Poetry of Physics and the Physics of Poetry

108 The Poetry of Physics and The Physics of Poetry

When one looks up at the sky on a cloudless day, one observes blue light.
This light is sunlight, which has been absorbed by air molecules in the
upper atmosphere and reradiated towards Earth. Because the amount of
light reradiated at any one particular frequency is proportional to the
fourth power of the frequency, more blue light than red is reradiated
towards Earth and hence, the sky appears blue. At sunset or sunrise, light
arriving from the Sun has a thicker envelope of air to travel through in
order to reach us. Since more blue light than red has been absorbed out
of the beam of sunlight as it travels through the atmosphere, the light
reaching us during a sunset or sunrise appears red.

Colour Wavelength, λ (cm) Frequency, f (sec-^1 )

red 7 × 10-^5 4.2 × 10^14

orange 6.5 × 10-^5 4.6 × 10^14

yellow 6 × 10-^5 5.0 × 10^14

green 5 × 10-^5 6.0 × 10^14

blue 4.5 × 10-^5 6.7 × 10^14

indigo 4.3 × 10-^5 6. 9 × 10^14

violet 4 × 10-^5 7.5 × 10^14

Maxwell’s identification of light with oscillations of the electric and
magnetic fields explains the wave nature of light. Long before Maxwell’s
identification, it was realized that light behaves as a wave. The wave
nature of light was first suggested by Christian Huygens, a contemporary
of Newton. In fact, he and Newton had a long-standing controversy
concerning the nature of light. Newton adopted the position that light
was a beam of particles and hence, could not display wave behaviour.
Huygens had a difficult time convincing the scientific world of the wave
nature of light because of the formidable reputation of his scientific foe.
After the results of a number of experiments corroborating Huygens
point of view became known, however, the science community finally
adopted the wave picture of light.
By an ironic twist of fate, however, experiments performed in the
early part of the 20th century have revealed that, although light behaves
in many situations as a wave, there are instances when it also behaves
like a beam of particles. So, there is also a sense in which Newton was
correct. However, from the point of view of the experimental evidence
that was available to Huygens and Newton, it was Huygens who made
the more accurate interpretation of the data.