No idea what you mean here. It seems you’re suggesting that spacetime is the same thing as a definition of ‘to exist’.
As for the definition itself, make a difference to what?
Whatever spacetime actually is, I suspect what it is doesn’t depend on it being designated as existing or not.
Again, this seems not to parse. I cannot substitute the phrase where ‘determines’ was and maintain coherent syntax.
And perhaps you imply that mathematics supervenes on the universe instead of the other way around, but I see no evidence of anything like that.
This from someone who just said:
OK, so now you’re idealistic (and incredibly anthropocentric) about the existence of time. Is this a general stance on existence, or is there anything (mind say) that doesn’t come into existence only when it is measured, read or talked about by someone on the earth?
You say ‘indeed’, but then contradict yourself, referencing energy (and ‘fuctuating’, ‘reaching’) in the absence of time, all quite self contradictory.
The universe has no total energy, and that energy isn’t conserved. That only works locally.
Another common pop-sci myth. A tachyon (were one to exist) exists on a spacelike worldline, and hence has no invariant speed or even direction that it’s going.
The point is that in one and the same universe, time can exist in different ways. It can begin (as spacetime) and end (as in a black hole)
Per relativity theory, time is indeed bounded by bangs, white and black holes, etc. In a view with a preferred moment in time, (anything but a block view), time is not bounded in any of these singularities, so it being bounded is interpretation dependent.