That's irrelevant. I'm not talking about whether it is technically possible, as this isn't an argument for the existence or otherwise of God. It is simply stating that IF an omniscient God exists then it means that they know in advance of you doing something what you will do, and there is no way you can not do what they know you're going to. If you could do something else then they wouldn't have known in advance. Thus not omniscient. That's what it means. The mechanism by which it is achieved is a red herring. Have we not posited the existence of an omniscient God? It is not "imaginary", therefore, within the argument. And as for being acausal: I don't know, nor do I need to know for the argument to still stand. How can you not be constrained to do what was seen, if what was seen is known to be a true foretelling of the future? Give me just one example of where your future is known (not just guessed at but actually known) and you then not doing what was known. Again, this isn't an argument for the existence or otherwise of an omniscient God, but the implications of the existence of such a God.