According to Feynman, a particle samples every path connecting point A and B, hence collecting information about the path to be taken. Manipulation of the experiment, e.g. closing one of the slits, will change information collected and the result observed.
The Grand Design
The laws of nature seem mysteriously crafted to allow for complex life. Scientific explanations involve the existence of multiple universes with different sets of laws. Thus, a universe with our set of laws is no more special than the unique configuration of our solar system or the very planet we live on.