In quantum mechanics, the path a photon of light takes is not the only path it takes, merely the most likely path it would take. In order to calculate properties of the light, all the possible paths must be considered, not just the most likely.
Stephen Hawking and Thomas Hertog proposed the same approach for the progression of the universe through time. The suggestion is that the Universe takes many paths through time and that the reality we live in is merely the most probable. In order to fully describe the universe though, all paths must be considered. It makes my head hurt just thinking about it.
'Cure' for the headache
