Werner Karl Heisenberg was born on December 5, 1901 in the Bavarian city of Würzburg, Germany. He was the second son of Dr. August Heisenberg, a professor of Middle and Modern Greek philology, and Anna Heisenberg, the daughter of a Gymnasium principal. The high social status enjoyed by the academics in pre-war Germany put the Heisenberg family in the upper middle strata of the then German society.
Schooling
At five, Heisenberg was admitted to the elementary school in Würzburg. His father inculcated a competitive spirit in him by always goading him to compete with his older brother. This was probably one of the reasons why Heisenberg became a precocious child. He was always way ahead of his classmates in school, especially in mathematics and science.
In 1910, Heisenberg’s father was offered professorship at the University of Munich. The family moved to Munich, and young Heisenberg completed the last year of elementary school here. He joined the Maximilians-Gymnasium the next year. The Gymnasiums were schools providing nine years of education and they prepared students for a university education.
Heisenberg received top grades in all subjects, ranging from classical languages to physics and mathematics. The only subjects in which his performance was relatively poor were German language and athletics. Heisenberg was also interested in classical music. He learned to play the piano under a great Munich maestro and even presented school concerts.
The major technological innovations of the period and the influence of a teacher, Christopher Wolff, inculcated in Heisenberg, a passionate love for mathematics and science. So strong was his love for these subjects that he studied Einstein's Theory of Relativity on his own, and learnt calculus all by himself to tutor a college student. He even tried his hand, though unsuccessfully, at proving the famous Fermat’s Last Theorem, which had eluded a proof for more than three centuries. His knowledge of mathematics and physics was much beyond that expected of a school student. He graduated by topping his class in 1920.
World War I
With the outbreak of the World War I in 1914, began the blockade of Germany and a life full of shortages. Especially in Bavaria, with little food and no fuel, life became tough. Heisenberg himself lived in a state of semi-starvation. Almost all able-bodied men had been sent to the front. The schools had to be closed down forcing the students to become independent in their schooling as well as in life, in general. Heisenberg enrolled at the military training unit of his school. As a member of this unit, he worked with the Bavarian agriculture service.
After the War ended in 1918, Germany became a Republic and the social Democrats took over power from the monarchy. In Bavaria, the Communists established a Soviet type Republic. This regime was crushed ruthlessly in May 1919 by troops sent from Berlin. After fierce street battles in Munich, social democratic rule was established. Heisenberg worked actively with one of these units from Berlin. During this period, he was stimulated by the atomic theories of Plato and other Greeks whom he read while on sentry duty on the roof of a seminary. He risked his life twice in trying to get past the warring troops to fetch food for his family.
The Youth Movement
The social and economic collapse of Germany after its humiliating defeat in the World War I bewildered the young of Heisenberg’s age forcing several of them to seek refuge in the German romantic tradition of ‘heading for the hills’. Feeling betrayed by the older generation and unable to comprehend and make sense of the world they lived in, they went on an often elusive search of simpler values and lost traditions. Heisenberg became an elected leader of such a group of boys associated with the New Boy Scouts, an extreme right-wing anti-modernist organization.
The New Boy Scouts dreamt of bringing back the monarchy in all its glory, and they were decidedly anti-Semitic. But Heisenberg was above such parochialism, and his group allowed Jewish boys to participate in its activities. He did not give in to the right-wing ideology totally and was active in educating adult workers.
Unlike others, Heisenberg’s group had a rather staid and upright character with Heisenberg as the paternal figure. Their weekly meetings would be devoted to German music, songs, and poetry. They had a rigid ethical and moral code – no smoking, no drinking, no interaction with women. Hiking and camping trips were also regular activities of the group. The youth movement was instrumental in shaping Heisenberg’s personality. It gave him the strength of character and developed in him love for the fatherland. Heisenberg was active in the youth movement until 1933 when Hitler banned all independent youth groups.
University Days
Heisenberg joined the University of Munich in 1920. According to Heisenberg:
My first two years at Munich University were spent in two quite different worlds: among my friends of the youth movement and in the abstract realm of theoretical physics. Both worlds were so filled with intense activity that I was often in a state of great agitation, the more so as I found it rather difficult to shuttle between the two.
