The Science Book

182 JAMES CLERK MAXWELL

T

he series of differential
equations describing
the behavior of
electromagnetic fields developed
by Scottish physicist James Clerk
Maxwell through the 1860s and
1870s are rightly considered one
of the towering achievements in
the history of physics. A truly
transformative discovery, they not
only revolutionized the way that
scientists viewed electricity,
magnetism, and light, but also
laid the ground rules for an entirely
new style of mathematical physics.
This would have far-reaching

consequences in the 20th century,

and today offers hope for unifying

our understanding of the universe

into a comprehensive “Theory of

Everything.”

The Faraday effect

Danish physicist Hans Christian

Ørsted’s discovery, in 1820, of

a link between electricity and

magnetism set the stage for a

century of attempts to discover

the links and interconnections

between seemingly unconnected

phenomena. It also inspired

a significant breakthrough by

IN CONTEXT

BRANCH

Physics

BEFORE

1803 Thomas Young’s double-

slit experiments appear to

show that light is a wave.

1820 Hans Christian Ørsted

demonstrates a link between

electricity and magnetism.

1831 Michael Faraday shows

that a changing magnetic field

produces an electric field.

AFTER

1900 Max Planck suggests

that in some circumstances,

light can be treated as if it

were composed of tiny “wave

packets,” or quanta.

1905 Albert Einstein shows

that light quanta, today known

as photons, are real.

1940s Richard Feynman

and others develop quantum

electrodynamics (QED) to

explain the behavior of light.

Michael Faraday. Today, Faraday

is perhaps best known for his

invention of the electric motor and

the discovery of electromagnetic

induction, but it was a less

celebrated discovery that provided

Maxwell’s departure point.

For two decades, Faraday

had been attempting, on and off,

to find a link between light and

electromagnetism. Then, in

1845, he devised an ingenious

experiment that answered the

question once and for all. It involved

passing a beam of polarized light

(one in which the waves oscillate

A magnetic field can change the

polarization of light.

The discovery of long-wavelength

radio waves (also part of the electromagnetic

spectrum) confirms the equations.

Light and magnetism are affectations

of the same substance.

Assuming light to be an electromagnetic wave,

it is possible to formulate equations to describe

mathematically the behavior of light.

This suggests that light may be an

electromagnetic wave.