If, years later, I do use the slit detector to observe which way the electron went, it will mean that many years earlier the electron must have passed through one slit or the other. But if I don't use the "slit detector," then the electron must have passed through both slits. This is, of course, extremely weird. My actions at the beginning of the twenty-first century can change what happened thousands of years ago when the electron began its journey. It seems that just as there are multiple futures, there are also multiple pasts, and my acts of observation in the present can decide what happened in the past. As much as it challenges any hope of ever really knowing the future, quantum physics asks whether I can ever really know the past. It seems that the past is also in a superposition of possibilities that crystallize only once they are observed.

Like the very quantum particles we study, we must be comfortable allowing our view of the world to exist in superposition.

There are many, many, many worlds branching out at each moment you become aware of your environment and then make a choice.

Choice, is what presents us with a multitude of paths, because choice creates a flow of electrons through the brain in a manner that inexorably leads to quantum superposition, and the many-worlds that are the inevitable result.