Electrons are legion. You can’t throw a transistor without touching an electron. Given the vastness of the universe, goes the folk wisdom, electrons must number beyond conception.
But electrons are famously alike: they all have the exact same mass, the same spin and electric charge, the same bowl haircut, and the same hackneyed opinions on the economy, no matter where or when you find one. This is often attributed to a rigid schooling system, or to a complete lack of schooling; in the 1920s some observers held both opinions simultaneously.
The truth is both simpler, with no moral for our own educational system, and utterly stranger. For there is only one electron, just one in the universe.
The key to unlock this mystery is the electron’s antimatter twin, the positron. The positron appears to be everything the electron is not: he has positive charge rather than negative, points his spin up rather than down, votes the straight Republican ticket, and so on. If you were dating an electron your mother would wish aloud you were seeing a nice positron instead.
But a positron is not the opposite of an electron. It is an electron going backward in time.
Take a video of an electron, run it backward, and you will be shocked to see a positron. It curves to the right rather than to the left in a magnetic field, eats dessert first and salad last, cries at the beginning rather than the end of Old Yeller.
You probably know the old wives’ tale that when an electron and a positron meet, they both disappear in a flash of gamma rays. Old wives in fact spend their time conducting careful physics experiments, and this tale like many others is correct.
Correct, that is, from a human point of view. But from the electron’s point of view something different happens. The electron decides to dig in its heels, sparking gamma rays, and reverse course. But instead of going backward in space, heading west rather than east, it goes backward in time, and is now, to us humans, a positron. The electron thinks it hasn’t changed at all.
And so the calendar flips backward, be it a few microseconds or a billion years, until the positron reverses course again in another shower of gamma rays and moves forward in time. To us humans, shackled by entropy to the forward lumbering of time, it appears a gamma ray creates an electron and a positron.
Yet it is really just the sole electron wearing two faces, as it weaves itself back and forth across the universe and across time. And when you see, for example, an atom of antimony buzzing with dozens of electrons, each electron is the same electron. The electron in this orbital is in its youth, the electron in that orbital is in its distant old age, having traveled to the end of the universe and back many times, and the electron over there, flirting with a photon a fraction of its age, is at the height of a billion-year midlife crisis, feeling both crowded and yet always alone.
The neutrino is cousin to the electron, part of the grand clan of leptons, named after the Greek word for light-fingered. Long ago, when prejudice and stereotypes were fashionable, it was held that leptons were pickpockets, thieves, and con artists. The neutrino of legend was portrayed as a bandit, famous for stealing from rich and poor alike (indifferent to its victims’ economic status, it was called il neutrino in Italy).
It was thus dismissed as mere myth, even though in 1930 Wolfgang Pauli proposed to take seriously the existence of the neutrino after his wallet went missing on a train platform in Heidelberg. Other physicists, Niels Bohr and Werner Heisenberg among them, instead proposed the possibility that money was simply not conserved on the quantum level. The neutrino remained an unknown until 1956, when Cowan and Reines published a splashy exposé, complete with scandalous photo of a Hollywood Hills pool party, in the pages of the Physical Review.
The reason the neutrino gained a reputation for being hard to find, as well as a thief and a pickpocket, is the lack of a money trail. Neutrinos’ spiritual beliefs do not allow them to use cash, to say nothing of credit cards, and even personal checks and money orders are forbidden. They rely on the generosity of strangers for a meal or a bed. No wonder neutrinos, with this extreme asceticism, are so thin that they were originally thought to be massless and remain nearly impossible to detect.
Neutrino religious beliefs, spectacularly divergent from Western traditions, have attracted the attention of scientists and science-fiction writers alike, and in recent years there has been a fad among SF authors to write in the voice of the neutrino, the most famous work being Le Guin’s The Left-Handedness of Darkness. This in turn has led to criticisms and claims of inappropriate appropriation, not least because most authors of a nonneutrino origin (aside from Le Guin, who had done her research) do not properly use the term handedness and were oblivious to the difference between Dirac and Majorana neutrinos.
But these are all human words. For the most part neutrinos, as they are wont to do, have held silent, gliding ghostlike through the cosmos, just watching and listening. Perhaps we should learn to do the same.
Quarks never appear in public alone but always in tightly knit groups of three. This inspired Murray Gell-Mann to lift a word from a line in James Joyce’s Finnegan’s Wake: “Three quarks for Muster Mark!” Gell-Mann’s coinage is deeply offensive to quarks; not only are they given a joke name rooted in Gell-Mann’s need to show off the enormous range of his intellect, even worse, quark sounds vaguely like qv∝rk, which cannot be translated in a family publication due to its obscene nature. Quarks refer to themselves by the phase Trχc = 0, which roughly means those whose true character is hidden.
