"If even the omnipotent God cannot act to change the past, it does not seem any more conceivable that the omniscient God can know with certainty the unformed future. He may well be able to make highly informed conjectures about its possible shape, he may have prepared his plans for any eventuality, but in his actual experience and knowledge he must be open to the consequences of the exercise of human free will and...the evolution of cosmic free process." (Science and Providence p.90)
Dr.Polkinghorne's attempt to update theology and religious tradition via modern science and the "Open Theism" project may deserve some respect, yet we should keep in mind the slightly subversive implications of Polkinghorne's G*d modifications. Traditional theologians generally have insisted upon G*d's omnipotence and omniscience--and that holds both for orthodox and catholic thinkers, going back before Calvin to St. Augustine, if not scripture. To deny either of those attributes was considered heresy (Pelagianism, which insisted believers could earn their way into Heaven by good works, was one type of heresy--the orthodox (in those days papists) wanted to make sure that Deus always had an override right via grace---otherwise, isn't G*d limited by human concepts of morality?? Thus the dogmatist generally affirms the second part of the Euthyphro dilemma (google), which is to say, the King-G*d's not limited by our conceptions of the Good, or Just--really, that becomes a type of occasionalism...which works for christian, muslim, or jewish zealots).
Contemporary believers such as Polkinghorne ("P.") and the "open theists" now routinely modify the definition of G*d, however. P. does make mention of the theological chestnuts--including Leibniz's grand assertion of the Principle of Sufficient reason (why..somethin', rather than nada)--yet goes on to question G*d's supposed omniscience. For an agnostic, or ..atheist, that seems allowable. The bright-boy agnostic might wonder, however, whether he should grant the believer's theological modifications. Various sects now have decided define G*d as they wish, and yet still call themselves Christians (or jew, muslim, etc).
By denying the supposed G*d His omnipotence, hasn't Polkinghorne denied....His existence? Wouldn't a G*d know what will happen tomorrow, if not a year, or 20 centuries from now? And He would know by definition what His creations, humanity (and all of nature) will do, like, forever (one rather fantastic implication of omniscience), as a sinister hacker knows what his viruses will do (a believer probably doesn't care to claim G*d's a script kitty, with no understanding of the code he spits out...). P. says G*d has some idea of the future, but is not able to really know, or alter future events substantially (to what degree, Dr. P??), anymore than He can change the past. In effect those who deny foreknowledge deny his Godliness, if not grant some possible manichean, or polydeistic alternative (does some other ...Deity have some knowledge, power or part to play in reality as well??) as well. Of course, divine foreknowledge, like any species of determinism, is problematic, even absurd, as many skeptics have pointed out (tho' it may not be as problematic as...indeterminism). Bertrand Russell for one never tired of satirizing the bizarre implications of predestination, whether read as Calvinist or catholic, and the fundies never relented in their attacks on Russell. Yet Polkinghorne more or less concedes the game, and really has NO grounds to define himself as a theist.>