Scientific proof for everything?

''I have no need for that hypothesis,'' Pierre-Simon Laplace famously responded when asked where God fit into his new astronomical theory. Using calculus and Newton's laws of gravity, he explained the forces that kept the planets from gradually drifting out of orbit, imparting some stability to the solar system. Newton had thought the Great Engineer must step in now and then to readjust the machine.

The theory didn't explain where the solar system came from. But Laplace also had an answer. The planets, he proposed, had congealed from a swirling cloud of gas and dust surrounding the sun.

O.K., so where did the sun and the mother cloud come from? And what set the whole thing revolving?

By now, scientists think they have even those answers, and they do not involve the intervention of any Great Engineer. The whole point of science for the last few hundred years has been to explain everything in terms of a physical process, something that can be described by equations.

The quest, however, is far from done. God, for those who want to use that term, can be invoked to account for phenomena that have not yet yielded to the scientific method. What is for some the ultimate question -- Does God exist? -- has become a matter of how much further the domain of the unknown will continue to contract, and if it will ultimately evaporate.

The momentum has been in that direction. The whirlpool of cosmic stuff that spawned the solar system spins because it is one small part of the great rotating galaxy, the Milky Way. When a random fluctuation causes enough gas and dust to bunch together, gravity takes over and celestial bodies begin to form. If you want to know where the galaxies came from, there are answers as well. Ultimately, it all comes down to the Big Bang.

That is where the chain of reasoning bottoms out. What caused the primordial explosion? At this point all but a few scientists go with Wittgenstein (''of what we cannot speak we must pass over in silence'') or with Kierkegaard, blindly taking the leap of faith into the abyss of the unknown, choosing what to believe.

Why there is something instead of nothing is not an issue that science is well equipped to address. As cosmologists understand it, the primordial eruption did not take place at a certain instant in a certain place. The Big Bang created absolutely everything, including space-time itself. How can anyone ask what set the whole thing going if there was no space or time for a creator to be in, much less any matter or energy for Him or Her or It to work with?

This rather formidable obstacle doesn't prevent a few people, some of them scientists, from trying to prove, or disprove, the existence of a deity. Almost any book or conference on science and religion inevitably includes what has become a metaphysical set piece:

The various parameters of the universe -- the charge of the electron, the strength of gravity, and so forth -- appear to be finely tuned to support the existence of stars and atoms and molecules and life. If the conditions at the instant of the Big Bang had been slightly different, the argument goes, then the universe (at least from an earthling's point of view) would have been a colossal waste of space-time. So we are the lucky benefactors of blind chance, or life was planned all along -- either by a Great Intender or by some physical or mathematical or logical law or process. Ignore the great Wittgensteinian whisper and you feel the queasy discomfort of a human mind pushed to the edge of what it is possible to know.

One theory is that the Big Bang actually spawned a plenitude of universes each randomly endowed with different physical conditions. People, of course, find themselves in one that is capable of supporting life.

''Universe'' used to mean everything that exists. To even think about this new scheme of things, the definition must be weakened to ''everything that we can get information about.'' We are required to believe in -- take on faith -- that there is something outside the universe. Might as well just call it God.

Whether the multiverse theory is more comforting than believing that human existence results from a senseless crapshoot or a holy decree is a matter of taste, not science. For many theorists it is also a betrayal of the great effort to explain the laws of physics. Some still hope to find ''a theory of the initial conditions of the universe,'' a supreme mathematical law, hidden perhaps in superstring theory, showing that the parameters of creation could have been set only in a certain way.

But then they would have to find a law to explain where the law came from . . . and ultimately an explanation of why the universe is mathematical and of where mathematics came from and what numbers are.

Like a petulant 8-year-old, we keep asking why, why, why, why. In the end, the answer is either ''just because'' or ''for God made it so.'' Take your pick

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