Time Travel: A History (28 page)

The hero (if that’s what he is) carries out a mission not of his choosing. His masters send him not only to the past but then to the future, too. Humans have survived, and so, concealing his eyes behind military-style sunglasses, he begs them to do what is necessary to enable their own existence. They must help, he says. They must: their very survival proves it. Here is paradox again: the narrator says, “This sophism was taken for fate in disguise.” When he returns to the past, as we know he must—
somewhere inside him, the memory of a twice-lived fragment of time
—his destination is Orly Airport. It is Sunday. He knows that the woman will be at the end of the pier. The wind ruffles her hair. She almost smiles. As he runs toward her, it occurs to him that somewhere, too, holding on to the railing, will be the child he once was. And then:
There was no way to escape Time.
He understands.
On ne s’évadait pas du Temps.
The future has followed him here. Only at the last instant does he realize whose death he had witnessed as a child.

*1
A rebellious elector in Virginia refused to cast his ballot for the vote winners, Richard Nixon and Spiro Agnew, in 1972 and voted instead for John Hospers, on the Libertarian line.

*2
Gödel’s proof “is more than a monument,” said John von Neumann, “it is a landmark which will remain visible far in space and time….The subject of logic has completely changed its nature and possibilities with Gödel’s achievement.”

*3
Also, the Gödelian universe does not expand, whereas most cosmologists are pretty sure that ours does.

*4
Gödel’s biographer Rebecca Goldstein remarked, “As a physicist and a man of common sense, Einstein would have preferred that his field equations excluded such an Alice-in-Wonderland possibility as looping time.”

*5
The Heinlein story inspired a 2014 film,
Predestination,
with Ethan Hawke and Sarah Snook playing instances of the time traveler.

*6
Wells might have admired this descriptive flourish: “The general impression which the contrivance gave was that of unreality. The right-angles, at which various bars joined each other, did not seem to be quite ninety degrees. The perspective was distinctly off; for regardless from which side one viewed it, the more distant side always seemed to be the larger.”

*7
Ralph Milne Farley, “The Man Who Met Himself” (1935). Of course the man is in a ten-year loop, too. He uses the time to make money in the stock market.

*8
Rudy Rucker, a mathematician and, later, an author of science fiction.

*9
The self-description he ultimately settled on: “filmmaker, photographer, traveler.”

TWELVE

What Is Time?

Why is it so difficult—so degradingly difficult—to bring the notion of Time into mental focus and keep it there for inspection? What an effort, what fumbling, what irritating fatigue!

—Vladimir Nabokov (1969)

PEOPLE KEEP ASKING
what time is, as if the right combination of words could slip the lock and let in the light. We want a fortune-cookie definition, a perfect epigram. Time is “the landscape of experience,” says Daniel Boorstin. “Time is but memory in the making,” says Nabokov. “Time is what happens when nothing else does”—Dick Feynman. “Time is nature’s way to keep everything from happening all at once,” says Johnny Wheeler or Woody Allen. Martin Heidegger says, “There is no time.”
^*1

What is time?
Time
is a word. The word refers to something, or some things, but surprisingly often the conversation goes off track when people forget whether they’re arguing about the word or the thing(s). Five hundred years of dictionaries have created the assumption that every word must have a definition, so what is time? “A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future” (
American Heritage Dictionary of the English Language,
fifth edition). A committee of lexicographers labored over those twenty words and must have debated almost every one. Nonspatial? That word is not to be found in this very dictionary, but all right, time is not space. Continuum? Presumably time is a continuum—but is that known for sure? “Apparently irreversible” seems a hedge. You sense they’re trying to tell us something they hope we already know. The challenge is not so much to inform us as to offer some discipline and care.

Other authorities offer entirely different constructions. Not one of them is wrong. What is time? “The general term for the experience of duration,” according to the
Encyclopaedia Britannica
(many editions). The very first English dictionary, Robert Cawdrey’s in 1604, avoided the problem and skipped right from
thwite
(“shave”) to
timerous
(“fearefull, abashed”). Samuel Johnson said “the measure of duration.” (And duration? “Continuance, length of time.”) A 1960 children’s book trimmed the definition to a single word:
Time Is When.
^*2

The people who compose definitions for dictionaries try to avoid the circularity that comes when they use the very word they are defining. With time it’s unavoidable. The lexicographers of the
OED
throw up their hands. They divide “time” (only the noun, not the interjection
^*3
or the obscure conjunction) into thirty-five distinct senses and almost a hundred subsenses, including:
a point in time; an extent of time;
a specific period of time;
time available…;
the amount of time taken up by something;
and
time viewed as a medium through which travel into the past or future is hypothesized or imagined to be possible.
(“Cf.
time travel.
”) They are covering all the bases. Perhaps their best effort is sense number ten: “The fundamental quantity of which periods or intervals of existence are conceived as consisting, and which is used to quantify their duration.” Even that definition merely postpones the circularity.
Duration,
period,
and
interval
are defined in terms of time. The lexicographers know very well what time is, until they try to define it.

Like all words,
time
has boundaries, by which I don’t mean hard and impenetrable shells but porous edges. It maps weirdly between languages. A Londoner might say, “He did it fifty times, at the very least,” while in Paris, where the word for time is
temps,
fifty times is
cinquante fois.
Meanwhile, when the weather is good, the Parisian says,
C’est beau temps.
A New Yorker thinks the time and the weather are different things.
^*4
And that is just the beginning. Many languages use a separate word to ask “What is the time?” as opposed to “What is time?”

