“To apply quantum theory to the entire universe... is tricky... particles of matter fired at a screen with two slits in it... exhibit interference patterns just as water waves do.

Feynman showed that this arises because a particle does not have a unique history.

That is, as it moves from its starting point A to some endpoint B, it doesn’t take one definite path, but rather simultaneously takes every possible path connecting the two points.

From this point of view, interference is no surprise because, for instance, the particle can travel through both slits at the same time and interfere with itself.

In this view, the universe appeared spontaneously, starting off in every possible way.”