Quarks are divided into six families, or flavors, as if they were blobs of ice cream rather than the building blocks of the universe. The most common are the up and down quarks, each individually small, but between the two of them they are the bedrock of protons and neutrons and planets and suns and indeed of all life. Quarks have their own names for their flavors, but you wouldn’t be able to pronounce them.
The names given to the flavors have little to do with their actual characteristics. Down quarks have a cheery, light-hearted nature, while up quarks are famously afraid of heights. Strange quarks admittedly do favor unusual hobbies, such as collecting and sorting lizard teeth and learning Mongolian, but charm quarks are wallflowers, always too shy to dance and turning red at a request to speak in public.
The rarest of all is the top quark, discovered less than twenty years ago. It is sometimes called the Godzilla particle, as it is born in a fiery nuclear furnace, rises from the unknown depths of the Dirac sea, and outweighs the up quark in roughly the same ratio as Godzilla outweighs you and me. Unlike Godzilla, however, the top quark has never visited Tokyo, its closest brush with Japan being a fondness for karaoke.
On occasion a quark might briefly hook up with an antiquark, a combination called a mesón after the kind of intimate Spanish inn they favor on such flings. But you will never find a lone quark, not out of unusual social dynamics, but out of fear of being groped by a physicist. And who can blame them? Physicists have spent millions of dollars and hundreds of man-years intensely searching for a singlet quark, like so many bachelors desperately scanning dating sites. Shrill protests that quarks should understand the scientists’ intentions are good, and that it is all in the name of science, are misplaced. Stand back, my fellow physicists, and allow the poor quark its privacy.
Electrons, neutrinos, and quarks are classified as fermions, after the French l’esprit fermé, or “closed-minded.” Fermions are notorious for their fixed opinions, lasting from the Big Bang until the end of time, and are so unwilling to hear another point of view they cannot stand to be even in the same room as another fermion. This is the famous Pauli exclusion principle (although the phrase itself originated when Wolfgang Pauli was banned from his aunt’s Berlin apartment for breaking an antique china teacup), and it’s a good thing. Without it chemistry wouldn’t exist, or at least would be a much simpler subject, for the Pauli exclusion principle means that atoms with differing numbers of electrons behave in unique ways. Hordes of high school and college students sweating over cations and anions and titration and counting the number of bonds may not feel grateful, but imagine if all the chemical elements behaved exactly the same way: not only would sugar and salt and monosodium glutamate and capsaicin all taste the same, there’d be no difference between a balsamic vinaigrette and a yeasty weissbier, or between beef jerky and a shimmeringly translucent slice of fugu.
A photon, however, is a boson, pronounced BOZE-on, like Bozo the Clown, and indeed photons are the clown princes of the subatomic world, quick with a joke, a magic trick, a song, anything to light up a smile. Unlike the single-minded electron, photons are fickle, quick to change their opinions, and easily swayed. Because of their malleable nature, photons and other bosons do most of the work of the subatomic world. The force between two electrons is really photons ferrying momentum back and forth. Photons spring up at the snap of an electron’s fingers, carry out a task, and then quietly disappear again. Photons illuminate a room, cook your microwave supper, carry messages like pigeons between cell phones, make a shadowgraph of your teeth for your dentist.
There is a dark side to all this. Not only is it easy to make a photon agree with you—a few seconds is all it takes to get a photon nodding that yes, it is night even if the clock reads 2 p.m., and that blindingly bright object in the sky must be the moon—it is even easier to get a roomful of photons in perfect agreement. Among humans we call such a thing a political convention, but for photons it is called a laser. A laser is nothing less than an army of photons marching in lockstep, left-right-left-right. A small platoon of photons powers the laser in your Blu-ray player and at the supermarket checkout, but don’t cheer yet: add more and more photons, and eventually you have a villain’s death ray, all on the backs of billions of cheerful photons, swarming in perfect agreement. Pause and think of that the next time you turn on a light.
The Higgs Boson
The Higgs boson has been nicknamed the God particle, an ironic name inasmuch as it came about because of a deal with the devil.
Samuel Higgs was not the worst physics student ever, but he was the worst who refused to be washed out of graduate school. He failed quantum mechanics a record seventeen times in eleven different PhD programs, the last one being at the University of Southern Louisiana, Northern Campus, in Outchipoulas, Louisiana.
One night in a bar on the interstate just outside Lafayette, a woman of dubious repute named Lupita told Sam if he slit the throat of a chicken at a crossroads at midnight and poured rum into the bleeding wound, the devil would come and bargain for his soul. Desperate, Sam went to a liquor store and an all-night poultry farm and then drove a lonely country road to a crossroads. The humid air lay across his shoulders like wet laundry, and the cicadas sawed noisily at the darkness. His hand trembling, Sam took a swig of the rum, and held the struggling chicken down in the dirt.
The next morning, he awoke, naked save for a large Mexican sombrero, and found scattered in the dust several pages of handwritten equations written in a tiny, cramped hand.
The theory of the Higgs particle solved two long-outstanding problems in particle physics, not only the question of how can one justify an even bigger and more powerful accelerator, preferably near good skiing in Switzerland, but also the origin of mass and inertia, explaining why it is so hard for teenagers to get up in the morning.
Despite the beauty of the theory, no one would publish an outlandish paper by a twenty-year graduate student. The devil had promised Sam the most important theory since Einstein, but he had not promised Sam credit.
Sam begged his second cousin Peter, also a physicist but with a classier accent, to submit the article under his name. A shy, quiet man, Peter Higgs put Sam down as first author, but a copy editor’s error left Sam’s name off, and ever after Peter’s attempts to cite his cousin were chalked up to eccentric British modesty.
When Peter Higgs won the Nobel Prize he offered his share to Sam, but Sam said it would just get sucked up by alimony to Lupita, whom Sam had married, then divorced, then married and divorced again. Sam now teaches physics to sullen premed students at a community college in Turlock, California, and at night can be found playing for a ska band in a dive bar.
In Geneva, physicists popped champagne (the real stuff, not just sparkling wine) and toasted one another. “The final piece of the puzzle!” they crowed. The next morning, however, they shuffled to their offices with gray, hollow faces, not because of a hangover, but because they realized that if the Higgs boson were the last to be discovered, if there were truly no more particles, no more mysteries, then they felt very much like Sam Higgs, a man with a gaping void where he once had a soul.
Physicists congratulate themselves on their rationality. But even they are susceptible to the allure of shadowy conspiracy theories.
The problem is gravity. Gravity is hard to ignore: it causes apples and rock climbers to fall, water to flow downhill, faces to sag. Gravity guides the moon around the earth, the earth about the sun, the sun pirouetting through the galaxy.
But on a subatomic scale, gravity doesn’t add up. You know how you thought you had enough money in your bank account, but when you finally sit down to balance the checkbook, you find, your face growing hot and stomach tightening into a sour knot, the numbers just don’t add up? It’s the same with gravity on the microscopic scale, only with really hard math and not the easy kind that caused you to fail calculus.
The solution, some physicists proposed over the objections of their struggling students, is even more, even harder mathematics. And so an elaborate, Rube Goldbergesque machinery was developed.
More math brought forth more particles. In the same way every particle has its evil twin antimatter antiparticle, goes the story, every particle also has a superpartner. Electrons are paired with selectrons, photons with photinos, quarks with squarks, and so on. This partnering is called supersymmetry, as if they were couples waltzing in perfect circles.
Not a single one of these superpartners, to date, has been seen. Occasionally one or another particle accelerator lab will announce they have discovered a supersymmetric particle, but upon closer inspection it turns out to be crumbs from the technician’s sandwich or the blond hair of a boyfriend. Still, this vast unseen particle mafia is invoked to ever so carefully balance the books so that the numbers for gravity add up. Behind the scenes, it is said, this hidden committee controls the greatest forces in the universe, manipulates the economy, picks the president, dictates to the UN.
Not everyone agrees. Gravity is an illusion, some physicists say with a shrug. Not something devised by a pantheon of supersymmetric particles in a smoky room planning the fate of everyone, but an accident. We all want there to be meaning in our lives, to be able write down an equation and look at it and say, So that’s why the tree fell on my house! That’s why my sister got breast cancer! That’s why my wife left me, why my boss won’t give me a raise, why I have persistent bad breath. But there isn’t always a reason, isn’t always someone behind the curtain pulling strings. Life just happens, and we are all souls like so many electrons, ping-ponging our away across the universe, across time.
Yet there are mysterious forces out there. Our mightiest telescopes see galaxies pinwheeling in space, held together by the bonds of gravity. But the grip of the gravitational force is greater than can be explained by the stars we count, greater even than the gravity generated by planets and clouds of gas drifting among the stars. When the cosmic account books are tallied up, all the quarks and electrons and neutrinos, etc., only contribute a small fraction to the weight of the universe.
The rest cosmologists call nonbaryonic dark matter. (The name doesn’t actually mean anything; it is the result of a bet, with the loser having to slip a nonsense phrase into the scientific literature.) What this dark matter is made of is a mystery. It may consist of the fabled superparticles, such as photinos, but that is mere speculation. Daily we pass through the dark matter, like the luminiferous ether of the nineteenth century, and in quiet basements physicists with massive cryostats try to detect the quivering of individual atoms from the dark matter wind.
