Agreed. And as you stated, before the big bang, all current theories break down. There is no math to describe what happened at this state. And no one has any evidence
against anything existing prior to the big bang or even at time zero, so really what can we hope for in the way of maths and evidence in a topic such as this? Does that mean we shut it down? Many of the great discoveries in this field were, while substantiated with math, initially nothing but conjecture and speculation. Speculation is not always senseless.
It can go too far, sure, but I don't see that it has--not that I'm in any position of authority or anything.
Anyway. I agree, spacetime is a great way to discuss time. It is the most widely accepted and supported view of time, but the implications of spacetime aren't really helpful with this question...I agree, I'm sure most would, with the evidence we have today, that the idea of time has no meaning at the big bang, and there is no meaning in talking about anything
before it. However, this thread asks a valid point, and one that has been asked specifically since we showed the plausibility of the big bang, and generally since the dawn of mankind.
It is easy to imagine the nothingness that humans "are" prior to birth and after death. Time stops for us totally, and there is
nothing--as far as we are personally concerned, but time itself had gone on before us and goes on after us. There is always something that exists external to us that we pop into existence
in. But with the big bang, we are saying that the universe had a beginning, about 13 billion years ago, but that
that is it. There was no before that. So while I can sort of wrap my head around that, I find it difficult to truly grasp, and because our universe functions in an apparently cause-effect fashion, it leads me to believe (here's my speculation, as that is all that one can do in this case) that something is amiss.
It is strange that a universe that functions under the watchful hand of cause and effect will have had no cause at all, but just have sprung into existence (with the help of a lot of fancy and impressive physics, to be sure, but those physics only describe what happened
after the singularity expaned). Which is why it is interesting to talk about, even if it is speculation.