But, among the scientific reasons why the universe cannot be past-eternal, there is this argument:
1. The series of events in time is a collection formed by adding one event after another.
2. A collection formed by adding one member after another cannot be actually infinite.
3. Therefore, the series of events in time cannot be actually infinite.
Essentially, this is the argument that you can’t put together an infinite collection of things one step at a time because you’d (literally) never get there.
Now, Hallquist makes the objection that this assumes that the universe started at a certain point, and that this is wrong-headed. The idea of an infinite past is that the universe has always been here, so that it didn’t ever start. Thus, it was always infinite–there’s no need to build it up to an infinite age one moment at a time.
Admittedly, someone as formidable as J.L. Mackie takes this approach. Still, I think it misses the real point of the argument. The claim of an infinite past is, after all, the claim that there are moments in history which are infinitely distant from the point we are now at. And that it is a logical impossibility for us to have reached this moment from those times in the infinite past. It makes no difference whether or not any of them are the “starting point” of the universe, or even that there would be no starting point.
So, one cannot get out of the argument simply by denying that infinitely distant moments weren’t the beginning. One would have to deny that there are no infinitely distant moments at all. But this last is agreeing with the idea that the universe isn’t past-eternal.
That being the case, Hallquist has not given us a reason to doubt that the universe has a cause of its coming into existence. In fact, he’s not adequately refuted any of the reasons for thinking that it has a cause.
But he needs to refute all of them for his argument to work.