He gave up his earlier plan of taking up pure mathematics after an unsuccessful interview with a mathematics professor. He decided to study theoretical physics under Professor Sommerfeld, a leading atomic physicist, who with Neils Bohr had proposed the ‘old quantum theory’. Soon enough, Heisenberg became Sommerfeld’s favorite student and he published his first paper on the old quantum theory of the atom in 1922. Following this, he went to Göttingen for a year to study under Max Born as a visiting student. Here, he learnt the application of sophisticated mathematical methods in atomic theory. As an affirmation of the above, he later wrote;
I learned optimism from Sommerfeld, mathematics at Gottingen, and physics from Bohr.
Doctoral Work
Heisenberg returned to Munich in May 1923, to attend the last semester and write his doctoral dissertation. Afraid that Heisenberg's original ideas in quantum physics would not be sympathetically received, Sommerfeld advised him to select a more conventional topic for his dissertation. A company had earlier commissioned Sommerfeld to study the feasibility of channeling the Isar River through Munich. Heisenberg was given an extremely difficult mathematical problem arising from this study. He submitted his dissertation titled On the Stability and Turbulence of Fluid Flow and it was even accepted for publication by the physics journal Annalen der Physik. The validity of his theoretical results could finally be confirmed only after about a quarter century.
The real challenge for Heisenberg was facing the examining committee for his final orals. He could deal with ease the abstruse questions in theoretical physics and mathematics, but he failed miserably in answering even elementary questions in experimental physics. The experimental physicist on the committee gave him an F, the lowest grade, whereas Sommerfeld gave him an A. Heisenberg received an overall grade of C for his doctorate. This came as something of a shock to Heisenberg. So depressed was he that he walked out of the party held by Sommerfeld for him that evening and left for Göttingen by the night train. In Göttingen, Heisenberg joined Max Born as his teaching assistant. He was away on sabbatical at Bohr's institute in Copenhagen, Denmark, during 1924-25. He returned to Göttingen in April 1925 and made his first major contribution to quantum mechanics by proposing matrix mechanics.
Heisenberg’s Matrix Mechanics
The old quantum theory of Bohr and Sommerfeld had seemed to be a reasonably good theory when it was first proposed. But several new discoveries showed the inadequacy of this theory and the need for a new quantum theory was strongly felt. Heisenberg set out to do this upon returning to Göttingen. In the spring of 1925, Heisenberg had to go to Heligoland to recuperate from an attack of allergy. In the solitude of the island he found the answer to the problem. Realizing the limitations of visual models he decided to make use of experimental data and mathematical speculations. Heisenberg managed to come up with a solution using his theoretical skills, but he could not understand the mathematical results. Max Born recognized this to be matrix mathematics. Later in the year, Heisenberg, Born and Jordan published a paper describing a new matrix-based quantum mechanics, the matrix mechanics. This new quantum mechanics could explain several of the newly discovered atomic phenomena. Heisenberg continued working on his new theory over the next year. In 1926, he was offered a teaching position at Bohr’s institute in Copenhagen.
Schrödinger’s Wave Mechanics
In early 1926, the Austrian physicist Erwin Schrödinger proposed another quantum mechanics, the wave mechanics. Matrix mechanics was too abstract to be of any help in visualizing atomic events, whereas wave mechanics consisted of much simpler mathematics and could be easily visualized. Therefore, most physicists readily accepted wave mechanics. Subsequently Schrödinger showed that matrix and wave mechanics were mathematically equivalent. Yet he claimed that wave mechanics was superior to matrix mechanics and this angered Heisenberg. The two met in Copenhagen and had heated debates. The debates only proved that neither of the two theories was complete. Both groups began a search for the physical meaning of their respective equations. This search led to the discovery of the Uncertainty Principle by Heisenberg, and the Copenhagen Interpretation.
Uncertainty Principle
Heisenberg revealed the uncertainty principle in a 14-page letter to Wolfgang Pauli in February 1927. He even came up with a thought experiment to prove his discovery. The results were the same even after Heisenberg corrected the flaws that Bohr had pointed out in the experiment. Heisenberg’s Uncertainty Principle states that it is impossible to determine exactly both the position and the momentum of a particle at the same time. These uncertainties in the measurements are inherent in nature and therefore have profound scientific and philosophical implications; the very notions of causality and the deterministic view of the world are brought into question. Therefore, this principle is also called the principle of indeterminacy.
