Zoom: From Atoms and Galaxies to Blizzards and Bees: How Everything Moves (25 page)

Room-temperature gas molecules typically dart about a bit faster than the speed of sound. Those in your freezer go fifty miles per hour slower. How fast atoms must move to begin an oxidizing or burning process depends on the substance. White phosphorus ignites at just below body temperature; merely holding it is dangerous.

Common combustibles usually require at least four hundred degrees to make their hydrogen combine with oxygen in the air and also in themselves.

What’s perilous about most reactions is that they are exothermic. They create heat.

We’re thus surrounded by substances poised and ready to burn and to keep burning. Only their atoms’ low everyday speed keeps them well behaved. But if some external agent pushes on their atoms to speed them up, the show begins. Once started, they supply enough heat to self-sustain. A simple match is the most common agent of creating such a runaway reaction, a Frankenstein.

The quest for a cheap, portable device that could start fires bore fruit in the eighteenth century and achieved practical success in the nineteenth. Before that, people carried bits of flint or other friction-based, spark-producing materials with them, or else they used a convex lens or concave mirror to concentrate sunlight onto a combustible substance. By the eighteenth century, those who could afford it kept chemical-laced sticks, which were plunged into jars of sulfuric acid to produce violent, dangerous, fire-starting reactions. But in the mid-1800s, white phosphorus’s low ignition point proved obvious and irresistible. People could buy “lucifer matches” at any general store. They became so commonplace that lucifers are regularly mentioned in Mark Twain’s books, as familiar a cultural touchstone as a smartphone in contemporary literature.

But white phosphorus is a dangerous compound and caused many accidental poisonings; it also became a favorite suicide method. By the turn of the twentieth century it had been largely replaced by red phosphorus and banned outright in many countries. Soon matches were available in two varieties, a situation that still pertains in the present day. Strike anywhere types have tips covered in a self-contained, combustible mix of phosphorus sesquisulfide and potassium chlorate. Quickly dragging the match across any rough surface, at a typical speed of six feet per second (four miles per hour), generates enough friction to raise the tip above its self-ignition point of 325 degrees Fahrenheit. Easy.

Sometimes too easy. Matches have never been allowed on planes or ships. The alternative is safety matches, which require contact between the matchbook’s scratchy surface, which contains a bit of red phosphorus and ground glass or another type of roughener, and the match head, which is about 50 percent potassium chlorate, famous for readily bursting into flame and releasing oxygen. The match head also contains a little antimony trisulfide, a safety component because it needs the combustion heat from the others to ignite. This witches’ brew requires a higher friction temperature of 450 degrees or so.

Once ignited, the match’s fire quickly reaches a temperature between 1,112 degrees Fahrenheit and 1,472 degrees Fahrenheit; the uppermost part of the flame is the hottest. Its molecules move so fast they can easily jostle those in other substances, which themselves soon reach a speed that lets them initiate their own burn reaction. Frankenstein has come to life. The speed needed to begin a self-sustaining “burning” event depends on the substance.

Fire—important enough to qualify as one of Aristotle’s elements—is a motion exhibit in several simultaneous ways. Flames lick the air and dance in a thousand mesmerizing patterns, while the unseen choreography is just as intriguing.

Paper “catches” easily. Its famous ignition temperature inspired the title of the 1953 Ray Bradbury novel, Fahrenheit 451, in which “firemen” went about burning books. Catchy, but in reality, different types and thicknesses of paper have distinct ignition points that vary from 424 degrees to 475 degrees. Real science is often less succinct than its fictionalized analogues. (Bradbury, who died in 2012, knew this, of course. He also knew that the title Somewhere Between 424 and 475 Fahrenheit would not have been as memorable.)

Coal ignites reluctantly, with a very high ignition point of 842 degrees. Kerosene is much more eager to go, at 444 degrees. Gasoline will ignite at 495 degrees, alcohol at 689, and hydrogen at 752. But there are nuances, especially with flammable liquids. When atomized as a spray, home heating oil burns brilliantly. But a two-foot-deep pool of it that has leaked into a basement is unlikely to ignite even if a lit match is tossed into it. Similarly, you can squirt Pam cooking spray into any candle flame and it’ll instantly whoosh as a brilliant blaze. But even if heated to its self-ignition point of 644 degrees Fahrenheit, cooking oil may not burn unless it’s atomized, which envelops it with needed oxygen. That temperature is slightly higher than what’s normally achieved in an oven, which is why oils aren’t frighteningly ablaze whenever you check on a baking eggplant Parmesan.

