• What came before the big bang?

    Can science explain how the universe began? Even suggestions to that effect have provoked an angry and passionate response from many quarters. Religious people tend to see the claim as a move to finally abolish God the Creator. Atheists are equally alarmed, because the notion of the universe coming into being from nothing looks suspiciously like the creation, ex nihilo, of Christianity. The general sense of indignation was well expressed by writer Fay Weldon. "Who cares about half a second after the big bang?" she railed in 1991 in a scathing newspaper attack on scientific cosmology. "What about the half a second before?" What indeed. The simple answer is that, in the standard picture of the cosmic origin, there was no such moment as "half a second before."

    To see why, we need to examine this standard picture in more detail. The first point to address is why anyone believes the universe began at a finite moment in time. How do we know that it hasn't simply been around for ever? Most cosmologists reject this alternative because of the severe problem of the second law of thermodynamics. Applied to the universe as a whole, this law states that the cosmos is on a one-way slide toward a state of maximum disorder, or entropy. Irreversible changes, such as the gradual consumption of fuel by the sun and stars, ensure that the universe must eventually "run down" and exhaust its supplies of useful energy. It follows that the universe cannot have been drawing on this finite stock of useful energy for all eternity.