I've been reading Brian Greene's "The Fabric of the Cosmos: Space, Time, and the Texture of Reality". It's quite readable, particularly since he likes to use the Simpsons in his explanatory metaphors. Some chapter names:
The Universe and the Bucket: Is Space a Human Abstraction or a Physical Entity?
The Frozen River: Does Time Flow?
Teleporters and Time Machines: Traveling Through Space and Time.
In this last one, Greene explores the concept of free will. If one accepts the tenets of classical physics then free will is an illusion. Bear with me while I try to explain.
In the beginning we had the Big Bang. All of the particles that make up the universe exploded outward in a specific way, their movement governed by the laws of physics. Therefore, if you knew the exact state of all of the particles in the universe at any given moment you could predict exactly where they would be at any other given moment. Therefore, you could predict the future. Everything that is happening is happening because it must. To quote Greene:
" You are made of a collection of particles, so if the laws of classical physics could determine everything about your particles at any moment -where they'd be, how they'd be moving and so on- your willful ability to determine your own actions would appear to be fully compromised."
Are you with me? This idea is simultaneously horrifying and incredibly comforting. On the one hand, you have no real choice. All of the good intentions and good will cannot avert disaster if that disaster is predetermined by what happened billions of years ago. If we are able to affect an event or to change something about ourselves it is only because that is how it must be. On the other hand, we can completely eliminate the dreaded what ifs. We agonize over decisions and when they do not turn out they way we want we think, what if? What if I had made another choice? Well, if you accept the deterministic view, then you made the only choice possible, there is no what if, not in this universe. This doesn't mean that we don't go on living each day, making choices, taking action; it just means that we make the only choices possible.
This is a very intriguing idea for someone like me. As has been noted, I have control issues. I have a lot of trouble just accepting things and spend a lot of time going over past events trying to find a way in which those events would have turned out differently. Faith that a higher power has things in hand is not an option; I just don't believe it. But this, this is science, logic, and reason. I understand it and I could accept that it is true, in spite of my need to control every last thing that happens. And if I can accept it and really believe it then it might release me from some of the endless rehashing of the past and worrying about the future (cue Doris Day singing Que Sera, Sera).
However, we do not live in a classical universe. Quantum theory changes things. It may be that even in a quantum universe particles behave in a predictable way, that if you could observe the quantum wavefunction for a particular particle you could use quantum mechanics (in this case an equation written by Schroedinger) to determine the wavefunction at any other given moment. But there is the problem of observation. Does the act of observing change the object being observed? Are we missing something, some part of the quantum reality? If that is so, it is quite possible that free will might play a part in physical laws.
Have I thoroughly confused you? Not to worry, as Greene points out, physicists exist in a state of confusion. And that is okay. We do not need to know everything but we do need to explore and to theorize and to dream of what is possible.