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Werner Heisenberg


Werner Karl Heisenberg (December 5, 1901 - February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics, and acknowledged to be one of the most important physicists of the twentieth century. He was born in Würzburg, Germany and died in Munich. Heisenberg was the head of German nuclear energy project, though the nature of this project, and his work in this capacity, has been heavily debated. He is most well-known for discovering one of the central principles of modern physics, the Heisenberg uncertainty principle.


He was the son of Dr. August Heisenberg, professor of Byzantine studies at the University of Wurzburg, Germany, and Annie Heisenberg (née Wecklein). In 1937, he married Elisabeth Schumacher with whom he had seven children, including neurobiologist and geneticist Martin Heisenberg.

Quantum mechanics

As a student, he met Niels Bohr in Göttingen in 1922. A fruitful and life long collaboration developed between the two.

He invented matrix mechanics, the first formalization of quantum mechanics in 1925, which he developed with the help of Max Born and Pascual Jordan. This is an entirely abstract picture of reality that cannot be translated into everyday concepts. The wavefunction description developed by Schrodinger-though mathematically identical in content-is less abstract and is the way the atom is viewed these days. Both Heisenberg's and Schrodinger's mathematical descriptions of reality involve h, Planck's Constant and i, the square root of minus one. It is the appearance of these two mathematical entities that characterizes all the equations of quantum physics.

Heisenberg's uncertainty principle, developed in 1927, states that the simultaneous determination of two paired quantities, for example the position and momentum of a particle, has an unavoidable uncertainty. Technically, he proved that "the action" in any interaction could not be less than Planck's Constant, the pixel or 'quantum' of action. The action being a measure of the 'amount of existence' of mass/energy in time. Events that disobey the uncertainty principle-in that their mass-in-time does not amount to a quantum of existence-are called 'virtual' events. Such virtual events-e.g. electron-positron pair production-cannot be directly observed but do have indirect effects that play a role in the structure of the material world.

Together with Bohr, Heisenberg formulated the Copenhagen interpretation of quantum mechanics. This is considered one of the best attempts to explain quantum physics using familiar classical concepts in a non-mathematical language.

Heisenberg received the Nobel Prize in physics in 1932 "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen" .

In the late 1920s and early 1930s, Heisenberg collaborated with Wolfgang Pauli, and along with Paul Dirac, developed an early version of quantum electrodynamics. However, at the time, nobody could get rid of the infinities plaguing the theory, and it was only after World War II that a technique called renormalization was invented to take care of the infinities.

After the discovery of the neutron by James Chadwick in 1932, Heisenberg proposed the proton-neutron model of the atomic nucleus and used it to explain the nuclear spin of isotopes.

During the early days of the Nazi regime in Germany, Heisenberg was harassed as a "White Jew" for teaching theories that Albert Einstein, a prominent Jew, had conceived. Teaching these theories was in contradiction to the Nazi-sanctioned Deutsche Physik movement. After a character investigation that Heisenberg himself instigated and passed, SS chief Heinrich Himmler banned any further political attacks on the physicist.

Work during the war

Nuclear fission was discovered in Germany in 1938. Heisenberg remained in Germany during World War II, ostensibly to help rebuild German science after the massive brain drain that occurred in the 1930s as a result of Nazi policies banning Jews from government jobs, which led to the expulsion of Jewish physics professors from the state universities. Heisenberg by all accounts was loyal to Germany, but not the Nazi regime. The Kaiser Wilhelm Institute for Physics (of which he was the Director) was appropriated by the Nazi Heereswaffenamt. He belonged to a team led by Walther Bothe to develop one of Germany's many nuclear weapon/nuclear power programs, but the extent of his cooperation in the development of weapons has been a subject of much controversy. Heisenberg's work consisted of various efforts to create sustained fission reactions. He chose to use heavy water as a moderator in the reaction as it was superior to the alternatives. The only heavy-water plant in German-occupied Europe was destroyed in Norway by a British raid which further hampered development. (The Americans chose to use the much less effective, but easy to obtain, ultra-pure carbon with great success.)

A rival atomic bomb project was led by Kurt Diebner for Heerswaffenamt, who, with Paul Harteck worked on uranium enrichment and a uranium-based atomic bomb. Neither team was successful before the end of the war, because of various factors including complications from various invasions toward the end of the war and lack of funding from the government.

