Just before our universe was created "out of nothing", another universe's last atom just decayed, and since there now was nothing left to prohibit that universe's cosmic expansion to make that universe expand to infinity in just a second, it then resulted in some "all-nothing" equilibrium which suddenly made everything to restart and created our universe.
I dont know what I just got that idea from, just making things up ninja
Some mystical or gnostic religions teach that the universe was not created from nothing, but organized. They teach that some things are eternal and have always existed such as space, matter and intelligence [or what makes you and me self aware]. Of course there is no scientific proof to this and the only way to "know" it is the same way the gnostics or prophets learned it. From a sentient being of a higher order.
It's a good question and one that is unsatisfactorily answered by the science that we have at this point. Perhaps someday.
An infinite amount of other universes, some believe. I heard that there are big bangs occuring nonstop out there while other universes die out just as quIckly. Our universe may only be around for a blink of an eye...relatively talking.
i would guess that if space is indeed an endless void, all matter will, due to gravity, eventually pull itself back together into one mass and everything will once again "bang". i'd think that before the universe "bang"ed last time there was another universe made of the same components, just in a different form.