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A brief etymology of particle physics

05/30/17

How did the proton, photon and other particles get their names?

Over the years, physicists have given names to the smallest constituents of our universe.

This pantheon of particles has grown alongside progress in physics. Anointing a particle with a name is not just convenient; it marks a leap forward in our understanding of the world around us. 

The etymology of particle physics contains a story that connects these sometimes outlandish names to a lineage of scientific thought and experiment.

So, without further ado, Symmetry presents a detailed guide to the etymology of particles—some we’ve found and others we have yet to discover.

Editor’s note: PIE, referenced throughout, refers to proto-Indo-European, one of the earliest known languages.

Discovered particles

Named by: William Whewell, 1834

Ions are atoms or molecules that are charged. The term “ion” was coined by 19th-century polymath William Whewell, who developed it for his contemporary Michael Faraday (see their correspondence), who made important discoveries in the realm of electromagnetism. “Ion" comes from the neuter present participle of Greek ienai, “go,” to describe the particle’s attraction, or tendency to move toward opposite charges. Ienai originates from the PIE ei, “to go, to walk.”

The suffix “-on” derives from “ion” and appears in the names of many particles.

Named by: Paul Dirac, 1945

Fermions (which include the proton and electron) were named for physicist Enrico Fermi. Fermi developed the first statistical formulas that govern fermions, particles that follow the Pauli exclusion principle, which states that certain particles can’t occupy the same quantum space.

Named by: Christian Møller and Abraham Pais, 1947

Leptons are a class of particles that includes the electron, muon, tau and neutrinos. The name “lepton” was suggested as a counterpart to the nucleon, a name for the particles that make up the atomic nucleus, according to a biography of Abraham Pais.

The first known lepton, the electron, is much lighter than a nucleon. Hence the root word for lepton: the Greek leptos, meaning “small, slight, slender, delicate, subtle,” which originates from PIE lep, meaning “peel” and “small shaving.” This root is also shared by the word “leprosy,” so named because it is a disease that causes scabbing and weakness.

According to a 1920 edition of Chemical Abstracts, chemists had suggested the name “lepton” for all electrons, atoms, ions and molecules, but it did not catch on.

Named by: George Stoney, 1891

Electrons are negatively charged leptons that orbit the nucleus of an atom. Late-19th-century physicist George Stoney came up with the term “electron” to describe what he called in a letter “this most remarkable fundamental unit of electricity.”

The word "electric” was first used to describe materials with an attractive force in the early 17th century. “Electric” itself derives from New Latin electricus, which was used in 1600 to characterize the magnetic attraction of amber when it was rubbed. Electricus was taken from Latin electrum, from Greek elektron, both of which refer specifically to amber.

Named by: Carl Anderson and Seth Neddermeyer, 1938

Muons are members of the lepton family and behave like heavier cousins to electrons.

The muon was originally called a “mesotron,” from the Greek word mesos, meaning “middle,” or “intermediate,” according to a letter published in Nature. That’s because its mass was considered to be in the middle, between those of an electron and a proton.

However, more particles with masses between that of electrons and protons were discovered, and “meson” became a general term to describe them, according to an article in Engineering and Science Monthly. Around 1949 the initial particle was renamed “mu-meson,” corresponding to the Greek letter mu (µ) (see article, subscription required).

Later, scientists discovered differences between the mu-meson and other mesons, which led to the mu-meson being reclassified as a lepton and having its name shortened to just “muon.”

Named by: Martin Perl, 1975

Known also as “the tau particle,” “tau lepton” and even “tauon,” this particle became the third charged lepton—after the electron and muon—when it was discovered in 1975. Because of its third-place finish, it was given the symbol tau (τ) for the Greek triton, meaning “third” (see paper). (Why they didn’t just name it a “triton” remains a mystery.)

