The World According to Physics

by Jim Al-Khalili

This does not mean that an electron is both a particle and a wave at the same time—but rather that, if we set up an experiment to test the particle-like nature of electrons, we find that they do indeed behave like particles. But if we then set up another experiment to test if electrons have wavelike properties (such as diffraction or refraction or wave interference), we see them behaving like waves. It’s just that we cannot carry out an experiment that would show both the wave and particle nature of electrons at the same time. It is absolutely vital to stress here that, while quantum mechanics correctly predicts the outcomes of such experiments, what it does not tell us is what an electron is—only what we see when we carry out certain experiments to probe it.