Copenhagen Interpretation
Bohr believed that both the wave/visual representation of wave mechanics and the particle/causal representation of matrix mechanics were essential to get a complete picture of atomic events, i.e. they were complementary to each other. Choosing either the wave picture or the particle picture sets limits to our knowledge, and this limitation is expressed by Heisenberg's uncertainty principle. Complementarily, uncertainty, and the statistical interpretation of Schrödinger's wave function make the physical meaning of quantum mechanics clear. This is called the Copenhagen Interpretation.
Heisenberg did not accept Bohr's views at first and he reacted with bitterness. He is even supposed to have burst into tears once. But later, he accepted Bohr’s interpretation and declared at the Solvay Physics Conference in Brussels, Belgium that quantum mechanics was complete. Though there were some scientists like Einstein and Schrödinger who objected to this interpretation, Heisenberg’s principles became widely accepted.
The Youngest Professor
Heisenberg was appointed the professor of theoretical physics at the University of Leipzig in October 1927. He was barely 25 years of age then and he became Germany's youngest full professor. He was the chief of the Institute for Theoretical Physics, a division of the Physics Institute. The very presence of Heisenberg attracted top-class students from all over the world to the Institute. Since its inception, the Leipzig years turned out to be quite fruitful. Collaborations produced new quantum theories of solid-state crystals, the structure of molecules, ferromagnetism, Hall effect, the scattering of radiation by nuclei, and the neutron-proton model of the nucleus. Progress was also made in the field of high-energy physics and relativistic quantum theory. Heisenberg traveled extensively during these years lecturing, attending conferences and meeting other physicists. He also visited India in 1929.
The Nobel Prize
The 1932 Nobel Prize for Physics was awarded to Heisenberg in December 1933. The Nobel Prize was "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen."
In his presentation speech by Professor H. Pleijel, Chairman of the Nobel Committee for the Royal Swedish Academy of Sciences, said and we quote;
Professor Heisenberg, it has fallen to you whilst young in years, to have given to physics, by means of the theory of quantum mechanics established by you, a general method for the solution of the manifold problems which have come to the fore as a result of restless experimental researches into the theory of radiation. From a study of the properties of the molecules, you have succeeded, among other things, in predicting that the hydrogen molecules would appear in two forms, which later has been confirmed. Your quantum mechanics has created new concepts, and has led physics into fresh trains of thought, which have now already proved of fundamental importance for our knowledge of the phenomena of physics.
The Royal Academy of Sciences has awarded you the Nobel Prize for Physics for 1932 in recognition of these studies, and I beg you to accept this distinction from the hands of His Majesty the King.Unquote
The Nazi Period
Alongside, Hitler became the dictator of Germany in January 1933. Though he was not a Nazi, Heisenberg remained in Germany even during Hitler’s rule. His Nobel Prize may have shielded him from more blatant attacks, but he too had to face the brunt of the Nazi police force, the dreaded SS. Such was the state even of a Nobel Prize winner that race discrimination rearing its ugly head, fetched even those blessed, the misfortune that was unparalleled.
The Nazi regime started its pogrom against the Jews by removing them from government positions, and this included academic positions at the universities. In their zeal to destroy anything remotely connected with Jews, they started repudiating even scientific theories proposed by them. Nazi physicists, mostly unrecognized and unsuccessful, led by the Nobel laureates Stark and Lenard began attacking non-classical physics as ‘Jewish world-bluff’ and developed what they called ‘German Physics’. An acrimonious battle broke out at the Würzburg Physics Congress of 1934 and physicists like Heisenberg who tried to defend modern physics ended up in the dock.
