What would you do if you had a pastward time machine? I've personally narrowed down my options to: a) going back to 2000 and redesigning the Florida "butterfly ballot," b) going back a couple of millennia to strongly suggest fireproofing the Library at Alexandria, or c) going back just a few years to prevent the rise of day-glo gardening clogs as acceptable public footwear. But of course, since time travel mostly rests safely in the SF drop file next to alien princesses and intelligent life on Mars, that's neither here nor there. That notion, however, is changing.
Pastward time travel (as opposed to futureward, which is entirely workable according to Einstein—see sidebar "Arriving Then, Now") might just be possible. That's the good news. The bad news is that, if it's possible, it requires amounts and types of energy our civilization isn't likely to possess for, say, at least a few thousand years. (Unless, that is, there's a enterprising inventor out there already with a practical method for creating and lassoing wormholes or generating a few suns' worth of energy.)
David Toomey, a UMass-Amherst professor of technical and nonfiction writing, explores the recent history of scientific inquiry into time travel in his book The New Time Travelers. That modern history began in earnest in the '80s, when, as Toomey explains, the cautious veneer of respectability scientists had hitherto grafted onto their experimentation (and their grant requests) was discarded in favor of openness. Toomey reports that the 1988 paper that changed cautious, smokescreen language like "causality violation" to more traditionally science fiction-y terms was called "Wormholes, Time Machines and the Weak Condition," by Michael Morris, Kip Thorne and Ulvi Yurtsever.
Toomey's book is engaging—such mind-boggling subjects aren't easily explained, but Toomey manages to take the details of esoteric physics inquiry and render them in easily understood, straightforward prose. The history of a bunch of people who spend their time puzzling over the "Copenhagen interpretation" could be stultifying, but, though it has its more tedious minutiae, the wildness of the frontiers of such thought and the ideas of scientists who thrive there prove fruitful narrative ground.
The Advocate recently spoke to Toomey about negative energy, wormholes and paradoxes.
Advocate: How has the book been received so far?
David Toomey: The Guardian and the Financial Times did nice reviews, as did the journal Nature, which is kind of important to me, because, as an English Ph.D., I was somewhat concerned that the physicists themselves might find errors.
How did you get interested in these serious inquiries into time travel?
I was reading another book, another "physics for the lay person" book. It had mentioned, almost in passing, that theoretical physicists were taking the subject of time travel seriously, and they'd written a number of papers on it. … No one had done a survey of the history of the study.
What do you think is the most plausible scenario these scientists have envisioned?
I think many of the physicists remain agnostic on that, and I would defer to them. All of [the proposals] require massive amounts of negative energy, which is maybe impossible to produce in the quantities necessary. All the scenarios are well beyond our technology and would require a technology of some super-civilization. But that doesn't mean they're impossible. The question becomes, " Is it a physical problem, or is it merely an engineering problem?" It may be merely a very difficult engineering problem.
What's "negative energy"?
Negative energy is a kind of anti-gravity that has been measured indirectly, and it is possible to produce in very, very small amounts at very great cost, and only for very, very short periods. All the time machines described by theoretical physicists would require great amounts of it for at least as long as it would take to hold the mouth of a wormhole open long enough for someone or something to get through.
How, as a writer, do you get such difficult subjects into easily understood form?
You put yourself in the place of the reader. You think about them a lot; you explain them out loud to friends. You try to find a metaphor, and, in most cases, when you've found the right metaphor, you know it. Something clicks, and there you go.
Physicists tend to be good writers, I'm finding. They tend to have advantages over other fields in that most of the time, the vocabulary doesn't change. What Newton meant by energy and mass is pretty much what we mean by energy and mass, so that helps a lot.
Do you think any of the classic paradoxes threaten to make all these thought experiments moot?
Well, there's the question! I think a minority of physicists think that the Grandfather Paradox is the show-stopper. And the Grandfather Paradox is that if I go back in time and kill my grandfather, then he could not have lived to sire my father and sire me, therefore I won't have lived to go back in time and kill my grandfather, therefore my grandfather will live, and therefore, and all that. So it seems to present an irresolvable paradox.
The physicist who put forth an idea on how to get around that is Igor Novikov, a Russian-born theoretical physicist. His idea was that nature is self-consistent and that I may be able to go back in time, that I can't kill my grandfather doesn't mean it's impossible for me to go back in time. It just means it's impossible for me to kill my grandfather. This is the view of a lot of time travel movies—you go back to the Civil War, and you really are traveling pastward in time, but you can't change anything. You can't save Abraham Lincoln's life; you can't kill Hitler at birth. But you will have been there, and then the movies come back and you see a picture on the mantelpiece and you never noticed your face is in there among the others.
Do you think Stephen Hawking's intuition that the laws of physics just won't allow for such stuff to happen (the "chronology protection conjecture") will prove correct?
Einstein used to say about a theory that it "smells right" or "smells wrong." And Einstein was known for that intuition, as is Hawking. Hawking modestly calls it a conjecture, and it is only a conjecture. He's proposed a couple of different mechanisms for this conjecture, but it's a long way from anything like a proof.
Any time machine creates a space where time travel is possible, separate from a space where it's impossible, and there's a boundary. It is what's going on at the boundary on very small scales, subatomic scales, that will determine whether it's possible. We can't get to those scales without a Theory of Everything. Something like what String Theory might be. The upshot is we'll have to have a Theory of Everything, sometimes called a Theory of Quantum Gravity, before we know whether time travel is possible.
What are you writing about next?
I'm moving more definitely into science writing. I'm going to be writing about a subject in astrobiology, something called weird life, which is theoretical biology, life that doesn't use DNA or amino acids or proteins.
The biologists themselves don't have a really good definition of life. I may spend a chapter talking about that. It's curious to me that it doesn't bother them that they don't have a definition—they just go on with the work.
Futureward time travel is accepted as a reality, through going, basically, really fast. How fast do you need to go to move into the future faster than everyone else?
You'd have to go pretty close to the speed of light. If you and I are sitting on a park bench and I get up and walk around and sit down again, I'm going to be younger relative to you than I would have been had I stayed on the bench. As we all move relative to each other, we're all traveling futureward in time at different rates. I suppose the human being who has traveled into the future furthest—or the human beings—would be the astronauts and cosmonauts who've been on the international space station the longest, and that's flying at, I think, 18,000 mph. If you do that for a year, upon your return to earth you will be maybe a second younger. You've got to go pretty fast!