A new book takes a hard look at the physics behind the possibility of time travel
Who hasn’t dreamed of time travel, going back in time and saying the right thing instead of the wrong thing, seeing Lincoln give the Gettysburg address—or buying Apple stock when it was $10 a share? Many a science fiction novel and TV show are premised on just that possibility, and we happily suspend disbelief, at least for the moment, before landing back in the here and now.
For a few scientists, time travel and its cousin, warp drive—spacecraft traveling faster than the speed of light—are intriguing indeed. Tufts faculty have occasionally taught courses on just those topics primarily for non-science majors to learn more about the laws of physics.
Now a new book, Time Travel and Warp Drives (University of Chicago Press), by Allen Everett, professor emeritus of physics and astronomy in the School of Arts and Sciences, explores the potential of dipping back to another century. He and co-author Thomas Roman, a professor at Central Connecticut State University, delve into the physics of time travel, and as you might expect, it’s much more complicated than Star Trek or Robert Heinlein would have you think.
Everett, who taught at Tufts for 42 years before retiring in 2002, opens with a bold move: he doesn’t dismiss the idea of warp speed or time travel. He explains the physics and the common sense objections to both notions, but allows that given some very specific conditions—and advances in scientific knowledge—either could be possible, even if the probability is still infinitesimal.
Allen Everett taught at Tufts for 42 years before retiring in 2002. Photo: Joanie Tobin“I wasn’t going to do anything with it, but one of my former graduate students, who’d gotten his Ph.D. with me, dragged me kicking and screaming into getting interested in the idea, and afterwards I was glad he did,” Everett says. “We worked together on it for three or four years and published articles on the idea of tachyons.”
Over the subsequent decade, as scientists found more inconsistencies in the tachyon theory, public interest in those particles faded. But that didn’t stop the theorizers. Now wormholes, portals to travel through time, are captivating popular imagination.
To picture how a wormhole might work, tunneling from one location in the space-time continuum to another, think of two sheets of paper, laid one on top of the other, Everett explains. Each sheet represents the spatial universe at different times, say 100 years apart.
“Picture making a hole in the two sheets of paper and gluing them together,” he says. “Now, if you want to go from one point on sheet number one to sheet number two, you can wait around for a century. Or you could go much more quickly by going through the hole, which may have a much shorter internal distance.”
Einstein’s general theory of relativity “leaves open at least the possibility that you can construct such an arrangement,” according to Everett. But to do that, you have to have a region of space where the energy density is negative (don’t ask for an explanation, it would take too long).
Physicists can show that there are states of matter where the energy is negative, “but it’s not entirely clear how you would go about creating one of these states,” says Everett. In other words, he says with a laugh, “You can’t rule out the possibility of wormholes—but the probability, that is another question.” (There is also Stephen Hawking’s chronology protection conjecture, which states that if you build a time machine, it will blow itself up when it you turn it on.)
Warp Factor 2
And then there are warp drives. You might remember Captain Kirk (or Picard, if you’re a later Star Trek fan) giving the command to engage at warp factor 2 on the starship Enterprise. You’d need to do that—zip much faster than the speed of light—to get from one star system to another.
Over the years, physicists have tried to think up ways to achieve warp speeds, and Everett spends a good amount of Time Travel and Warp Drives explaining the physics of how that can—and cannot—happen. Getting through the details in the book isn’t the easiest going: you need to remember your high school or college algebra, and the authors clearly violate Stephen Hawking’s law of physics publishing, which postulates that for each equation you include, you lose half your readers. (The really serious math, though, is relegated to seven appendices.)
While it is true that you can’t move faster than the speed of light relative to your immediate surroundings, Everett says that one potential solution that makes warp drives possible is “to construct distributions of matter that produce a bubble of space that moves at arbitrarily high speeds relative to distant observers.”
Translated, that means some form of matter that we currently don’t know about might be able to burst through space going faster than the speed of light. So if a starship Enterprise had such a bubble of matter surrounding it, the spaceship itself would be moving at less than the speed of light—and maybe not moving at all relative to the interior of the bubble. But people far away outside the bubble would see the bubble with the Enterprise in it moving at arbitrarily high speeds.
Freezing Time
If all these ideas are more theoretical than practical, there’s one method of time travel that involves more biology than physics. You could do what legendary Red Sox slugger Ted Williams did: have yourself cryogenically preserved, with instructions to bring yourself back to life at some time in the future.
“The point is, your body is a kind of clock,” Everett says. “If you could cool your body to the temperature of liquid helium, say, your heart would beat much more slowly, so in effect, you would age much more slowly. When you wake up at the other end, you would be more or less the same biological age.”
If your objective is to know what the world will be like in 200 years, he says, this method could help you to do that—presuming the biology would allow it and the world as you know it is around to be enjoyed.
Taylor McNeil can be reached at taylor.mcneil@tufts.edu.
