Authors: Natalie Angier
Here it is worth a final reversion to metaphor. If the nucleus of an atom were a basketball located at the center of Earth, the electrons would be cherry pits whizzing about in the outermost layer of Earth's atmosphere. Between our nuclear Wilson and the flying pits, however, there would be no Earth: no iron, nickel, magma, soil, sea, or sky. Once again, there would be nothing, literally, to speak of. Inner space, outer space, galactically, atomically, no matter. We live in a universe that is largely devoid of matter. Yet still the Milky Way glows, and still our hemoglobin flows, and when we hug our friends, our fingers don't sink into the vacuum with which all atoms are filled. If in touching their skin we are touching the void, why does it feel so complete?
L
ET'S SAY THAT
an asteroid portentously resembling a
Tyrannosaurus rex,
a giant trilobite, or Steven Spielberg were to slam into Earth tomorrow, annihilating the bulk of human civilization and the billions of civilians therein. What small sliver of human culture would be most worth preserving? What single piece of knowledge, what insight into the nature of the universe, would prove most useful to the few survivors as they struggled to rebuild all hope and opus of
Homo sapiens?
Lovers of the arts might suggest the collected works of William Shakespeare or Johann Sebastian Bach. The medically minded might vote for antibiotics, anesthesia, a general recognition of what not to do with the contents of one's chamber pot. Richard Feynman, the great physicist and titularly designated Genius and Joker, took seriously the problem of post-apocalypse reconstruction. "If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words?" Feynman asked rhetorically during one of his famed lectures. "I believe it is the atomic hypothesis, or the atomic fact, or whatever you wish to call it, that all things are made of atoms. Little particles that move around in perpetual motion, attracting each other when a little distance apart but repelling upon being squeezed into one another." Take that one sentence, he said, stir in "just a little imagination and thinking," and you have
The History of Physics,
Phoenix Rising edition.
Physics is one of those modest disciplines that, in the words of a popular text by Steven Pollock, a physics professor at the University of Colorado, is nothing less than "the study of what the world is made of, how
it works, and why things in the world behave the way they do." And the less said, the better. Physics revels in reductionism, a word that to many implies "simplistic" and "probably not applicable to anybody in my social circle," but really is another way of saying "understanding something complex in terms of its constituent parts." That, of course, is what most sciences seek to do, but physics goes the furthest, breaking apart the constituent parts until they're crying for Muster Mark.
*
Physics is the science of starter parts and basic forces, and thus it holds the answers to many basic questions. Why is the sky blue? Why do you get a shock when you trudge across a carpeted room and touch a metal doorknob? Why does a white T-shirt keep you cooler in the sun than a black one, even though the black one is so much more slimming?
As the science of starter parts and forces, physics can also be defended as the ideal starter science. Yet standard American pedagogy has long ruled otherwise. In most high schools, students begin with biology in tenth grade, follow it with chemistry, and cap it off in their senior year with physics, a trajectory determined by the traditional belief that young minds must be ushered gently from the "easiest" to the "hardest" science. More recently, though, many scientists have been campaigning for a flip in the educational sequence, teaching physics first, the life sciences last. Leading the charge for change is Leon Lederman, a Nobel laureate in physics and professor emeritus at the University of Illinois, who has the distinctive shock of almost fluorescent white hair with which the elder statesmen of physics are so often blessed.
Lederman and others argue that physics is the foundation on which chemistry and biology are built, and that it makes no sense to start slapping the walls together and hammering on the roof before you've poured the concrete base. They also insist that, taught right, physics is no "harder" than any other subject worth knowing. Some schools have adopted the recommended course correction, and others are sure to follow. I not only agree with the logic of Lederman's from-the-ground-up approach; I also trust his populist heart. Lederman, it so happens, has long been lobbying the networks to do their bit for science's public image by starting a television series based on a team of laboratory scientists. Physicists, biochemists, drama or sitcom, Lederman doesn't care; what counts is that the characters defy geek stereotypes with their emotional struggles and interpersonal parries, their drive and self-doubt, their prominent cheekbones and stylish footwear.
