My branes hurt.

Theoretical physics is confusing.

[S]tring theory requires the universe to have at least 10 dimensions, as opposed to the usual three in space and one in time that we perceive. "In string theory you learn one thing—you are in higher dimensions," says string theorist Burt Ovrut of the University of Pennsylvania. "Then the question is, where does our real world come from? That's a damn good question."

Paving the way for an answer in 1995 were Petr Horava, then at Princeton University, and Ed Witten of Princeton's Institute for Advanced Studies, who showed that strings could also exist in a more fundamental, 11-dimensional theory. They collapsed one of these dimensions mathematically into a minuscule line, yielding an 11-dimensional spacetime, flanked on either side by two 10-dimensional membranes, or branes, colorfully dubbed "end of the world" branes. One brane would have physical laws like our own universe. From there, Ovrut and colleagues reasoned that six of those 10 dimensions could be made extremely small, effectively hiding them from everyday view and leaving the traditional four dimensions of space and time.

Early in 2001, cosmologists Justin Khoury and Paul Steinhardt of Princeton, another inflationary pioneer, Neil Turok of the University of Cambridge, and Ovrut put their branes to work on the big bang. By turning back the clock in string theory, they found that as our universal brane passed through its starting singularity in reverse, it went suddenly from a state of intense but finite heat and density to one that was cold, flat and mostly empty. In the process, it shed another kind of brane into the 11-dimensional gap. Run forward in time, the big bang appeared as nothing more than two branes smacking into each other like cymbals.

[...]

The branes' oscillating motion would work to pump space into our universe like a bellows, explaining the acceleration that we see today. So "when you ask why is the universe the way it is," Turok explains, "well, it's because it has to be that way in order to repeat the next time around."

Uhhh, I like cheeseburgers.