[ByronT]

It seems a bit pompous to say that we've set up electrons the same way and observed that they go in two different directions for no reason. You can't eliminate reasons that you don't know about.

Have you heard about the EPR paradox [1]? Einstein, Podolsky, and Rosen believed there may have been "hidden variables" in the language of quantum mechanics which were not yet accounted for. These hidden variables, if discovered, would render quantum mechanics more deterministic.

This idea was essentially shattered by Bell's theorem [2]. The universe probably is not deterministic (at least in the sense we think about determinism). That's a hard pill to swallow, and it goes against all human intuition. But the majority of physicists do seem to accept this fact, however uncomfortable it might initially feel.

[1] http://en.wikipedia.org/wiki/EPR_paradox

[2] http://en.wikipedia.org/wiki/Bell%27s_theorem

[dragonwriter]

> The universe probably is not deterministic (at least in the sense we think about determinism). That's a hard pill to swallow, and it goes against all human intuition.

It really doesn't contradict "all human intuition". Strong determinism has always been a controversial position, though its popular with the people that view science as a new complete-and-all-encompassing religion rather than a utilitarian tool.

[mtdewcmu]

"Probably is not deterministic" is not quite the same as "provably is not deterministic." Physicists have opinions on a lot of things, but I don't think they can fundamentally answer this.

[ByronT]

In your original post, you state that we might as well assume determinism. Why? Given the widely accepted nondeterminism of quantum behavior, why wouldn't we assume nondeterminism instead?

I realize what you're grasping at is that deterministic behavior might somehow underly this seemingly nondeterministic behavior. Bell's theorem, however, has made it difficult to reject that the this fundamental aspect of the universe is hard to explain without assuming nondeterminism (or superdeterminism).

I agree you can't prove it. You just haven't really explained why you're leaning toward the deterministic side.

[mtdewcmu]

I didn't make myself clear. I meant assume in the mathematical sense, as in, to take as an axiom. If you do a science experiment, you are assuming that you will get back a repeatable result, and you won't be measuring something perfectly random. Otherwise, people might assume you're crazy. :)