So you’re challenging premise 2. You don’t believe the universe began to exist, but rather believe that the universe undergoes an infinite series of expansion and contraction. To explain to others who might not know, on this view the universe expands with a big bang and then eventually collapses in on itself with a “big crunch.” Some speculate that after the big crunch, the universe might expand again in another big bang. Thus, we have an infinite cycle of universes, it goes on forever. Do you have any good reasons to believe in such a model? I think there are, however, good reasons to doubt the legitimacy of the cyclic model.
The cyclic model only succeeds if the density of all the matter in the entire universe is greater than what scientists call “critical density.” Critical density is the value at which the universe is at balance, and expansion is stopped. If the density of matter in the universe is greater than the critical density, then gravity will overpower matter and pull it back in, thus initiating the big crunch process. But if the density of the universe’s matter can’t succeed critical density, then the gravity is not strong enough to pull the matter back in and initiate a big crunch, and so the universe just expands forever.
However, most cosmologists think a big crunch very unlikely, given that most of the matter in the universe is “dark matter,” which has enough mass and gravitational force to keep the universe expanding forever. The truth is, the current evidence we have doesn’t show that there will ever be a big crunch. For instance, the most recent evidence of space expansion shows that the universe isn’t being slowed down by gravity, but rather is accelerating.
But even if the universe could contract and expand again, this does not show that it could have contracted and expanded forever. This is because whenever the universe would collapse and experience a big crunch, there would be an intense build up of disorder (entropy) that would carry over into the new expanding universe. This build up of entropy would have the effect of creating larger and longer big bang expansions each successive cycle. The physicist Duane Dicus explains this by showing that entropy will only “enlarge the cosmic scale from cycle to cycle” which means if we look backwards in time, we’ll notice that each earlier cycle “generates less entropy,” thus showing it would have a smaller cycle time and cycle expansion. This means as one traces the cycles back in time, each expansion becomes smaller and smaller until you come to the one that is infinitely small (or zero). This would be the beginning of the universe.
In fact Stephen Hawking even says on his own website that this entropy build up disproves the cyclic model: “One would expect that the universe would become more disordered each oscillation. It is therefore difficult to see how the universe could have been oscillating for an infinite time.” Furthermore, Hawking’s formulation of singularity theorems with Roger Penrose imply an absolute beginning to the universe. To quote Hawking one more time from, The Nature of Space and Time, singularity theorems “led to the abandonment of attempts (mainly by the Russians) to argue that there was a previous contracting phase and a non-singular bounce into expansion. Instead almost everyone now believes that the universe, and time itself, had a beginning at the big bang.”
