Theoretical physicist and World Science Festival co-founder Brian Greene kicked off TED 2012 last week with an 18-minute tour of the multiverse, a hypothetical collection of universes that accounts for everything in existence, past and future. Greene began his TED talk with a brief history of modern day physics and string theory—from Edwin Hubble’s landmark discovery that the universe was expanding to the recent confirmation that the expansion is speeding up, not slowing down as once thought:

...repulsive gravity, now also known as dark energy, is exactly what we need in order to explain the concept that as galaxies push away from each other, they cause the expansion to speed up, not slow down.

When the astronomers tried to work out precisely how much dark energy must be infusing space to account for cosmic speedup they found a number that is, well, “spectacularly small”. So the mystery became to explain this number. “We want it to emerge from laws of physics. But so far no one has found a way to do that,” says Greene.

Enter string theory—Greene’s particular area of expertise. String theory is a mathematical framework that calls for extra dimensions of space way too small to detect. These tiny curled up dimensions might explain the mystery of cosmic inflation. Check out the TED blog to find out how: The Multiverse in Three Parts: Brian Greene at TED2012. Video of the event will be posted as soon as it is made available.

Confused about extra dimensions? Watch Brian’s explainer: