Werner Heisenberg

• 1. Introduction

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  Werner Heisenberg was born on the 5th of December 1901 in Würzburg, Germany, the son of a secondary school teacher who would become Germany's only ordinarius professor of medieval and modern Greek studies. That background in language and philosophy would shadow Heisenberg his entire life. At 25, he became the youngest full professor in Germany. By 32, he held the Nobel Prize. And yet the same mind that rewrote the laws of physics also participated, quietly and controversially, in the Nazi government's attempt to build an atomic weapon. How do you hold both things together? How does the man who told us that reality itself is unknowable become entangled with the most destructive political regime of the 20th century? Those questions hang over every chapter of Heisenberg's life, from a pollen-free island in the North Sea where he had his great breakthrough to a guarded country house in England where he sat with other German scientists and listened to the news from Hiroshima.

• 2. Plato on a Hiking Trail

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  In his late teenage years, Heisenberg read Plato's Timaeus while hiking in the Bavarian Alps, and the encounter was not casual. He later said that his mind was formed by studying philosophy and that modern physics had definitively decided in favor of Plato's view that the smallest units of matter are not physical objects but forms expressible only in mathematical language. That philosophical conviction would shape not just his science but his spiritual life, his political behavior, and the way he wrote about himself.

  His father's trajectory gave Heisenberg an unusual bridge between the humanities and the sciences. Growing up in a household centered on classical language and Greek scholarship, Heisenberg arrived at the Ludwig-Maximilians-Universität München in 1920 with a mind already primed for abstract structure. He studied physics and mathematics there under Arnold Sommerfeld and Wilhelm Wien, and also worked with Max Born and James Franck at the University of Göttingen and with David Hilbert in mathematics.

  In June 1922, Sommerfeld brought the young Heisenberg to Göttingen for the Bohr Festival, a series of lectures by Niels Bohr on quantum atomic physics. Heisenberg met Bohr for the first time at this event, and the encounter had a lasting effect on him. Bohr would become the most important intellectual relationship of his professional life, the colleague he worked with most closely during the years when the new quantum theory was being built from scratch.

  Alongside his physics training, Heisenberg was a Scout leader in the Neupfadfinder, a German Scout association and part of the broader German Youth Movement. In August 1923, he and Robert Honsell organized a trip to Finland with a Scout group from Munich. That same spirit of outdoor adventure would stay with him, and decades later his family's summer retreat at Urfeld am Walchensee in southern Germany, which he bought in 1939, served as a refuge throughout the chaos of the war years.

• 3. The Island Breakthrough

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  On the 7th of June 1925, after weeks of failing to relieve a severe bout of hay fever with aspirin and cocaine, Heisenberg retreated to the pollen-free North Sea island of Helgoland to focus on quantum mechanics. What he produced there would rewrite physics. His seminal paper, later known as the Umdeutung or reinterpretation paper, was published in September 1925 and established modern quantum mechanics.

  The paper's core move was to replace the Fourier expansions used to describe the positions of particles with matrices that corresponded to transition coefficients in the virtual oscillator model. Heisenberg justified this by appealing to Bohr's correspondence principle and to the idea, which he associated with Wolfgang Pauli, that quantum mechanics must be limited to observables. Things you cannot measure, Heisenberg argued, should not appear in the theory.

  When he gave the paper to Max Born to review before submission, Born recognized that the mathematical structure could be transcribed into the systematic language of matrices, which Born had learned from his own study under Jakob Rosanes at Breslau University. Born and his assistant Pascual Jordan began immediately, and their paper extending Heisenberg's results was received for publication just 60 days after Heisenberg's original. A third paper, by all three authors together, followed before the end of the year. Matrices, previously regarded as belonging to pure mathematics, had entered physics.

  From the 17th of September 1924 to the 1st of May 1925, Heisenberg had been doing research at the University of Copenhagen with Niels Bohr under a Rockefeller Foundation fellowship. It was back in Copenhagen, in 1927, that he developed the uncertainty principle while working on the mathematical foundations of quantum mechanics. On the 23rd of February 1927, he described the new principle in a letter to Wolfgang Pauli before publishing it formally. In the paper itself, Heisenberg used the German word Ungenauigkeit, meaning imprecision, not uncertainty, to name it.

  In 1927, Heisenberg was appointed ordinarius professor of theoretical physics at the University of Leipzig, where he gave his inaugural lecture on the 1st of February 1928. In his first published paper from Leipzig, he used the Pauli exclusion principle to solve the long-standing mystery of ferromagnetism. That first Leipzig paper was just the beginning: his students and postdoctoral researchers there included Edward Teller, Robert Oppenheimer, Felix Bloch, Isidor Isaac Rabi, Rudolf Peierls, and a roster of others who would go on to shape postwar science on both sides of the Atlantic.

