The Britannica Guide to Relativity and Quantum Mechanics
This volume deals with relativity and quantum mechanics. Both of these are
quite new areas of physics. The beginning of relativity can be dated quite
precisely, to the year 1905, when a clerk in the Swiss patent office published a
paper “On the Electrodynamics of Moving Bodies.” The beginnings of quantum
mechanics can be dated to 1900 when the German physicist Max Planck
explained the emission of light from a blackbody as the emission not of a
continuous stream of particles or waves, but a stream of discrete packets of
energy called quanta.