The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [15]
With these two regions in mind, we can see what it means for the physical facts to fix all the facts—including the chemical, biological, psychological, social, economic, political, and other human facts. In the distant duplicate of our Earth-and-moon region, there are also animals and people, cities and shops, libraries full of books, paintings on the walls and refrigerators full of food, in every way physically indistinguishable from our own region of space-time. It would have to be the case that the distant arrangement of all the molecules, atoms, and their parts would also have to have a duplicate in it for everything that exists in our world. This must include every single biological creature, every human being, with all the same relationships in it that exist here and now in our own corner of the universe. What is more, since each of the brains of all the inhabitants of this distant world have to be identical to one and only one of the brains in this world, they would have all the same emotions, attitudes, and memories (or the feeling that they remembered) that the brains in our world have.
That distant region would have to be exactly like ours, no matter what the actual history of that distant chunk of matter and energy had been up to just before the moment of perfect duplication. It would have to be a duplicate of our region of space even if it had been organized and synthesized in a few moments of random fluctuation as opposed to the 4 billion years it took to produce us and our memories. A perfect physical duplicate of our world would have to be a perfect chemical, biological, neurological, psychological, social, economic, and political duplicate, too. It would have to—if the physical facts fix all the facts.
Before you reject this idea of a physically duplicate region of space-time, there are two observations to be made. First, no one is saying this really happens—ever. We are using this idea to illustrate what we mean when we say that the physical facts in our little corner of the universe (and every little corner, for that matter), fix, determine, establish, create, bring about, generate (or whatever word you want to use) all the other facts about it—including the biological, psychological, and social ones that obtain here and now.
Second, as a disquieting aside, the idea that there might be a duplicate corner of a distant part of the vast universe is, I regret to say, something that a number of cosmologists actually think is physically possible and has a nonzero probability (try Googling “Boltzmann brains”). Take the arrangement of all the atoms that compose your body and, in particular, your brain. If our actual universe is infinitely large, there is a tiny probability that all the fundamental particles in some other distant but finite part of it will, just by chance, take on exactly the same arrangement as the atoms that make up your brain right now. If the universe is infinitely large, there are an infinite number of such regions, each with a tiny nonzero probability of duplicating your brain. When you add up an infinite number of such infinitesimally small but positive probabilities, the sum has to approach 1. Ergo, for any brain that exists around here and that has, for example, consciousness, it’s an almost 100 percent chance that there is a duplicate arrangement of molecules somewhere else in the universe having exactly the same conscious thoughts. Of course, if the universe is not infinite but just huge, the probability of a duplicate of you somewhere else will be smaller.
So the argument goes. I am not going to take sides on this cosmological speculation. All I can say is that