• 4. Uncertainty and Anti-Realism

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  Albert Einstein, in 1928, nominated Heisenberg, Born, and Jordan for the Nobel Prize in Physics. The announcement for the 1932 prize was delayed until November 1933, when it was declared that Heisenberg had won for the creation of quantum mechanics, with the citation noting that the work had led to the discovery of the allotropic forms of hydrogen.

  The prize recognized a revolution that also created a philosophical rift. Einstein and Louis de Broglie were realists: they believed particles had objectively true momenta and positions at all times, even if both could not be simultaneously measured. Heisenberg took the opposite view. In his book The Physicist's Conception of Nature, he argued that one can only speak of the knowledge that describes something about particles, not of the particles themselves: "We can no longer speak of the behaviour of the particle independently of the process of observation." For Heisenberg, science itself had become an actor in a performance rather than a neutral observer watching from outside.

  This was not merely a technical disagreement. Heisenberg's anti-realism was tied to his reading of Plato, to his Lutheran faith, and to his later interest in Eastern philosophy. He described himself as in complete agreement with the book The Tao of Physics and said that conversations with the poet and philosopher Rabindranath Tagore about Indian philosophy had made ideas in quantum mechanics suddenly make sense. He referred to nature as God's second book, the first being the Bible, and wrote that physics was a form of divine service because it reflected on the ideas by which God created the world.

  In his last letter to Einstein, who continued to insist that quantum physics must be incomplete because it implies an indeterminate universe, Heisenberg wrote: "We can console ourselves that the good Lord God would know the position of the subatomic particles, thus He would let the causality principle continue to have validity." The two men never resolved the disagreement.

• 5. White Jew

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  After Adolf Hitler came to power in 1933, Heisenberg was labeled a "White Jew" in the press, meaning an Aryan who was said to behave like a Jew. The attack came from supporters of Deutsche Physik, a movement that combined anti-Semitism with hostility to theoretical physics and whose most prominent academic backers were the Nobel Laureates Philipp Lenard and Johannes Stark.

  The conflict came to a head when Heisenberg sought to succeed his doctoral advisor Arnold Sommerfeld, who achieved emeritus status on the 1st of April 1935 at the Ludwig-Maximilians-Universität München. The faculty listed three candidates, all former Sommerfeld students: Heisenberg, Peter Debye, and Richard Becker. Deutsche Physik supporters and elements in the Reich Education Ministry refused, and the battle dragged on for over four years, until the 1st of December 1939.

  One attack was published in Das Schwarze Korps, the newspaper of the SS, calling Heisenberg a White Jew who should be made to disappear. Heisenberg fought back with an editorial and a direct letter to SS chief Heinrich Himmler. The resolution came through a personal connection: Heisenberg's mother visited Himmler's mother, and the two women knew each other because Heisenberg's maternal grandfather and Himmler's father had both been rectors and members of the same Bavarian hiking club.

  On the 21st of July 1938, Himmler sent two letters simultaneously, one to SS Gruppenführer Reinhard Heydrich and one to Heisenberg. To Heydrich, he wrote that Germany could not afford to lose Heisenberg, who would be needed to train a generation of scientists. To Heisenberg, he cautioned him to separate professional physics from the personal and political attitudes of the scientists involved. The chair at Munich ultimately went to Wilhelm Müller, a man who was not a theoretical physicist, had not published in a physics journal, and was not even a member of the German Physical Society. Heisenberg kept his position at Leipzig.

• 6. The Uranverein Years

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  The German nuclear weapons program, known as the Uranverein, was formally constituted on the 1st of September 1939, the day World War II began in Europe. Its first meeting was held on the 16th of September in Berlin, organized by Kurt Diebner. Heisenberg joined at a second meeting held shortly after.

  On the 4th of June 1942, Heisenberg was summoned by Albert Speer, Germany's Minister of Armaments, to report on whether the Uranverein's research could be turned toward building a nuclear weapon. Heisenberg told Speer that a bomb could not be built before 1945, and that it would require significant monetary resources and a large number of personnel. The program's focus shifted toward nuclear power production rather than weapons, and it was subsequently divided among a number of institutes.

  At a scientific conference in late February 1942, Heisenberg had addressed Reich officials directly. His lecture was, as he later wrote in a letter to Samuel Goudsmit, adapted to the intelligence level of a Reich Minister. He told the officials that the fission of a single atomic nucleus could release 250 million electron volts of energy, and stressed that pure U-235 had to be obtained for a chain reaction to proceed.

