10 Controversial Theories About The Universe's Toughest Questions
3. Cyclic Universe: A Wheel Within A Wheel
We have just described a universe that was created in a gigantic fireball, cooled, expanded to infinity and is due to die an ignominious death of a billion supernova. But there are other theories: One such theory is the cyclic universe theory, but even that one branch has many leaves.
Some propose a universe in which gravity eventually wins again and drags everything back together in a "big crunch". As the galaxies merge and condense into smaller and smaller space, the heat and energy would increase, causing matter to fly apart into its constituent energies thereby providing the conditions for a new big bang with no information retained from the previous universe. This was actually the favoured model for quite some time until the Hubble space telescope showed the expansion of the universe accelerating.
This should really be the end for the cyclic universe then right? Well, not necessarily. It depends on what you mean by cyclic. One of the components of the inflation model is that the background energy fields were much stronger in the past than they are today. That potential to fluctuate is what makes inflation work but it can also be extrapolated to show that the potential could have continued before time zero and not actually reach zero energy.
What this means is that if the background field was large, causing high levels of energies, then fell away giving rise to lower energy levels (the ones where matter can exist and we can live), and if that energy then increases again over time one can see how the expansion of the universe, the big bang and a cyclic potential all fall into place. As the universe expands and the space between space becomes so large, matter can no longer be sustained and would drop to a background state.
As all the matter in the universe breaks apart the energy levels of the background would start to increase exponentially. Since we are now back in a state where time and space are meaningless the energy of our universe which was absorbed back into the void would be expelled again violently in another big bang, making the universe not so much a circle, but a wheel within a wheel.