Im sure this is a commonly used viewpoint, but nevertheless, I shall post it.

The Christian Bible characterises God as being all knowing. This must include the future, all things that have happened, are happening, and will happen.
The point I hope to make, is that if God knows the future, which given the attribute of omniscience, he must, then he is powerless to change the future. Which of course is to show he is lacking of free will.
If we accept for arguement that there was a god, and he created all things, we can begin. Lets assume we are viewing god at the point of which he has just created Adam and Eve. Now, he knows that Eve will be tempted, and eat of the fruit. Suppose that Eve prayed for the power to resist the temptation. There is nothing whatsoever God could have done about it. Before she prayed, he would have known that she would, and he would know the outcome. So that would be the future he knew.
Imagine his knowledge as a book. The events in the book can not be swayed. For if the events were to take a different course, it would already be known, and thus no amending would be neccisary.
So God, knowing all the events of the future, must know how they will occur, or it is to lie to say he knows all and how all will occur. If he knows all, then he cannot change it, for he would already know he would change it, and with prior knowledge of the change, no change would indeed occur, it would already be planned. This must go back all the way untill the first bit of knowledge of what will occur was present to god. Of course, if God was eternally present, and the attribute of all knowing was eternally with him, then he always knew exactly what was going to happen, and had no choice whatsoever as to whether or not it would occur that way. Since you cannot go back to a specific time in which god was given information as to what will happen, since there is no time, then logically, God has always been powerless. The occurence of events has been following along on its own since it began, with no interference from God. It is funny that one with a belief in such things would tell one who believed the Universe just exists that he is off his rocker.

this of course does away with any power of prayer, to say the least.

A few points in no particular order:

Can we possibly do this though? If God is outside time (as goes the mainstream Christian theology) then how can we view him at any "point" in time?

The obvious fault I see in this is that it doesn't allow the possibility that the future is contingint upon God's actions. ie You are assuming your conclusion.

My argument is that humans and God wrote the book in the first place with their wills. "Time" is merely an acting out of what is in that book. We know from physics that time is merely a dimension and in an absolute sense is non-existent. My guess is that "reality" as we know it is merely a four (or 10 or however many) dimensional "book".

What do you think of the idea that God knows all possible futures as opposed to God knowing the future? (I'm not entirely sure what I think, and I'm not entirely convinced that they are different things)

Meta =>Not so fast there, Belzabub. I don't buy the argument that God couldn't change the future. Nor do I buy the argument that God has to know the future in its entirity, although I'm willing to admit the probably does.

First, while it is true that it would hoplessly confusing for a finite mind to grasp, God is not finite and thus could keep track of an infinity of possible realms all of which compete for concresence. Any action taken by God would change the outcome of previous concresences, but it wouldn't mean that God would be unable to accomplish it.

This assumes that God is outside of time and that time presents all movments as one etenral now. To that exent than God's actions can be accomplished in one event of creation; but our experince of time's arrow still allows us to us freewill within the freamework of concresence.

In other words, since God doesn't experince time as an arrow he doens't have to continually consider what to do. He does it all once and it's all done.

AT that point the mistake is in thinking that this eliminates our ability to change out minds.It does not, it merely means that we are within the flow the arrow and so to us it seems that we are changing our minds all the time. But God would see that all as one continuous action and thus can affect all of his actions at once. So he doesnt' control our decisions, but he knows what they will be becasue he sees them as past accomplished facts.

Secondly, it could be that God doesn't know the future, but is go vastly intelligent that he can anticipate what will happen and what outcomes will be. This eleminates God's omnisicence as we usually concieve of it, but guess what, the Bible never says that God is omnicient.

Now I've seen atheits argue against this that "well I guess your God doenst' know anything than." That is a reall slippery slope. Or to say that if God doesnt' know everything than he isn't trust worthy, that is also illogical. There is a lot of ground left to cover between not knowing all future events within 100% certainty and not knowing anything or not being trustwrothy. If God doesn't know all future events, as for example Hartshorne thought, than he would still anticipate better than anyone else.