The Universe had no unique beginning, instead, the countless “alternative worlds” of string theory may actually have existed, said Stephen Hawking of the University of Cambridge and Thomas Hertog of the European Laboratory for Particle Physics at CERN in Geneva.

We should picture the Universe in the first instants of the Big Bang as a superposition of all these possibilities, they say; like a projection of billions of movies played on top of one another.

call their theory “top-down” cosmology, because instead of looking for some fundamental set of initial physical laws under which our Universe unfolded, it starts “at the top,” with what we see today, and works backwards to see what the initial set of possibilities might have been. In effect, says Hertog, the present “selects” the past.