2
Relativity Theory
and Quantum Theory
Einstein's life ended. .. with a demand on us for synthesis.
W. Pauli[Pl]2a. Orderly Transitions and Revolutionary Periods
In all the history of physics, there has never been a period of transition as abrupt,
as unanticipated, and over as wide a front as the decade 1895 to 1905. In rapid
succession the experimental discoveries of X-rays (1895), the Zeeman effect
(1896), radioactivity (1896), the electron (1897), and the extension of infrared
spectroscopy into the 3 /un to 60 /an region opened new vistas. The birth of quan-
tum theory (1900) and relativity theory (1905) marked the beginning of an era in
which the very foundations of physical theory were found to be in need of revision.
Two men led the way toward the new theoretical concepts: Max Karl Ernst Lud-
wig Planck, professor at the University of Berlin, possessed—perhaps obsessed—
by the search for the universal function of frequency and temperature, known to
exist since 1859, when Gustav Robert Kirchhoff formulated his fundamental law
of blackbody radiation (19a)*; and Albert Einstein, technical expert at the Swiss
patent office in Bern, working in an isolation which deserves to be called splendid
(3).
In many superficial ways, these two men were quite unlike each other. Their
backgrounds, circumstances, temperaments, and scientific styles differed pro-
foundly. Yet there were deep similarities. In the course of addressing Planck on
the occasion of Planck's sixtieth birthday, Einstein said:
The longing to behold... preestablished harmony** is the source of the inex-
haustible persistence and patience with which we see Planck devoting himself
to the most general problems of our science without letting himself be deflected
by goals which are more profitable and easier to achieve. I have often heard
that colleagues would like to attribute this attitude to exceptional will-power*In this chapter, I use for the last time parenthetical notations when referring to a chapter or a
section thereof. Thus, (19a) means Chapter 19, Section a.
**An expression of Leibniz's which Einstein considered particularly apt.