I'm having trouble grasping this concept. In my into philosophy book it explains (or at least I think it explains) that it is the theory that particles behave differently if observed than not observed. It says that if a particle is measured it will behave as a particle and if it is not measured it will behave as a wave. It then says that this affects free will and goes against classic physics by saying that the world is random and to paraphrase Einstein, "That God is playing dice with the universe." Am I missing something, as all of this doesn't seem to make sense to me.

Can anybody help me understand this?