The wave nature of matter (matter waves) was proposed by:

Louis Victor de Broglie (1892-1987) was a French physicist and a member of a noble family (he held the title of duke). In his PhD thesis in 1924, he proposed that not only light, but all matter, such as electrons, protons and even larger objects, has a dual nature: it behaves both as particles and as waves. This is called the wave-particle duality of matter.

De Broglie suggested that a moving particle has a wavelength associated with it, called the de Broglie wavelength:

λ = h / p = h / mv

where h is Planck's constant (about 6.626 × 10⁻³⁴ joule-second), p is the momentum of the particle, m is its mass and v is its velocity. This means that particles with smaller mass and lower speed have longer wavelengths.

For large, everyday objects, such as a cricket ball, the wavelength is so incredibly small that wave behaviour cannot be observed. But for tiny particles like electrons, the wavelength is comparable to the distance between atoms in a crystal, so wave effects become noticeable.

De Broglie's idea was confirmed experimentally in 1927 by Clinton Davisson and Lester Germer in the USA, and separately by George Paget Thomson in Britain, who showed that electrons are diffracted by crystals, just like X-rays. De Broglie received the Nobel Prize in Physics in 1929. Davisson and Thomson shared the Nobel Prize in Physics in 1937.

De Broglie's hypothesis was an important foundation of quantum mechanics. It led Erwin Schrödinger to develop his famous wave equation in 1926. The wave nature of electrons is used in the electron microscope, invented by Ernst Ruska and Max Knoll in 1931, which can magnify objects far more than an optical microscope because electrons have much shorter wavelengths than visible light.

Why not the other options?

• ✗Albert Einstein explained the photoelectric effect (1905), showing the particle nature of light (photons); Nobel 1921.
• ✗Max Planck proposed the quantum theory of radiation (1900); Nobel 1918.
• ✗Niels Bohr proposed the model of the atom with fixed electron orbits (1913); Nobel 1922.