That's why I said fukk how this would happen. It's more a thought experiment.
I am definitely open to the possibility of multiple universes. Just not necessarily ones that contained identical copies of people like I'm positing here.
If we are to assume there are multiple universes, in order for one to contain another version of yourself, there would have to be another universe which held all the same 17 or 20 or whatever number it is of physical constants that keeps this universe from collapsing on itself. And it would also have to contain another Earth-like planet near a Sun-like star, and the process of life would've had to occur in the same manner as it did here...all the same geological activity and pelting of meteorites and radiation and magnetic properties, etc. People would've had to have evolved the same way under the same conditions. You would have had to have the same group of genetic ancestors and family tree up to your parents. And the DNA base-pairings that comprise you would have to have happened exactly the same way and produced an identical copy of you. The odds of that for all practicality, nil.
But if it did happen, you still might have slightly different experiences and environment, that could alter your decisions and behaviors, so free will not being real isn't really relevant here. A slight alteration in experiences could lead the other you to make a different decision about something crucial than you did here. Or someone else could make a different decision based on their experience that affected you.