Physics, then, is the pylon science, the discipline on which the others are piled, if sometimes peevishly. And as Feynman proposed in his Duck and Recovery plan, the most fundamental facet of this foundational field is the atom.
Everything, every single thing deserving of the designation "thing," is made of atoms. Even those things that are not obviously thingly can, in the end, be stripped to their atomic Skivvies. Thoughts, for example. As they drift from your brain and through the Sheetrock of your office cubicle, they seem defiantly fleeting, robustly substance-free. Yet the brain cells that gave rise to your thoughts are all built of atoms, and if one thought triggers another it does so via the transmission of neurochemicals along synaptic pathways in your brain, which again are vast assemblages of atoms; and if you tap your thoughts down in an electronic journal for later dissemination as friendly spam, you despoil an innocent screen by rearranging the atoms of its phosphor-coated surface.
The atomic Tinkertoy set of which we are constructed happens to be a magnificent system for getting things right.
"If you want to replicate something, you will make fewer mistakes if it is made up of discrete units than if it is made up of continuous material," said Ramamurti Shankar, a professor of physics at Princeton University. "By analogy, you will make fewer mistakes if you are trying to spell a word than if you are trying to reproduce a color." It's good to know, at a gut level, he added, "that there are only a hundred-odd different letters, different types of atoms, to worry about."
That all matter is built of atoms is one of those profound insights into the nature of reality that gestated in larval, largely figmental form for some two thousand years, before twentieth-century physicists like Albert Einstein and Niels Bohr finally offered experimental evidence of the atom's existence. The Greek philosopher Democritus argued circa 400
B.C.
that everything was made of invisible, indivisible particles, which varied in shape, size, and position and which could be mixed and matched to yield every manner of matter. Democritus called these particles
atomos,
meaning "unbreakable" or "uncuttable." Among the fiercest opponents of this early version of atomic theory was Aristotle, who, for all his brilliance, had a habit of dismissing some really fine ideas. Aristotle insisted that the world was composed, not of discrete
particles, but of four essences or qualitiesâearth, fire, air, and water. Aristotle's woolly, wrong-headed, but admittedly evocative schema held sway for hundreds of years, and still claims a sizable fan base among followers of astrology.
The early models of atoms resembled our solar system, with the nucleus as the sun and the electrons orbiting like planets around it. Another familiar portrayal of the atom is the Spirograph-style icon from the 1950s, of a central disk surrounded by three or four ellipses, like the official emblem for Arco, Idaho, which proudly describes itself as the "First City in the World to Be Lit by Atomic Power." An atom doesn't look anything like a solar system or a kitschy city logo, though. You can't really say what it looks like, in the ordinary visuospatial sense of the phrase. Not merely because the atom is invisible to the unaided eye. Cells and bacteria are "invisible," too, but you can see a cell or a microbe perfectly well with the right microscope. The problem with atoms, as Brian Greene made plain to me, is that they are so small they fall into the perilous domain ruled by Werner Heisenberg's uncertainty principle: you view it, you skew it.
"If we could blow up an atom to something the size of, say, a paperweight on your coffee table," I asked Dr. Greene, even as I noted that his coffee table was free of any papers in need of weighting, "what would we see?"
"'See'?" he echoed, so slowly the word sounded multisyllabic. "What would we see? I don't want to sound Clintonesque here, but it depends on your definition of see.
"When we talk about seeing things in the everyday world, we're talking about light," he explained. "We're talking about photons of light, particles of light, banging into our eyes and allowing us to see. But when you get down to the scale of the atom, those photons can change the nature of the thing you're seeing." The electrons that surround the atom can absorb and emit photons, he said, and when they do, the electrons jump around, altering the atom's conformation. "We long to impose the everyday experience of sight on the tiny little atom, but to do so requires that we change the atom itself. We can't literally see down there."
OK, forget the literal paperweight, I said. What might we figuratively not really see?
"A cloud," he said. "A picture of an electron cloud is a reasonably accurate way to think about it." Like a tumbling dust bunny that you can never quite catch with your DustBuster? I asked. Or the cloudy smear on a television news report when the identity of a moving figure must
be concealed? Well, sort of, Greene replied. But not like a swarm of gnats. Not an aggregate of many distinct objects. The image of an electron cloud is really a device to depict probability distributions, he said, telling you where an atom's electrons are likely to be found, and to give you a sense of how the electron's potential positions are distributed.
