And another one of those brain waves: I am not convinced that what appears as the big bang to us was really the beginning. We might never know, it seems to be an event that destroys any information of what was there before. However, here is one idea I had about it. I am not a physicist, so my ideas about this topic might be total nonsense.
There is this theory that the world will end in a “big rip”, with everything flying apart faster and faster, because dark energy, whatever that is, is rising. Now, if things like planets, stars and atomic nuclei are ripped apart, energy has to be put into them in order to do so. So the big rip is putting energy into the universe (one could view this dark energy as an external source of energy). At some points, when the level of dark energy has reached a high enough value, virtual particles separated by the ripping force will be endowed with enough energy to become real particles. So instead of the universe becoming emptier and emptier, new matter and radiation would be created, starting with long wavelength, low energy stuff and then moving to higher and higher energies. One could think of this as the vacuum itself being ripped apart.
As a result, the universe would be filled with extremely hot and dense radiation and matter. So the big rip would lead to a refill of the universe. Any information from the previous universe would be diluted and dispersed by the expansion, so you get a state with very low entropy. Also, the resulting universe is very flat.
If there are fluctuations in the dark energy, it could drop to near zero in some areas. These areas would suddenly cease to expand quickly. From the inside, such areas would look like universes after a big bang. So the big rip would lead to a similar result as the eternal inflation scenario, with universes arising as bubbles in a quickly expanding environment of radiation and matter.
Another way of looking at this, that I guess is equivalent, is this: the further away something is from us in the expanding universe, the faster it moves, from our point of view, because the space in between is expanding. At some point, the speed of moving away is higher than the speed of light. From our point of view, there is an event horizon at that distance. If the speed of expansion increases, this event horizon would come nearer. It would behave similar to the event horizon of a black hole. Some pairs of virtual particles are separated, with one of the pair disappearing behind the event horizon and the other one moving our way. The nearer the event horizon is moving, the hotter it becomes. In the big rip, the event horizon around each point becomes very near and very small (in fact, microscopic) and the radiation (akin to Hawking radiation) becomes very intense. Information (entropy) from the previous universes disappears behind the event horizons, so you get a high temperature, high density, flat, low entropy starting condition.
I guess both descriptions are equivalent. The expansion creates energy and matter and does so ever more intensely, the faster it is getting. Dark energy (of which there seems to be an inexhaustible amount) turns into normal energy. As a result, new universes are created. The big bang would then be a consequence of the big rip of the previous universe.
Warning: I am not a physicist. I arrived at these ideas in a completely intuitive, non-mathematical way and I am not god enough in math to try to turn this into a mathematical theory. In fact, these ideas might turn out to be nonsense. Also, the big rip idea put forward by some physicists might turn out to be totally wrong, so one should not take me too serious. It is possible as well that these ideas are not new at all, but I have not seen them anywhere. I am outside my scope of expertise here and these ideas might be rooted in misunderstandings. I leave it to the physicists to decide if this is crap.