Who Discovered Quarks and Where do the subatomic particles that make up protons and neutrons come from?

First scientists identified plant fibers, then individual cells. Then scientists conceived of atoms and molecules. In the early twentieth century, scientists discovered electrons and then the existence of protons and neutrons.

In each case, scientists believed that they had finally discovered the smallest possible particle of matter. Each time this belief proved wrong.

The discovery of quarks (fundamental particles that make up protons and neutrons) in 1962 led science into the bizarre and alien quantum world inside protons and neutrons, a world of mass with no mass and where mass and energy are freely exchanged. This discovery has taken science one giant step closer to answering one of the most basic questions of all: What really is matter made of? At each new level the answer and the world grows stranger.

As the nineteenth century closed, Marie Curie broke open the atom and proved that it was not the smallest possible particle of matter. Soon scientists had identified two subatomic particles: electrons and protons. In 1932 James Chadwick discovered the neutron. Once again scientists thought they had uncovered the smallest particles of all matter.

When particle accelerators were invented in the mid-1930s, scientists could smash neutrons into protons, and protons into heavier nuclei to see what the collisions would produce. In the 1950s Donald Glaser invented the “bubble chamber.” Subatomic particles were accelerated to near light speed and flung into this low-pressure, hydrogen-gas-filled chamber. When these particles struck a proton (a hydrogen nucleus), the proton disintegrated into a host of strange new particles. Each of these particles left a telltale trail of infinitesimally small bubbles as they sped away from the collision site. Scientists couldn’t see the particles themselves. But they could see the trails of bubbles.

Scientists were both amazed and baffled by the variety and number of these tiny tracks on bubble chamber plots (each indicating the temporary existence of a previously unknown particle). They were unable to even guess at what these new subatomic particles were.

Murry Gell-Mann was born in Manhattan in 1929. A true prodigy, he could multiply large numbers in his head at age three. At seven, he beat twelve-year-olds in spelling bees. By age eight, his intellectual ability matched that of most college students. Gell-Mann, however, was bored and restless in school and suffered from acute writer’s block. He rarely finished papers and project descriptions, even though they were easy for him to complete.

Still, he sailed through undergraduate school at Yale and then drifted through MIT, the University of Chicago (where he worked for Fermi) and Princeton (where he worked for Oppenheimer). By the age of 24, he had decided to focus on understanding the bizarre particles that showed up on bubble chamber plots. Bubble chamber plots allowed scientists to estimate the size, electrical charge, direction, and speed of each particle, but not its specific identity. By 1958 almost 100 names were in use to identify and describe this forest of new particles that had been detected.

Gell-Mann decided that he could make sense of these particles if he applied a few fundamental concepts of nature. He assumed that nature was simple and symmetrical. He also assumed that, like all other matter and forces in nature, these subproton sized particles had to be conservative. (Mass, energy, and electrical charge would be conserved, not lost, in all collision reactions.)

With these principles as his guides, Gell-Mann began to group and to simplify the reactions that happened when a proton split apart. He created a new measure that he called strangeness that he took from quantum physics. Strangeness measured the quantum state of each particle. Again he assumed that strangeness would be conserved in each reaction.

Gell-Mann found that he could build simple patterns of reactions as particles split apart or combined. However, several of these patterns didn’t appear to follow the laws of conservation. Then Gell-Mann realized that he could make all of the reactions follow simple, conservative laws if protons and neutrons weren’t solid things, but were, instead, built of three smaller particles.

Over the course of two years’ work, Gell-Mann showed that these smaller particles had to exist inside protons and neutrons. He named them k-works, then kworks for short. Soon afterward he read a line by James Joyce that mentioned “three quarks.” Gell-Mann changed the name of his new particles to quarks.