The Physics of Time Travel

By Jennifer Ghandhi

Perry Gerakines says it should be possible to travel backward through time—theoretically.

The ability to travel through time seems to be one of humankind’s favorite fantasies, an object of fascination for scientists and artists alike. But UAB physicist Perry Gerakines, Ph.D., is ready to go on the record that this science-fiction staple is already science fact. “We are traveling in time right now,” he says with a grin—“at a rate of one second per second.”

As for larger leaps through time, Gerakines says that Albert Einstein’s special theory of relativity, which describes the motion of particles traveling at close to the speed of light, does indeed open the door to time travel through physics. For example, imagine you’re an astronaut on a ship traveling nearly as fast as the speed of light. When you return to earth after what to you felt like a few weeks, you would discover that a few centuries had passed for those left behind. (Observers watching from the ground would see your ship’s clock moving very slowly.)

Traveling backwards in time would be more difficult, but this concept also relates to relativity. “One of the ideas behind relativity is that time is a dimension just like any of the space dimensions,” says Gerakines. So just as there are three mathematical space dimensions—basically length, width, and height—there should also be more time dimensions. “For some reason, we’re going in just one direction in time,” he says. “But theoretically, it should be possible to go in the other direction, or to somehow change your coordinate system so that you go from one part of our universe to another one where the time coordinate is rotated.”

One theory for switching time dimensions involves black holes, where matter exerts such a strong gravitational force that anything nearby is pulled toward its center. In practical terms, you can travel in only one space direction inside a black hole—toward the center. That is similar to how time operates on earth, Gerakines says. “There’s a black hole of time, and we’re all heading toward the singularity,” he says. “If you could suddenly go into a black hole and come back in a different time direction,” you might be able to travel backward in time.

But will leaping forward or backward in time ever be practically possible, even if it’s theoretically possible? “Physicists have thought it up,” Gerakines says. “It’s an engineering problem after that. Somebody else can build it.”