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Max Planck: Einstein’s supportive skeptic in 1915

This November marks the 100th anniversary of Albert Einstein completing his masterpiece of general relativity, an idea that would lead, one world war later, to his unprecedented worldwide celebrity. In the run-up to what he called “the most valuable discovery of my life,” he worked within a new sort of academic comfort. And in just ten years, he had moved from the far margins of science to the epicenter of scientific prestige. This position and this move came about in no small part because of his friend Max Planck, twenty-one years his elder.

The major shift in Albert Einstein’s career began in 1905, when he submitted a number of revolutionary papers to the leading physics journal, Annalen der Physik. Max Planck, the lead editor for theoretical work, was among the first to read them. At the time, Einstein, the young patent clerk, was truly an outsider. But Planck recognized the work’s innovative genius, and he green-lit publishing the articles, including two that outlined what we now call the special theory of relativity.

Planck, who took a very broad view of physics (and physical chemistry, philosophy, linguistics, et cetera), was already primed for relativity. In 1898 and 1899, he had exchanged a series of letters with the Dutch physicist Hendrik Lorentz, trying to reconcile the crazy-making results from speed of light experiments. After some clever but fruitless head scratching, he returned to the work that would soon give the world a quantum breakthrough and a new fundamental constant, h. But Planck now understood that classical physics had a nasty problem when it came to the speed of light as measured by different observers.

So when Planck the journal editor first encountered Einstein’s ideas concerning space, time, and the universal speed of light, he welcomed and helped broadcast the update: An absolutely constant measure of light’s speed had to replace the comforting and quaint notion that our rulers and clocks would never mislead us. He then wrote one the first major follow-ups to Einstein’s 1905 relativity work, demonstrating how the dynamics of bodies could be treated properly in this new, elastic spacetime. Planck then defended Einstein from waves of skeptics, writing to him that they “must stick together.”

Planck would be less encouraging on the road to Einstein’s self-labeled “theory of incomparable beauty,” general relativity. By pushing his original ideas beyond special, limited cases, Einstein flirted with rewriting Newton’s theory of gravitation. As he began this work, Planck shook his head. “As an older friend, I must advise against it,” he wrote in 1913. “In the first place, you won’t succeed, and even if you do, no one will believe you.”

Fritz Haber and Albert Einstein at the Kaiser-Wilhelm-Institut fuer physikalische Chemie und Elektrochemie, Berlin-Dahlem, 1914 by S. Tamaru. Used with permission by Archiv der Max-Planck-Gesellschaft, Berlin-Dahlem.
Fritz Haber and Albert Einstein at the Kaiser-Wilhelm-Institut fuer physikalische Chemie und Elektrochemie, Berlin-Dahlem, 1914 by S. Tamaru. Used with permission by Archiv der Max-Planck-Gesellschaft, Berlin-Dahlem.

But putting these doubts aside, Planck carefully built an ideal nest for Einstein’s labor. Planck led the charge to create the teaching-free job offer, with record salary, that enticed Einstein to Berlin in 1913. Here, Einstein would spend an incredibly fruitful yet uncomfortable 19 years, spanning the end of the German Empire and the rise of political extremism. Some of his new colleagues wanted Einstein to advance their own fields. The chemist Fritz Haber, for instance, dreamt of a partnership in physical chemistry. Instead, Einstein threw himself into his greatest idea and the difficult mathematical road ahead. Meanwhile, his friendship with Planck grew. He told a colleague that he remained in Berlin because, “to be near Planck is a joy.”

In November of 1915, Einstein completed his theoretical masterpiece. Newton’s falling apple no longer felt the heavy tug of a force; it simply followed the gentle warp and weave of spacetime near our massive planet. But Einstein had not convinced that many colleagues, and major experimental tests would have to wait.

The war years posed challenges for both men, but more so for Planck. He lost his eldest son at Verdun and both of his twin daughters to complications in childbirth. “Planck’s misfortune wrings my heart,” Einstein wrote to a friend. “I could not hold back the tears when I saw him… He was wonderfully courageous and erect, but you could see the grief eating away at him.” The two sometimes played music together in Planck’s home to escape their times and probably to escape talking politics. Planck, the concert-grade pianist, bound himself to his nation and its Kaiser, but Einstein, the casual violinist, leaned strongly to the left.

After the war, dramatic measurements confirmed general relativity by showing Einstein’s predicted deflection of starlight near the sun, a ghostly effect now called gravitational lensing. A war-weary planet cheered the likable genius with front-page headlines and countless invitations. Planck wrote with delight to his friend, changing his ever-flexible mind and calling general relativity an “intimate union between the beautiful, the true and the real.” He signed this letter, “cordial greetings from your devoted servant, M. Planck.”

Their friendship would later be wrecked between Planck’s conflicted patriotism and Einstein’s prescient horror during the rise of the Nazis. The music and the letters ceased. But after Max Planck died in 1947, Einstein, who never set foot in Germany again, wrote a moving tribute to Planck on behalf of America’s National Academy of Sciences. And more privately, he wrote a short note to Planck’s widow, telling her, “The hours that I spent in your home, and the many conversations that I conducted in private with the wonderful man will for the rest of my life belong to my beautiful memories.” In some sense, their concert – including all their tension – plays on, as general relativity and quantum theory stand awkwardly together as two irreconcilable pillars of modern physics.

Featured image credit: Black hole by NASA. Public Domain via Wikimedia Commons.

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