The most virulent attack on Heisenberg began in 1937 with an article titled 'White Jews in Science’ in Das Schwarze Korps, the official weekly of the SS. According to the paper, ‘Heisenberg is only one example among many others… they are all representatives of Judaism in German spiritual life who must all be eliminated just as the Jews themselves’. He was called a traitor, and a Nazi functionary said that the most suitable place for him was the concentration camp. Heisenberg got reprieve after a year-long investigation, and that too after he appealed directly to the chief of the SS, Heinrich Himmler.
Marriage
In 1937, prior to the SS episode, Heisenberg married Elisabeth Schumacher. She was the daughter of a famous economics professor of Berlin, and had a degree in German literature. She was as interested in music as he was. They say music unites and that's what exactly happened in case of Heisenberg and Elisabeth. At a common friends place where a concert was held, they met for the first time. Heisenberg was 35 and Elisabeth then was 25.They exchanged nuptial wows on April 29, 1937.
He was suppose to join work at Munich in March but due to the impending wedding, he got his departure postponed till August. Finally, he and his wife arrived at Munich in July only to learn that his appointment had been blocked by the Nazi authorities. She later gave birth to twins nine months later, the first of the couple’s seven children.
World War II
The relations between Heisenberg and the Nazi regime which had soured after the SS episode, thawed out once the World War II began in 1939. This truce was necessitated by the dictates of the war; the Nazis required better weapons. Though Heisenberg had already been drafted into a reserve mountain infantry unit, he received orders to report at the Army Weapons Bureau in Berlin.
The German Bomb
An atom consists of a central nucleus with electrons revolving around it. In nuclear fission the nuclei of uranium atoms are split and this releases tremendous energy. Energy produced in controlled fission process can be used to produce electricity. If the fission reaction is uncontrolled, the entire energy is released almost instantaneously leading to an explosion. This is a nuclear or atomic bomb.
Nuclear fission had been discovered in Germany by Otto Hahn in 1938. Heisenberg was put in charge of exploring the possibility of, and actually developing a nuclear bomb. Heisenberg sent a two-part survey on its feasibility to the Weapons Bureau within three months. Until 1942, the fission project was handled by two groups, one in Leipzig and the other in Berlin. Heisenberg had to shuttle between the two cities to coordinate the work. He left Leipzig in 1942 to join the University of Berlin as professor of theoretical physics. He also became the head of Germany's main nuclear reactor research facility, the Kaiser Wilhelm Institute for Physics. Heisenberg sent his family to the safety of their summer home in Bavaria, while he stayed in Berlin working on the nuclear fission project till the end of the war.
The frightening possibility that this German effort might succeed in providing Hitler with a nuclear weapon was one of the driving forces of the Manhattan Project in the United States, which produced the nuclear weapons dropped on Japan in August 1945.
Though nuclear fission was a German discovery and Germany had the necessary infrastructure to build the bomb, it failed miserably in accomplishing the task. One theory is that Heisenberg joined the atomic bomb project with the hidden agenda of sabotaging it. Probably that was the reason why he only concerned himself with the administration of the project instead of working on the scientific details. He was more interested in high-energy particle physics on which he published significant papers during this period. Another view, less sympathetic to Heisenberg, is that his being a ‘mere’ theorist was responsible for the failure of this practical project. Whatever be the reasons for the failure, the fears that the Germans might develop the bomb gave the necessary impetus to the American efforts of building the bomb.
Prisoner of War
After Germany’s final defeat in the War, Heisenberg and nine other German nuclear scientists were arrested by Alsos Mission, an Allied science intelligence division. They were interned for six months at Farm Hall, a country house in Godmanchester, near Cambridge in England. The British used concealed microphones to tap and record the private conversations of the German scientists to get to know the exact nature of the progress made by Germans in developing the bomb. It turned out that the Germans were not only nowhere near developing the atomic bomb, but they had also underestimated the American potential to build one.
Post-war Period
After his release in January 1946, Heisenberg settled in Göttingen. He reorganized the Kaiser Wilhelm Institute for Physics with the aim of making it a center of excellence in physics so as to rejuvenate research in the newly created West Germany. It was renamed the Max Planck Institute for Physics in 1948. The main areas of research were experimental and theoretical high-energy physics, and astrophysics. The Institute was moved to Munich in 1958 and renamed the Max Planck Institute for Physics and Astrophysics. Although Heisenberg was an honorary professor at the Universities of Göttingen and Munich, he never held a full professorship after the war. Heisenberg also became more involved in the activities and research at CERN.