Named by: Enrico Fermi, 1933

In 1930, physicist Wolfgang Pauli was studying the problem of energy going missing in a type of particle decay. He proposed that the energy was being carried away by a neutral particle that scientists could not detect. According to an article published by the American Institute of Physics (subscription required), he called this a “neutron,” a combination of the root of the word “neutral”—which derives from Latin neuter meaning “neither gender”—with the suffix “-on.”

However, in 1932, another neutral particle was discovered and also called a “neutron.” This second neutron was heavy and existed in the nucleus. In 1933, physicist Enrico Fermi discovered the original particle Pauli had been describing. To distinguish it from the second neutron, which was more massive, he added to the name the Italian diminutive suffix “-ino.”

Neutrinos come in three flavors that correspond to their charged-lepton cousins: electron, muon and tau.

Named by: Murray Gell-Mann, 1963

Cheese Curds

Quarks are elementary particles that form hadrons such as protons and neutrons, as well as more exotic particles and states of matter like quark-gluon plasma. They were proposed simultaneously by Murray Gell-Mann and George Zweig (who wanted to call them “aces”), and different types of quarks were discovered throughout the rest of the 20th century by multiple different teams of physicists.

Gell-Man wrote about the name in his popular science book The Quark and the Jaguar:

In 1963, when I assigned the name “quark” to the fundamental constituents of the nucleon, I had the sound first, without the spelling, which could have been “kwork.” Then, in one of my occasional perusals of Finnegans Wake, by James Joyce, I came across the word “quark” in the phrase “Three quarks for Muster Mark”.

Since “quark” (meaning, for one thing, the cry of the gull) was clearly intended to rhyme with “Mark,” as well as “bark” and other such words, I had to find an excuse to pronounce it as “kwork.” But the book represents the dream of a publican named Humphrey Chimpden Earwicker. Words in the text are typically drawn from several sources at once, like the “portmanteau” words in Through the Looking-Glass. From time to time, phrases occur in the book that are partially determined by calls for drinks at the bar.

I argued, therefore, that perhaps one of the multiple sources of the cry “Three quarks for Muster Mark” might be “Three quarts for Mister Mark,” in which case the pronunciation “kwork” would not be totally unjustified. In any case, the number three fitted perfectly the way quarks occur in nature.

Some scholars suspect that the quark in Joyce’s epic derives from the German quark, which is a type of cheese curd. The German quark is likely taken from West Slavic words meaning “to form”—potentially a reference to milk solidifying and becoming curd. Serendipitously, “to form” is also the non-dairy quark’s role as the main constituent of matter.

Physicists have discovered six types of quarks, named “up,” “down,” “strange,” “charm,” “top” and “bottom.”

up and down quarks: Gell-Mann named these quarks in 1964 for their upward and downward isospin, which is a quantum property of particles related to the strong nuclear force.

strange: Unlike up and down quarks, strange quarks were observed before the quark model was developed, as constituents of composite particles called kaons. These particles were deemed "strange" because they had unusually long lifetimes, due to some of their decays occurring through the weak force. Gell-Man called them “strange” quarks in 1964.

charm: The charm quark was predicted in a paper by two physicists, Sheldon Glashow and James Bjorken, in 1964. As they explained in a New York Times article: “We called our construct the ‘charmed quark,’ for we were fascinated and pleased by the symmetry it brought to the subnuclear world.” “Charm,” meaning “pleasing quality,” is derived from the Latin carmen, “song, verse, enchantment.”

top and bottom: Physicists Makoto Kobayashi and Toshihide Maskawa predicted the existence of the last two quarks in 1973, but they did not assign names to the new particles. Many scientists unofficially called them “truth” and “beauty.”

In a 1975 paper, physicist Haim Harari gave them names that stuck. To preserve the initials “t” and “b” and create a fitting counterpart for up and down quarks, Harari called them “top” and “bottom” quarks.

