As time and space only came into existence with the big bang, the question of what happened before it makes no sense to cosmologists. But why did time and space suddenly switch on? And where do the laws of physics come from?by prospect / June 20, 2001 / Leave a comment
These days most people know that the universe began with a bang-a big bang. But as soon as they try to imagine this event, an awkward question presents itself: what happened before the big bang? Since the idea of something happening without any prior cause is alien to us, the question seems to demand an answer. Yet many cosmologists insist that there is no answer to the question of what happened before the big bang, not because the origin of the universe must forever lie beyond the scope of human inquiry, but because the question itself is meaningless.
It is a subject charged with emotion. Books and lectures on the big bang often provoke a passionate response. Religious people see the scientific attempt to explain how the universe came into existence as a move to finally abolish God the creator. Atheists are also alarmed, because the notion of the universe coming into being from nothing looks suspiciously like the creation ex nihilo of Christianity.
Today, few cosmologists doubt that the universe did have an origin at a finite moment in the past. The alternative-that the universe has always existed in one form or another-runs into a basic paradox. The sun and stars cannot keep burning forever: sooner or later they will run out of fuel and die. The same is true of all irreversible physical processes; the stock of energy available in the universe to drive them is finite, and cannot last for eternity. This is an example of the so-called second law of thermodynamics, which, applied to the entire cosmos, predicts that it is stuck on a one-way slide of degeneration and decay towards a final state of maximum entropy, or disorder. As this final state has not yet been reached, it follows that the universe cannot have existed for an infinite time.
Fortunately we do not have to rely on theoretical reasoning alone to deduce that the universe had a definite origin. Direct evidence for the big bang comes from three different sorts of observations. The most straightforward reason for believing that a gigantic explosion started everything off is that the universe is still expanding today: the galaxies are rushing away from each other. By running the movie backwards it is possible to estimate that the big bang occurred between ten and 15 billion years ago. The fact that the Earth is known to be 4.5 billion…