Microscopic particles, including electrons and photons, have wave-particle duality. Wave-particle duality is a property. It is not that essential light, as an electromagnetic wave, behaves as a wave in its propagation behavior, but that diffracted and interfered light behaves as particles in its interaction with matter.

For example, photoelectric effect and Compton effect conform to the behavior of particles, photons have momentum and energy, and the interaction with matter also satisfies the conservation of energy and momentum.

Photoparticle electron

After Einstein put forward the particle nature of light, Louis Victor de Broglie made a reverse thinking. He wrote in his paper: Since19th century, he has only paid attention to the study of light fluctuation and neglected the study of particle properties. Did he make the opposite mistake in the study of physical particles? In 1924, he noticed that the stable motion of electrons in atoms needs to be described by introducing integers.

Similar to other phenomena involving integers in physics, such as interference and vibration normal modes, De Broglie hypothesis is constructed, and it is proposed that physical particles have wave-particle duality just as light has wave-particle duality. He related the incident wavelength to the momentum p as follows: incident = h/p = h/mv; M: mass, v: frequency, h: Planck constant.