My hypothesis is that the universe is actually a series of spacetime bubbles that are created by gravity. When black holes start eating enough matter they become super dense and with every atom they become more dense until they start to eat entire galactic superclusters and eventually they merge with other black holes until the effect of gravity becomes so strong that it literally rips a hole in space-time. When this happens it becomes a new Big-Bang. I think of this multiverse as being like the structures of a sponge. Each new Big-Bang creates a new bubble in space-time that is interconnected with the universe that caused this new Big-Bang. This would explain the rapid expansion of the universe from a single point. Eventually in a future so far that we can only express using very large exponents, all the matter in our universe will merge due to gravity and eventually the process will repeat itself and as our universe dies a new one will be born.

We are still left with question of where did all the matter/energy come from to start the whole process. The complete vastness of our still growing universe is so large that it can't really be understood in anything but mathematical terms that lose all meaning to humans.