Among all the human senses, sight is thought to be the most important. Almost all our activities are dependent on our ability to see. Visible light makes all these possible, because no one can see anything without it. But what was really the mystery behind light?
When St. John the Evangelist said. “God is Light”, there was an implicit message that light is so mysterious to be studied. Many well known philosophers and scientists attempted to explain the nature and behavior of light.
THE NATURE OF LIGHT
The debate on whether light is made of streams of particles (corpuscles) or waves dates back from the time Sir Isaac Newton proposed his article on corpuscular theory of light as opposed to Christian Huygens’ (1629-1695) wave theory of light.
Newton rejected Huygens idea that under some circumstances, light does spread out. According to Newton light travels only in straight lines (diffraction had not yet been discovered then). This explains why a shadow is formed when an object is placed in a beam of light.
During that time, Newton’s theory was favored over Huygens’ wave theory, partly because Newton was the most eminent scientist of his day, and partly because there was not enough experimental evidence to provide an adequate basis for comparing the two theories.
In 1801, Thomas Young (1773-1829) discovered the diffraction and interference of light which can be explained only in terms of the wave theory. The wave theory was further established when James Clerk Maxwell predicted in 1860 that changing electric and magnetic fields could propagate through space as electromagnetic waves and that light itself is an electromagnetic wave. Maxwell’s theory was confirmed when Heinrich Hertz discovered experimentally in the 1880’s the existence of electromagnetic waves through radio waves. Hertz found that the electromagnetic waves he produced shared common properties with light such as reflection and thus supported Maxwell’s assumptions. This marks the end of the classical particle, wave and electromagnetic theories of light, and the beginning of the quantum theory of light.
In 1900, Max Planck (1858-1947) introduced his postulates to explain blackbody radiation. A blackbody is a surface or object that is capable of absorbing all radiation falling on it. He proposed that energy comes in discrete units called quanta. The word quantum means the smallest possible unit.
Later in 1905, Albert Einstein (1879-1955) theorized that light is composed of bundles of wave energy later called photons, in agreement with Planck’s findings.
Arthur Compton’s (1892-1962) experiments in 1923 showed that photons of X-rays decreased in energy when colliding with electrons. This suggested that radiation, including light, behaves like a particle.
A year later, Louise-Victor de Broglie (1892-1987) extended the possibility further by proposing that matter can have wave properties and thus reinforced the fact that light, and even matter, has a dual nature.