A t the end of "A Brief History of Time," his 1988 best-seller about the latest scientific thinking on the cosmos, the British physicist Stephen W. Hawking posed a tough question in deceptively simple terms. "Why," he asked, "does the universe go to all the bother of existing?"

Musing on the answer, he pointed out that in the last couple of centuries most scientists had been too busy with new theories about what the universe is to ask the question why it is. But, he wrote, it was not always that way. Philosophers -- the people who ask why -- used to take all of human knowledge for their field, admitting no division between scientific questions and religious ones.

Flexible thinker that he is, professor Hawking famously concluded his book with a thought that may have surprised his colleagues. "If we do discover a complete theory [of the universe]," he wrote, "it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of "why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason -- for then we would know the mind of God."