Named by: Paul Dirac, 1945

Bosons were named for physicist Satyendra Nath Bose. Along with Albert Einstein, Bose developed a theory explaining this type of particle, which had integer spins and therefore did not obey the Pauli exclusion principle. Because bosons don’t obey the exclusion principle, they can essentially exist on top of one another, or in superposition. Bose’s work developing a theory for bosons, a class that include force-carriers such as photons and gluons, is an integral part of the Standard Model.

Named by: unclear

Photons are sometimes called particles of light. Although the concept of a particle of light (as opposed to a light wave) had been around for over two decades by the time Einstein’s seminal paper on the photoelectric effect was published in 1905, there was still not a widely accepted name for the phenomenon, according to a paper by historian of science Helge Kragh. The term “photon” became accepted in 1927 after Arthur Compton won the Nobel Prize for the discovery of Compton scattering, a phenomenon that demonstrated unquestionably that light was quantized.

The modern origins of the idea of light as a particle date back to 1901. Physicist Max Planck wrote about “packets of energy” as quanta, from the Latin quantum, meaning “how much.”

This was adapted by Albert Einstein, who referred to discrete “wave packets” of light as das Lichtquant or “the light quantum” (see paper, in German).

The first known use of the word “photon” was by physicist and psychologist Leonard Troland, who used it in 1916 to describe a unit of illumination for the retina. Photon derives from the Greek phos, “light,” from PIE bha “to shine.”

Five years later, Irish physicist John Joly used the word to describe the “unit of luminous sensation” created by the cerebral cortex in his effort to create a “quantum theory of vision.”

In 1924, a French biochemist used the word, and in 1926, a French physicist picked it up as well. But the word did not catch on among the physics community until a few months later, when American physical chemist Gilbert Lewis (famous for discovering the covalent bond) began using it.

As described in Progress in Optics, Lewis’ concept of a photon was fundamentally different from Einstein’s—for one, Gilbert incorrectly posited that the number of photons was a conserved quantity. Still, the term finally stuck, and has been used ever since.

Named by: unclear

The Higgs boson is the particle associated with the field that gives some elementary particles their mass. It is called the “Higgs” in honor of British theorist Peter Higgs, who predicted its existence in 1964.

However, Higgs wasn’t the only theorist to contribute to the theory of the particle. Others credited with its prediction include Robert Brout, Francois Englert, Philip Anderson, Gerald Guralnik, Carl Hagen, Tom Kibble and Gerard t’Hooft.

The particle has also been called the “Bout-Englert-Higgs” particle, the “Anderson-Higgs” particle, or even the “Englert-Brout-Higgs-Guralnik-Hagen-Kibble” or “ABEGHHK’tH” particle.

According to an article in Nature, this extensive list of names was pared down by theorists such as Benjamin Lee, who referred to it as the “Higgs,” and by Steven Weinberg, who (mistakenly) cited Higgs in a paper (subscription required) as having provided the first theory to explain why some particles have mass.

In an effort to drive popular support for the search for the Higgs boson, physicist Leon Lederman gave it the moniker “The God Particle.” For his part, Higgs the theorist often refers to the “scalar boson” or “so-called Higgs particle.”

Named by: T.D. Lee and C.N. Yang, 1960

Carriers of the weak nuclear force in charged current interactions, W bosons were first predicted and named in a paper (subscription required) in 1960. W bosons likely draw their name from the weak nuclear force, so called because its field strength over a given distance is much weaker than the strong and electromagnetic forces. The word weak comes from Old Norse veikr “weak” with potential origins tracing back to PIE weik, “to bend, wind.”

Named by: Sheldon Glashow, 1961

Desert

Like W bosons, Z bosons are mediators for the weak force. Unlike W bosons, though, Z bosons have no charge, so exchanges of Z bosons are called “neutral current interactions.”

When Sheldon Glashow theorized them in a paper in 1961, he did not provide an explanation. Some theories allege that Z stands for “zero” because of the neutral current’s lack of charge. Zero has its roots in Italian zero, which comes from Medieval Latin zephirum. Italian mathematician Leonardo Fibonacci coined zephirum, meaning “zero,” from Arabic sifr, “nothing.” Sifr is likely a translation of Sanskrit sunya-m, “empty place, desert.”