Even for the simplest atom, hydrogen, which has just one electron whizzing about the single proton of its nucleus, the electron has so many points it may be found, so many places it has been and will be again, that the entire boundary of the hydrogen atom can be envisioned as a spoonful of cloud.
Yet before we get carried away with this lovely image of electron distribution plot as Pre-Raphaelite hairdo, we must keep in mind that Aristotle erred: matter is not a sweep of qualities all blending seamlessly together. Atoms may and often do attract each other. Atoms form bonds, usually by sharing electrons consigned to each participant atom's outermost orbit. Through the artful bartering of electrons along their frontiers, two hydrogen atoms and one oxygen atom conjoin to form a molecule of water. But, importantly, the atoms do not merge, or invade one another's comparatively vast expanse of empty inner space. The atoms remain discrete entities, distinct particles composed of protons and neutrons in the nucleus, a huge amount of hollow space, and a cloud cover of electrons located far, far from the nucleus. The hollow space is, as a rule, a sacred place. Neither the electron clouds nor the nuclear particles of one atom will penetrate the inner void of another atom and take a tour, maybe sidle up to the foreign nucleus, wave hi and bye, and then head home again. Only under extraordinary conditions, as in the high-pressure furnace of the interior of a star, can two atoms be squashed together, at which reaction their nuclei combine to form a new, heavier type of atom, another element further along the periodic scale, a subject we'll visit later.
Most of the time, though, atoms maintain their autonomy and ethnic identity, including when they are in a stable molecular relationship with other atoms. The hydrogen and oxygen atoms with which the oceans are filled remain hydrogen and oxygen to their core and can be plucked free from one another, although it takes energy to cleave the bonds of a water molecule or any other molecule and isolate the constituents. It is an astonishing thought that every last backdrop and foreprop of our lives, the sweet air we breathe, the cool water we drink, the speed bumps we bump over, all consist of discrete, hollow particles, trillions upon quintillions of vacuum-filled atoms that will get close to each other, but never too close. As Feynman said, atoms will attract if
they're a little distance apart, but if you start getting pushy, they push right back.
What is it that keeps atoms discrete, and in such anally compulsive need of their "space"? And why, if most of matter is empty, am I sitting here on a reasonably comfortable mahogany chair rather than falling plunkity-plunk through the hollow atoms of the furniture, floor, planet, to join poor Commander Frank Poole in his death drift across the velvet void of outer space?
The answer lies in the dispositional humors of the subatomic particlesâthe pieces of which an atom is constructedâand the ploys, counterploys, and compromises in which they tirelessly engage. In the nucleus are the heavyweights, the protons and neutrons, which manage to make up more than 99.9 percent of an atom's mass while occupying only a trillionth of its volume. All atoms are not the same, of course. Our world trembles and gleams with atoms of gold, silver, bismuth, platinum, lead, sodium, mercury, indium, iridium, xenon, carbon, silicon, and some one hundred other basic syllables of being that we call the elements. The elements are substances that refuse to be reduced to simpler substances through normal chemical or mechanical means. If you have a sample of pure lead, you can break it apart or melt it down into smaller lumps of lead, but each piece will still be composed of lead atoms, and not the gold you might covet or the strontium you probably don't, unless you're in the pyrotechnics business and appreciate its flammability. And while the different atoms are all about the same sizeâa tenth of a billionth of a meter acrossâthey diverge in their mass, in the number of protons and neutrons with which their nucleus is crammed. Hydrogen, the lightest and by far the most common element in the universe, has the maximum minimalist of a nucleus, composed of a single proton; however, there are variants of the atom, given the unflattering designation of "heavy hydrogen," which possess one or even two neutrons in addition to the single proton. Many of the more familiar elements have pretty much the same number of protons and neutrons in their hub: carbon the egg carton, with six of one, half dozen of the other; nitrogen like a 1960s cocktail, Seven and Seven; oxygen an aria of paired octaves of protons and neutrons.