One of the annoying/fascinating things about quantum mechanics is the fact the world doesn't seem to be quantum-mechanical. When you look at something, it seems to have a location, not a superposition of all possible locations; when it travels from one place to another, it seems to take a path, not a sum over all paths. This frustration was expressed by no lesser a person than Albert Einstein, quoted by Abraham Pais, quoted in turn by David Mermin in a lovely article entitled "Is the Moon There when Nobody Looks?":
I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I looked at it.
The conventional quantum-mechanical answer would be "Sure, the moon exists when you're not looking at it. But there is no such thing as `the position of the moon' when you are not ...
