If we are all made of particles, and each of those particles is being effected by specific forces and energy, would it not be possible to take a situation and, taking into account the infinate number of factors effecting every particle, predict the future?

For example, if I hold a pen up and drop it onto the desk, I can predict that it will fall and land on the desk, due to gravity. If you took into account every environmental factor influencing the pen for the duration of the fall, couldn't you predict exactly how its going to land?

Now, say you applied this concept to the universe. Could you not say that the future of the universe is set; that no matter what we do we cannot deviate from the course the universe is 'destined' to follow? Ignoring such phenomena as divine intervention, miracles, acts of god, or otherwise supernatural (belief dependant) occurances.

Just an idea. Am I wrong? Kind of depressing if I think about it too long.