Time Travel: A Writer's Guide to the Real Science of Plausible Time Travel

Introduction

INTRODUCTION It is sofull of invention and the invention is so wonderful. . . it must certainly make your reputation. from an 1894 letter by the editor of the New Review to H.G. Wells, commenting on the not-yet-published The Time Machine. "The science of time travel?" you ask with a smile. IVe got to be kidding, right? Everybody knows time travel is impossible because of something called paradox (something or other about killing your grandfather—or is it your nephew—before he has had a chance to create your mom or dad). Oh, sure, you'll admit that maybe you can travel into the future if you zip around the cosmos in a very fast rocketship. (Didn't Einstein prove that? Or maybe you saw it on TV's Nova.) Nevertheless, if you're honest you'll admit that even if Einstein did say that was OK, it still sounds pretty odd. But no way, you'll insist, could anyone travel into the past. Probably every physicist alive would have agreed with you on this issue twenty-five years ago. Here's what one wrote, for example, in a 1971 issue of the scholarly journal Studium Generate (David Park, "The Myth of the Passage ofTime"): Let us consider time travel in the manner of H.G. Wells. Suppose that I were really to travel in time back to my fifth birthday. Here are some children sitting around a table. I am five years old and know nothing of the time machine in my future. If I really go back, then all traces of my interveningyears, inside and outside me, aregone. (The italics are my emphasis. How this logic works escapes me, and Professor Park offers no explanation.) There is nothing remarkable about the birthday party. It is indistinguishable from the original one; in fact, it isthe original 2 Time Travel one. There are no consequences to time travel. A statement that time travel can, or cannot, or does, or does not take place is unverifiable and therefore, in my logic as a physicist,meaningless . What is usuallycalled time travel should be called lack of time travel; Wells's picture is that I take my present mind back to past events. This I take to be fiction. Up until recent years even the most speculative, wild-eyedphysicist wouldhave agreed with this skeptical reaction (one, I will claim as we go through this book, that has no connection at allwith physics ). The only place you could find people writing positively about time travel and time machines was in science fiction, and even science fiction writers didn't really believe the concept was anything more than a fantasy.They wrote time travel stories because readers loved the idea, and editors would pay for what the writers produced; but that didn't mean time travel might actually be possible. This was in distinct contrast to, for example, stories about space travel. Traveling to the moon, or Mars or even the nearest star would clearly be a very big engineering job, but it wouldviolate no known laws of physics. But time travel?No, that was just nonsense, fairy tale stuff. But now it's time to reevaluate. The real world is starting to look more like science fiction than the science fiction pulps ever did. Once, "computer brains" existed onlyon the pages ofthe pulps; now every other high school kid inAmericahas one inthe bedroom connecting him or her to the Internet. Once, trips into space were ridiculed as simply escapist twaddle, but now the space shuttle rumbles up to orbit and back on a regular schedule (and each time gets maybe thirty seconds of notice on CNN). And, once, talk of time travel was pretty far out even for science fiction, but now the theory of time machines is regular fare in the most important physics journals, in articles by some of the very best physicists in the world. Today, a writer of science fiction who wants to use high-tech stuff like computers or space travel in a story has to constantly keep in mind that modern readers are not the teenage boys of the 1930s Introduction 3 that kept Thrilling Wonder Stones and Amazing Stories in business. Today's readers know all about (or at least think they know all about) computer operating systems, high-speed electronics, Newton's laws of motion, the biochemistry of DNA, and certainly that a...