Theorizing that one could time travel within his own lifetime...

Physicist Ronald Mallett wants to build a time machine.

Mallet's proposal seems innocuous enough: He's currently designing a table-top experiment using a ring of high-powered lasers. The idea is that light carries energy, and, as Einstein showed, energy is equivalent to mass - therefore beams of light can distort spacetime, just as large masses do. (The warping of spacetime by large masses was the prediction that made Einstein famous; the idea was confirmed when starlight was seen to be displaced by our sun during a solar eclipse in 1919.)

Inside Mallett's circle of laser beams, empty space would become "twisted" in much the same way that milk in a coffee cup begins to swirl when the coffee is stirred. If the beams of light are intense enough, the warping of space and time close to the beams could be severe enough to create a "loop" in time, Mallett says.

But don't buy a gun to shoot your granddaddy just yet.

Mallett's work has brought mixed reactions. The head of his department at the University of Connecticut, William Stwalley, told New Scientist that although he was intrigued by the challenges of the experimental design, making any sort of time machine "seems like a distant improbability." Two physicists at Tufts University, meanwhile, recently wrote a critique of Mallett's theory, suggesting that any closed timelike curves he creates would need to be bigger "than the radius of the visible universe."