I was reading The Thinker’s excellent blog, Atheism and the City, and was reminded about a post I did a few years back for Debunking Christianity:
Here is a criticism about God’s omniscience and omnipotence based upon a point made by John D. Barrow in Impossibility, drawing on the work of cognitive scientist Donald Mackay. To put it into simple terms, it might be easier to state it as follows:
It has long been understood that with God’s omniscience, he cannot be contrary to his own predictions. For example, if you were claimed as being omniscient and omnipotent and you predicted beforehand that you would make yourself spaghetti bolognaise for supper on Friday, then when it came to making Friday’s supper, you would have no choice but to make the spaghetti bolognaise. This is because if you decided to be contrary to your own prediction and cook, say, pizza, then your prediction would have been incorrect. This would render your omniscience faulty, and would leave you with the characteristic of fallibility.
Likewise, God does not have omnipotence, because he cannot do something that would invalidate his infallible predictions.
So, logically, God can never be contrary to his own predictions. This constrains his free will quite significantly. However, it is far more serious than this. If he is creating the universe and knowing every particular outcome (even if one argues that he is somehow still allowing free will), then he has made predictions about every event that will come to pass. His foreknowledge is effectively one long prediction.
Thus, from the beginning of time onwards, everything must come to pass exactly as God had predicted at the actualisation of the cosmos. This has far-reaching consequences: God does not have free will, intercessory prayer is pointless, God cannot change his mind, God’s own future and interferences on earth are determined, and the passage in the bible where God changed his mind over the fate of Nineveh is patently false.
(Jonah 3: 10 “When God saw their deeds, that they turned from their wicked way, then God relented concerning the calamity which He had declared He would bring upon them. And He did not do it.”)