Einstein writes to his close friend just four months after the armistice that marked Germany’s defeat in World War I. Demonstrations, often violent, by right- and left-wing extremists frequently disrupt the capital and its university. Food shortage is exacerbated by the British naval blockade, which continues until the Versailles conference that summer. As a professor of theoretical physics at the University of Leiden in neutral Holland, the Vienna-born Ehrenfest has escaped all this misery. During the war, Einstein was one of the rare academics in Germany to openly oppose the country’s militarism.

The letter’s final sentences refer to the only experiment of Einstein’s career—carried out with Wander De Haas in 1915. By looking for a torque when they suddenly reversed the magnetization of a magnetized object, Einstein and De Haas were, in effect, measuring the electron’s Landé g factor—and they got it wrong by about a factor of two.

Berlin, 22 March 1919

Dear Ehrenfest,

Shame on me for taking so long to respond to your [the familiar Diene] heartwarming invitation. It was because I didn’t know whether to say yes or no. I am mightily drawn to visit you. On the other hand, traveling is dreadful, especially for someone with queasy intestines…. I would really like to get to know Bohr, with his marvelously intuitive gift. But it can’t be done…. I’m way behind in the lectures I’m giving here, partly because of my Zürich lectures, and partly because many lectures here had to be canceled because the university was shut down by disruptions. Finally, I’m passionately preoccupied by a problem in general relativity that won’t leave me in peace, day or night.

I’m very disillusioned with politics right now. Those countries [the Allied powers] whose victory I thought, during the war, would be by far the lesser evil, now show themselves to be an only slightly lesser evil. On top of that, there’s the thoroughly dishonorable domestic politics: the reactionaries with all their shameful deeds in repulsive revolutionary disguise. One doesn’t know where to look to take pleasure in human striving. What makes me happiest is the [prospective] realization of a Jewish state in Palestine. It seems to me that our brethren [Stammgenossenen] really are nicer [sympathischer] (at least less brutal) than these awful [scheusslichen] Europeans. Maybe it can only get better if the Chinese alone survive; they lump all Europeans together as “bandits.”

I find Schouten’s thoughts on relativistic precession very clever, though not entirely compelling…. 2 A very good experimenter in Zürich (Dr. [Emil] Beck) finds that the gyromagnetic effect measured by De Haas and me is only half as big as required by theory [and later experiments]. 3 The man is to be taken quite seriously. To settle the matter, the experiments should be repeated.

Warm greetings from your

Einstein

1.
The Collected Papers of Albert Einstein
, vol.
9
,
D. K.
Buchwald
 et al, eds.,
Princeton U. Press
,
Princeton, NJ
(
2004
), p.
15
.
2.
Jan Schouten’s 1918 paper deals with what is now called the geodetic precession of a gyroscope orbiting in the curved spacetime around a massive body.
3.
For discussion of the experiments and the motivating theory, see
The Collected Papers of Albert Einstein
, vol.
6
,
A. J.
Kox
 et al, eds.,
Princeton U. Press
,
Princeton, NJ
(
1996
), p.
145
.