Consider a universe which arose from nothing. The catalyst for such an event can only be speculated upon as there were no witnesses. There would be many who would insert a god as a catalyst, others who might guess it spontaneous or caused by something unknown. There is no proof of any nature to substantiate that it was a god or that it was spontaneous. It must remain unknown.
If you started with nothing then the balance of what might be created would have to equal nothing. There would have to be equal quantities of matter and anti-matter so that the balance of the universe would equal nothing. Matter and anti-matter cancel each other out.
Presently we have a universe where there is a preponderance of matter and a much less quantity of anti-matter. With this discrepancy considered then the universe would have had to start with something. Convention is that this something was energy squeezed into an unimaginably dense point which exploded. Perhaps this is the case.
Suppose instead that the universe did start from nothing. Suppose there is antimatter equal to matter. We can see the universe only to a finite horizon with our limited means. Is it possible that the balancing quantity of the antimatter which need exist is coagulated in a sphere at the edge of the universe, surrounding it? Pluses and minuses it is said attract. Being opposites it is easy to speculate that they must attract. If antimatter attracts matter then this might explain the acceleration of the galaxies from one another. Surrounded by an enormous globe of concentrated antimatter the universe we know would surely rush toward the outer edge and soon become nothing once more. This sphere of antimatter may be in the form of an antimatter universe that is accelerating in as fast as our universe is accelerating out. In the beginning there may have been more of each, matter and antimatter, but that antimatter that remained within reach of matter, cancelled some of both out.
Of course this is just imagination at work. As non-provable as any god or big bang.