There are even stranger phenomena out there: the accelerating expansion of the universe, anxious to get away from itself; how our perception of time is woven from the gnawing growth of entropy. In the end, despite our city-sized accelerators and massive space telescopes, despite supercomputers and libraries full of intricate, subtle mathematics, it seems we only understand a tiny fraction. Why does the universe exist? What happens in the end, when the stars wink out and even black holes sublimate away? Are there twenty kinds of particles, or just one? Why don’t we get the love we are so desperate for, and, equally, why does anyone love us at all when we are so ugly inside? Perhaps some future generation will answer these questions.
The Short, Happy Half-Life of an Elementary Particle
It’s easy to think of elementary particles in cold, clinical terms, as part of an equation, or a table of statistics, or the clicks of a Geiger-Müller counter. But I’ve come to know elementary particles a more personal way.
My wife and I were walking through the park one day when we came across a muon lying on the path, wheezing. “Oh my god,” my wife said, pulling up short. Then she knelt down and put a gentle hand on his shoulder. “Are you okay?”
“Just a stumble,” the muon said. “Bit of a doozy, that first step,” he added, looking up.
I knelt by my wife. “Must have been produced by a cosmic ray,” I said to her, as I helped the muon to stand. “High-speed protons hit the atmosphere, produce pions which then decay to muons.”
Muons are cousins to the electron, with nearly the same properties, but two hundred times heavier, making them prone to heart disease and diabetes.
“Thank you very much, sir,” the muon said, dusting himself off and giving a brief bow.
“Do you have somewhere to go?” I asked. My wife tugged at my arm—even though she was the first to go to his aid, I am the soft-hearted one—but I stood firm.
“Well,” said the muon, scratching himself. “I don’t really know anyone around here. I hate to impose, but perhaps for just a night, until I get my feet. . . .”
“We have a comfortable couch,” I said.
As our guest was washing up, my wife pulled me aside. “Be careful,” she said.
“Muons are perfectly harmless,” I said. “They can go effortlessly through several feet of solid steel. In fact, some people are trying to use muons to scan shipping containers at ports—”
“That’s not what I mean,” she said. “I know how attached you get. And”—here her gaze flicked in the direction of the bathroom—“don’t muons have very short half-lives?”
I shrugged. “A few nanoseconds. Or maybe picoseconds.”
“Much shorter than a dog, then, and remember how devastated you were when we had to put her down? You couldn’t go out for a week.”
I waved a hand. “Don’t worry. A muon isn’t a pet.”
In the morning I pressed breakfast on the muon, who first demurred, but then devoured a huge plate of eggs and bacon and a bowl of cooked oatmeal covered with brown sugar and cream. “You are a most generous host,” he said as he pushed himself from the table and tried to hide a small belch. “And I really can’t impose any further. I suppose I should go look for work.” He stared down at the floor, for, really, what work could a muon with a short resume find?
“Listen,” I said. “I happen to be a physics professor. I’m sure I can find something for you around the lab.”
The muon was a big hit with our junior physics majors, regaling them with stories of the subatomic world and the constant bashing of cosmic rays on the upper atmosphere, how traveling at close to the speed of light slows down time exactly as predicted by Einstein’s relativity. “Wow, Professor Johnson, he really makes it come alive, you know?” one student said to me.
That night after dinner I took him down to the university pub, where we ran into a knot of cosmologists, and together we drank late into the night, speculating on the nature of the universe and cursing the university administration. The muon knew a surprising number of dirty jokes, most of them involving deans, vice-chancellors, and provosts, and had us laughing so hard we could hardly breathe.
And so the muon and I became fast friends. We didn’t go out to the pub often, for which my wife was silently grateful, but we frequently stayed up late talking. Sometimes it was about semiotics and signs, sometimes it was gossip over politics in physics funding. One of our biggest running battle was what sport constitutes football.
“There’s football,” I said, “and then there’s soccer.”
The muon shook his head. “You Americans.”
That night I slipped into bed as quietly as I could. In the darkness my wife spoke. “Have you noticed how gray he’s getting?”
“We’re all getting gray, my love,” I said, though my heart beat a little faster.
“And he moves a little slower, especially in the mornings, have you noticed?” She turned over and put a hand on me. “He’s been a good friend, and I like him,” she said. “It’s just—”
I must have been in denial nonetheless, for the end came quickly, more quickly than I expected. “I’m sorry,” the muon said, wheezing on our bed where we had put him. “I didn’t mean to cause so much trouble.”
I squeezed his hand. “No trouble at all.”
He decayed shortly after that, turning, as is the way of muons, into an electron, an electron antineutrino, and a muon neutrino. We buried him under an oak tree in the park, not far from where we first met him. My wife put her arms around me and laid her head upon my chest. As a eulogy I said, “Over a century ago we physicists believed the universe was invisibly filled with a luminiferous ether. Today we say it’s the Higgs field. A hundred years from now we may postulate something else entirely. But then and now and until the day the sun dies, there is one true constant we search for, one thing we seek to fill the emptiness inside. Love. Love and friendship. And for that there is no theory.”