In 1916, Albert Einstein published his general theory of relativity. His special theory of relativity had come first, propounded in his annus mirabilis of 1905; one of that idea’s basic premises is that the faster a clock moves, the more it slows down. (This has been demonstrated, by putting one atomic clock on a passenger jet circling the globe, while keeping another one stationary.)
FIRST FRONTIERSMAN: So far, no one has found fault with Mallett’s time-travel equations, which are based on Einstein’s general theory of relativity.
More than a decade of number-crunching later, Einstein unveiled another idea. If his special theory was concerned primarily with motion’s effect on time, his general theory had to do with gravity’s. One of the latter’s basic upshots, says UConn’s Dr. Ronald L. Mallett, is that “the stronger gravity is, the more time will slow down.”
In other words, at the earth’s surface, where gravity is stronger, time runs slower than at higher altitudes, where it’s not. This too, has been demonstrated. That’s why clocks aboard GPS satellites have to be calibrated to account for the difference — only fractions of a second, but hugely significant fractions nonetheless — between time in space and time on earth.
So there’s that: the notion that gravity can affect time. And there’s also this: whereas Isaac Newton had surmised that it was only matter that created gravity — the earth creates gravity which keeps us stuck to the ground, the sun creates gravity that keeps the earth orbiting around it — Uncle Albert had other ideas.
“In Einstein’s theory, not only can matter create gravity, light can create gravity too,” says Mallett. “Light doesn’t have mass, but light has energy. The energy of light can create gravity.”
To recap: if gravity can change time, and light can create gravity, then light can affect time.
Suddenly, Mallett felt like Archimedes in the bathtub. And, after much cogitation and scribbling, he came up with a theory of his own. “What I found was that, if you circulate beams of light” — directed light, like lasers — “it causes the empty space, around which the light is circulating, to get twisted.”
The best illustration of this is a cup of black coffee. If the liquid represents space, a stirring spoon would be akin to Mallett’s laser beams, swirling it around.
And, if that sort of causation in space could be proven, the next step would be to drop something tiny — a neutron, in Mallett’s experiment — into that twisted space, just as a sugar cube would swirl around the coffee mug. If all went according to plan, that subatomic particle would travel back in time.
“In Einstein’s theory, space and time are connected to each other,” Mallett says. “Whatever you do to space, also happens to time. So, time normally flows in a straight line, from the past to the present to the future. But as space is getting twisted around, if it gets twisted around strongly enough, what will happen is that timeline will get twisted into a loop. So you can see what’s going to happen: if you’re traveling along that loop in time, you can go from the future back to the past.”