lol. These questions seem never-ending. The idea that a tree doesnt make a sound if it falls over was put to rest by the fact that we can have devices that can measure sound (microphone) and store it (tape recorder) and know, though not 100%, that the event took place without oneself actually being there.
However, quantum phsyics and experiments thereof could dispell this. Schrodingers cat problem basically states that if a cat is sealed off in a box and left with cyanide or whatever and there's exactly a 50:50 chance of it dying; then until the experiment is measured; the cat is considered BOTH dead AND alive.
fantastic link to get a taste of the weird world of quantum: http://www.youtube.com/watch?v=DfPeprQ7oGc
If what is happening is true, and there has never been an experiment in quantum phsyics that has never not worked, then Decuis' comment is also invalid. To explain this it seems that it is probable that the future affects the past, or perhaps to be precise, future thought affects the past. I'm a bit dodgy on the ins and outs of this and how it relates to space, time and/or spacetime, but essentially experiments in parapyschology (and these are in mainstream journals) show that a person a few hours in the future thinks of a question and that a quantum computer (one that can calculate instantaneoulsy without 'steps'
gives the answer that time period before. Thus, either the answer id the question or the effect is the cause (relative to convention). This is all a little weird, and physics is not equipped to answer these questions yet. But, nonetheless, if we determine free will as a function of teh knowledge of past events, as Decuis suggests, we may in fact be wrong, for future events may also affect past ones.
On a speculative note to those who understand these experiments more than I do, is quantum pushing at the fact that maybe every single atomic and subatomic particle knows each other both in the present and in the past. Does the mind work on relativistiv principles at its scale and thus are the quantum world and the normal world actually two different worlds. We've discovered a lot; but only a fraction.