What is the standard atheist response to this "proof" of God's existence?

[Pleonast]

@begbert2

Hey now, the “now point” entered this discussion in my logically-formatted argument and was defined there quite explicitly, in a way that does fit in with any notion of time that is consistent with a discussion of ‘is there a beginning to time’.

Well, that’d be a problem then, because science’s current understanding of the universe is that there is a “beginning” of space-time and that “now” is not meaningful.

You have defined potential time as unbounded, which we all agree with. That’s basically axiomatic to the discussion. But this discussion necessarily distinguishes the amount of time that has already passed and the amount that might have passed if there was no beginning of time, and you have not argued that the amount of time that has actually passed is infinite, any more than the ability to recite larger and larger diameters means that the earth is infinitely huge.

Then I think we probably agree. If time has no beginning, then asking how much time has “passed since the beginning” is nonsense, given that there is no beginning. It’s analogous to asking how far am I from the East Pole of the Earth.

And, on a tangent, and I’ll just admit my relative ignorace of relativity here and ask, what is space-time curved with respect to?

There’s more than one way to answer this. The usual way: it’s curved with respect to itself, as described by the metric tensor (mathematical object that how a coordinate system varies as a function of position in space-time). Physicists use that math to avoid introducing “metric dimensions” (my term) through which space-time could alternatively be called to curve through. But one could do use additional dimensions to describe the curvature, with the understanding that these are not actual dimensions particles can move through.