Wave-Particle Duality

The photo-electric effect showed that under certain circumstances light can behave in a particle-like manner rather than its usual wave-like manner. The next step in the development of a quantum view of the world was due to an aristocratic French physicist, Prince Louis de Broglie.

If light can sometimes be particle-like, might there not conversely be situations in which sub-atomic particles behave in a wave-like manner? De Broglie set out to search for such behaviour. He found that, if you take a beam of electrons and pass it through a pair of slits (a classical wave experiment), you get diffraction and interference - properties characteristic of a wave rather than a particle. If you reduce the intensity of the electron beam to a single electron at a time, the detector on the other side of the slits will still gradually accumulate a trace that looks like an interference pattern. Explaining this in classical terms is impossible - if the electrons go through one slit or the other the pattern would look quite different.

There is a good discussion of the two-slit experiment in terms of quantum theory in Paul Davies’ God and the New Physics, p108-111.

Email link | Feedback | Contributed by: Dr. Christopher Southgate
Source: God, Humanity and the Cosmos  (T&T Clark, 1999)