Super-computers running a million-million cycles a second take millions of seconds (months) to simulate not just what a photon does in a million-millionth of a second, but in a million-millionth of that (Wilczek, 2008) (p113). How can these tiniest bits of the universe with no known structures make such complex choices? The answer proposed is that “a photon” is a vast set of processing instances.
Feynman’s sum over histories method predicts how light goes from A to B by calculating all the paths, then choosing the one with the least action integral (Feynman et al., 1977) p26-7. It was accepted as a method because it works but not as a theory because no physical particle can do that. Like the rest of quantum theory, it was a physical impossibility that just happened to predict perfectly.
In quantum realism, Feynman’s method works because it describes what the photon actually does. Photon instances do take all available paths and physical reality is decided down the line by the first photon restart. The instance that happens to take the fastest path to a detector reincarnates as the photon in a physical event making its path the path the photon took. The server restart makes all other instances disappear, like a clever magician removing the evidence of how a trick is done.
Indeed, how else could a law of least action arise? A photon can’t know in advance the best way to an unknown destination before it leaves, so it takes them all and picks the fastest later. In a virtual reality, calculating and taking a path are the same thing. Knowing nothing in advance, the photon simply spreads instances down every path and the first to cause an overload at a detector becomes “the photon”. What reaches a detector by the fastest route isn’t a solitary particle magically knowing the best path in advance but a quantum ensemble that explores every path and disbands when the job is done.
In quantum realism, every physical event derives from a myriad of quantum events. The quantum world tries every option and the physical world takes the best and drops the rest, so if this isn’t the best of all possible worlds, it isn’t for lack of trying. The physical law of least action comes from a quantum law of all action, that:
Everything that can happen in physical reality does happen in quantum reality.
Feynman’s “Whatever isn’t explicitly forbidden must happen” is the same as Gellman’s quantum totalitarian principle. Both imply the evolutionary physics introduced in the next chapter.