Zoom: From Atoms and Galaxies to Blizzards and Bees: How Everything Moves Read Online Free PDF

slothfulness. Speaking of which, those three-toed mammals didn’t earn their reputations for nothing. A sloth, even when motivated, only walks at 0.07 miles per hour. “Breeze it, buzz it, easy does it”—as Ice sang in West Side Story; the most excited sloth would need a long summer day to cover a single mile. Even giant sea turtles lope 25 percent faster.
    Perceived speed is a tricky business. We regard something as fast only if it moves its own body length in a short time. For example, a sailfish swims ten of its lengths per second and is thus viewed as very swift. But a Boeing 747 airliner approaching for a landing only manages to traverse one of its lengths, 230 feet, in a second. It’s visually penalized by its own enormity. From a distance, a descending jumbo jet seems virtually motionless because it takes an entire second to fully shift its position. Yet it actually moves four times faster than the fish.
    Now consider bacteria. Half the known varieties have the ability to propel themselves, usually by whipping their flagella—long helical appendages that look like a tail. Are they slow? In one sense, yes. The fastest bacteria can traverse the thickness of a human hair each second. Should we be impressed?
    Zoom in, however, and this motion becomes remarkable. First, that bacterium has moved one hundred times its own body length each second. Some manage two hundred body lengths. Relative to their size, they swim twenty times faster than fish. It’s equivalent to a human sprinter breaking the sound barrier.
    Moreover, the covered distance quickly adds up. Germs can transport themselves one or two feet per hour. That’s the speed of a minute hand on a wall clock. No wonder diseases spread.
    In our homes, other eerie motion unfolds as well, all the time. Dust in the air, for example, much of which consists of tiny bits of dead skin. Watch a sunbeam cast its rays through a window and your home’s omnipresent suspended dust becomes obvious. After all, light rays are invisible in and of themselves. In our homes we see a beam only when it strikes countless slow-drifting particles. In very humid conditions, minuscule water droplets catch the light. But in dry air it’s always dust.
    A quick glance makes it seem as if the suspended particles aren’t going anywhere. They move up or down with the slightest air current. But leave the room alone—at night, for example, when nobody is disturbing anything—and all this dead skin and other detritus settles at the rate of an inch an hour. That’s ten times slower than all those scurrying bacteria. Who suspected that our homes are so creepy?
    In the visible realm, the standard archetypes for intimate slow mo are our fingernails. And hair.
    Fingernails grow a quarter of an inch longer every two months. That’s half the rate of hair growth. If we neglected our barber appointments the way Newton and Einstein did, we’d find our hair six inches longer each year.
    But nails vary in interesting ways. Our longer fingers grow their nails more speedily. Pinkie nails advance sluggishly. Toenails grow at only one-fourth the rate of fingernails. That is, they grow at that rate unless you like to walk barefoot, which stimulates growth. Fingernails respond to stimulation, too. That’s why typists and computer addicts enjoy the fastest-growing nails of anyone. Maybe this explains why so many of us writers like to bite them.
    Nails grow faster in summer, faster in males, faster in nonsmokers, and faster in pregnancy. But nails do not grow at all after you’re dead. That macabre myth probably started because the skin on dead fingers pulls back, exposing more nail within two days after a person has passed away.
    Probably the most dramatic example of slow motion on earth is the earth itself. In caverns, stalactites and stalagmites typically extend at the rate of one inch every five hundred years. By comparison, mountains are downright speedy; they push themselves higher—in the case of