Eerily enough, cool molecules can sometimes move faster and faster on their own until before you know it your house has burned to the ground. No spark or flame is needed. This spontaneous combustion begins when something with a relatively low ignition temperature, such as rags, straw, or even wheat flour, remains in contact with moisture and air. These substances supply oxygen and allow bacterial growth that encourages fermentation. This in turn generates heat, as anyone with a compost pile or a stack of rotting hay can confirm. If the heat is confined and unable to dissipate (e.g., if oily rags are crammed in a pail or buried in a pile of hay, which is a good thermal insulator on its own), the temperature rises, eventually exceeding the ignition point. The result is a thermal runaway.

Pyrophoric substances are those whose molecules can explosively increase their speed with very little provocation. They’re wound up and raring to go. They burst into flame at room temperature or less. Sodium is a famous example. Its autoignition temperature is exceeded almost everywhere in everyday life, and it will undergo a violent reaction when in contact with water or even moisture.

There have been grain elevator fires in which no culprit spark triggered the explosion. Items as seemingly innocuous as corn have blown up when moisture was allowed to accumulate. Among the substances most susceptible to spontaneous combustion are pistachio nuts. You can’t make this stuff up.

The point is, it’s all motion. Heat is motion. Atoms’ motion is heat. When you run a fever you might complain that your temperature is 102. But you could just as well tell the doctor, “I feel awful. My body’s molecules are moving three miles per hour faster than normal.”

Then he’d hand you some aspirin, saying, “Here. This will slow them down.”

You can also get a rough idea of atomic speed and temperature by a substance’s color when heated. It’s wonderfully simple. It doesn’t matter what it is. Cast iron, copper, the tungsten in lightbulbs—when a noncombustible object starts glowing, the color of that light is an accurate guide to its temperature.

TRANSLATING GLOW COLOR INTO TEMPERATURE

If a substance glows a dull red, just barely visible in the dark, it’s 752°F.

A red heat visible in subdued lighting means 885°.

If the red can be seen in daylight, it’s 975°.

If it’s visible as red in direct sunlight, it’s 1,077°.

If it’s cherry red, it’s 1,650°.

Orange indicates 2,012°.

Yellow means 2,370°.

White indicates a temperature of 2,730° or higher.

Upon attaining the color white, you may well have trespassed beyond the object’s melting point. In any case, white is the end of the line. In theory, an even hotter substance would glow blue—just as blue stars are the hottest in the universe—but by then all earthly materials would have melted if not boiled into gas.6 Finding a substance that would remain solid when white hot was what created so many headaches for Edison as he struggled to perfect his electric light. He finally found tungsten, the element with the second-highest melting point, which stays solid until it’s a whopping 6,170 degrees Fahrenheit. This was vital: a thin lightbulb filament is asked to remain at an amazingly high 4,500 degrees for hours or even days at a time; that’s about twice as hot as melting steel. (Carbon has a slightly higher melting point but is too brittle to be practical as a filament.) The incandescent bulb’s fantastic heat would ultimately prove its own undoing: it is now being replaced by LEDs or fluorescents or banned outright. The complaint is that incandescent bulbs utilize most of their electricity for the production of heat rather than light.

Aluminum melts at a mere 1,220 degrees Fahrenheit. For copper it’s 1,976; for gold, 1,945. Unlike common steel, which melts at 2,500 degrees or so, these metals turn liquid at lower temperatures than their glow-white point. That’s why you’ll never see a white-hot aluminum ingot, just as you never see a red-hot chunk of solid tin or lead, which melt before they can glow in any way.

As for their atoms’ speeds, the main motion in a solid is a very small amplitude vibration around its equilibrium position. These vibrations grow larger and more frantic with increasing temperature until the melting point frees them. But only atoms in gases break the sound barrier.