Named by: Murray Gell-Mann, 1962

Glue Bottle

Gluons are mediators of the strong force, which is what holds the nucleus together. Interactions through the strong force can be thought of as exchanges of gluons.

Gluons were ostensibly named for their glue-like properties and ability to keep the nucleus together (see paper, subscription required). “Glue” derives from Early French glu and has its roots in Latin gluten “to glue,” which is also the origin of gluten, the “nitrogenous part of grain.” However, there are no foods that are gluon-free.

Named by: Lev Okun, 1962

The term “hadron” was coined at the 1962 International Conference on High Energy Physics (see report) to refer to heavier partner particles to leptons. Hadron comes from the Greek hadros, meaning “thick, bulky, massive.” It was later discovered that hadrons were composite particles made up of quarks surrounded by a haze of gluons.

Named by: Abraham Pais, 1953

Baryons are a kind of hadron that is made of three quarks held together by gluons. Protons and neutrons, which make up the nucleus of atoms, are both baryons.

The use of the word “baryon” appeared in 1953, when physicist Abraham Pais proposed it in an article as a name for nucleons and other heavy particles. It draws from barys, the Greek word for “heavy.”

Named by: Ernest Rutherford, 1920

The proton is one of the three constituents of an atom, along with neutrons and electrons.

According to an article published in the American Journal of Physics (subscription required), physicist Ernest Rutherford proposed the name in honor of 19th century scientist William Prout. In 1816 Prout proposed calling the hydrogen atom a “protyle,” from the Greek protos, “first,” and húlē, “material.” Prout believed hydrogen was the constituent atom for all elements.

Prout was later proven wrong, but Rutherford suggested calling the particle he discovered either “proton”—after Prout’s hypothetical particle—or “prouton”—after Prout himself. Rutherford and other scientists eventually settled on proton, whose root was also the Greek protos.

Named by: unclear

Neutrons are particles made of up and down quarks. According to a letter published in Nature, it is unclear whether physicist William Harkins or physicist Ernest Rutherford referred to the electrically neutral nucleon as a “neutron” first. What is clear is that both came up with the same name for the same particle in 1921, likely drawing on the same etymology of the root word “neutral.”

Named by: Homi J. Bhabha, 1939

Mesons are particles made of both a quark and an anti-quark.

Mesons were originally referred to as “heavy electrons,” as their masses were between the electron and the proton, or as “U-particles” for their unknown nature, or as “Yukawa particles” after physicist Hideki Yukawa, who first theorized them in 1935. In the past, mesons were also used inaccurately to refer to bosons.

Carl Anderson and Seth Neddermeyer, co-discoverers of the muon, suggested calling the particle a “mesotron,” derived from the Greek word mesos, meaning “middle,” for their intermediate masses. Physicist Homi J. Bhabha, considered the father of nuclear physics in India, suggested in an article (subscription required) the shorter name “meson” in 1939.

Many mesons, such as kaons and pions, are simply contractions named after the letters used to represent them (K-meson, Pi-meson).

Named by: unclear

Particles of matter have partner particles of antimatter, which share the same mass, but have opposite electrical charge and spin. When a matter-antimatter pair meets, the particles annihilate one another.

In 1928, theorist Paul Dirac theorized in a paper what he called the “anti-electron,” the first hypothetical particle of antimatter. However, when Carl Anderson discovered the particle in 1932, he called it a “positron” because of its positive charge. (According to an article by theoretical physicist Cecilia Jarlskog, an international group of physicists suggested in 1948 that the positron should be called a “positon” and the electron should be renamed a “negaton,” but the effort never quite caught on.)

Around 1937, Dirac’s original “anti-” prefix came back into use to describe particles like the positron (see article, subscription required).

