The Letter Diary of Physicist Max Planck

by Brandon R. Brown

Four college buddies tour Italy and, in this giddy time, they make one another a promise. Let’s keep a joint diary, they say, taking turns and mailing it back and forth every two months. This is for our eyes only and we’ll keep it going forever, so deep is our friendship. It makes for a heartwarming story. Assuming the friends are observant writers, and they keep the project going for decades, you might even want to eavesdrop on this journal, the letter diary.

What if the resulting book chronicled Germany from 1878 to 1927? And what if one of the college buddies, a late bloomer, grew into the physicist who launched quantum theory and nurtured the young Albert Einstein?

Bernard Karsten, Adolf Leopold, Carl Runge, and Max Planck mailed this book to and fro, off and on, through births, deaths, weddings, and wars. Karsten became a lawyer, Leopold a teacher, and Runge a brilliant mathematician. Planck went on to embody German science after revolutionizing humanity’s view of matter, light, and energy.

New2 After a long interest in Max Planck, I have only recently “discovered” the Brieftagebuch, literally the “letter day book,” of the four friends. With my primitive German skills, I translate the entries like an amateur paleontologist might unearth a trove of bones: fearing damage, embracing a glacial pace, and delighting in each new glimpse beneath the dust.

As a student of physics, one is marched through a chronology of luminaries and their key discoveries. Era by era, twenty-somethings move the needle: Isaac Newton at twenty-four; Albert Einstein at twenty-six; Marie Curie and Satyendra Nath Bose both at the old age of thirty. Young physics students can recognize a weighty if misleading pressure. I have five to ten years of brain wick to burn before I go scientifically stale.

With this backdrop, I was elated, at nineteen, to find the dour and balding Max Planck in my textbook. At an ancient forty-two, Planck hedged and stumbled his way into quantum theory. As he tried to maintain his posture, all of physics and German history lurched and then pivoted quickly around him. I dreamed then of writing about Planck. I would construct a book about his life and work, painting him as a fulcrum-like figure. I have only now, at the age of forty-five, had the chance to attempt it. Planck’s long, high-profile life provides a study in the weathering of our minds, energies, outlooks, and dreams. How do our many unspoken, barely conscious assumptions and habits become nostalgic relics, crisp in hindsight like old photographs?

Few figures have been shaped and eroded by their times like Planck; his life (1858-1947) perfectly enclosed the formation, rise, madness, and dissolution of the German Empire. He survived two world wars, the passing of a dear spouse, and the demise of their four children. He discovered and coddled young Einstein. He came face to face with Hitler, leaving with his tail tucked, yet never bowing low enough to ensure his family’s safety.

My first voyage into Planck’s life predated my full knowledge of the Brieftagebuch. I had read about his travel and correspondence with college friends, but that was about it. Given my fascination with his life, his work, and the arc of aging, I decided to write, as an exercise, a type of birthday journal. This would serve as background work to an eventual New1biography. Over the course of several months, I wrote about eighty annual entries, from his supposed seven-year-old voice until his eighty-seventh year in Germany’s 1945 collapse and partition. I learned a great deal about his life and times in trying to authenticate the major events, the people, and the backdrop of each year from 1865 to 1945, as well as his various obsessions at different stages. When I moved into writing the biography proper, this birthday journal exercise went permanently into deep digital storage, but it had illuminated the many pressure points of his life’s arc.

When nearing the final stages of a rough-draft biography last year, I spent some time with the German historian of science Dr. Dieter Hoffmann, now retired and living in Berlin. He told me more about the Brieftagebuch and said that, while it was out of print, he might be able to locate a copy for me. A month later, I had the unvarnished joy of a child when this artifact arrived in the mail.