Heisenberg did not approve of the insular existence of science and scientists, and their subordination to the political masters. He sought a more active role for science in directing public affairs. He did find a sympathetic audience in the new federal chancellor, Konrad Adenauer. The German Research Council was founded in 1949 with this express purpose. Its president was Heisenberg and it had 15 leading scientists as its members. In Germany, science had always been under the control of the ministries of culture of the provinces. The cultural ministers had a parallel organization, the Emergency Association of German Science. The scientists’ council had to bow down to the politicians’ maneuverings. The two associations were merged in 1951 to form the German Research Society. Heisenberg was elected to its Presidium. He was responsible for coordinating nuclear research as the chief of its Commission for Atomic Physics.
The Allied Forces had forced Germany into discontinuing fission research because they did not want it to emerge as a nuclear threat. Heisenberg believed that nuclear energy was going to be the energy source of the future, driving the industry and economy. His efforts led to the Allies lifting restrictions on nuclear development for peaceful purposes in 1955. Serving on the various atomic commissions, he helped West Germany become an exporter of nuclear technology in a short span of time.
In 1957, this very Heisenberg fiercely opposed his government’s acceptance of North Atlantic Treaty Organization’s plans to install tactical nuclear weapons in West Germany. He and 17 other West German scientists issued the ‘Göttingen Manifesto’ criticizing this move.
The Internationalist
Heisenberg was appointed President of the Alexander Von Humboldt Foundation in 1953. Under his stewardship, the foundation invited scientists from around the world to work at German institutes. He himself traveled extensively to other countries to give lectures. The most famous are his Gifford lectures of 1955-56 at St. Andrews University, Scotland. These were later published as a monograph Physics and Philosophy.
In 1952, Heisenberg led the German delegation to the European Council for Nuclear Research. He was part of the body responsible for setting up the European accelerator for high-energy physics, CERN, Conseil Européen pour la Recherche Nucléaire, near Geneva, Switzerland. He was Chairman of the Scientific Policy Committee of the International Institute of Atomic Physics at Geneva for many years, and then continued as a member of this Committee.
There is an interesting event of this period which shows the linguistic influence of his father that led him to rename the particle 'meson' as it is named and spelt. When the Japanese physicist Yukawa discovered the particle now known as the meson and the term "mesotron" was proposed for it, that the Greek word "mesos" has no "tr" in it, with the result that the name "mesotron" was changed to "meson". The son of a linguist father who too was keen in the early state of life to pusue an academic excellence in the languages had scored yet another decisive victory.
In the later half of his life, Heisenberg did research in plasma physics and thermonuclear processes, and also worked on the philosophical foundations of science. His primary interest, however, was in trying to develop a unified quantum theory of elementary particles. He collaborated with Wolfgang Pauli to produce a new unified theory called Weltformel, the world formula, in 1958. The new theory was not successful and even Pauli withdrew his endorsement of the theory. Heisenberg continued his search for a unified theory in the 60s as well.
Heisenberg retired from the directorship of Max Planck Institute in 1970, and resigned as President of the Alexander Von Humboldt Foundation in 1972. He died of cancer in Munich on February 1, 1976.
Werner Karl Heisenberg was one of those rare geniuses who dared to overturn all the opinions sacredly held hitherto, and whose influence is felt much beyond their narrow field of work. His Uncertainty Principle is the cornerstone of quantum physics. This theory shook science out of its arrogant complacency by questioning its basic premises of causality and determinism, and it also blurred the boundary between physics and philosophy. He was awarded the 1932 Nobel Prize for Physics for this spectacular work that he did while still in his mid-twenties.
A brilliant academician with international exposure, he was a giant among those who were suppose to have unraveled the mysteries of the atom. and to help mankind search alternative energy forms. He was considered to be a controversial personality. His knowledge was suspected as Germany under Hitler was unable to build an atomic bomb. Germans then considered him to be a betrayer as he and his team of scientists could not meet the German atomic aspirations. But he had always been a fervent nationalist inspite of all the indignities and restrictions that had been imposed upon, by the Nazis. Read more about this brilliant personality.
