In quantum mechanics, the behavior of a single photon can exhibit both particle-like and wave-like characteristics, depending on how it is observed and measured. This phenomenon is known as wave-particle duality. Let's explore how this duality manifests for a single photon:
Wave-like behavior: When a single photon is not being observed or measured, it can be described by a wave function that represents a probability distribution of its possible states. This wave function follows the rules of wave mechanics, similar to how waves in classical physics propagate and interfere. This wave-like behavior of the photon allows it to exhibit phenomena such as diffraction and interference, as observed in the double-slit experiment.
Particle-like behavior: When a single photon is detected or measured, it manifests as a discrete particle, localized at a specific position. Upon measurement, the wave function "collapses" to a single point, corresponding to the photon being detected at a particular location. This particle-like behavior is observed when the photon interacts with a detector or is absorbed by a material, for example, in the photoelectric effect.
It's important to note that the behavior of a single photon cannot be fully explained by classical concepts like a tiny billiard ball or a classical wave. The dual nature of light, as both particle and wave, is a fundamental characteristic of quantum mechanics. Quantum theory provides a mathematical framework to describe and predict the behavior of photons and other quantum particles, which can exhibit wave-like or particle-like behavior depending on the experimental setup and observation.
The wave-particle duality is not limited to photons but is a fundamental principle that applies to all quantum particles, such as electrons and atoms. It represents a fundamental departure from classical physics and is a cornerstone of quantum mechanics.