Albert Einstein

In 1905 Einstein received his doctorate from the University of Zurich for a theoretical dissertation on the dimensions of molecules, and he also published three theoretical papers of central importance to the development of 20th-century physics.

In the first of these papers, on Brownian motion, he made significant predictions about the motion of particles that are randomly distributed in a fluid. These predictions were later confirmed by experiment.

The second paper, on the photoelectric effect, contained a revolutionary hypothesis concerning the nature of light. Einstein not only proposed that under certain circumstances light can be considered as consisting of particles, but he also hypothesized that the energy carried by any light particle, called a photon, is proportional to the frequency of the radiation.

Einstein's third major paper in 1905, "On the Electrodynamics of Moving Bodies," contained what became known as the special theory of relativity (The theory included his famous equation e=mc 2). At the heart of his special theory of relativity was the realization that all measurements of time and space depend on judgments as to whether two distant events occur simultaneously. The full general theory of relativity was not published until 1916. In this theory the interactions of bodies, which heretofore had been ascribed to gravitational forces, are explained as the influence of bodies on the geometry of space-time (four-dimensional space, a mathematical abstraction, having the three dimensions from Euclidean space and time as the fourth dimension). On the basis of the general theory of relativity, Einstein accounted for the previously unexplained variations in the orbital motion of the planets and predicted the bending of starlight in the vicinity of a massive body such as the sun. The confirmation of this latter phenomenon during an eclipse of the sun in 1919 became a media event, and Einstein's fame spread worldwide.