The four-dimensional frame led as if by iron necessity to the Universe Rigid. If you believed in the laws of physics in those days—and the students of the Normal School in the nation of Newton most assuredly did—then apparently the future must be a strict consequence of the past. Wells proposed to design a “Universal Diagram” by which all phenomena would be logically deduced.
One began with a uniformly distributed ether in the infinite space of those days and then displaced a particle. If there was a Universe rigid, and hitherto uniform, the character of the consequent world would depend entirely, I argued along strictly materialist lines, upon the velocity of this initial displacement.
And then? Chaos!
The disturbance would spread outward with ever increasing complication.
Edgar Allan Poe, similarly inspired by scientific speculation, wrote in 1845, “As no thought can perish, so no act is without infinite result.” In a story called “The Power of Words,” published in the Broadway Journal, he invents some angels who explain:
We moved our hands, for example, when we were dwellers on the earth, and, in so doing, we gave vibration to the atmosphere which engirdled it. This vibration was indefinitely extended, till it gave impulse to every particle of the earth’s air, which thenceforth, and for ever, was actuated by the one movement of the hand. This fact the mathematicians of our globe well knew.
The actual mathematician Poe had in mind was the arch-Newtonian Pierre-Simon, Marquis de Laplace, for whom the past and the future were nothing more or less than physical states, rigidly connected by the inexorable mechanics of the laws of physics. The present state of the universe (he wrote in 1814) is “the effect of its past and the cause of its future.” Here is the Universe Rigid:
Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective positions of the beings which compose it, if moreover this intelligence were vast enough to submit these data to analysis, it would embrace in the same formula both the movements of the largest bodies in the universe and those of the lightest atom; to it nothing would be uncertain, and the future as the past would be present to its eyes.
Some people already believed in such an intelligence; they called it “God.” To Him nothing would be uncertain or unseen. Doubt is for us mortals. The future, as the past, would be present to His eyes. (Or would it? Perhaps God would be content to see creation unfold. Heaven’s virtues might include patience.)
This one sentence by Laplace has more enduring life than the rest of his work combined. It pops up again and again in the philosophizing of the next two centuries. Whenever anyone starts talking about fate or free will or determinism, there is the marquis again. Jorge Luis Borges mentions his “fantasies”: “that the present state of the universe is, in theory, reducible to a formula, from which Someone could deduce the entire future and the entire past.”
The Time Traveller invents “an omniscient observer”:
To an omniscient observer there would be no forgotten past—no piece of time as it were that had dropped out of existence—and no blank future of things yet to be revealed. Perceiving all the present, an omniscient observer would likewise perceive all the past and all the inevitable future at the same time. Indeed, present and past and future would be without meaning to such an observer: he would always perceive exactly the same thing. He would see, as it were, a Rigid Universe filling space and time—a Universe in which things were always the same.fn4
“If ‘past’ meant anything,” he concludes, “it would mean looking in a certain direction; while ‘future’ meant looking the opposite way.”
The Universe Rigid is a prison. Only the Time Traveller can call himself free.
Your body moves always in the present, the dividing line between the past and the future. But your mind is more free. It can think, and is in the present. It can remember, and at once is in the past. It can imagine, and at once is in the future, in its own choice of all the possible futures. Your mind can travel through time!
—Eric Frank Russell (1941)
CAN YOU, citizen of the twenty-first century, recall when you first heard of time travel? I doubt it. Time travel is in the pop songs, the TV commercials, the wallpaper. From morning to night, children’s cartoons and adult fantasies invent and reinvent time machines, gates, doorways, and windows, not to mention time ships and special closets, DeLoreans, and police boxes. Animated cartoons have been time traveling since 1925: in “Felix the Cat Trifles with Time,” Father Time agrees to send the unhappy Felix back to a faraway time inhabited by cavemen and dinosaurs. In a 1944 Looney Tunes episode, Elmer Fudd dreams his way into the future—“when you hear the sound of the gong it will be exactly 2000 AD”—where a newspaper headline reveals, “Smellevision Replaces Television.” By 1960 Rocky and His Friends was sending the dog Mr. Peabody and his adopted boy, Sherman, through the WABAC Machine to straighten out William Tell and Calamity Jane, and the next year Donald Duck made his first trip into prehistory, to invent the wheel. “Wayback Machine” became a thing, so a sitcom character says, “Dave, don’t mess with a man with a Wayback Machine—I can make it so you were never born.”
Children learn about “time whirlwinds” and “time-travel stones.” Homer Simpson accidentally turns a toaster into a time machine. No explanation is necessary. We’ve outgrown the need for professors expounding on the fourth dimension. What’s not to understand?
China’s official State Administration of Radio, Film, and Television issued a warning and denunciation of time travel in 2011, concerned that such stories interfere with history—“casually make up myths, have monstrous and weird plots, use absurd tactics, and even promote feudalism, superstition, fatalism, and reincarnation.” Indeed. Global culture has absorbed the tropes of time travel. In The Onion, a photograph of a man with a futuristic-looking e-cigarette occasions an article about a time-traveling “soldier of fortune with off-world military training.” People can work out his whole story just by looking at him. “Judging by his cool, calm demeanor and the fact that he was inhaling what looked like e-fumes from some kind of shiny black mecha-cigarette, I’m just going to assume this guy has journeyed here from hundreds of years in the future to apprehend a dangerous digi-convict of some kind,” says an onlooker. “Imagine his knowledge of future events. He could probably share information about so many astounding secrets if we dared ask.” Others reckon his sunglasses hide advanced ocular cybernetics and that he’s traversing the space-time continuum armed with a pulse rifle or particle cannon. “Further sources speculated, with growing alarm, that the man’s very presence in the bar might somehow cause an irreversible temporal paradox of some kind.”
Nor does time travel belong solely to popular culture. The time-travel meme is pervasive. Neuroscientists investigate “mental time travel,” more solemnly known as “chronesthesia.” Scholars can hardly broach the metaphysics of change and causality without discussing time travel and its paradoxes. Time travel forces its way into philosophy and infects modern physics.
Have