people view time.
The opposing view, argued for centuries by other smart people such as Immanuel Kant, is that time is not an actual entity. It is not a kind of “container” that events “move through.” In this view, there is no flow to time. Rather, it’s a framework devised by human observers as they attempt to give organization and structure to the vast labyrinth of information whirling in their minds.
If this latter view is true, and time is only a kind of intellectual framework along the lines of our numbering systems or the way we order things spatially, then it certainly cannot be “traveled,” nor can it be measured on its own.
This means that clocks do not determine or keep track of time, but merely offer evenly spaced events as one digital number is replaced by another, or a minute hand is now here and now there. While these events proceed, other reliable rhythms simultaneously unfold elsewhere. And, of course, the lengths between each tick and tock are arbitrary, having been agreed upon by human council rather than some decree of nature.
The tick-tock idea began with Sun-based changes observed by people occupying a far more outdoorsy world than today’s. Sumerians and Babylonians more than six thousand years ago utilized the concepts of “day” and “year” and “month.” Soon after, the ancient Hindus defined specific units of time such as the kālá, which corresponds to 144 seconds.
The Hindus created a dizzying variety of intervals. At either end of their time spectrum the units were so extreme, they were useless in practical terms—and close to incomprehensible. These included the Paramaṇu, with a length of about 17 millionths of a second, and the Maha-Manvantara, which is 311.04 trillion years. Their long-interval units meshed with their creation and destruction myths, in which the cosmos undergoes cycles of clarity alternating with periods of human darkness, each called a yuga.
More practically, the ancient agrarian world relied on seasonal ways of reckoning, and these cycles were determined with amazing accuracy in civilizations like the Maya. Smaller units than months and days trickled into everyday usefulness, first with the creation of the dripping-water or falling-sand hourglass, and later the discovery of the pendulum effect by Galileo Galilei. In 1582 he noticed that the chandeliers hanging from long chains in the Piazza del Duomo kept swaying back and forth in the same period regardless of the swing’s amplitude, and—following an impressive bit of procrastination—wrote about this in 1602. This effect, experienced by children in playgrounds, amounts to the fact that when a parent gives a child a strong push, the swing’s period of travel from one end of its oscillation to the other is no different from when she is just sitting quietly with the swing barely moving at all.
The period is basically determined by the length of the chain, a property called isochronism. It turned out, a string or chain 39 inches long produces a back-and-forth period of exactly 2 seconds. It wasn’t long before this principle was utilized in grandfather clocks, whose long metal rods, just over 6 feet, ticked off near-perfect seconds.
Portable timekeeping took a leap with the invention of the balance spring watch in the second half of the seventeenth century, thanks to breakthroughs by Robert Hooke and Christiaan Huygens. Then accuracy skyrocketed after the 1880 discovery by the Curie brothers, Jacques and Pierre, that quartz crystals naturally vibrate when a bit of electricity is applied to them. If cut to a particular size and shape, they’ll reliably oscillate 32,768 times a second, which is a “power of 2”—it’s 2 multiplied by itself 15 times over. An electronic circuit has no trouble counting these oscillations and thus marking off evenly spaced seconds. This ultimately made precise portable timepieces—the quartz movement still utilized today—cheaply available beginning in 1969. With everyone now able to agree on the “right time,” the busy modern world with its appointments and scheduling settled into a shared, time-focused reality.
Through it all, however, the fact of pendulum swings, mechanical balance beam oscillations, and quartz vibrations was still no evidence of time. They all merely provided regular repetitive motions. One could then compare some repetitive events with others. One could notice, for example, that while a grandfather clock pendulum makes 1,800 swings, a candle might burn down 1 inch, and Earth would turn one-forty-eighth of a full rotation. Certainly, one could call the elapsing of all these events “a half hour,” but that didn’t mean that the time period had some independent reality, like a watermelon.
Then the whole business suddenly grew much odder with the discovery that some events could start unfolding faster than they had before, relative to others. Things started to become seriously disconcerting with Einstein’s strange but grudgingly logical ideas that he incorporated into both his special and general relativity theories of 1905 and 1915, respectively. In them, Einstein elaborated on and explained curiosities and paradoxes noted in the preceding decades by George FitzGerald and Hendrik Lorentz. In a nutshell, a totally unexpected revelation emerged: Even if time is an actual entity, it cannot be a constant like lightspeed or gravity. It flows at different rates. The presence of a gravitational field retards the passage of time, as does rapid motion.
We’re intuitively ignorant of this because we all attended a high school where everybody hung out in the same gravitational field—and never, even in our wildest teenage years, sped our car in a joyride faster than an eight-millionth of the speed of light. Because one must go 87 percent of lightspeed to feel time slow by half its normal rate, we’ve never even come close to directly experiencing time’s fickleness—a function of our still-sluggish ground vehicles rather than any personal wisdom.
Astronauts do better. Orbiting at one-twenty-six-thousandth the speed of light, they can actually gauge the amount by which their time runs slow, using sensitive clocks—which brings up a seldom discussed puzzle. Though they move faster, astronauts have also traveled away from Earth’s surface into a weaker gravity, which has the opposite effect, speeding their passage of time. Turns out, their high-speed factor prevails. They age less quickly than people on the ground. They’d have to be eight times higher than the International Space Station’s orbit, or two thousand miles above Earth’s surface, before the weaker gravity there exactly balanced their now slower orbital speed to let them age at the same rate as those back home. Still farther away, timepieces on the Moon tick faster than those at mission control in Houston—even if nobody compensated Apollo crews with early Social Security benefits.
These time distortions aren’t subtle, nor are they merely of academic interest. Those GPS satellites simply wouldn’t work if continual compensations weren’t added for various time-warping effects. Since receiving precise time signals from each satellite lies at the very heart of that navigation system, anything that throws off the instruments’ or receivers’ time passage will blow the whole thing.
Are you a truly nerdy, geeky person who cares about such technological or physics details? If so, consider the many wrinkles in how time seems to flow, all introduced by the very technology designed to measure it:
Wrinkle one: Satellites travel at 8,700 miles per hour, slowing their clocks.
Wrinkle two: They’re distant from Earth in a reduced gravitational field, which accelerates their time relative to Earth’s surface.
Wrinkle three: GPS users on the Earth’s surface are located at various distances from Earth’s center (at Denver’s high altitude versus low-altitude Miami, say), producing a variety of time-passage rates.
Wrinkle four: The difference in Earth’s rotation speed at separate ground-based locations produces inconsistencies in their agreement about the passage of time, which is called the Sagnac effect.
Wrinkle five: Time runs slower for all earthly observers (as compared to any future lunar colonists) because of our planet’s 1,040-mph equatorial spin. (The speed decreases the farther one is from the equator.)
Wrinkle six: Satellites’ time passage continually changes because their slightly elliptical orbits make them speed up and slow down, plus they zoom through irregularities in Earth’s gravitational field due to things like our planet’s equatorial bulge.
All told, six separate Einsteinian time distortions