Cycles of Creation

摘要

What happened before the big bang? If some physicists are to be believed, the question is about as meaningless as asking what is north of the North Pole. But others don't give up so easily. According to two cosmologists, before the big bang there was another big bang. And, before that, another. "If we're right," says Neil Turok of the University of Cambridge, "the big bang is but one in an infinite series of big bangs stretching back into the eternal past." And into the eternal future. What Turok and his colleague Paul Stein-hardt of Princeton University are advocating is a new version of an idea that dates back to the 1920s. Back then the Russian physicist Aleksandr Friedmann, the father of the big bang idea, realised that if the gravity of all the matter in the Universe is powerful enough, it could stop the expansion of the cosmos and turn it around. The Universe would then carry on contracting down to a "big crunch". If both expanding and re-collapsing universes are permitted, it's a simple step to imagine the one changing seamlessly into the other. From the big crunch the Universe would bounce or rebound in a new big bang and the whole cycle would begin again.