The present doesn't ground the past

I will run an argument against the thesis that facts about the past are grounded in the present on the basis of the intuition that that would be a problematically backwards explanation.

Suppose for a reductio:

1. Necessarily, facts about the past are fully grounded in facts about the present.

Add the plausible premises:

2. Necessarily, if fact C is fully grounded in some facts, the Bs, and the Bs are fully causally explained by fact A, then fact A causally explains fact C.

As an illustration, suppose that the full causal explanation of why the Nobel committee gave the Nobel prize to Bob is that Alice persuaded them to. Bob’s being a Nobel prize winner is fully grounded in his being awarded the Nobel prize by the Nobel committee. So, Alice’s persuasion fully causally explains why Bob is the Nobel prize winner.

3. It is possible to have a Newtonian world such that:

   1. All the facts about the world at any one time are fully causally explained by the complete state of the universe at any earlier time.

   2. There are no temporally backwards causal explanations.

   3. There are at least three times.

Now, consider such a Newtonian world, and let t₁ < t₂ < t₃ be three times (by (3c)).

Suppose that t₃ is now present. Let U_i be the fact that the complete state of the universe at time t_i is (or will be or was) as it is (or will be or was). Then:

4. Fact U₁ is fully grounded in some facts about the present. (By (1))

Call these facts the Bs.

5. The Bs are fully causally explained by U₂. (As (3a) holds in our assumed world)

Therefore:

6. Fact U₁ is fully causally explained by U₂. (By (1))

7. So, there is backwards causal explanation. (By (6))

8. Contradiction! (By (7) and as (3b) holds in our assumed world)

I think we should reject (1), and either opt for eternalism or for Merricks’ version of presentism on which facts about the past are ungrounded.