The dual nature of light, exhibiting both wave-like and particle-like properties, is a fundamental aspect of quantum mechanics. It is captured by the wave-particle duality principle, which states that particles, including light, can exhibit characteristics of both waves and particles depending on how they are observed or measured.
In certain experiments and observations, light behaves as a wave, exhibiting phenomena such as interference and diffraction. These behaviors are well-described by the wave nature of light, where light is treated as an electromagnetic wave propagating through space.
On the other hand, in other experiments and observations, light behaves as discrete, localized packets of energy called photons. These particle-like properties are evident in phenomena like the photoelectric effect and the observation of discrete energy levels in atomic and subatomic systems.
The understanding of why light exhibits this dual behavior has developed through the framework of quantum mechanics. In quantum mechanics, particles, including photons, are described by wavefunctions, which are mathematical representations that capture both wave-like and particle-like aspects. The wavefunction encodes the probability distribution of where a particle might be located or how it might behave when measured.
According to the Copenhagen interpretation of quantum mechanics, the act of measurement or observation collapses the wavefunction, causing the particle to manifest as a definite state—a particle or a wave—depending on the nature of the measurement. This collapse is a probabilistic process, meaning that the outcome of a measurement cannot be predicted with certainty but follows a probability distribution.
While the wave-particle duality of light is well-established and experimentally confirmed, the underlying reasons for this behavior are still a subject of ongoing research and philosophical debate. The wave-particle duality is deeply rooted in the fundamental principles of quantum mechanics, and understanding its origins requires delving into the fundamental nature of quantum reality, which is an area of active scientific inquiry.