In 1924 Louis de Broglie was the first physicist to formulate hypotheses about the wave behavior of matter. He used Einstein's mass-energy relationship and Planck's equation to describe how you can derive the wavelength of matter from its mass, velocity, and Planck's constant. Although this equation could not be well demonstrated, it was based on the assumption that matter behaved like light and had nanometer-scale wave properties. The wavelike behavior of light was proven three years later by two scientists who were able to observe that a beam of electrons diffracted when hitting a nickel surface which is exactly how an X-ray beam behaves in the same situation. This proof of the wave properties of matter validated de Broglie's equation and allowed the advancement of quantum mechanics.