The original Brieftagebuch, spanning eight different volumes, has been lost, presumably during the chaos of World War II. But, Carl Runge’s daughter Iris found parts of it in 1927 while going through her father’s effects after his death. In setting out to write her father’s biography, Iris Runge transcribed seventy-nine entries from Carl and thirty-seven from Max Planck, spanning 1883 to 1927, with just a few from the other friends. (History makes for a cruel editor.) The posts from Planck span the center of his life, from his twenties to his sixties. In 1999, a pair of German scholars, Klaus Henschel and Renate Tobies, put Iris Runge’s notes in book form, and my version is one of the few copies resulting.

Though the artifact is in no way a birthday journal or private diary, it still brings my humble exercise to more exciting life. We see a young Max Planck using multiple exclamation marks and underlining things. We see him shyly mention that he’s engaged. In his last entry, we see his shortest sentences yet. A wizened man with so much lost calmly claims the book is no longer relevant, since not much of life remains, and certainly nothing worthy of update.

My German is poor – sehr schwach – and I translate entries slowly. In the pages of the Brieftagebuch, even the less eventful offerings are treasures. I delight in seeing a young academic from the late nineteenth century grouse about his course enrollments and worry about his career, especially when he was headed for physics immortality. Planck was also refreshingly relaxed about his work when talking with his friends. The father of quantum theory was notoriously cautious about his work in public, even more than a decade after his pivotal discovery. But with his friends, he could unbutton his intellect a bit. He even speculated that quantum effects, far from being about particles and energies, might be native to space and time themselves. While quantized spacetime is now a familiar, if not everyday, topic among theoretical physicists, Planck’s 1908 Brieftagebuch speculations predate any published mention by at least twenty years.

In his first of the existing entries, dating to 1883, a twenty-five-year-old Max Planck lived with his parents in Munich. He’d been teaching in an essentially unpaid instructor position at the local university. He congratulates his friend Runge on his first academic job. “Good luck with the first [classes]. I am very eager to see if you like the taste, and if you’re not going to be a little hung-over after the first few meetings. At least I was almost always unhappy with myself in the beginning.” 

Max Planck, age twenty-one. 1879. Courtesy of the Archiv der Max-Planck-Gesellschaft, Berlin-Dahlem.

Fast-forward twenty-four years: Planck was settled as arguably the leading voice in theoretical physics in the world. He lived with his wife and four teenagers in an affluent Berlin suburb. This was arguably the happiest and most comfortable time in his life. And he apparently took the chance to look back through the Brieftagebuch. “It gave my wife and my children great pleasure when I read them the entries… 1878-1907! 29 years, which is also (already) the span of a human life.”

By Planck’s last entry, everything had changed. By 1927, World War I had crushed the German Empire. The doomed Weimar Republic wobbled, surrounded on all sides by extremists. And Max Planck was no longer at the helm of theoretical physics, as men like Werner Heisenberg and Niels Bohr had commandeered the rudder of quantum physics and steamed further into the waters of mathematics, disappearing from the shores of human intuition. And in the ashes of World War I, Planck had lost four dear family members. He writes to Adolf Leopold, the only other surviving member of the college friends. Carl Runge had just died. “Carl’s oldest daughter gave me this book that she found among the ancient documents of her late father … and in which she had read my name. I see from this fact that Runge ‘broke the rule.’ Because he kept the book in which I had the last entry nine years ago more than two months.” (I read Planck there as teasing himself and his old obsession with rules for the book. In 1888, he had proposed penalties if, for instance, a writer didn’t surpass “a minimum for the number of rows or provided facts.”)

Closing his last entry without fanfare, Max Planck announced the end. “A continuation of the book in the previous way could not be more out of place,” he wrote in 1927. “Because we both know the only time left to us is even easier to report by letter.”

One can also leaf through the stages of a father’s efforts to understand a challenging and often miserable son. In 1888, Max Planck and his young wife Marie had their first child. “… I must announce that on 9 March this year… a son was born… yesterday we even thought we detected the first smile.” Just ten months later, “My lad is also doing well, with him it’s mainly just rashes, apart from the unpleasant side effects of teething.”