There has been speculation that Heisenberg had moral qualms and tried to slow down the project. Heisenberg himself may have attempted to paint this picture after the war, and Thomas Powers' book Heisenberg's War and Michael Frayn's play Copenhagen adopted this interpretation. This is because during a June 1942 meeting with Albert Speer, the minister for Nazi munitions, Heisenberg did not champion the project in a way which got it much attention or funding (which Samuel Goudsmit of the Alsos project interpreted as being partially because Heisenberg himself was not fully aware of the feasibility of an atomic bomb). At best, he tried to hinder the German project; at worst, he was just unable to create an atomic bomb.

The debate about Heisenberg's views on the use of atomic weapons is centered on the period from 1939-1942, during which time Germany made a decision not to pursue a nuclear weapons programme. During this period, several events give insight into Heisenberg's role in that decision. At various points evidence during the period suggested that Heisenberg deliberately was steering Germany's research efforts toward developing nuclear energy, rather than nuclear weapons. Some evidence suggests that Heisenberg attempted to communicate these views to the Allies. For example, in April 1941 a German Jewish physicist, Fritz Reiche, arrived in the United States bearing a message from Heisenberg's colleague and friend Fritz Houtermans which was relayed to American officials in the following handwritten note:

"a reliable colleague Houtermans who is working at a technical research laboratory asked him Reiche to let us know that a large number of German physicists are working intensively on the problem of the uranium bomb under the direction of Heisenberg, that Heisenberg himself tries to delay the work as much as possible, fearing the catastrophic results of a success."1

Next, there was Heisenberg's visit with an old friend Niels Bohr in occupied Copenhagen in September 1941, the purpose of which has been the subject of great debate. Further, German scientist Hans Peter Jensen visited Niels Bohr in Copenhagen during 1943, of which Bohr wrote that Jensen

"talked about efforts to increase the production of heavy water in Norway and hinted in this connection that the German physicists were only considering general technical energy generation."2

Finally, in May 1943, the German spy Erwin Respondek passed a report to Sam Woods, an American consular official in Zurich, that

"the Kaiser Wilhelm group where Heisenberg was chief of theoretical work in Berlin purposely raised 'difficulties' to slow down work on the project."3

According to some Heisenberg critics, the German war efforts stalled in 1940 not because of moral qualms, but because Heisenberg had made a gross overestimate of the "critical mass" of fissionable material (Uranium 235) required for a bomb. An estimate of this amount was crucial to the decision about proceeding with a serious nuclear weapons program because of the enormous difficulty and expense of separating the U235 from the U238 that makes up the vast bulk of natural uranium, and the length of time it would take to develop a reactor capable of transmuting the uranium into plutonium. According to some critics, Heisenberg had miscalculated the "critical mass" by not taking into account the "drunkard's walk" trajectory of the slow neutrons emitted, thereby overestimating the amount needed as being in the order of tons, not kilograms as was in fact the case.

However, the contention that Heisenberg had wrongly determined in 1940 that a uranium bomb was not technically feasible is at odds with other evidence. First, during the 1941 visit with Bohr, Heisenberg stated that

"in the preceding years Heisenberg had devoted himself almost exclusively to the question and were quite certain that it could be done," and that he "felt certain that the war, if it lasted sufficiently long, would be decided with atomic weapons."4

According to Bohr's later notes,

"Heisenberg said explicitly that he did not wish to enter into technical details but that Bohr should understand that he knew what he was talking about as he had spent 2 years working exclusively on this question."

It is unclear why Heisenberg would report to Bohr in 1941 that his research efforts had led him to conclude that a usable nuclear weapon was feasible if, in fact, a miscalculation in 1940 had led him to conclude that it was not feasible.

Second, after the war, Heisenberg and other German physicists were taken by the British to Farm Hall, where their conversations were monitored. The transcripts, however, are ambiguous, and subject to debate. At points, it appeared that Heisenberg had miscalculated the critical mass of uranium required for an atomic bomb-covert eavesdropping revealed that, on hearing of the Allied bombing of Hiroshima, he was at first convinced it was a propaganda trick, so sure was he that the critical mass was impracticably large. Some historians have questioned the reliability of the transcripts, as Heisenberg probably knew he was being monitored.

