Light: a wave or a particle?

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Light: a wave or a particle?


Around 1700, Newton concluded that light was a group of particles (corpuscular theory). Around the same time, there were other scholars who thought that light might instead be a wave (wave theory). Light travels in a straight line, and therefore it was only natural for Newton to think of it as extremely small particles that are emitted by a light source and reflected by objects. The corpuscular theory, however, cannot explain wave-like light phenomena such as diffraction and interference. On the other hand, the wave theory cannot clarify why photons fly out of metal that is exposed to light (the phenomenon is called the photoelectric effect, which was discovered at the end of the 19th century). In this manner, the great physicists have continued to debate and demonstrate the true nature of light over the centuries.


Let’s look at some of the arguments:

Light is a wave! Light is a particle!
  • Light diffracts
  • Light’s wavelength can be measured and it’s wavelength is said to be 1 mm according to Fresnel & young.
  • According to James Clerk, light is a type if an electromagnetic wave. Electromagnetic waves are produced by electricity and magnetism.
  • Two crossing beams do not collide, which is only possible if light was a wave
  • light beams travel at only one speed, like a wave.
  • The photoelectric effect* can only be explained when light is referred to as particles not waves
  • The periphery of the shadows light creates are extremely sharp and clear
  • it travels in straight lines
  • light beams are localized in space
  • Light transfers energy to atoms in metal, with Quanta

*photoelectric effect: Albert Einstein (1879 to 1955) conducted research on the photoelectric effect, in which electrons fly out of a metal surface exposed to light. The strange thing about the photoelectric effect is the energy of the electrons (photoelectrons) that fly out of the metal does not change whether the light is weak or strong. (If light were a wave, strong light should cause photoelectrons to fly out with great power.) Another puzzling matter is how photoelectrons multiply when strong light is applied. Einstein explained the photoelectric effect by saying that “light itself is a particle,” and for this he received the Nobel Prize in Physics.


It was finally concluded that light had dual nature, both particle and wave. It is said to be a particle (photon) and the flow of photons is a wave. Though scientists have continued to debate on the topic, there is yet a definite answer to be found.

What do you think? Is light a particle or a wave? You can comment your thoughts, answers and queries in the comment box below.

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