The Science Book

306 MURRAY GELL-MANN

to be fundamental. This merry
circus of new species was
dubbed the “particle zoo.”

The Eightfold Way
By the 1960s, scientists had
grouped particles according to
how they were affected by the
four fundamental forces: gravity,
electromagnetic force, and the
weak and strong nuclear forces.
All particles with mass are
influenced by gravity. The
electromagnetic force acts on any
particle with an electric charge.
The weak and strong forces
operate over the miniscule ranges
found within the atomic nucleus.
Heavyweight particles called

“hadrons,” which include the

proton and neutron, are “strongly

interacting” and influenced by all

four fundamental forces, while the

lightweight “leptons,” such as

the electron and neutrino, are

unaffected by the strong force.

Gell-Mann made sense of the

particle zoo with an octet ordering

system he called the “Eightfold

Way,” a pun on the Buddhist Noble

Eightfold Path. Just as Mendeleev

had done when arranging the

chemical elements into a periodic

table, Gell-Mann imagined a

chart into which he placed the

elementary particles, leaving

spaces for as yet undiscovered

pieces. In an effort to make the

most economical design, he

proposed that hadrons contained

a new and as-yet-unseen

fundamental subunit. Since the

heavier particles were no longer

fundamental, this change reduced

the number of fundamental

particles down to a manageable

number—hadrons were now simply

combinations of multiple

elementary components. Gell-

Mann, with his penchant for wacky

names dubbed this particle a

“quark” (pronounced “kwork”), after

a favorite line from James Joyce’s

novel Finnegans Wake.

Real or not real?

Gell-Mann was not the only person

to suggest this idea. In 1964, a

student at Caltech, Georg Zweig,

had suggested that hadrons were

made of four basic parts, which he

called “aces.” The CERN journal

Physics Letters refused Zweig’s

paper, but that same year published

a paper by the more senior Gell-

Mann outlining the same idea.

Gell-Mann’s paper may have

been published because he did

not suggest that there was any

underlying reality to the pattern—

he was simply proposing an

organizing design. However, this

design appeared unsatisfactory,

since it required quarks to have

fractional charges, such as –^1 / 3 and

+^2 / 3. These were nonsensical to

Three quarks for Muster Mark!

James Joyce

The standard model
arranges the fundamental
particles in a table according
to their properties. The Higgs
boson, predicted by the model,
was discovered in 2012.

up

≈2.3 MeV/c²

≈4.8 MeV/c²

0.511 MeV/c²

<2.2 eV/c² <0.17 MeV/c² <15.5 MeV/c² 80.4 GeV/c²

105.7 MeV/c² 1.777 GeV/c² 91.2 GeV/c²

≈95 MeV/c² ≈4.18 GeV/c²

≈1.275 GeV/c² ≈173.07 GeV/c² 0 ≈126 GeV/c²

0

U

down

d

strange

s

bottom

b

tau

훕

photon

후

Z boson

Z

W boson

W

electron

e

muon

훍

electron

neutrino

훖e

muon

neutrino

tau

neutrino

charm

C

top

t

gluon

g

Higgs

boson

H

훖훍 훖훕

up

≈2.3 MeV/c²

U Gauge bosons

Quarks

Leptons

Mass

Symbol

Name

Higgs boson

Fermions Bosons