Unbeknownst to Eadweard Muybridge, ultrafast rhythms that rule virtually every aspect of our lives are not rare phenoms, nor could they ever be captured by his or anyone else’s camera, then or now.

These astonishing discoveries began in the late nineteenth century, when physicists started finding strange small-scale vibrations. Probably the coolest and most useful example is the piezoelectric effect, discovered by the Curie brothers, Jacques and Pierre, in 1880. They found that many kinds of crystal (they liked to work with quartz) naturally vibrate tens of thousands of times a second if a little electricity is applied to them. And it works the opposite way, too. If a crystal is compressed or distorted or struck so that it vibrates, it briefly produces electricity. It’s a two-way street.

A flood of technology arose from this. Breakthroughs occurring between 1921 and 1927, mostly at Bell Labs, resulted in the creation of a superaccurate clock that relied on those quartz vibrations. Vacuum tubes and other bulky components confined the early devices to laboratories, where they kept America’s official time to a new level of precision on behalf of the National Bureau of Standards (now the National Institute of Standards and Technology) for thirty years, until atomic clocks took over in the 1960s.

Cheap semiconductor technology enabled manufacturers to mass-produce quartz watches beginning in 1969, when they replaced mechanical spring watches and made it possible for everyone to have a personal timepiece accurate within one second per month. Your watch’s quartz crystal is shaped to naturally vibrate 32,768 times a second. This is, conveniently, a power of two (it’s two multiplied by itself fifteen times over), which lets digital circuitry easily convert it into whole seconds.

Pulsating crystals are now in every home. For example, you may own one of those barbecue grill lighters—the ones with an annoyingly hard trigger. Pulling the trigger strikes a crystal, which piezoelectrically creates a momentary high voltage, thus producing a quick spark. No battery is ever needed. Indeed, gas stoves now use vibrating crystals to create the spark that ignites the gas. If you hear repeated “snaps” whenever you turn it on, that’s what’s happening.

Thirty-two thousand vibrations a second may seem fast. But it turns out it’s not just crystals that undulate. Absolutely everything vibrates. The molecules that make up every substance around us display complex atomic harmonic oscillations.

We may imagine that a simple common compound such as water, made of two hydrogen atoms bonded electrically to an oxygen atom, has a rigid structure. Not so. The atoms stretch away from each other a bit and then snap back as if on a rubber band. At the same time they twist around and then return to shape. They also rock back and forth like a metronome. Each of these repetitive atom motions—twisting, stretching, rocking, bending, and wagging—has its own precise period that is somewhere between one trillion and one hundred trillion times per second. You’d think this shaking would dampen out and stop. It never does.

Meanwhile, light itself consists of waves of magnetism and electricity whose pulsation rates depend on the color. Green light’s waves, for example, pulse 550 trillion times per second. These vibrations are not just extraordinarily regular. They have in-your-face consequences.

To give one example, an automobile parked in sunlight heats up because the pulsation rate of the infrared waves that are inside it coincidentally match the atomic vibration rate of the car’s glass. This creates a chaotic boundary, blocking the heat from escaping through the windows the way light does. Instead, light gets in, but the heat it creates can’t get back out. It makes the car’s interior very uncomfortable when you step inside. People have been arrested for leaving pets and children in such parked cars. The charges probably didn’t specify that the suspects “ignored the lethal perils of ultrafast vibrations,” but that’s what it amounts to.

As another example, consider the chrome that adorns motorcycles and makes the exposed metal parts of cars look so shiny. This happens because the outer electrons of the element chromium absorb and then reradiate the photons of light that hit them. But the light doesn’t get too much farther. That metal’s inner electrons are held so tightly in their orbits that they have too little flexibility to vibrate and give off light. The end result is that sunlight striking chrome and most other metals isn’t fully absorbed, nor does the light pass through. It’s neither transparent nor dull but something else: gleamy.

So we’re immersed in more than mere animation. Nature doesn’t just go wild with countless pulsations producing powerful everyday experiences. It also never tires of repeating itself within time frames of the tiniest fractions of a second—or in milliseconds, whole seconds, minutes, years, centuries, millennia, you name it. Ours is a shimmering, vibrating universe on multiple levels. These patterns, which interact with each other, influence everything—even if we’re unaware of virtually all of them.