And with Karl just two years old, father Max shows dreams for his son already. “With the education of Karl now beginning, I have lately, perhaps unconsciously for this reason, read a few books on education.” The education would cause a great deal of strife between a driven, disciplined father and his meandering, unfocused son.

Grete, Karl, and Emma Planck. Undated. Courtesy of the Archiv der Max-Planck-Gesellschaft, Berlin-Dahlem.

In the fall of 1908, Karl was twenty, and his father fifty. “My eldest,” Planck tells the Brieftagebuch, “who was originally becoming a lawyer, is changing seats and has become a geographer—a scary jump.” He “made his case” to Karl but decided that he could only be so forceful. Other letters detail further conflict over the years to come, as Karl wanted to change his major focus again, this time to music history. Karl’s younger brother Erwin was often a mediator in arguments that clouded family gatherings.

By 1912, the first official meeting on quantum theory had transpired, an exhilarating and exhausting time for Max Planck. He wrote to his friends of interacting with Marie Curie and others. On the home front, Max related that the children were fine, but “Karl makes me worry with a fit of depression that prevents him from working and threatens to be psychologically damaging. I have in the meantime put him in a sanatorium… These things, as I hear, unfortunately often take quite a while.”

When the war erupted in 1914, both Planck boys enlisted. French troops captured an injured Erwin at the Battle of the Marne, and he was then a prisoner for years to come. Karl survived his initial battles and visited the Planck home, itching to return to the front. In looking back from the vantage of 1917, Planck wrote that Karl “was one of those who was healed by the war. Never in my life has his being and his development brought me so much joy as in those months in which he, full of devotion to the highest goals, gathered together all his strength…” Yet, by the summer of 1916 Karl, “found a hero’s death at Verdun…” As Max Planck wrote to a friend, “Without the war I would never have known his value, and now that I know it, I must lose him.”

To spend time with the Brieftagebuch feels at times like trespassing in both time and culture. And my quest to know Max Planck is naïve. In a 1929 joint interview with Planck, Einstein once compared our efforts to contemplate a higher power to those “of a little child entering a huge library.” He said the child “dimly suspects a mysterious order.” In the same way, I could never hope to deeply comprehend an upright Prussian gentleman of the nineteenth century. He was born to candlelit rooms and horse-drawn carriages. In 1858, a modest spread of duchies and kingdoms sprawled where Germany would later rise. But I propose that my obsession with the physicist and human Max Planck mirrors in a small way his own obsession with knowing nature, “always the still far flung thing that glimmers in the distance and is unattainable.” Planck said it was not the capturing of this knowledge, but the many steps of pursuit, that enriches the seeker.


Key References

Brown, Brandon R. Planck: Driven by Vision, Broken by War. Oxford: New York, 2015.

Heilbron, John. The Dilemmas of an Upright Man: Max Planck and the Fortunes of German Science. Cambridge: Harvard University Press, 1996.

Heilbron, John. “Max Planck’s compromises on the way to and from the Absolute,” in Quantum Mechanics at the Crossroads. New York: Springer, 2007.

Hentschel, K. and R. Tobies (ed.). Brieftagebuch swischen Max Planck, Carl Runge, Bernhard Karsten und Adolf Leopold. Berlin: ERS-Verlag, 2003.

Hoffmann, Dieter. Max Planck: Die Entstehung der modernen Physik. München: Verlag, 2008.



About the Author

Brandon R. Brown is a Professor of Physics at the University of San Francisco. Born in Houston, Texas, he grew up with interests in science, literature, basketball, and music. His writing for general audiences has appeared in New Scientist, SEED, The Huffington Post, and other outlets. His biophysics work on the electric sense of sharks, as covered by NPR and the BBC, has appeared in Nature, The Physical Review, and other research journals. Brown’s book Planck: Driven by Vision, Broken by War (Oxford University Press) is scheduled to come out in the spring of 2015. Please visit this website for more about his book: