Zoom: From Atoms and Galaxies to Blizzards and Bees: How Everything Moves (28 page)

White light is a rainbow in a blender.6

But in a vacuum, all colors fly at the same speed. It is the fastest speed anything can move, and, indeed, nothing with any weight can quite attain it. Light travels a foot of distance in a nanosecond, a billionth of a second. So when we see something ten feet away, we view its image not as it is now but as it was ten nanoseconds ago. We always view the past.

We observe the sun as it was eight and a half minutes ago. If it should blow up at this moment, we’d be given a short reprieve from this disconcerting news. We see the stars as they were years or centuries ago. Galaxies as they were millions or billions of years ago.7

We use light’s fast but finite speed for some of our favorite technologies. A GPS satellite contains an atomic clock that sends out time signals. Your car’s GPS receiver recognizes that it’s the wrong time. Wrong because the signal, traveling at light speed, required one-twentieth of a second to arrive at your Camry from the satellite eleven thousand miles overhead. Your GPS, which knows the right time, then instantly calculates how far away that satellite must be for the signal to have been delayed for exactly that amount of time. It does this with three or four satellites and thus triangulates what your position must be. All by using the known speed of light.

But light’s constancy is too perfect. It doesn’t make sense. If you fly toward the sun while measuring its incoming photons, the act of colliding with them should, logically, make them hit you faster, the result of your own speed added to theirs. Or if you race away from a lightbulb at nearly the speed of light, you’d think each photon would barely catch up to you and that its measured speed of arrival would be slower. Not so. In all cases, light always strikes you going 186,282 miles a second.8

While orbiting the sun, Earth whooshes toward the orange star Antares at nineteen miles a second in August, and we rush directly away from it each February. But do its photons arrive here at different seasonal speeds? Not in the least. It’s as if we’re standing still.

So light’s constant speed is worse than counterintuitive. It’s screwy. And amazing.9

Turns out distances shrink and time alters its rate of passage in ways we don’t even notice, all so that we perceive light going the same speed no matter what. There’s something about that 186,282 miles per second business. Light somehow occupies a more fundamental reality than time and space and everything else we used to think was unalterable.

To conclude our story about trying to find light’s true speed—that migraine-inducing quest that endured for so many centuries—we last applauded Ole Rømer’s Jovian moons method, which delivered a figure just 25 percent off. But wouldn’t it be marvelous and satisfying, and win accolades from colleagues, if one could measure it here on Earth? Newton and his contemporaries tried standing on hilltops with bright lanterns blocked by a quick-release shade. They had a confederate stationed on another hill a few miles away, instructed to unveil his own lantern the moment he saw the first one’s light. The first person should simply be able to time the interval between opening his own shade and seeing his partner’s returning beam. But when this was done, the delay was always the split-second interval expected from human reflexes. (Turns out the reflection from a mirror positioned even twenty miles away would actually yield a delay of only one five-thousandth of a second.)

The fog finally lifted in 1850, when Léon Foucault improved on an apparatus invented by another Frenchman and nailed light speed at last. The idea was to bounce light from a fast-spinning polygonal mirror onto a flat mirror and back again. During the photon’s brief flight through the air, the rotating mirror’s angle changes, and the beam reflects in a slightly different direction, readable through a microscopelike device calibrated with fine markings. Knowing the mirror’s spin rate and hence its angle’s change, and knowing the total distance the beam travels, which in Foucault’s case was twenty miles, one can measure light’s speed with certainty. Albert Michelson refined the method seventy-five years later, and that’s when light speed was confidently known with a margin of error of just two miles a second.

By the time I was performing this demonstration in college, the whole apparatus fit in a lab room, the margin of error was less than one mile a second, and nowadays lasers make the beam smaller and even more precise.

The only thing that remains perplexing is that old conundrum of how our own speed toward or away from a light source fails to change its measured velocity. Why should photons from a rapidly approaching Corvette headlight hit our testing device at the same speed as those from a parked car? It’s as if we were to stick an arm out of that zooming race car and feel the air remain dead calm. It doesn’t make sense.

As far as light is concerned, we’re still back in Genesis on a stationary Earth.

As far as light speed is concerned, the motion of everything else doesn’t exist.

Everyone contemplating this, including generations of physicists and science lovers, shakes his or her head in wonder and disbelief.

The untented Kosmos my abode,

I pass, a wilful stranger:

My mistress still the open road

And the bright eyes of danger.

—ROBERT LOUIS STEVENSON, “YOUTH AND LOVE: I” (1896)

Barely more than a century ago, on June 30, 1908, a black-bearded man sat on the front steps of his cabin in one of Earth’s most isolated regions. It was exactly 7:14 in the morning, though he had no knowledge of the time, because he owned no clock. Tall, straight pines surrounded his modest home in south-central Siberia, built without the benefit of power tools. The spot was chosen because of plentiful water from an adjacent brook in this animal-abundant region northwest of Lake Baikal.

Then and there, he witnessed the largest meteor impact in recorded history.

A brilliant blue ball, nearly rivaling the sun, “split the sky in two.” But unlike the bolides, or exploding meteors, that lucky observers may witness every few years over their own homes, this one neither vanished at the horizon nor fizzled into a shower of sparks. Instead it simply exploded in the air forty miles northeast of where he stood gaping, shielding his eyes against the low morning sun that was visible in the same general direction.

Immediately he felt intense heat on that side of his body, “as if my shirt was on fire,” he explained years later. He wasn’t sure if he should rip off his clothes; wouldn’t his bare skin then be perilously exposed to whatever this was? His indecision ended when he heard a loud thump, the earth shook, and “hot wind raced between the houses like from cannons, which left traces on the ground like pathways.” This violent wind immediately blew him sideways into the air and hurled him ten feet. He lay in the dirt, barely conscious.

When the first Soviet expeditions reached the ground-zero area more than ten years later (a larger scientific team arrived in 1927, a delay understandable in those tumultuous times), they found eight hundred square miles of utterly destroyed, charred trees that had been blown down radially, all pointing away from a spot three to six miles beneath where the intruder exploded. Later analysis showed that it had been either a small comet or stony asteroid the size of a large house. Its explosion had released a force of between five and fifteen megatons, rivaling a thousand Hiroshima bombs.1 Just a tiny comet or asteroid fragment. Smaller than a movie theater. Nothing out of the ordinary. Its speed alone had made it dangerous.

The worrisome thing is that it has two hundred thousand cousins.

In what became the strangest celestial coincidence in recorded history, a somewhat smaller air-bursting meteor exploded over Siberia once again, this time on February 15, 2013. We know it was smaller (probably the size of a bus) and blew up when it was higher, because this one hurled no one through the air and didn’t knock down a single tree, though its shock wave broke many windows, causing a thousand injuries. It was a coincidence not just because the target was Siberia once again but also because this occurred on the same day as the closest-ever observed flyby of a substantial (football field–size) asteroid—which missed us by a mere seventeen thousand miles.

There had previously been only a single rigorously documented instance of human injury from a meteor. Suddenly, in 2013, the world’s total casualty list from extraterrestrial objects went from one person hurt in five thousand years of recorded history to a thousand people.

Nothing in the universe is stationary. Absolutely everything moves.

We don’t even have to cast our nets to galactic distances. The velocities we can probably most easily relate to are those in our immediate neighborhood. These entities affect us. The moon and sun align either together or on opposite sides of the heavens—both configurations exert an identical “pull”—to create maximum tides every fortnight. Creatures that depend on the tides, such as clams—especially those in the extensive marine marshes—and their predators, such as gulls, display behavior patterns attuned to the four daily tidal extremes and also to the larger biweekly ones. Celestial rhythms thus echo from the skies and spill over into the animal kingdom.

Remaining relatively near to Earth, to the places our robot surrogates have visited, we might begin with one of the four celestial bodies on which humans have left garbage: the moon.2 It so happens that the moon is one of the cosmos’s slowest entities. The moon requires four weeks to make a single rotation. And, famously, it orbits around us in precisely that same amount of time—27.32166 days. But this seemingly bizarre coincidence turns out to be logical and commonplace. Nearly all the 166 moons in the solar system—which mostly have names like Greip and Puck and Neso, which few people have ever heard of—rotate and revolve in matching periods, too. Their months and days are the same.

It simply means that when two celestial bodies share the same neighborhood, they influence each other. The larger one’s gravity dominates the system and exerts a braking tidal action on its neighbor. The smaller one’s spin gradually slows until one hemisphere is locked in place, this half forever facing its parent planet. Thus our situation of always seeing one familiar side of the moon, with markings that seem glued in place and with a hidden hemisphere perennially pointing away, is as common as tuna on white.3

The moon is the only object in the known universe that moves its own width in one hour. Here, in a photograph taken in the Libyan desert in 2006, it has just finished using that hour to fully cover up the sun. (Terry Cuttle)

This doesn’t mean the moon is devoid of cool animation. Far from it. It’s the only celestial body whose speed through space is “one diameter per hour.”

This manifests itself to our naked eyes and always has. During an eclipse, when the moon either passes into Earth’s shadow or blocks the sun, it duly requires very nearly one hour to become immersed. And on any night, our nearest neighbor shifts one “moon width” against the background stars every fifty-seven minutes as it chugs through space at 2,289 miles per hour. (This is its average. It can move 126 miles per hour faster or slower in its oval path around us.)

Motionwise, the nearest planets to Earth—Venus and Mars—play the character roles of George Burns and Gracie Allen. They are Mr. Normal and Ms. Peculiar. Mars, the straight man, has a spin remarkably similar to ours. Its day is 24.5 hours long. But Venus is strange. It is the slowest-rotating object in the universe. A Venusian day is 244 Earth days. It barely spins at all.

Confining our musings to our four nearest planetary neighbors, we discover that Jupiter provides a fantastic contrast, because it’s the quickest-turning body. Despite its huge size—1,300 Earths could fit inside a hollow Jupiter—it rotates in just under ten hours. This is a planet with attitude. Its equator moves twenty-four times faster than ours. So fast that its clouds are horizontal streaks and resemble paint thrown onto a spinning turntable—especially when viewed by spacecraft from above either of Jupiter’s poles. That planet whirls so fast that its equator bulges outward, making Jove not remotely round but squashed at the poles.

To visualize these disparate planetary spins, picture yourself strolling along each equator’s bike path. On Venus, simple walking speed would be enough to outpace its rotation. A brisk promenade would keep night from ever falling.

On the moon you’d need to trot a bit faster, but still a marathoner could keep the sun from setting. Its rotation is just ten miles an hour. That’s the speed at which the shadows cast by lunar mountains creep along crater floors. But Jupiter’s equator zooms along at twenty-five thousand miles an hour. Fifty times faster than a bullet.

In addition to its spin speed, each planet has its own unique forward speed as it orbits the sun counterclockwise (as seen from above, or north of, the solar system; all planets move in the same direction, a one-way procession).

Planet speeds have an easy, logical sequence. The rule is simple. The closer you are to the sun the faster you must move to maintain a stable orbit and not get pulled into its gravitational field and become vaporized. Tiny Mercury zooms along at thirty miles a second.

Venus whizzes at twenty-two miles a second. Our world moves at 18.5 miles per second. Mars goes at fifteen miles per second. You see how it works. Planets farther from the sun move more slowly. Poor demoted Pluto lopes along at just three miles a second.

In our celestial vicinity, none of the speeds particularly stands out. None is off the charts. The planets are like adjacent sprinters on a circular track, each in its own lane. The nearest planet to us on the sun’s side goes just 3.5 miles per second faster than we do. The one on the outside goes 3.5 miles per second slower. Nobody moves too crazily compared to its neighbors. That’s why meteors streaking across our night sky seem fast but not insanely so. Nearly all of them are broken pieces of comets or asteroids whose parents orbit the sun in our general vicinity. Their speeds resemble ours.