Indeed, there are indications that Heisenberg had made the correct calculation earlier. In June 1942, Heisenberg answered a question about the size of the fissionable core of a bomb by holding his hands to suggest something the size of a football or pineapple, which would have been roughly right. Indeed, after presenting the "incorrect" calculation to the Farm Hall scientists (including those sympathetic to the Nazi regime), one of Heisenberg's confidants, Otto Hahn, questioned Heisenberg's remark that "tons" of U-235 were needed for a bomb "But tell me why you used to tell me that one needed 50 kilograms of 235 in order to do anything. Now you say one needs two tons." Later, Heisenberg told Hahn,

"Quite honestly I have never worked it out as I never believed one could get pure 235. I always knew it could be done with 235 with fast neutrons. That's why 235 only can be used as an explosive. One can never make an explosive with slow neutrons, not even with the heavy water machine the German nuclear reactor, as then the neutrons only go with thermal speed, with the result that the reaction is so slow that the thing explodes sooner, before the reaction is complete."

Ultimately, upon seeing the reports of the bombing of Hiroshima, Heisenberg told his friend, von Weizsäcker

"I was absolutely convinced of the possibility of our making an uranium engine reactor but I never thought that we would make a bomb and at the bottom of my heart I was really glad that it was to be an engine and not a bomb. I must admit that."

Whatever the cause, it is clear that on June 4, 1942, Heisenberg met with German Minister Albert Speer concerning possible uses of Heisenberg's nuclear research, and particularly its potential suitability for the development of nuclear weapons. Notwithstanding Heisenberg's September 1941 report to Bohr that he felt certain nuclear weapons could be constructed and powerful enough to conclude the war if it lasted long enough, during this meeting with Speer he highlighted the technical difficulties and vast time and materials required to separate the uranium needed for the project.

It was this meeting, and Speer's report on it to Hitler, that effectively scuttled any military applications for his work, and limited Heisenberg's work during the remainder of the war to theoretical uses of nuclear energy. As Speer wrote,

"Difficulties were compounded, Heisenberg explained, by the fact that Europe possessed only one cyclotron, and that of minimal capacity. Moreover, it was located in Paris and because of the need for secrecy could not be used to full advantage."

Curiously, albeit perhaps tellingly, Heisenberg did not mention the cyclotron in Copenhagen as a possible source for enriching uranium.

Biography and controversy

In 1956, journalist Robert Jungk published a book titled Brighter Than a Thousand Suns, which painted Heisenberg as having single-handedly and purposely derailed the German project for moral reasons. To justify the claim, in the Danish edition of the book, Jungk printed an excerpt from a personal letter from Heisenberg. The excerpt, however, was taken heavily out of context, and in the full letter,5 Heisenberg was far more demure about whether he had taken a strong moral stance. After reading the excerpt, Bohr was understandably flustered that Heisenberg was (apparently) claiming to have purposely derailed the Nazi bomb project, as it did not match his own perception of Heisenberg's war work at all.

Some historians of science have taken Bohr's draft letters as evidence against Heisenberg's contention that he had met with Bohr to signal that Germany's scientists would not pursue the development of nuclear weapons. Others have argued that Bohr profoundly misunderstood Heisenberg's intentions at the 1941 meeting, and that his reaction to Jungk's work was overly passionate. Significantly, Bohr's draft letters confirm virtually all of Heisenberg's recollection to Jungk of the substance of the meeting. However, as a piece of evidence the letters cannot provide an answer to the question of why Heisenberg broached the topic of nuclear weapons-but not their technical aspects-with Bohr, or whether Bohr formed the correct "impression" of what Heisenberg wanted to say. Heisenberg's motives will most certainly continue to be debated, but it cannot be questioned that he knew Bohr was going to be escaping to the allies when he spoke to him in 1941, and that Heisenberg was risking his life by speaking to anyone about atomic power or atomic weapons.

It is also thought that Italian scientist Gian Carlo Wick approached Heisenberg in January 1944 as an emissary for the OSS as part of Operation Sunrise, to negotiate the capitulation of Nazi scientists to the Allies' Operation Alsos. Allied intelligence through Stockholm continued to sound the alarm about Nazi uranium research right up to war's end, but this was part of Diebner's project, not Heisenberg's.


