The behavior of light as both waves and particles is a fundamental principle of quantum mechanics and is often referred to as wave-particle duality. It is a concept that challenges our classical understanding of physics but has been supported by numerous experimental observations.
In certain experiments, light exhibits wave-like properties, such as interference and diffraction, which can be explained using the wave nature of light. For example, the double-slit experiment demonstrates that when light passes through two closely spaced slits, it creates an interference pattern on a screen, suggesting that light waves interfere with each other.
On the other hand, light can also exhibit particle-like behavior, as observed in the photoelectric effect and the Compton effect. In the photoelectric effect, light interacts with matter as discrete packets of energy called photons, where each photon acts as a particle. The Compton effect involves the scattering of X-rays by electrons, and the observations can only be explained by treating light as particles.
The wave-particle duality of light (and matter) arises from the wave nature of the underlying quantum entities (such as photons) and their probabilistic behavior when interacting with the environment. The behavior exhibited in a particular experiment depends on the experimental setup and the conditions imposed.
It is important to note that particles, such as electrons and other subatomic particles, can also exhibit wave-like behavior under certain conditions. This phenomenon is known as matter wave or de Broglie wave, named after Louis de Broglie, who proposed that particles have a wave-particle duality similar to light. This wave-particle duality applies to all quantum entities, including both light and matter, and is a fundamental concept in quantum mechanics.