In quantum mechanics the wave function is a term used to describe a quantum mechanical system. The function specifies conditions of space and time that satisfy Schrödinger's equation. In an alternative use, a wave function (i.e., a Dirac function) describes functions of space and time (using space and time coordinates) that can be used to describe particle spin properties.

In 1921, German American physicist Albert Einstein was awarded the Nobel Prize for physics. What is surprising, perhaps, is that Einstein was honored not for relativity (still considered in 1921 to be too controversial a subject) but rather for his explanation of the photoelectric effect.

Einstein had introduced the concept of light-quanta, or photons, and thus had ascribed particle-like behavior to light, which had been understood in terms of wave mechanics since English physicist Thomas Young's famous double-slit experiment in 1801.

A young French aristocrat had become...