In the early expansion of the universe there has to be a close balance between the expansive energy (driving things apart) and the force of gravity (pulling things together). If expansion dominated then matter would fly apart too rapidly for condensation into galaxies and stars to take place. Nothing interesting could happen in so thinly spread a world. On the other hand, if gravity dominated, the world would collapse in on itself again before there was time for the processes of life to get going. For us to be possible requires a balance between the effects of expansion and contraction which at a very early epoch in the universe's history (the Planck time) has to differ from equality by not more than 1 in 1060. The numerate will marvel at such a degree of accuracy. For the non-numerate I will borrow an illustration from Paul Davis of what that accuracy means. He points out that it is the same as aiming at a target an inch wide on the other side of the observable universe, twenty thousand million light years away and hitting the mark!
Dr. John Polkinghorne is a quantum physicist, and president of Queens College, Cambridge.
John Polkinghorne, "One World" (London: SPCK, 1987), p.57-58
Ravi Zacharias, "Can Man Live Without God" (Word) 1994, p. 84.
For more information on this topic see: Design and the Anthropic Principle