For Paul Steinhardt and Neil Turok, the Big Bang ended on a summer day in 1999 in Cambridge, England. Sitting together at a conference they had organized, called "A School on Connecting Fundamental Physics and Cosmology," the two physicists suddenly hit on the same idea.

For decades, physicists have accepted the notion that the universe started with the Big Bang, an explosive event at the literal beginning of time. Now, computational physicist Neil Turok is challenging that model -- and some scientists are taking him seriously.