Party for a Particle

A little particle called the electron is celebrating its 100th birthday this week, and scientists are spinning out lectures, TV shows, special issues of magazines, Web pages, symposiums, colloquia--a regular cornucopia of electrifying stuff.

“The electron is a very big deal this year,” said physicist Allan D. Franklin of the University of Colorado, who has already given his talk, “Are There Really Electrons?” five times in four different countries.

The electron, says UC Berkeley chemist Marvin Cohen, “is a marvelous particle.”

The trouble is, it’s hard to say exactly what kind of “particle” an electron really is. “Particle” implies something you can get a handle on. But an electron has no physical dimensions; it’s a point, with no height, width or depth. It’s as close to being not there as you can get. Trying to imagine what an electron looks like can “get pretty scary,” said Cohen, who spends his life shuffling electrons around to create new kinds of matter.

And yet, when you stub your toe and hop off howling in pain, you can blame the electron. When you fall in love, or think deep thoughts, blame the electron. In fact, just about everything in your daily life gets its properties from electrons, from the colors of begonias to the get-up-and-go of the gasoline in your car to the flavor of toothpaste. Electrons, in fact, are behind all chemistry, making sugar sweet, dynamite explosive and blood red, and making the DNA that encodes all your genes stick together.

Clouds of electrons buzz around the outer edges of atoms, giving each element its individual characteristic. When atoms combine, they reach out and touch each other through their electrons, so ultimately it’s electrons that determine whether oil and water mix, or what combinations of atoms smell rotten or explode. The molecules and cells that make up the human heart and brain and hormone system communicate by shifting around electrons--making everything you see, hear, think and feel a matter of electricity.

Of course, electrons were working all of these miracles long before April 30, 1897, when British physicist J.J. Thomson first reported his discovery that electricity comes in discrete “corpuscles” of electric charge, which later became known as electrons. They had just been doing it incognito, hidden from the probing eyes of people.

Indeed, before Thomson decided that the green glow of his glass vacuum tube was a stream of “particles of electric charge,” people thought of electricity as a kind of fluid or current that flowed from one place to another. Thomson figured out that the stream was actually composed of corpuscles 2,000 times lighter than the lightest atom (hydrogen). The notion that something could be smaller than an atom was shocking, because atoms were still considered the smallest possible bits of stuff. Indeed, many scientists still thought atoms were only metaphors, not real physical entities. Thomson’s discovery settled the reality of the atom once and for all.

“Atoms became irresistibly real when they began to fall apart,” said Stanford Linear Accelerator Center physicist Chris Quigg.

The birth of the electron itself (rather than its discovery by humans) probably goes back to the origin of the universe at the Big Bang. Electrons popped out of the primordial energy ball in great numbers along with their anti-matter counterparts, the positrons. When electrons and positrons meet, they annihilate each other, melting back into pure energy.

Scientists would love to know why the universe today is composed mainly of electrons. Where have all the positrons gone? For now, that remains but one of many juicy mystery about electrons.

Eventually, the universe cooled down enough for electrons to attach themselves to protons and neutrons, forming the first atoms. Without electrons, atoms would be naked nuclear skeletons, with no way to attach themselves to other atoms, forming carbon atoms into diamonds and DNA, for example. Electrons are the bits of glue that hold molecules together and determine how they stack together or fold into intricate shapes. Aside from the furious buzzing about of electrons, matter is almost entirely empty space. Electrons even perform action at a distance--sending energy from the sun to light up the day and set up chemical cascades in green plants that turn dirt and water into food.

If electrons are so ubiquitous and important, one might wonder why no one noticed them before J.J. Thomson came along. After all, they do have mass. They are a unit of electric charge.

On Earth, however, nearly all electrons are bound tightly into atoms by their attraction to positively charged protons in the atomic nucleus. And electricity is a formidable force--many trillions of times stronger than gravity. Electrons hang onto their atoms fiercely, and it takes a great deal of energy to shake one loose--whether the energy comes from a person shuffling across the carpet in their slippers and making sparks on the doorknob, thunderclouds ripping electrons off molecules to make lightning, or the heat of a flame boiling them off and jiggling them around.

In order to discover the electron, scientists had to pry it loose from the atom. Curiously, Thomson, who performed this experimental feat, was known as something of a klutz, according to physicist and Nobel laureate Steven Weinberg of the University of Texas. Weinberg quotes an account from one of Thomson’s assistants: “J.J. was very awkward with his fingers, and I found it necessary not to encourage him to handle the instruments.”

In the years following Thomson’s discovery at Cambridge University’s Cavendish Laboratory, physicists there offered an annual toast: “The electron: May it never be of use to anybody!” But physicists--as much as chemists and engineers--have put the little particle to good use.

Electrons are used as subatomic probes, for example, to look inside the atomic nucleus. In the 1970s, electrons bombarding nuclear particles produced the first firm evidence for the existence of even more fundamental particles known as quarks.

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In everyday life, the electron has spawned everything from the Internet to lasers, microwave ovens to cellular phones.

Still, the electron is shrouded in mystery. Why, for example, are there two other particles exactly the same as electrons, but heavier--the muon and the tao? “Why does it have these two siblings?” asked Burton Richter of the Stanford Linear Accelerator Center, who won a Nobel prize using electrons to probe the nucleus for quarks.

There is also the peculiar fact that quarks appear to have one-third of a unit of electric charge. If the electron is the fundamental unit of electricity, how can anything have one-third of a unit? “It’s weird,” said Richter. “No one understands it.”

Years ago, physicist Frank Oppenheimer brought a dozen friends to his Exploratorium science museum in San Francisco to talk about how best to describe the elusive electron to the public. One teacher at the meeting bemoaned the fact that electricity was difficult to get a handle on because you couldn’t see it.

On the contrary, said physicist Philip Morrison of MIT, “It’s the only thing you can see.”