Transcript: Wave-particle duality not only means that light has some of the properties of particles, carrying energy from one place to another and acting as if the waves are concentrated in a packet. It also means that particles share properties with waves. Physicist William de Broglie, a hundred years ago, was the first to give a formal description of this fundamental attribute of matter, of matter being wave-like, meaning that it can suffer the properties of diffraction just as a wave can. Another way to think of this is of the orbits of an electron in an atom. Rather than thinking of them as fixed and discrete orbits, imagine the orbits as waves on a string where a string can oscillate with a fundamental vibration frequency and different harmonics but not at frequencies in between the harmonics. This is the case of electron energy levels in an atom which are discrete and fixed and not continuous.