During rcccnt years many people have asked the following questions: "Docs light really consist of waves or of particles? Is the electron really a particlc, or is.it a wave?"
These questions cannot be answered by one of the two stated alternatives. Light is the name that wc have given to a part of nature. The name refers to all of the properties that light has, to all of the phenomena that arc observed in a system containing light.
Some of the properties of light resemble those of waves, and can be described in terms of a wave length. Other properties of light resemble those of particles, and can be described in terms of a light quantum, having a certain amount of energy, /*v, and a certain mass, hv/<r. A beam of light is neither a sequence of waves nor a stream of particles; it is both.
In the same way, an electron is neither a particle nor a wave, in the ordinary sense. In many ways, the behaviour of clcctrons is similar to that expected of small spinning panicles, with mass—/w, electric chargc—e, and certain values of angular momentum and magnetic moment. But electrons differ from ordinary particles in that they also behave as though they had wave character, with wavelength given by the dc Broglic equation. The electron, like the proton, has to be described as having the character both of a particle and of a wave.
After the first period of adjustment to dicsc new ideas about the nature of light and of electrons, scientists became accustomed to them, and found that they could usually prcdict when, in a certain experiment, the behaviour of a beam of light would be determined mainly by its wavelength, and when it would be determined by the energy and mass of the photon; that is, diey would know when it was convenient to consider light as consisting of waves, and when to consider it as consisting of particles, the photons.
Similarly, (hey learned when to consider an electron as a particle, and when as a wave. In some experiments the wave character and the particle character both contribute significantly, and it is then ncccssaiy to carry out a careful theoretical treatment, using the equation of quantum mechanics, in order to predict how the light or the electron will behave.