<P> The relationship, called the de Broglie hypothesis, holds for all types of matter: all matter exhibits properties of both particles and waves . </P> <P> The concept of wave--particle duality says that neither the classical concept of "particle" nor of "wave" can fully describe the behavior of quantum - scale objects, either photons or matter . Wave--particle duality is an example of the principle of complementarity in quantum physics . An elegant example of wave--particle duality, the double slit experiment, is discussed in the section below . </P> <P> In the double - slit experiment, as originally performed by Thomas Young and Augustin Fresnel in 1827, a beam of light is directed through two narrow, closely spaced slits, producing an interference pattern of light and dark bands on a screen . If one of the slits is covered up, one might naively expect that the intensity of the fringes due to interference would be halved everywhere . In fact, a much simpler pattern is seen, a simple diffraction pattern . Closing one slit results in a much simpler pattern diametrically opposite the open slit . Exactly the same behavior can be demonstrated in water waves, and so the double - slit experiment was seen as a demonstration of the wave nature of light . </P> <P> Variations of the double - slit experiment have been performed using electrons, atoms, and even large molecules, and the same type of interference pattern is seen . Thus it has been demonstrated that all matter possesses both particle and wave characteristics . </P>

What are the problems that led to quantum concepts