Its not even uncommon to encounter an atheist who advocates an eternal cause to the universe (they say however that it is not god and dull matter)
How can you explain the nature of existence without a cause of all causes?
ok... two possibilities
1) in future humans will develop a technology that is capable of transferring particles back in time, the humans send the particles back in time that annihilates and causes Big Bang which gives rise to the universe, perhaps it is the same reality of universe as the one these humans of future are in, perhaps it is another reality of universe then that of those humans of future. Perhaps humans are not even responsible for universe creation, black holes might as well be transferring particles back in time until all matter is transferred and another/or same exact Big Bang occurs to create a universe. time lapse basically. All this based on the fact that matter dissapears in black holes...or as we like to say gets crushed to infinite singularity. And space grid is like time. no space grid is no time. (All from Einstein concepts)
2) Humans create a universe within a universe. Humans within that universe create another universe within their universe, whereas within that universe another universe is created. Perhaps it is not humans who create a universe within universe but laws of the universe.
These are the possibilities and not just the GOD who supposevly governs everything and makes big bang not create chaos but something as complex as humans, meanwhile humans are more chaos than there was before.