The behavior of light as both a particle and a wave is a fundamental characteristic of quantum mechanics, known as wave-particle duality. This duality means that light, as well as other particles such as electrons and atoms, can exhibit properties of both particles and waves, depending on how they are observed or measured.
When light behaves as a particle, it is described as a discrete bundle of energy called a photon. Photons have properties commonly associated with particles, such as having a specific position, momentum, and energy. When light interacts with matter, such as when it is absorbed or emitted by an atom, it behaves as individual photons.
On the other hand, when light behaves as a wave, it exhibits characteristics similar to classical waves, such as interference and diffraction. These wave-like properties are evident when light is allowed to propagate freely, such as when it passes through a double-slit experiment or when it forms interference patterns.
The wave nature of light can be described by its wavelength, frequency, and amplitude. Light waves have a specific frequency, which determines the color of light, and a corresponding wavelength. The amplitude of a light wave corresponds to the intensity or brightness of the light.
The wave-particle duality of light is mathematically described by quantum mechanics through the concept of wave functions. In quantum mechanics, particles like photons are described by wave functions, which are mathematical descriptions that evolve over time according to the Schrödinger equation. These wave functions encode the probabilities of different measurement outcomes, such as the position or energy of the particle.
When a measurement is made, the wave function collapses into a particular state, revealing a particle-like behavior. However, between measurements, the wave function evolves according to the laws of quantum mechanics and can exhibit wave-like interference patterns.
It is important to note that the wave-particle duality is not unique to light but is a fundamental aspect of all quantum particles. While it may be challenging to reconcile the classical notions of particles and waves, quantum mechanics provides a mathematical framework that accurately describes and predicts the behavior of particles at the microscopic level.