In 1924, Louis-Victor de Broglie formulated the de Broglie hypothesis, claiming that all matter,[REF][REF] not just light, has a wave-like nature; he related wavelength (denoted as λ), and momentum (denoted as p): .
This is a generalization of Einstein's equation above, since the momentum of a photon is given by p = \tfrac{E}{c} and the wavelength (in a vacuum) by λ = \tfrac{c}{f}, where c is the speed of light in vacuum.