> My main problem with this is that the possibility of describing the
> evolution of a physical system in the future (ignoring, for the moment,
> questions about how do define "now") does not mean those future points
> actually exist. I can plot the trajectory of a projectile, but even though
> I can plot (or calculate) its impact point, the impact is not *real* in any
> sense until the projectile actually comes down! The fact that time-like
> world curves can be ploted (or it is alleged that they can be plotted) in
> 4-space does not mean that the "future" of those curves (all points later
> than "now") actually exist, or are real.
>
> I think (and I do say this with considerable humility--and trepidation)
> that physicists who try to give a realist interpretation to such things are
> forgetting that solutions to mathematical models are no more than
> theoretical entities. If I solve a simple quadratic equation to determine
> the length of the board I need to cut for the sloping roof of a dog house
> I'm building, I don't have to wonder if I should cut it at 28" or
> *negative* 28". The latter is an artifact of the mathematical model, but
> corresponds to no physical reality; it is physically unrealistic. Of
> course you and other cosmologists know this. But why then should you think
> that all solutions to, say, Einstein's field equations are physically
> realistic, or that if you can solve (theoretically) for complete world
> curves in space-time, that the segment of the curves which are later than
> "now" correspond to anything real?
>
> (Whew, after writing that, I feel like I've painted a target on my back and
> invited all astrophysicists to jump on me!)
>
> The upshot is I disagree significantly with what you wrote about God
> knowing the future in virtue of knowing the entire world curve of an
> individual.
>
> Interestingly, this view in essence is not new. Boethius (ca. 500) and
> Thomas Aquinas (ca. 1200) both use the image of a watchman on top of a
> mountain or in a tower observing a line of travellers below. The
> travellers represent moments in time; they each pass a fixed point (="now")
> successively, but the entire line (="all moments of time") are equally
> present to the watchman (=God). But as others have shown conclusively,
> this image only works if the future points *actually already exist.* But
> if time is dynamic, if temporal "becoming" is real, then these
> illustrations break down, and so do any contemporary analogues which ground
> God's foreknowledge in the exsitence in space-time of complete world lines
> of individuals.
>
> Note: I am not denying God's foreknowledge. I merely maintain that God
> does not know the future because it actually exists. For I maintain that
> there is an ontological assymetry between past and present, on one hand,
> and future on the other; the future does not exist. So God's knowledge of
> the future is grounded differently.
There is not a clean division between physicists & others on
this. John Polkinghorne agrees with the argument you give here - but
he's a particle physicist, not a general relativist.
_One_ problem with your argument is that it would seem to
require some preferred reference frame: "Now" is relative. Suppose
events at times later than t = 0 in my rest frame don't really exist.
For another observer who happens to be right next to me at my t = 0 but
who is moving, some of those events should be in his/her present.
Does God have a preferred space-time coordinate system? Taking
the Incarnation seriously might make us want to say so, but we need to
work out the implications of such an idea.
George Murphy