From a Reddit Question and Answer with Greg Boyd:
I apologize beforehand if I butcher any concepts about science or Open Theism in this question. I realize the potential for pitfalls are numerous here, but here goes:
From what I can understand, Open Theism seems to operate under the fact that time is somewhat constant. But we know that time is relative, it moves at different paces based on different factors, like how fast you’re moving. (I think that’s why Einstein refers to it as space-time). Given that this is the case, how is it even possible for God and humanity to have the same time-reference to make Open Theism make sense? It seems to me that it wouldn’t even take a diety to see “into the future”, it would just take someone with the appropriate technology on another plane of time, and they can “look into our future” by observing Earth from their position. I guess what I’m basically asking is, does the fact that time is relative render Open Theism incoherent?
The theory of relativity states that WHEN an event takes place is relative to the distance an observer is from the event and the speed they’re traveling relative to that event. But the starting point of the theory is the event itself. It works from the present to the past. We each have our own “now.” But never is there a perspective that experiences the event BEFORE the event takes place. RT has nothing to say about the nature of the future, in other words.
Moreover, because it is a scientific theory, it applies to finite observers within the universe, relative to each other. It says nothing about what an omnipresent observer would observe. For such an observer — God — there would be a “cosmic now” that embraces and correlates all the finite “nows.”