Werner Heisenberg

Heisenberg had a special, intuitive way of getting to the essential point. This together with an incredible force of persistence and determination, made him the most prolific and successful physicist of the recent past.

Victor Weisskopf

“If Einstein had not discovered relativity theory, it would have been discovered sooner or later by someone else, perhaps by Poincare or Lorentz. If Hahn had not discovered uranium fission, perhaps Fermi or Joliot would have hit upon it in a few years later. I don’t think we detract from the great achievement of the individual if we express these views. For that very reason, the individual who makes crucial discovery cannot be said to bear greater responsibility for its consequences than all other individuals who might have made it. The pioneer has simply been placed in the right spot by history, and has done no more than perform the task he has been set.

Werner Heisenberg on the morality of scientific research

Werner Heisenberg was one of the most creative physicists of the twentieth century. He played a pioneering role in the development of quantum mechanics. In 1932, he was awarded Nobel Prize in Physics for “the creation of quantum mechanics, the application of which has led, among other things, to the discovery of the allotropic forms of hydrogen.” He discovered the Matrix Mechanics, one of the two standard formulations of quantum mechanics in 1925 at the age of 24. The other formulation called Wave Mechanics, was discovered by Erwin Schrodinger. Apparently the two formulations look very different from each other. However, Carl Eckart and Schrodinger demonstrated the equivalence between the two.

As Victor Weisskopf stated quantum mechanics marked “a turning point in man’s understanding of nature comparable to Newton’s discovery of the universal nature of gravity, Maxwell’s electromagnetic theory of light, and Einstein’s relativity theory.”
Heisenberg is best known for his uncertainty principle. It posits limits to the accuracy of knowledge about atomic behaviour. Heisenberg also made important contributions to the theories of the hydrodynamics of turbulence, the atomic nucleus, ferromagnetism, cosmic rays, and elementary particles.

Above all he was a good human being. His son Jochen H. Heisenberg wrote: “He was a good father, a warm, caring and compassionate human being who taught us his love for the outdoors, for mountain climbing, music or the spiritual which he called the central order.”

Heisenberg was born in Wurzburg on December 05, 1901. His father August Heisenberg rose from school teacher to a Professor of Greek Philology at the University of Munich. His mother Annie Hiesenberg (nee Wecklein) was the daughter of a headmaster in Maximillian Gymnasium at Munich. Heisenberg’s initial schooling was in a primary school in Wurzburg before his father moved to Munich in 1910. At Munich, Heisenberg attended Elisabethenschule for a year before he joined the Maxmillian Gymnasium, where his maternal grandfather was the headmaster.

During the World War I, when studies at school were disrupted, Heisenberg undertook independent study. His records at school were excellent. His mathematical abilities were proverbial. It has been reported that when he was at school, Heisenberg tutored a family friend who was at university in calculus. In the Gymnasium, Heisenberg led a somewhat right wing youth movement called German Youth Movement, with anti-modernist romantic leanings. Heisenberg’s personality was influenced by his association with this movement. During this period Heisenberg also worked with a voluntary organisation, which sent its volunteers to help in the fields in spring and summer. In 1918 Heisenberg was sent to work in a diary farm in Upper Bavaria. This was the first occasion for Heisenberg when he was away from home. The work in the farm was quite laborious and what is more there was not even sufficient food. In his spare time Heisenberg played chess and he played it very well. He also studied mathematics. By this time he had become interested in number theory. He read Leopold Kronecker’s work and he even tried to work out a proof of Pierre de Fermat’s last theorem.

The First World War ended in 1918 but by this time the political situation in Germany had become quite fluid. Different factions were fighting with each other to grab power. Heisenberg joined the military suppression of the Bavarian Soviet forces. Though it was a serious business but it seems young Heisenberg treated it like a game as he later said: “I was a boy of 17 and I considered it a kind of adventure. It was like playing cops and robbers.”

Heisenberg joined the University of Munich in 1920 to study physics under Arnold Sommerfeld. At the beginning he did not make up his mind to plunge wholeheartedly in theoretical physics. He mostly attended mathematics classes to ensure that he could return to mathematics in case theoretical physics went badly. At the University his mathematical interest shifted from number theory to geometry. However, it did not take much time for him to be engrossed in theoretical physics and he started attending all the classes of Sommerfeld. He also took courses in theoretical physics, as they were compulsory. At the beginning he toyed with the idea of doing research in relativity. But Wolfgang Pauli, who was carrying out a major survey of the theory of relativity, advised him against it. Pauli told Heisenberg that there was much to be done in the field of atomic structure, as the existing theory had no experimental basis. Recalling his early years at the university, Heisenberg wrote: “My first two years at Munich University were spent in two quite different worlds: among my friends of the youth movement and in abstract realm of theoretical physics. Both worlds were so filled with intense activity that I was often in the state of great agitation, the more so as I found it rather difficult to shuttle between the two.”

