The secret to time-travel

...is, of course, the donut:

In a paper published in the latest issue of the Physical Review journal, the scientist offers a theoretical model, based on mathematical equations describing conditions that, if established, could help lead to the development of a time machine of sorts. But rather than building an actual device, Ori explains that "the machine is space-time itself."

Time travel research is based on bending space-time so far that the time lines actually warp back on themselves to form a loop.

"We know that bending does happen all the time, but we want the bending to be strong enough and to take a special form where the lines of time make closed loops," explains Ori. "We are trying to find out if it is possible to manipulate space-time to develop in such a way."