The more than one thousand letters and several dozen writings included
in this volume cover the years immediately before the final formulation
of new quantum mechanics. The discovery of the Compton effect in 1923
vindicates Einstein's light quantum hypothesis. Niels Bohr still
criticizes Einstein's conception of light quanta and advances an
alternative theory, but Walther Bothe and Hans Geiger perform a
difficult experiment that decides in favor of Einstein's theory. At the
same time, Satyendranath Bose sends a new quantum theoretical derivation
of Planck's law to Einstein and he discovers what is now known as
Bose-Einstein condensation. Einstein attempts to reformulate a unified
theory of the gravitational and electromagnetic fields.
In early November 1923, Einstein flees overnight to the Netherlands in
the wake of threats on his life and anti-Semitic rioting in Berlin. He
rejoins the International Committee on Intellectual Cooperation in June
1924, and supports the idea of a European union. He joins the board of
governors of Hebrew University, which opens in April 1925, and
celebrates the event in Buenos Aires while on a seven-week lecture tour
of Argentina, Uruguay, and Brazil. During this period, he delivers
lectures, meets with heads of state, visits major institutions, and
attends receptions hosted by the local Jewish and German communities. He
has a serious, but short-lived, falling out with his son Hans Albert and
his first wife Mileva Maric-Einstein over how to invest part of the
Nobel Prize money and he rescues his sister Maja and her husband from
debt on their house. Einstein has a fourteen-month romantic relationship
with his secretary, Betty Neumann, which he ends in October 1924.