I'm posting my side of an email exchange I recently had:
It's conventional to argue that if God knows the future, then the outcome is certain. But is there a sense in which we could argue the same thing in reverse?
Past and future are relative in the sense that, say, Archduke Ferdinand's present or future lies in my past, while my present lies in his future. If I know he was assassinated on June 28, 1914, was it possible for him not to be assassinated?
An obvious response would be that if he hadn't been assassinated, then that's what I'd now know. The future is in some measure the result of what people do in the present. If they do something differently, the future will turn out differently.
But is it that simple? It tacitly assumes that my future doesn't already exist when Ferdinand is assassinated. Clearly it doesn't exist for him. 1914 isn't 2016.
Yet according to the B-theory, past, present, and future all exist. They don't exist at the same times. 2016 didn't exist in 1914. Rather, 2016 exists in 2016! A later time isn't simultaneous with an earlier time.
But the entire timeline exists. Because the whole exists, each part exists.
If, therefore, 2016 existed at the time Ferdinand was assassinated (as well as before), even though it didn't exist in 1914 (i.e. a later time does not exist as an earlier time), and if, in 2016, I know that he was assassinated in 1914, then isn't his assassination inevitable?
Perhaps one would say that's not about knowledge but a theory of time. Yet it shows a relationship between knowledge and a theory of time. An implication between the two.
Seems to me that Craig's explanation is inadequate. (In fairness, he wasn't responding to me.)
The question is whether, given the B-theory, future knowledge of a past event entails the past event. Does that carry an entailment relation?
It's not just at as of now, I know that Ferdinand was assassinated way back then. Rather, even as of then, the future in which I know that Ferdinand was assassinated existed–or coexisted with past event (although they are not concomitant, obviously). And if cause and effect coexist, then I should think it's too late for the precipitating event to be other than it was.
In addition, it seems to be that Craig fails to distinguish between logical relations and what's metaphysically possible. Sure, he can recast the issue in terms of a conditional proposition, viz. If Ferdinand hadn't been assassinated, then my future knowledge of the past would be different–since the past itself would be different. No doubt. That's a tautology.
But just because we can recast the relationship in conditional terms doesn't ipso facto mean the conditional proposition or counterfactual scenario is metaphysically possible.
For instance, suppose we say that if Steve Hays was born in 18C China, he'd speak Mandarin.
Well, considered in isolation, that self-contained proposition might be true. But it's not possible for me to be born in the 18C. It's not possible for me to be born before my parents were born, or born to other parents.
And one can't just push my parents back two centuries, since their ancestors were the product of various developments in European history. It's all interwoven.
In the B-theory, the timeline is a set of internal relations. You can't change one variable without changing everything (or nearly everything) beforehand or afterwards.
Of course, people like Craig can (and does) attack the B-theory directly. But for now I'm just considering a possible implication of the B-theory. Combining the B-theory with knowledge of a past event.