Back in the 17th century, two conflicting sets of information existed about light theory. One set of scientists suggested that light is a wave while another group suggested that light is a particle. Each theory had valid explanations and justified why light showed certain phenomena. But no one theory could fully explain all the effects of light that were observed, effects such as reflection, refraction, interference, diffraction and the photoelectric effect. Where one theory fell short, the other theory was able to give an explanation. Instead of continuing the fight like bitter rivals, the supporters of each theory began to accept the other and a dual theory emerged and began to be accepted. Light is now accepted as both a wave and a particle.

Light as a particle

Albert Einstein and Isaac Newton suggested that light was a stream of particles that travelled in a straight line.  Using this theory it was easy to explain why light was able to reflect at boundaries and why it refracted. It also explained how some metals absorbed light and lose electrons as a result, an effect referred to as the photoelectric effect. The wave theory of light could not explain the photoelectric effect. (You don’t need to know about the photoelectric effect for your CSEC Physics exams).

Light as a wave

Christiaan Huygens and Thomas Young on the other hand proposed that light behaved more like a wave. This theory also became widely accepted because it was able to explain some of the effects that the particle theory could not explain. Like how interference patterns occurred from a single source of light and also why light was able to travel around corners, spreading through openings to fill a room. This is essentially diffraction and you’ll learn more about it later.

The Scientific Method is at play

This general acceptance of the wave-particle theory of light is a good reminder of the scientific method . You can click the link to read about it if you haven’t already. Theories in science are acceptable explanations for an observation. They don’t really exist as hard core facts. Where many experiments support the same theory, the theory is stronger or more sound. But it never eliminates the possibility that an experiment can disprove it eventually.

It is possible that new information could arise to disprove the wave-particle theory of light or even show that the concept of explaining them as light and wave is faulted. But until then, we can only use the information we have.