Possibly the first reference to modern antimatter came in 1948 (see article, subscription required). It’s likely that it took so long to come up with a generic term due to the limited number of particles and antiparticles that had been discovered at that time.

The actual first use of the term occurred in 1898 as part of a somewhat whimsical letter published in Nature (subscription required) proposing the existence of matter with “negative gravity.”

The prefix “anti-“ originates from Greek anti, meaning “against, opposed to, opposite of, instead.” The word “matter,” meaning “physical substance,” is a 14th-century construction that comes from materie, “subject of thought, speech, or expression,” itself deriving from Latin material, or “substance from which something is made.” This comes from Latin mater "origin, source, mother.”

Hypothetical particles

Named by: Frank Wilczek, 1978

Axion Laundry Box

Axions are hypothetical particles and candidates for the dark matter that is thought to potentially make up most of the mass in the universe. Frank Wilczek said in a Nobel lecture that he “named them after a laundry detergent, since they clean up a problem.”

Said problem is known as “the Strong CP problem,” which is an unsolved question of why quark interactions and anti-quark interactions seem to follow the same rules.

Named by: Justin Khoury and Amanda Weltman, 2003

Chameleon

The chameleon particle is a hypothetical particle of dark energy.

The word “chameleon” comes from the Greek cognate khamaileon, whose root khamai means “on the ground.” Its other root, leon means lion; thus “ground lion.” But the name chameleon comes from the defining characteristic of lizards of that name. In a 2003 paper (subscription required), physicists Justin Khoury and Amanda Weltman proposed and named the particle, the physical characteristics of which would depend on its environment.

Named by: Dmitri Blochinzew and F. M. Gal’perin, 1934

The graviton, an undiscovered particle associated with the force of gravity, is one of the oldest hypothetical particles (see paper, in Russian). It takes its name from the English “gravity,” which itself comes from Old French gravité meaning “seriousness, thoughtfulness.” The Latin root, gravis “heavy,” was repurposed as gravity for scientific use in the 17th century to mean “weight.”

Perhaps the earliest use of the word comes from the 1644 philosophical text Two Treatises: of Bodies and of Man’s Soul. It would be another 40 odd years until Isaac Newton made gravity mathematically rigorous in his Principia.

Named by: Y. Chikashige, Rabindra Mohapatra, and Roberto Peccei, 1980

In particle physics, “lepton number” is the number of leptons in a particle reaction minus the number of antileptons. As far as we know, lepton number must be conserved from the beginning to the end of an interaction.

A majoron is hypothetical type of boson proposed to solve problems with the conservation of lepton number thought to exist in some high-energy collisions (see paper, subscription required). Majorons were named after Majorana fermions, named after physicist Ettore Majorana, who hypothesized the existence of particles that were their own antiparticles. “Majorana,” a variant of Maiorana, an Italian surname popular in Sicily, owes its roots to the herb marjoram, which is common in that area.

Named by: Gerald Feinberg, 1967

Proposed in a 1967 paper (subscription required) as a name for hypothetical faster-than-light particles, tachyons take their name from the Greek takhys for “swift.”

Named by: Abdus Salam, J. Strathdee, 1974

Supersymmetry is a theory that about doubles the number of particles in the Standard Model of particle physics. It states that every particle has a (usually more massive) “super” partner.

Although supersymmetry comes in many forms and flavors and took many years to develop, it owes the name “supersymmetry” to a 1974 paper (subscription required). Super comes from “supergauge,” used to describe the high power of gauge operator, and symmetry, because the theory is global rather than local (see paper, subscription required).

The nomenclature for supersymmetric particles was put forward in 1982 in a paper by physicists Ian Hinchliffe and Laurence Littenberg.

To identify the supersymmetric partner particle of a boson, add the suffix “-ino.” (For example, the supersymmetric partner of a photon would be called a photino.) And to identify the partner of a fermion, add the prefix “s-.” (For example, the partner of a muon would be a smuon.)