Einstein's explanation of wave-particle duality is rooted in his work on the photoelectric effect, which earned him the Nobel Prize in Physics in 1921. His explanation challenged the classical wave theory of light and laid the foundation for quantum mechanics.
According to classical wave theory, light was understood as a continuous wave propagating through space. However, observations of the photoelectric effect, where light incident on a material surface causes the emission of electrons, couldn't be explained by classical wave theory alone.
Einstein proposed a revolutionary idea in 1905, known as the "photon theory" or "light quantum hypothesis." He suggested that light consists of discrete packets or quanta of energy, which he called photons. Each photon carries a specific amount of energy proportional to its frequency, according to the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency of the light.
In the photoelectric effect, Einstein explained that when light interacts with a material surface, it does so in discrete quanta or photons. The energy of the incident photons can be transferred to the electrons in the material. If the energy of a photon exceeds the work function (the minimum energy required to release an electron from the material), the electron can be ejected from the surface.
Einstein's explanation of the photoelectric effect was supported by experimental observations and successfully resolved the observed phenomena that classical wave theory couldn't explain. His photon theory suggested that light exhibits both wave-like and particle-like properties, which is the essence of wave-particle duality.
Wave-particle duality states that particles, such as photons, electrons, and other quantum objects, can exhibit both wave-like and particle-like properties depending on how they are observed or measured. They can exhibit interference and diffraction patterns characteristic of waves under certain experimental conditions, and yet they can also behave as discrete, localized particles with specific energies and momenta.
Einstein's work on the photoelectric effect and the photon theory laid the groundwork for the development of quantum mechanics, which provided a more comprehensive and mathematical framework to describe the behavior of particles at the microscopic scale.