The ups and downs of oscillating universes

John Wheeler was one of the first to stress the physical significance of the fundamental Planck scales of mass, length, and time. He recognized their quantum gravitational significance and speculated upon the strange things that might happen when the universe crossed that mysterious threshold where general relativity and quantum theory meet to consummate their arranged marriage. For Wheeler, Einstein's conception of cosmology always implied a universe that was finite in size and total lifetime, a “closed” universe evolving from a Big Bang in the past to a Big Crunch in the future. We still do not know whether these two singular points of the evolution signal merely a breakdown of the nonquantum theory of gravity that we are using or whether they have special significance and will remain even in a future quantum theory of cosmology.

If our expanding universe of stars and galaxies did not appear spontaneously out of nothing at all, then from what might it have arisen? One option that has an ancient pedigree is to sidestep the question and propose that it had no beginning. It always existed.