The rain could not have caused people to bring an umbrella, because people brought an umbrella before it rained. Regardless of whether or not the universe can unfold in any other way than the way it does, something cannot be caused by another thing that occurred after it. It's in the definition of "cause and effect."
Also, given that the entire point of the paradox is to illustrate a problem in decision theory, it seems a particular waste of time to deny that anything has a decision. Read the original statement of the problem. Read it closely. Don't read junk on the Internet or jabbering by Christian apologists desperate for credentials. The problem has absolutely nothing to do with free will vs. determinism.
What do you think is the point of it's not about free will? The only paradox is the assumption that you can make a choice that's not predictable. But, if conditions such that there will be rain or conditions such that you will pick AB exist then you will pick AB.
Sure, if you can lie to the oracle and say you’re going to pick B and actually pick AB then clearly that’s the better option, but if they can look past that lie and see how you think (aka read your source code) then that’s not a viable option. If you say to the oracle I am going to pick B because you know what I am going to do and something predictable changings you’re mind you still lose. The only option is to pick B and for that to be truth, and if it’s the truth you pick B on stage.
PS: As apologists, you seem to be stuck with the idea that thought is anything other than a predictable electro chemical process in your brain no different than a complex computer program. We can make pseudo random choices which are very useful in decision theory, but ‘free will’ does not exist. In the end we are no less predictable than the rain.
The predictability or non-predictability of a given decision is irrelevant; there's no need to assume that an unpredictable choice can be made. Choosing both boxes always gets the maximum amount of money available on the table.
The point is about decision theory, which has two approaches considered "rational" that yield different results. That's why it's a paradox. It's all spelled out in the paper: http://faculty.arts.ubc.ca/rjohns/nozick_newcomb.pdf
Go ahead, search the document for the phrases "free will" or "determinism." I'll wait.
Also, given that the entire point of the paradox is to illustrate a problem in decision theory, it seems a particular waste of time to deny that anything has a decision. Read the original statement of the problem. Read it closely. Don't read junk on the Internet or jabbering by Christian apologists desperate for credentials. The problem has absolutely nothing to do with free will vs. determinism.