Originally Posted by LarryS
No of course we don't "know" this. None of us was around when it happened.
This is what the best models show to be the case. That's all we got. But time and time again that has been more than adequate for our purposes. Science don't really need to "know". All science needs is sufficiently predictive models that given real world inputs spits out what we can expect to observe.
But sure, if you want the literal interpretation then no, we don't "know" any of this. We can't. Does it matter?