I'd left off on my future shock series of posts at a point where I hypothesized that the future may be predictable. The idea behind the posts was only to introduce the concepts related to that school of thought (determinism, that Demon thing etc).
That said, the first concept that could do with some clarity is what might happen when the Demon acts to change the future she's foreseen. There was a movie about this sort of thing, called Next, starring Nicholas Cage. Anyyyways... The paradox that immediately plays out is very simply this:
The demon foresees being hit by a car at a spot x, at a time (t+t1) in the immediate future. Being averse to the whole car-accident thing, she steps to one side at the exact moment, and in so doing, avoids being hit by the car. The future she'd seen is no longer true. In fact, what's to say it was true in the first place?
Two points about this scenario:
1) It's not quite as damaging as the grandfather paradox (where if you were able to travel back in time and defertilize your gramps, you wouldn't be born...and so wouldn't have been able to go back in time) because this construct interferes with the concept of time travel, but as a thought experiment, you're atleast able to go so far back as to visit your gramps before you begin the defertilization ritual.
--> Read the post above - "Yesterday"
2) What if the demon did not act to change the future and did indeed get hit by the car? Then the future she saw at time t was correct. This means that for any value of t, the future at t+t1 for an incremental value of t1, is a series of possibilities (she could've been hit, she could've avoided being hit, etc) rather than being a pre-defined path.
On point #2
As good a time as any to make reference to the concept of unitarity (wiki: "the sum of probabilities of all possible outcomes of any event is always 1. This is necessary for the theory to be consistent.") This simply means that the future must occur, or that time will continue its march, much like the flawed 2nd law of thermodynamics.
Consider then that our demon, Billie, has an evil twin sister, Jean. In our movie (surely there's a movie? atrocities like Cage's Next or Denzel Washington's Déjà Vu can't be our only mainstream tributes to Q.physics), where Billie is pitted against Jean, this clash will result either in a fantastic series of near-death escapes for both or the driest movie since wall-e. These extremes (near-death escapes or nothing interesting happening) follow from the concept of unitarity, but warrant a longer discussion than in the scope of this post.
The chance that Billie or Jean has of foreseeing a future that will happen have dropped to 50-50. If there are more such demons, each interfering with events they've foreseen, the chance that the future seen by any of the other demons will unfold drops further. That then reduces my fascination with Laplace Demons. If all they're able to do is make a guess about what might happen in the future, they're doing no better than us non-demons.
About determinism then: It seems that if at a time t we begin to observe the past (say an event at a time t-t1), all that happened was truly the result of what went before it. The past is definitely deterministic. The future though is an infinite number of possibilities. We can change it by doing what we will. We'll reap what we sow, and our will remains free. Amen.
P.S. Apologies for the Billie Jean angle. It was that or the cross-dressing siblings, Eleanor and Rigby.