  By late 1944, the program's principal reactor materials had been moved to facilities near Hechingen and Haigerloch on the edge of the Black Forest, away from Allied bombing. In December 1943, Heisenberg had visited German-occupied Poland. From the 24th of January to the 4th of February 1944, he traveled to occupied Copenhagen, after the German army had confiscated Bohr's own institute. During December 1944, the United States Office of Strategic Services sent agent Moe Berg to attend a Heisenberg lecture in neutral Switzerland, carrying a pistol with orders to shoot Heisenberg if his lecture indicated that Germany was close to completing an atomic bomb. Berg did not fire.

• 7. Farm Hall and Hiroshima

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  Ten German scientists, including Heisenberg, were held at Farm Hall in Godmanchester, England, after the war, under Operation Epsilon. Farm Hall had been an MI6 safe house. The scientists' conversations were recorded throughout their detention, and the transcripts were released in 1992.

  On the 6th of August 1945, the scientists at Farm Hall learned from media reports that the United States had dropped an atomic bomb on Hiroshima, Japan. At first, several of them refused to believe it. In the weeks that followed, the Germans discussed how the United States might have succeeded. The Farm Hall transcripts show that Heisenberg, Otto Hahn, and Carl Friedrich von Weizsäcker were glad the Allies had won. Heisenberg told the other scientists that he had never contemplated building a bomb, only an atomic pile to produce energy.

  When German physicist Manfred Popp analyzed the transcripts after their 1992 release, alongside the Uranverein documentation, he found that Heisenberg admitted he had never calculated the critical mass of an atomic bomb before Hiroshima. When Heisenberg subsequently attempted the calculation, he made serious errors. Edward Teller and Hans Bethe saw the transcript and concluded that these were the same kind of first-attempt errors they themselves had made. A week later, Heisenberg gave a lecture to his fellow detainees on the physics of the bomb, correctly identifying many essential aspects including the efficiency, though still underestimating it. For Popp, this was evidence that Heisenberg had genuinely not spent time on nuclear weapons during the war.

  On the question of whether the Germans could have built one, Heisenberg remarked at Farm Hall: "We wouldn't have had the moral courage to recommend to the government in the spring of 1942 that they should employ 120,000 men just for building the thing up." He was moved across France and Belgium and flown to England on the 3rd of July 1945. He would not see his family again for eight months.

• 8. Rebuilding and Reckoning

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  On the 3rd of January 1946, the Operation Epsilon detainees were transported to Alswede in Germany. Heisenberg settled in Göttingen, in the British zone, and immediately set about rebuilding German science. He became director of the Max Planck Institute for Physics after the Kaiser Wilhelm Society was dissolved by the Allied Control Council. Max von Laue was appointed vice director, and Karl Wirtz, Carl Friedrich von Weizsäcker, and Ludwig Biermann joined him.

  In 1951, Heisenberg agreed to represent the Federal Republic of Germany at a UNESCO conference aimed at establishing a European laboratory for nuclear physics. On the 1st of July 1953, he signed the convention establishing CERN on behalf of West Germany. He was asked to become CERN's founding scientific director but declined; instead he chaired its science policy committee and shaped its early scientific program.

  In 1957, Heisenberg signed the Göttinger Manifest, a public statement by scientists opposing the Federal Republic arming itself with nuclear weapons. He thought politicians would probably ignore it, but believed the manifesto would influence public opinion in ways that politicians would eventually have to acknowledge. He wrote to Walther Gerlach that they would probably have to keep returning to the question in public for a long time because of the danger that public opinion would slacken.

  His political record remained contested. The Dutch physicist Hendrik Casimir recalled hearing Heisenberg say in 1943 that German world domination was a historical necessity, given the weakness of liberal democracy and the alternative of Soviet Communism. Rudolf Peierls reported that Heisenberg told an emigre colleague in England in 1947 that after another fifty years in power the Nazis would have become quite decent. Lise Meitner quoted Heisenberg's 1948 response to being confronted with German atrocities: "Unfortunately, every spiritual upheaval has always been accompanied by great cruelty."

  Heisenberg died of kidney cancer at his home on the 1st of February 1976. The following evening, his colleagues and friends walked in remembrance from the Institute of Physics to his home, lit a candle, and placed it in front of his door. His widow Elisabeth published her account of his life in 1980, characterizing him as first and foremost a spontaneous person, then a brilliant scientist, then a highly talented artist, and only in fourth place, from a sense of duty, a political being.