Is Light a wave or a particle?

Light: a wave or a particle? This is a celebrated question that has long bewildered scientists. Many researchers through the history of time have taken up the challenge of finding out the nature of light. The progress of the study of light has been made by scholars from different fields.  In this article let us find the answer to this question by travelling through history.

Corpuscular Theory vs Wave Theory

In 1700, Newton was the first to propose the corpuscular theory that concluded that light was a group of particles. Then there were others who strongly believed in the wave theory of light that portrayed light as a wave. Because light travelled in a straight line, Newton naturally concluded light to be made of extremely small particles that were emitted by a light source and reflected by objects. This theory, however, could not explain the wave nature of light such as diffraction and interference. On the other hand, the wave theory could not explain why photons are emitted when a metal is exposed to light as what happens in a photoelectric effect. The photoelectric effect of light was discovered at the end of the 19th century.

Light is a wave!

The wave theory of light describes the light to be a wave. In 1655, physicist Francesco Maria Grimaldi discovered the phenomenon of diffraction of light and pointed out that the light indeed behaves as a wave. Later, in 1678, Christian Huygens developed this theory by establishing the wave theory of light and announced the Huygens principle. 

Light is a particle!

Sir Issac Newton observed the light to have frequency-like properties when a prism was used to split sunlight into its component colours. Nevertheless, he comprehended light to be of particle nature because of the periphery of the shadows it created. The periphery was extremely sharp and clear.

Light is unmistakably a Wave!

A century later, physicist Augustin-Jean Fresnel proposed that light waves be made of extremely short wavelength and mathematically proved light interference. In 1815, he came up with physical laws for light refraction and reflection. Later, Thomas Young, not only figured out that the light’s wavelength is 1 μm or less but also realized that light was a transverse wave. At this point in time, the particle theory of light was disregarded and was replaced by the wave theory.

Light is an electromagnetic wave!

The theory put forward by James Clerk Maxwell predicted the existence of electromagnetic waves and out of this prediction came the concept of light being an electromagnetic wave. Up until that point of time, the electric field and magnetic field were considered to be unrelated to one another. This thought process was changed when Maxwell presented the four equations for the electromagnetic theory that inextricably linked the magnetic fields and the electric fields. 

Light is also a particle!

The corpuscular theory of light completely vanished until the end of the 19th century when Albert Einstein revived it. Now that the dual nature of light was proved, the essential theory further evolved from electromagnetics into quantum mechanics. Einstein believed the light to be a particle(photons) that flowed in a wave-like manner. The various properties of light is due to the extremely small particles known as photons that are invisible to the naked eye. 

 

From this, we can conclude that light exhibits the dual nature of being both a wave and a particle. The light phenomena of reflection, refraction, interference and doppler shift demonstrate the wave nature of light. On the contrary, light phenomena such as the photoelectric effect demonstrates the particle nature of light. The evolution of the idea of light being both a wave and a particle has contributed to diverse scientific and technological advances such as the development of electron microscopes. 

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