The Tragic Fate of Physicist Paul Ehrenfest

The Unraveling of a Probing Mind.


Physics is not immune from tragedy. Even brilliant minds sometimes grapple with inner demons. The worst situations involve not just the physicists themselves but also their families. Consider the tragic case of Paul Ehrenfest and his son Wassik.

Paul Ehrenfest, Courtesy of Wikimedia Commons

Wassik Ehrenfest was a friendly boy with Down Syndrome who, like many children of his time with that condition, spent much of his life in hospitals and institutions. He lived for some time in a facility in Jena, Germany that was progressive for its age but expensive. Little is known of his life, except through his correspondence with his parents. Encouraged by his teachers, he sent many postcards to his parents to show them what he was learning. When the Nazis rose to power in spring 1933, he was transferred to the Waterink Institute for Afflicted Children in Amsterdam, Holland, founded by educational reformer Jan Waterink.

Jan Waterink, founder of the Waterink Institute, Courtesy of http://resources.huygens.knaw.nl

On September 25, 1933, Wassik’s father Paul Ehrenfest arrived in the waiting room of the Waterink Institute. He was carrying a pistol. He shot Wassik and immediately turned the gun on himself. Wassik survived his father by a few hours. Arguably the homicide/suicide was one of the most horrific tragedies in the history of modern physics, yet it is known by only a few within the field and discussed by even fewer.


The first time I heard of Paul Ehrenfest was in a graduate physics course, taught by my advisor Max Dresden at Stony Brook University. No matter what course I took with Dresden, the highlight was always his anecdotes. Dresden loved being dramatic.

Max Dresden, Courtesy Stony Brook University

One day Dresden came into class and said something like, “I am very troubled.” He paused for dramatic effect. “Ludwig Boltzmann committed suicide. His student Paul Ehrenfest committed suicide. Ehrenfest’s student, George Uhlenbeck, was my advisor. If Uhlenbeck commits suicide, I’m next.”

Dresden died of cancer in 1997, but I still remember his passion for the history of physics, even its darker side. Several years later I was privileged enough to meet Yale physicist Martin Klein, who was a friend of Dresden and Ehrenfest’s biographer. Klein’s biography is unusual because it is labeled “Part One” and stops in the middle of Ehrenfest’s life. I asked Klein when he planned to release “Part Two.” He replied that the end of the tale was too depressing and that he was not sure if he would ever be able to complete it.

Martin Klein, Courtesy New York Times

Paul Ehrenfest, at his best, was an extraordinarily gifted physicist and mentor to many students. He was a good friend of Einstein and Bohr. Einstein, in particular, was like a brother to him and an uncle to his children when visiting his house in Leiden, Holland.

Paul Ehrenfest’s house in Leiden in recent years; Photo by Paul Halpern
Paul Ehrenfest, his son Paul Jr. and Albert Einstein, Courtesy Wikimedia Commons

Ehrenfest was born in Vienna, then the capital of Austria-Hungary, on January 18, 1880. He studied at the University of Vienna under Boltzmann, learning about kinetic theory. A man of international interests, Paul married a Russian mathematician, Tatyana Afanassjewa.

Tatyana Afanassjewa-Ehrenfest, Courtesy of http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Ehrenfest-Afanassjewa.html

They took classes at the University of Göttingen with some of the brightest minds of the day, taught by notables such as Felix Klein and David Hilbert. Following in Boltzmann’s footsteps, Ehrenfest became an expert in statistical mechanics and wrote an influential summary article on the subject.

When the esteemed physicist Hendrik Lorentz stepped down from his professorship of theoretical physics at the University of Leiden, Ehrenfest was appointed to the position. He never felt worthy enough to fill Lorentz’s shoes, but aspired to make his mark by establishing an excellent seminar series that drew physicists from all over. At the seminars, he was an expert at asking probing questions that revealed the essence of the problem. He was also a diligent research advisor to Uhlenbeck, Samuel Goudsmit, Hendrik Kramers and many others. While he had many reasons to be proud, he was nonetheless plagued with depression.

I once had the chance to examine Ehrenfest’s notebooks. They revealed an incredibly inquisitive mind that was always thinking up deep questions about nature, such as:

In Newton’s three-dimensional space, planetary orbits are closed. What about non-Euclidean spaces?

His inquiries led to a fascinating paper about why space is three-dimensional.

The Ehrenfests were strong advocates of education, particularly in mathematics. Aside from Wassik, they home-schooled their children: two daughters and another son. Family activities included playing the game “colloquium” where the kids delivered their own “lectures.” One of the girls fashioned a dollhouse out of a cardboard model of a hyperboloid. They certainly were a brainy family.

At the 1927 Solvay conference, Paul Ehrenfest played a key role in moderating the famous debates about probabilistic quantum mechanics between Einstein and Bohr. Einstein simply wouldn’t believe that randomness could play a fundamental role in nature. Ehrenfest was saddened that two of his best friends were engaged in such a heated quarrel.

As Heisenberg reported:

After the [debates] continued for a few days … Ehrenfest said: ‘Einstein, I am ashamed of you; you are arguing against the new quantum theory just as your opponents argue about relativity theory.’ But even this friendly admonition went unheard.

In the face of the rapid changes in theoretical physics, by the late 1920s Ehrenfest began to feel out of touch with the new developments. Thanks to brilliant minds such as Heisenberg, Schrödinger, Pauli and Dirac the field progressed very rapidly. Ehrenfest felt increasingly inadequate and antiquated. He once wrote to his students:

Every new issue of the Zeitschrift für Physik or the Physical Review immerses me in blind panic. My boys, I know absolutely nothing.

Once the Great Depression began in 1929, the global economy collapsed and Ehrenfest desperately looked for new positions. He was convinced that he would be let go from Leiden, and felt that he needed a backup career. He wrote to his brother Hugo, who worked in Saint Louis as a physician, asking for advice. Unsympathetically, Hugo wrote back to Paul, condemning his “annoying inferiority complex.”

Ehrenfest also tried unsuccessfully to get a position in the Soviet Union, where Tatyana had family connections. Meanwhile, in his depression, he began an affair with a young, cultured artist named Nelly. He felt awful about the liaison, and sunk even deeper into despair.


By 1931, he was already warning his friends about the possibility of suicide. They didn’t know how to soothe his pain. Many months before he carried out his dreadful scheme, he wrote a suicide note, which he never sent, addressed to Bohr, Einstein, and several other close friends. Found in his possession after his death, it read in part:

In recent years it has become ever more difficult for me to follow the developments in physics with understanding. After trying, ever more enervated and torn, I have finally given up in desperation. This made me completely weary of life … I did feel condemned to live on mainly because of the economic cares for the children. I tried other things but that helps only briefly. Therefore I concentrate more and more on the precise details of suicide. I have no other practical possibility than suicide, and that after having first killed Wassik. Forgive me …

Einstein was devastated when Ehrenfest carried out his horrific plan. As he wrote in a tribute to his late friend:

He was not merely the best teacher in our profession whom I have ever known; he was also passionately preoccupied with the development and destiny of men, especially his students. To understand others, to gain their friendship and trust, to aid anyone embroiled in outer or inner struggles, to encourage youthful talent — all this was his real element, almost more than his immersion in scientific problems.