We don't even know if there was a big bang....plenty of true believers tho...
Wrong, we do know in what form the current Universe started out and then developed and that is via the process that has been termed "The Big Bang". The evidence overwhelmingly shows that the Universe started off very small and without any matter and that it underwent inflation and cooling as the energy density changed. But we can only make such a determination to the Planck Time because our current science does not currently lend itself to describing before that point.
An important point is that the Big Bang Theory limits itself to describing how
our Universe developed, it does not pretend to explain all possible existences (if there are such things), just the single one that we can observe.
As I have said we don't have good evidence of what cause there might be due to the inherent nature of looking outside the confines of space-time in which we exist, what we have is a number of competing hypothesis and the search is on for the evidence that will confirm or falsify those hypotheses. However it is perfectly possible to establish that an event has taken place without establishing what the precise cause was.