In 1880 the United Kingdom enacted a legislative definition of time, the Statutes (Definition of Time) Act. This declared itself to be “an Act to remove doubts as to the meaning of Expressions relative to Time occurring in Acts of Parliament, deeds, and other legal instruments.” It was enacted “by the Queen’s most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal [Time Lords!], and Commons.” If only these wise men and woman could have solved the problem by fiat. Removing doubts about the meaning of time is an ambitious goal. Alas, it turns out that they were not dealing with
What is time?
but only
What is the time?
The time in Great Britain, as defined by the act, is Greenwich mean time.
^*5

What is time? At the dawn of the written word, Plato struggled with the question. “A moving image of eternity,” he said. He could name the parts of time: “days and nights and months and years.” Moreover:

When we say that what has become is become and what becomes is becoming, and that what will become is about to become and that the nonexistent is nonexistent—all these are inaccurate modes of expression. But perhaps this whole subject will be more suitably discussed on some other occasion.

Here Aristotle, too, found himself in difficulties. “To start, then: the following considerations would make one suspect that it either does not exist at all or barely, and in an obscure way. One part of it has been and is not, while the other is going to be and is not yet.” The past has gone out of existence, the future has not yet been born, and time is made up of these “things which do not exist.” On the other hand, he said—looked at differently—time seems to be a consequence of change, or motion. It is “the measure” of change.
Earlier
and
later,
faster
and
slower
—these are words that are “defined by” time.
Fast
is a lot of motion in a little time,
slow
is a little motion in a lot of time. As for time itself: “time is not defined by time.”

Later, Augustine, like Plato, contrasted time with eternity. Unlike Plato, he could hardly stop thinking about time. It obsessed him. His way of explaining was to say that he understood time very well, until the moment he tried to explain. Let us reverse Augustine’s process: stop trying to explain and instead take stock of what we know. Time is not defined by time—that needn’t paralyze us. When we leave aside the search for epigrams and definitions, it turns out we know a great deal.
^*6

—

WE KNOW THAT
time is imperceptible. It is immaterial. We cannot see it, hear it, or touch it. If people say they perceive the passing of time, that’s just a figure of speech. They perceive something else—the clock ticking on the mantel, or their own heartbeat, or other manifestations of the many biological rhythms below the level of consciousness—but whatever time is, it lies outside the grasp of our senses. Robert Hooke made this very point to the Royal Society in 1682:

I would query by what Sense it is we come to be informed of Time; for all the Information we have from the senses are momentary, and only last during the Impressions made by the Object. There is therefore yet wanting a Sense to apprehend Time; for such a Notion we have.
^*7

Yet we experience time in a way that we do not experience space. Close your eyes, and space disappears: you may be anywhere; you may be big or small. Yet time continues. “I am listening not to Time itself but to the blood current coursing through my brain, and thence through the veins of the neck heartward, back to the seat of private throes which have no relation to Time,” says Nabokov. Cut off from the world, with no sensory perception, we may still count the time. Indeed, we habitually quantify time (“…and yet we conceive of it as a Quantity,” said Hooke). This leads to a plausible definition:
Time is what clocks measure.
But what is a clock?
An instrument for the measurement of time.
^*8
The snake swallows its tail again.

Once we conceive of time as a quantity, we can store it up, apparently. We save it, spend it, accumulate it, and bank it. We do all this quite obsessively nowadays, but the notion is at least four hundred years old. Francis Bacon, 1612: “To choose Time, is to save Time.” The corollary of saving time is wasting it. Bacon again: “Prolix and florid Harangues…and other personal Speeches are great Wasters of Time.” No one would have begun thinking about time as a bankable commodity who was not already familiar with money.
Time hath, my lord, a wallet at his back, / Wherein he puts alms for oblivion.
But is time really a commodity? Or is this just another shabby analogy, along with time the river?

We go back and forth between being time’s master and its victim. Time is ours to use, and then we are at its mercy.
I wasted time, and now doth time waste me,
says Richard II;
For now hath time made me his numbering clock.
If you say that an activity
wastes
time, implying a substance in finite supply, and then you say that it
fills
time, implying a sort of container, have you contradicted yourself? Are you confused? Are you committing a failure of logic? None of those. On the contrary, you are a clever creature, when it comes to time, and you can keep more than one idea in your head. Language is imperfect; poetry, perfectly imperfect. We can occupy the time and pass the time in the same breath. We can devour time or languish in its slow-chapp’d power.

Newton, who invented the idea of mass, knew that time didn’t have any, that it’s not a substance, yet he said that time “flows.” He wrote this in Latin:
tempus fluit.
The Romans said
tempus fugit,
time flees, or at any rate that motto began appearing on English sundials in the Middle Ages. Newton would have seen that. True, the hours speed by and are gone, once we learn to measure them, but how can time flee? It’s another figure of speech. And how can time flow, if it has no substance?

Newton took pains to distinguish two kinds of time. We might call them physical time and psychological time, but he lacked those words, so he had to struggle a bit. The first kind he called, with a flurry of adjectives, “time absolute true and mathematical” (
tempus absolutum verum & Mathematicum
). The other was time as conceived by the common people—the
vulgus
—and this he called “relative” and “apparent.” True time—mathematical time—he inferred from a technological feature of his world, the consistency of clocks. He and the clockmakers both leaned on Galileo here—it was Galileo who established that a swinging pendulum of a given length divides time into regular pieces. He measured time by using his pulse. Shortly thereafter, doctors began using clocks to time pulses. The ancients looked to the heavens for measuring time: the sun, the stars, the moon—those were reliable. They gave us our days, months, and years. (When Joshua needed more time to smite the Amorites, he asked God to halt the sun and moon in their tracks—“Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon.” Who among us has not wanted to stop time?) Now machinery takes over the reckoning.