FUNDAMENTAL BUILDING BLOCKS 307
accepted theory, which only
allowed for whole-number charges.
Gell-Mann realized that if these
subunits remained hidden, trapped
inside hadrons, this didn’t matter.
The predicted omega particle (Ω–),
made up of three quarks, was
detected at Brookhaven National
Laboratory, New York, soon after
Gell-Mann’s publication. This
confirmed the new model, which
Gell-Mann has insisted should be
credited both to him and to Zweig.
Initially, Gell-Mann was
doubtful that quarks could ever
be isolated. However, he now
emphasizes that although he
initially saw his quarks as
mathematical entities, he never
ruled out the possibility that quarks
might be real. Experiments at the
Stanford Linear Accelerator Center
(SLAC) between 1967 and 1973
scattered electrons off hard
granular particles within the
proton, revealing the reality of
quarks in the process.
The standard model
The standard model developed from
Gell-Mann’s quark model. In this
model, particles are divided into
fermions and bosons. Fermions are
the building blocks of matter, while
bosons are force-carrying particles.
The fermions are further split
into two families of elementary
particles—quarks and leptons.
Quarks group together in twos and
threes to make up the composite
particles called hadrons. Subatomic
particles with three quarks are
known as baryons, and include
protons and neutrons. Those made
of a quark and antiquark pair are
called mesons, and include pions
and kaons. In total there are six
quark “flavors”—up, down, strange,
charm, top, and bottom. The
defining characteristic of quarks is
that they carry something called
“color charge,” which allows them to
interact via the strong force. The
leptons do not carry color charge and
are not affected by the strong force.
There are six leptons—the electron,
muon, tau, and the electron, muon,
and tau neutrinos. Neutrinos have no
electrical charge and only interact
via the weak force, making them
extremely hard to detect. Each
particle also has a corresponding
“antiparticle” of antimatter.
The standard model explains
forces at the subatomic level as
the result of an exchange of force-
carrying particles known as
“gauge bosons.” Each force has
its own gauge boson: the weak
force is mediated by the W+,
W–, and Z bosons; the strong
electromagnetic force by photons;
and the strong force by gluons.
The standard model is a robust
theory and has been verified by
experiment, notably with the
discovery of a Higgs boson—the
particle that gives other particles
mass—at CERN in 2012. However,
many consider the model inelegant
and there are problems with it,
such as its failure to incorporate
dark matter or explain gravity in
terms of boson interaction. Other
questions that remain unanswered
are why there is a preponderance
of matter (rather than antimatter) in
the universe, and why there appear
to be three generations of matter. ■Murray Gell-Mann
Born in Manhattan, Murray
Gell-Mann was a child
prodigy. He taught himself
calculus at 7 years old and
entered Yale at 15. He earned
a doctoral degree from the
Massachusetts Institute of
Technology (MIT), graduating
in 1951, and then decamped
to the California Institute of
Technology (Caltech), where
he worked with Richard
Feynman to develop a
quantum number called
“strangeness.” Japanese
physicist Kazuhiko Nishijima
had made the same discovery,
but called it “eta-charge.”
With wide-ranging
interests and speaking some
13 languages fluently, Gell-
Mann enjoys displaying his
polymath’s breadth of
knowledge with plays on
words and arcane references.
He is perhaps the originator
of the trend for giving new
particles funny names. His
discovery of the quark won
him the 1969 Nobel Prize.Key works1962 Prediction of the
Ω– Particle
1964 The Eightfold Way:
A Theory of Strong
Interaction SymmetryOur work is a delightful game.
Murray Gell-Mann