It is interesting to note that Heisenberg almost failed in the oral examination conducted by the famous physicist Wilhelm Wein, who was the examiner. Wein asked Heisenberg some questions related to experimental techniques and after getting no satisfactory replies he declared the candidate failed. However, after an animated dispute, Sommerfeld procured the lowest grade called ‘rite’ for passing the examination for his outstanding student. One of Wein’s questions that Heisenberg failed to reply was concerned with the resolving power of optical instruments due to the finite wavelength of electromagnetic radiation. This question impressed on Heisenberg as fundamental. He continued to think about it and the result was his discovery of the Uncertainty Principle.

During 1922-23, when Sommerfeld was away in the United States, Heisenberg spent a session at the Gottingen University studying with Max Born, James Franck, and David Hilbert. He worked on atomic theory and he wrote a joint paper with Born on helium. He received his PhD in 1923. His doctoral dissertation was on turbulence in fluid streams. After obtaining his PhD, he first went on a trip to Finland and then returned to the Gottingen University to work with Max Born. He worked with Niels Bohr at the University of Copenhagen as Rockefeller Fellow during 1924-1925. It was at Copenhagen that Heisenberg first met Albert Einstein. In 1926 Heisenberg was appointed Lecturer in Theoretical Physics at the University of Copenhagen. In 1927 he was appointed Professor of Theoretical Physics at the University of Leipzig, a post he held till 1941. At the time of his appointment as Professor at the Leipzig University he was just 26 years old. He became the youngest full professor in the country. In 1929 he went on a lecture tour to the United States, Japan and India.

Heisenberg’s Matrix Mechanics was developed by questioning the old planetary model of the atom, originally proposed by Bohr and subsequently modified by Sommerfeld. Bohr’s concept was based on the classical motion of electrons in well-defined orbits around the nucleus and the quantum restrictions were imposed arbitrarily so that the consequences of the atomic model fit in with the existing experimental results. Borhr’s model was a great success in explaining the existing knowledge and a direction for new research but it failed to reconcile the results of new research. Heisenberg found this model not only inadequate but also without sufficient firm foundations. Heisenberg stated that at any given point the position of an electron in space cannot be assigned. Similarly its movement in an orbit cannot be followed. This means that it cannot be assumed with sufficient certainty that the planetary orbits of electrons postulated by Bohr really exist. The orbital picture visualised for this model could never be put to the test of experiment. Heisenberg argued that it was a mistake to think of the structure of the atom in visual term at all. What we really know of the atom is what we can really observe of it. Thus Heisenberg proposed to construct a theory for describing the structure of the atom in terms of quantities which can be actually observed such as frequencies and intensities of the light emitted or absorbed by atoms. Heisenberg argued that mechanical quantities, such as position, velocity etc., should be represented, not by ordinary numbers but by abstract mathematical structures called matrix. In 1925, while recupertating from an attack of hay fever at Hogland, an island in the North Sea, Heisenberg formulated his new theory in terms of matrix equation. Heisenberg, after completing his paper, sent it to Pauli. Heisenberg wrote: “…I dare to send you this brief preliminary manuscript of my work because I believe that it….contains actual physics…I must beg you to return it to me in 2-3 days, since I must either make its existence known in the next few days or burn it.” Pauli, who was Heisenberg’s friend and also a critic, wrote back: “It was the first light of the dawn in quantum theory.” After showing it to Pauli, Heisenberg showed the paper to Born, who in turn sent it to the German journal Zeitschrift fur Physik, where it was published in its September issue. The paper, entitled “Quantum theoretical re-interpretation of kinematic and mechanical relations”, completely reformulated the existing quantum theory. The details of the matrix-based quantum mechanics were worked out jointly by Heisenberg, Born and Pascual Jordan. Their joint paper, which later became known as `three-man paper’, was also published in Zeitscrift fur Physik. Heisenberg’s quantum mechanics made possible a systemisation of spectra of atoms. When Heisenberg applied his theory to molecules consisting of two atoms he found that the hydrogen molecule must exist in two different forms, which should appear in some given ratio to each other. This prediction was subsequently experimentally verified.

