made its "quantum leap from eternity into time," as the physicist Dr. Sidney Coleman of Harvard once put it.

Some physicists speculate that on the other side of the looking glass of Time Zero is another universe going backward in time. Others suggest that creation as we know it is punctuated by an eternal dance of clashing island universes.

In their so-called quantum cosmology, Dr. Stephen Hawking, the Cambridge University physicist and author, and his collaborators envision the universe as a kind of self-contained entity, a crystalline melt of all possibilities existing in "imaginary time."

All these will remain just fancy ideas until physicists have married Einstein's gravity to the paradoxical quantum laws that describe behavior of subatomic particles. Such a theory of quantum gravity, scientists agree, is needed to describe the universe when it was so small and dense that even space and time become fuzzy and discontinuous. "Our clocks and our rulers break," as Dr. Andrei Linde, a Stanford cosmologist likes to put it.

At the moment there are two pretenders to the throne of that ultimate theory. One is string theory, the putative "theory of everything," which posits that the ultimate constituents of nature are tiny vibrating strings rather than points. String theorists have scored some striking successes in the study of black holes, in which matter has been compressed to catastrophic densities similar to the Big Bang, but they have made little progress with the Big Bang itself.