Distinguishing eternalism and growing block at the end of time

Imagine that Alice lives in a classic growing block world, while Twin Alice lives in an eternalist world. Otherwise, the two worlds are exactly alike at all times. Moreover, in both worlds time started at noon, and ends at midnight.

Now let’s consider things from the point of view of both Alices right at the last moment of time, namely midnight.

In both cases, reality is a four-dimensional block, twelve hours long along the temporal axis. In both cases, there is a past but no future. However, the following would be true as asserted by Alice, but not as asserted by Twin Alice:

1. An hour ago, the block of reality was eleven hours long.

Question: What grounds the fact that (1) is true for Alice but not for Twin Alice? In other words, what grounds the fact that Alice inhabited a growing block world rather than an eternalist world?

This seems quite mysterious to me. And this seems to me to weaken the main arguments for why growing block is preferred to presentism and moving spotlight, namely that growing block gives you a better account of the grounds of claims about the past. But not in the case of (1). It seems that the growing blocker needs to ground (1) in one of the ways in which the presentist grounds claims about the past, say by positing a past-tensed fact at midnight of the block of reality having been eleven hours long an hour ago, or a past-tensed property, etc. And even so we have a puzzle.

My puzzle looks different depending on whether the eternalist world has A-eternalism or B-eternalism. If it has A-eternalism, then we can distinguish the two worlds as follows: the growing block world at the last moment of time does not have a spotlight anywhere, while the A-eternalist world does have a spotlight shining on midnight. But if that’s the answer we take, then there is a cost: there seems to be no difference between the growing block world at midnight and the B-eternalist world at midnight, and yet (1) is true in the growing block world and false in the B-eternalist world.

What did I mean by a classic growing block world? Well, in response to Merricks-style arguments that growing blockers can’t know that their thoughts are happening now, some have opted or a faded growing block, on which the past is missing some properties, like consciousness. On such a modified growing block theory, we have some hope of grounding the difference at the last moment of time between growing block and B-eternalism, because the B-eternalist world does not have a faded past. But now we can modify the story: suppose the B-eternalist world literally had a faded past (a past with no consciousness, say).

I think that if I was a growing blocker, I would be inclined to say something like this. The growing block theory is necessarily true in any world with time. What grounds the difference between being in a growing block world and an eternalist world is that an eternalist world doesn’t have time—it just has a fourth spatial dimension that enters differently into the laws of nature from the other three. Moreover, it is a necessary truth that at time t, time t is at leading edge of reality. This necessary truth does not need further grounding, but itself grounds (1) when combined with the fact that currently reality is twelve hours long.

I don’t like this invocation of an ungrounded necessary truth here. I wonder if it is much better than a Merricks-style presentism where truths about past facts are ungrounded (though admittedly contingent).