Using math to investigate possibility of time travel

After some serious number crunching, a researcher says that he has come up with a mathematical model for a viable time machine: a Traversable Acausal Retrograde Domain in Space-time (TARDIS). He describes it as a bubble of space-time geometry which carries its contents backward and forwards through space and time as it tours a large circular path. The bubble moves through space-time at speeds greater than the speed of light at times, allowing it to move backward in time.

(via WSJ)