We know the characteristics of substances, but what are some of the
characteristics of waves? Not all waves behave similarly. Sound, one clas-
sic example of a wave, can go around corners. Light doesn’t. Water waves,
another obvious type of wave, can interfere with each other. When two
water waves collide, the resulting wave can be either stronger or weaker
than the original waves—stronger where the high points of both waves
reinforce each other, and weaker where the high points of one wave coin-
cide with the low points of the other wave.
Such was the almost universal reverence in which Newton was held that
few efforts were made to either validate or dispel the wave theory of light
for more than a century, even though the noted physicist Christian Huy-
gens (1629–1695) strongly favored the view that light was a wave phenom-
enon. The individual who would finally perform the definitive experiment
was Thomas Young, a child prodigy who could read by age two and who
could speak twelve languages by the time he was an adult. In addition to
being a child prodigy, fortune had favored Young in other respects, as he
was born into a well-to-do family.
Thomas Young was a polymath whose accomplishments extended into
many of the realms of science, and even beyond. He made significant
contributions to the theory of materials; Young’s modulus is still one of
the fundamental parameters used to describe the elasticity of a sub-
stance. Young was also an Egyptologist of note, and was the first individ-
ual to make progress toward deciphering Egyptian hieroglyphics.
After a brilliant performance as a student at Cambridge, Young decided
to study medicine. Young was extremely interested in diseases and condi-
tions of the eye. He constructed a theory of color vision, observing that in
order to be able to see all colors, it was only necessary to be able to see red,
green, and blue. While still a medical student, he discovered how the
shape of the eye changes as it focuses. Shortly after, he correctly diag-
nosed the cause of astigmatism, a visual fuzziness caused by irregulari-
ties in the curvature of the cornea.
Young’s fascination with the eye led him to begin investigations into
color vision and the nature of light. In 1802, he performed the experiment
that was to show once and for all that light was a wave phenomenon.
The Double-Slit Experiment
Particles and waves behave differently as they go through slits. If one im-
agines waves coming onto shore, blocked by a jetty of rocks with one nar-
row opening, the waves spread out in concentric circles around the
opening. If there are two narrow openings reasonably close to each other,All Things Great and Small 47