If this is so, problems arise for determinism: if all universes are determined, yet all universes are possible, then the fact of determinism bears no relation to what may or may not happen in our universe.Yes, I'd like a clarification on this specific part. I don't understand how infinite possible universes negates, in any way, the set path within any one particular universe. Perhaps you're saying that, although determined, the future could still take any theoretical course because we could be in any theoretical universe? But if this is indeed what you mean, I don't see how it makes a difference whether there are infinite universes, or just this one. In either case, we do not -CAN not- know the position of every existent molecule at every moment in time. So, whether everything is determined or not, it makes no difference in terms of how we approach the universe/reality itself. I think the evolution of our ability to grasp "possibility" as a concept was a tool enabling us to somewhat surpass our own biological(i.e., sensory and data-processing) limits, allowing us to weigh different potential outcomes before they become extant, thus giving us some ability as a sort of biological time-machine by living in not only "the" future, but many possible "futures." The downside being that we often get swept up into silly notions like luck and free will, going so far as to see things as vital central aspects of our human nature, and so come to mistake the tool for the goal.
It's a very slightly different interpretation of the word "determined" in each case, I think. In the normal view of determinism, all events (effects) are determined by the original cause (Big Bang, God, Cosmic Penis Monster, whatever). However, if the deeper levels of physical universes are probabilistic to any extent (as QP suggests?), and all possibilities must happen (again, as QP suggests?), then everything which might exist does exist, in some corner of the "multiverse": that is, both everything
and every thing
are determined, rather than only one singular complex string of cause/effect relationships. I believe the problem, as far as I see it, is this: while all realities are determined ("at all times", from our human perspective), no one reality is determined at any one point, though it will be seen to have been determined (in hindsight). I'm a little bit too sober at the moment to fully grasp the idea myself, but something in my brain is saying "there's a schism, here, between what supposedly must happen and what must happen in reality". Perhaps to say "problems arise for determinism" is wrong, and it is more correct to say "problems arise for what I understand to be the commonly held view of determinism".
On a similar note, my girlfriend (a psychologist, but interested in philosophy to a good extent) suggested that an individual might move his/her awareness/consciousness from a body in one reality to the related body in another, in some circumstances (we've had some pretty bizarre [some weirdos might say "psychic" or similar] experiences to do with "other realities", "divination", "past lives", etc., though not as goofy/retarded as those phrases suggest - don't worry, we're sceptical). Perhaps to say "an individual might move" is misleading: it's not "free will", in the traditional sense of the term, in that whether one's awareness moves or not is, as far as I remember from what she told me, determined as well. However, the theory does allow for an "individual" to move out of one possible sequence of events and into another, thus the experience of a life need not necessarily extend through a sole reality. I'll ask her to fully flesh out the idea, since it pertains to this discussion, and I can't quite do it justice.