Heisenberg was one of the founding generation of quantum science. His matrix description of the quantum world is still in use. His 'uncertainty principle' that established the quantum of action as the limit of interaction and observation is still a core principle of the new science.

See also

  • Niels Bohr


  1. ↑ Thomas Powers, Heisenberg's War: The Secret History of the German Bomb., New York, NY: Knopf. ISBN 0394514114
  2. ↑ Translation 8., Niels Bohr Archive. Retrieved August 11, 2007.
  3. ↑ Thomas Powers, Heisenberg's War: The Secret History of the German Bomb., New York, NY: Knopf. ISBN 0394514114
  4. ↑ Translation 6., Niels Bohr Archive. Retrieved August 11, 2007.
  5. ↑ Two Letters from Werner Heisenberg to Robert Jungk., Jochen Heisenberg. Retrieved August 11, 2007.

Publications by Heisenberg

  • Heisenberg, Werner. 1990. Across the frontiers; translated from the German by Peter Heath. Woodbridge, CT: Ox Bow Press. ISBN 0918024803 (Hardcover) ISBN 0918024811 (Paperback).
  • -1989. Encounters with Einstein: and other essays on people, places, and particles. Princeton, NJ: Princeton University Press; Reprint edition. ISBN 0691024332
  • -1966. Introduction to the unified field theory of elementary particles. Hoboken, NJ: Interscience. ISBN 0470369000.
  • -1981. Natural law and the structure of matter English version by the author. 1970 Warm Wind Books. ISBN 0900615273
  • -1953. Nuclear physics. Philosophical Library. ISBN 0806530332.
  • -1961. et al, On modern physics. English translation by M. Goodman and J.W. Binns.
  • -1979. Philosophic problems of nuclear science. Translated by F. C. Hayes. 1952; Woodbridge, CT: Ox Bow Press. ISBN 0918024145 (Hardcover) ISBN 0918024153 (Paperback).
  • -1930. Physical principles of the quantum theory, translated into English by Carl Eckart and Frank C. Hoyt. Mineola, NY: Dover Publications. ISBN 0486601137.
  • -1970. Physicist's conception of nature. Translated from the German by Arnold J. Pomerans. Portsmouth, NH: Greenwood Press Reprint. ISBN 0837131073.
  • -1971. Physics and beyond; encounters and conversations. Translated from the German by Arnold J. Pomerans. London, UK: HarperCollins Publishers Ltd. ISBN 0049250205.
  • -1999. Physics and philosophy : the revolution in modern science, introduction by F.S.C. Northrop. New York, NY: Harper Perennial Modern Classics. ISBN 1-57392-694-9 (Paperback) ISBN 0061305499 (also Paperback)
  • -1982. Tradition in science. 1981 Continuum Intl Pub Group. ISBN 0826400639
  • -1949. Two lectures. Lanham, MD: University Press. ASIN B0007IW8LO.
  • -1977. et al. Uncertainty principle and foundations of quantum mechanics : a fifty years' survey , edited by William C. Price, Seymour S. Chissick.
  • -The Part and The Whole about his life, his friendship with Bohr, and the evolution of quantum physics.


  • Cassidy, David C. 1993. Uncertainty: The Life and Science of Werner Heisenberg. New York, NY: W. H. Freeman. ISBN 0716725037.
  • Glanz, James. 2002. "New Twist on Physicist's Role in Nazi Bomb" The New York Times. February 7, 2002.
  • Walker, Mark. 1990. German National Socialism and the Quest for Nuclear Power, 1939-1949 London, UK: Cambridge University Press. ISBN 0521364132 (Hardcover) ISBN 0521438047 (Paperback).
  • Powers, Thomas. Heisenberg's War: The Secret History of the German Bomb. New York, NY: Knopf. ISBN 0394514114 (Hardcover) ISBN 0316716235 (Paperback).
  • Lawrence Rose, Paul. 1998. Heisenberg and the Nazi Atomic Bomb Project, 1939-1945: A Study in German Culture. Berkeley, CA: University of California Press. ISBN 0520210778.