IN TRYING TO DEVELOP a unified theory, Einstein worked closely with Peter Bergmann (left) and Valentine Bargmann (right), two young German-born physicists who also had fled the Nazis and who went on to become renowned scientists in their own right. Bargmann's wife, Sonja, was the one who translated Einstein's Scientific American article (and many other manuscripts) into English. This picture was taken in 1940. Image: LUCIEN AIGNER Corbis
When Albert Einstein started his efforts to develop a unified theory of physics in the early 1920s, it was such a hopeful enterprise. Existing theories, including both relativity and the emerging quantum mechanics, raised as many questions as they answered, so most physicists agreed on the need for a grander framework. Ideas poured forth from figures such as Hermann Weyl, Arthur Stanley Eddington and Theodor Kaluza. Although these pioneering efforts fell short of achieving unification, they introduced theorists to such fruitful concepts as gauge symmetry and extra dimensions.
Thirty years later Einstein stood alone. He had published and retracted a string of unified theories. Other scientists saw his approach as a dead end--an assessment that has been borne out by the progress of physics since his death in 1955. Whereas Einstein sought to base a unified theory on general relativity, quantum mechanics has proved the best starting point.
This article was originally published with the title Forces of the World, Unite.