The Science Book

247

See also: James Clerk Maxwell 180–85 ■ Albert Einstein 214–21 ■ Erwin Schrödinger 226–33 ■
Werner Heisenberg 234–35 ■ Richard Feynman 272–73

A PARADIGM SHIFT

numbers of fermions interact with
one another. In 1926, Dirac’s PhD
supervisor Ralph Fowler used his
statistics to calculate the behavior
of a collapsing stellar core and
explain the origin of superdense
white dwarf stars.

Quantum field theory
While much of schoolbook physics
focuses on the properties and
dynamics of individual particles
and bodies under the influence of
forces, a deeper understanding
can be gained by developing field
theories. These describe the way
that forces make their influence felt
across space. The importance of
fields as independent entities was
first recognized in the mid-19th
century by James Clerk Maxwell
while he was developing his
theory of electromagnetic radiation.
Einstein’s general relativity is
another example of a field theory.
Dirac’s new interpretation of
the quantum world was a quantum
field theory. In 1928, it allowed him
to produce a relativistic version of
Schrödinger’s wave equation for

the electron (that is, one that could

take into account the effects of

particles moving close to the speed

of light, and therefore model the

quantum world more accurately

than Schrödinger’s nonrelativistic

equation). The so-called Dirac

equation also predicted the

existence of particles with identical

properties to particles of matter but

with opposite electric charge. They

were dubbed “antimatter” (a term

that had been bandied around in

wilder speculations since the late

19th century).

The antielectron particle,

or positron, was experimentally

confirmed by US physicist

Carl Anderson in 1932, detected

first in cosmic rays (high-energy

particles showered into Earth’s

atmosphere from deep space),

and then in certain types of

radioactive decay. Since then,

antimatter has become a subject

for intense physical research,

and also beloved of science-fiction

writers (particularly for its

habit of “annihilating” with a burst

of energy on contact with normal

matter). Perhaps more importantly,

however, Dirac’s quantum

field theory laid the foundations

for the theory of quantum

electrodynamics brought to fruition

by a later generation of physicists. ■

Paul Dirac Paul Dirac was a mathematical

genius who made several key

contributions to quantum

physics, sharing the Nobel

Prize in Physics with Erwin

Schrödinger in 1933. Born in

Bristol, England, to a Swiss father

and an English mother, he earned

degrees in electrical engineering

and mathematics at the city’s

university, before continuing his

studies at Cambridge, where he

pursued his fascination with

general relativity and quantum

theory. After his groundbreaking

advances of the mid-1920s, he

continued his work at Göttingen

and Copenhagen before

returning to Cambridge, having

been appointed the Lucasian

Chair in Mathematics. Much of

his later career was focused on

quantum electrodynamics. He

also pursued the idea of unifying

quantum theory with general

relativity, but this endeavor met

with limited success.

Key works

1930 Principles of Quantum

Mechanics

1966 Lectures on Quantum

Field Theory

When a particle

and its antiparticle

come together,

they annihilate.

Their mass turns

into photons of

electromagnetic

energy in accord

with the equation

E = mc^2.

Annihilation

Electron

Positron

Photon

Photon