And an infinite space doesn’t contain only exact copies of you. It contains many more people who are almost like you, yet slightly different. So if you were able to go meet the closest person out there in space who looked like your spitting image, this person would probably speak an alien language you couldn’t understand and would have experienced a life quite different from yours. But out of all your infinitely many look-alikes out there on other planets, there’s also one who speaks English, lives on a planet identical to Earth, and has experienced a life completely indistinguishable from yours in all ways. This person subjectively feels exactly like you feel. Yet there may be some very minor difference in how the particles move in your alter ego’s brain that’s too subtle to make a perceptible difference now, but which in a few seconds will make your alter ego put this book aside while you read on, causing your two lives to start diverging.