The mathematical devices called matrices had been known since the 1850s but Heisenberg was the first to apply them in physics. For a non-mathematician the concept of matrices is not easy to understand. Even Schrodinger, who formulated the wave mechanics, found it difficult to understand. Schrodinger wrote: “My theory was stimulated by de Broglie and brief but infinitely far-seeing remarks by Einstein. I am not aware of a generic connection with Heisenberg. I, of course, knew of his theory but was scared away, if not repulsed, by its transcendental algebraic methods which seemed very difficult to me.” So it was not surprising that physicists preferred the more usual language of wave equations used in the equivalent system of Schrodinger

In 1927 Heisenberg discovered the Uncertainty Principle, another aspect of quantum mechanics. Heisenberg stated that it was impossible to determine exactly both the position and momentum of fundamental particles such as electron. The principle states “the more precisely the position is determined, the less precisely the momentum is known in this instant and vice versa.” To demonstrate his observation Heisenberg used a thought experiment. He argued that if we attempt to locate the exact position of an electron we must use radiation of very short wavelength such as gamma rays. But while irradiating with gamma rays, the electron’s momentum will be changed. But now if one uses a lower-energy wave, the momentum of electron will not be much disturbed but then as lower-energy implies larger wave-length such radiation will lack the precision to provide the exact location of the electron. The uncertainty principle removed absolute determinacy, or cause and effect, from physics for the first time and replaced with statistical probability. Einstein and some other scientists were deeply troubled by this development but later it was generally accepted.

After the Nazis came to power many scientists left Germany. Heisenberg remained in Germany throughout the Nazi era including the period of the Second World War. He was not a Nazi himself. However, he thought that being a German it was his duty to remain in Germany to preserve traditional scientific values developed in Germany for the next generation.

In 1939 Enrico Fermi wanted to know what made Heisenberg stay in Germany. To this Heisenberg replied: “I don’t think I have much choice in the matter. I firmly believe that one must be consistent. Every one of us is born into a certain environment very early in life, he will feel most at home and do his best work in that environment. Now history teaches us that sooner or later, every country is shaken by revolutions and wars; and whole populations obviously cannot migrate every time there is a threat of such upheavals. People must learn to prevent catastrophes, not to run away from them. Perhaps we ought even to insist that everyone brave what storms there are in his own country, because in that way we might encourage people to stop the rot before it can spread.”

The Nazis did not relish Heisenberg’s refusal to compromise his support for the physics of Einstein in any way. This was the time when the Nazis termed the works of scientists of Jewish origin as “Jewish science”. So the relativity theory was termed as “Jewish physics.” In fact the whole theoretical physics itself was viewed as Jewish. This was the reason that when he wanted to move to the University of Munich to succeed his teacher Sommerfeld, he was vehemently opposed by the press controlled by the Nazis. As a result the post finally went to the little-known W. Muller.

Soon after the outbreak of the Second World War on September 01, 1939, Heisenberg was asked to join Germany’s nuclear fission research as a part of its war effort. Initially he headed a small reactor at Leipzig and at the same time he also visited Berlin to advise a larger group working there on the same project. In 1942 he was asked to take charge of the fission research conducted at Kaiser Wilhelm Institute for Physics at Berlin. On the development of a nuclear reactor he worked with Otto Hahn, one of the discoverers of the nuclear fission. His role in Germany’s war effort during the Second World War has been widely debated. Today we know that Germany’s project for preparing the Atom Bomb was a failure. When Heisenberg learned of the Hiroshima bomb on August 06, 1945, Heisenberg’s first reaction was of disbelief. Heisenmberg believed that a bomb could not be made before the war. He once declared “I never thought we would make a bomb.” Perhaps this was the reason that he did not feel the urgency to argue the case strongly enough before the German government. He never thought that the Allies would ever succeed.

There have been lot of controversies about Heisenberg’s role in the Second World War with respect to development of the atomic bomb. Heisenberg has been accused of misleading others in the aftermath of the Second World War by his claim of having purposely undermining the German Bomb effort. Heisenberg’s wartime visit to Niels Bohr has been dramatised in Michael Fryan’s play “Copenhagen”. But then it has also been argued that there was no reason for Heisenberg to do it because he was fully aware that the bomb could not be made before the end of the World War. Heisenberg’s son Jochen H. Heisenberg wrote: “Looking at the feasibility was essential for my father, because as he said if it was trivial building one then nobody could avoid doing so, however, if it was impossible, the point was moot. Of course there is a lot of grey area between those two extreme possibilities. My father at this time had made a serious effort to estimate the requirements for such a bomb project. While they had not solved all the problems, they knew enough to make a realistic assessment of such a task. In an interview with the `Spiegal Magazin’ in 1967 he states that his estimates were that it would require a critical mass about the size of a pineapple. This would translate into development time frame of about three years under the best of circumstances; and those definitely did not exist in wartime Germany. This was exactly how he, Otto Hahn and other scientists presented the situation to the government. Albert Speer’s memoirs confirm this. My father knew very well that this recommendation meant that these were the objective facts. He did not have to distort anything as the facts alone necessitated the conclusion.”

