Wave–particle duality
Today, these experiments have been done in so many different ways by so many different people that scientists simply accept that both matter and light are somehow both waves and particles. Scientists are still unsure about how this can be, but they are quite certain it must be true. Although it seems impossible to understand how anything can be both a wave and a particle, scientists do have a number of equations for describing these things that have variables for both wavelength (a wave property) and momentum (a particle property).  This seeming impossibility is referred to as the wave-particle duality.