The search for the true nature of light goes
back centuries and includes contributions from some of the most illustrious
scientists in history.
To the ancient Egyptians, light was the gaze of their supreme god,
Ra, and it emanated from the sun and the moon, Ra’s eyes. The
ancient Greeks believed the reverse: Pythagoras thought internal
fires in the human eyes illuminated the world, while Plato believed
sight was only possible when the fires of the eye met and combined
with daylight, the fire of the sun.
In 1000 AD, a Persian scientist named Abu Ali Hasan Ibn al-Haitham
(known in the west as Alhazen) used a combination of logic and experimentation
to show that light did not shoot out from our eyes, but entered into
them, to produce vision. Centuries later, his work influenced Roger
Bacon and Johannes Kepler, among others.
In the seventeenth century, a debate erupted over the definition
of light. Christiaan Huygens believed light was a wave, while Isaac
Newton argued that it was a particle. Due mainly to his well-established
reputation, Newton’s particle theory won out and was accepted
for more than a century.
The pendulum swung the other way in the early nineteenth century.
In 1801 Thomas Young performed a series of ingenious experiments
showing that light rays could interfere with one another in a way
similar to water and sound waves.
A half-century later, the Scottish scientist James Clerk Maxwell
showed that electric and magnetic fields travel through space together
in the form of intertwined waves. Maxwell further demonstrated that
these “electromagnetic” waves travel at precisely the
speed of light, leading him to correctly propose that light was an
electromagnetic wave.
The debate seemed settled and Huygens appeared vindicated, but in
the early twentieth century, the work of Max Planck, Albert Einstein,
and many others revealed a strange third possibility, which repeated
experiments have since confirmed: Both light and matter, it turns
out, exhibit properties of both waves and particles. Called wave-particle
duality, this is a central concept in quantum mechanics.
—Ker Than |