A few days before the surrender of Germany, Heisenberg was captured by the Allied forces. He was kept with other leading German nuclear scientists such as Otto Hahn, Carl von Weizsacker, Max von Laue, Karl Wirtz and Walter Gerlach at Farm Hall, a country estate near Cambridge. The house in which the scientists were kept was bugged and their conversations were recorded for six months.

Heisenberg played a very important role in reconstructing post Second World War German science. In 1946, after returning from England, Heisenberg became the Director of Kaiser-Wilhelm Institute, the name of which was later changed to Max-Plank Institute and it moved to Munich. In 1958 Heisenberg was appointed as Professor of Physics at the University of Munich. In 1953 he became the President of the Alexander von Humboldt Foundation. As a president Heisenberg did much to further the policy of the Foundation, which was to invite scientists from other countries to Germany and to help them work there.

Heisenberg was interested in the philosophy of physics. He believed that new insights into the problems of Part and Whole and One and Many would help discovery in microphysics.

Heisenberg loved music in addition to physics and saw a deep affinity between these two interests. He was an accomplished pianist. His son Jochen H. Heisenberg wrote: “Music was my father’s equivalent to emotional passion. ....He played regularly for himself and with others, and music was a connector to the people who were not his scientific peers. As children we benefited from this common language our parents taught with such great care. If I know him so well now, it is partly because of the many hours of music we played together. It was through music that he shared the depth of his feelings about beauty and transcendence with us, although he did not go for the so-called romantic excess of emotion at all. A clean and classical exuberance was more his style, but above all else the slow movements were his true strength.”

Among his writings were: Philosophical Problems of Quantum Physics (Ox Bow Press, 1979), Physics and Philosophy—the Revolution in Modern Science (Harper & Row, 1958) and Physics and Beyond—Encounters and Conversations (George Allen & Unwin 1971) and Encounters with Einstein and Other Essays on People, Places, and Particles (Princeton University Press, 1983). Commenting on Heisenberg’s writings N. Mukunda wrote: “Heisenberg’s writings on many profound subjects are so beautiful that they appear deceptively simple. One enjoys reading him many times over to truly appreciate his thinking.” Two important books on Heisenberg’s life and works are: Uncertainty—The Life and Science of Werner Heisenberg by David C. Cassidy (W. H. Freeman, 1992) and Recollections of a Life with Werner Heisenberg by his wife Elisabeth (Birkhauser, 1984).

Heisenberg died of cancer on February 01, 1976 at Munich.

Heisenberg not only set the limit to accuracy of experimental observation but perhaps also believed in the limit of man’s capacity to understand nature. He said: “Almost every progress in science has been paid for by a sacrifice, for almost every new intellectual achievement previous positions and conceptions had to be given up. Thus, in a way, the increase of knowledge and insight diminishes continually the scientist’s claim of `understanding’ nature.”

References

1. Singh, Virendra. Werner Heisenberg (1901-1976): His Life and Science. Resonance, Vol. 9, No.8, pp.3-5, 2004.
   
   
2. Mukunda, N. Books by and about Werner Heisenberg. Resonance, Vol. 9, No.8, pp.83-86, 2004.
   
   
3. A Dictionary of Scientists. Oxford: Oxford University Press, 1999.
   
   
4. The Cambridge Dictionary of Scientists (2nd Edition). Cambridge: Cambridge University Press, 2002.
   
   
5. Kragh, Helge. Quantum Generations: A History of Physics in the Twentieth Century. Hyderabad: Universities Press (India) Ltd., 2001.
   
   
6. Heilborn, J. L. (Ed.) The Oxford Companion to the History of Modern Science, Oxford: Oxford University Press, 2003.
   
   
7. Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. Cambridge: Cambridge University Press, 2004.
   
   
8. Heisenberg, Joachen H. Fryan’s “Heisenberg”: Fact or Fiction? Reproduced in Resonance, August 2004.
   
   
9. Parthasarathy, R. Paths of Innovators in Science, Engineering & Technology. Chennai: East West Books (Madras) Pvt. Ltd, 2000.