1901 Born on 5 December in Würzburg, Germany.
1906 Joined the primary school in Würzburg.
1910 Moved to Munich.
1911 Started studying at the Max-Gymnasium.
1918 Participated in the Bavarian agricultural service.
1919 Supported troops after suppression of the Bavarian Soviet Republic.
Became a leader of younger boys in the youth movement.
1920 Joined the University of Munich as student of Sommerfeld.
1921 Submitted his first paper for publication.
1922 Started studies with Max Born in Göttingen.
1923 Obtained his doctorate.
1924 Met Einstein for the first time.
Became an International Education Board fellow with Bohr in Copenhagen.
1925 Receipt of paper providing breakthrough to quantum mechanics.
1926 Appointed as lecturer in Bohr's institute.
1927 Receipt of paper on the uncertainty principle.
Attended Como conference where Bohr presented complementarily.
Appointed Professor of Theoretical Physics in Leipzig.
Attended Solvay Congress in Brussels.
1929 Traveled to the United States, Japan, China, and India.
1932 Receipt of his first paper on the neutron-proton model of nuclei.
1933 Received the 1932 Nobel Prize for Physics.
1936 Heisenberg and theoretical physics attacked in the Nazi party newspaper.
Presented the theory of cosmic-ray showers involving multiple processes.
1937 Married Elisabeth Schumacher in Berlin.
Heisenberg and other physicists attacked in the SS newspaper.
1938 Twins born, the first of seven children.
Exonerated of SS charges by Himmler.
Joined the fission research project in Berlin.
1941 Leipzig uranium pile shows first neutron multiplication. Visited German-occupied Copenhagen for discussions with an alarmed Bohr.
1942 Made a presentation to Reich officials on nuclear fission after Army withdrew funds.
Briefed Albert Speer on nuclear research.
Appointed interim director of the Main Reactor Research Lab in Berlin. Laid plans for the construction of a reactor.
Proposed the S-matrix theory of elementary particle physics.
1943 Appointed Professor of Theoretical Physics in Berlin.
Lectured on nuclear fission before Göring's Aerodynamics Academy.
1944 Traveled to German-occupied Copenhagen to free the Bohr Institute from the control of occupation authorities.
1945 Joined his reactor team in Black Forest.
U.S. forces arrested Heisenberg at his family home in Urfeld, Bavaria.
Heisenberg held as a prisoner at Farm Hall, England.
1946 Released in January, settles in Göttingen.
Appointed director of Kaiser Wilhelm (later Max Planck) Institute for Physics.
1949 Became founding president of the German Research Council.
1950 Proposed unified theory of elementary particles involving a nonlinear spinor field.
1951 Heisenberg in Presidium of the German Research Association formed by the merger of the German Research
Council and the Emergency Association.
1952 Led the German delegation to European Council for Nuclear Research for the founding of CERN.
1953 Appointed president of the Alexander Von Humboldt Foundation.
1957 Issued a declaration with 17 other West German scientists opposing Germany’s acceptance of tactical nuclear weapons provided by NATO.
1958 Proposed with Wolfgang Pauli a unified field theory of elementary particles and the Weltformel.
Moved his institute and family to Munich.
1970 Resigned as Director of the Max Planck Institute.
1975 Resigned as President of the Alexander Von Humboldt Foundation.
1976 Died of cancer on 1 February at his home in Munich.
THE UNCERTAINTY PRINCIPLE
Classical physics states that it is possible to characterize the motion of a body in terms of its position in space and its momentum. Momentum of a particle is the product of its mass and velocity. The knowledge of the present position and momentum of a body would allow us to predict the future course of the body. Thus, the classical world is a deterministic world in that the present state of the universe is considered to be precisely measurable in terms of positions and momenta of particles, and its future state accurately predictable. But this turns out to be true only of the macroscopic world.
Heisenberg showed that at micro-level, this certainty breaks down. In an atom, electrons revolve around a central nucleus very much like the planets revolving around the sun. It is possible to measure the positions and momenta of planets and accurately predict such phenomena as the eclipses. Heisenberg showed that it is impossible, even theoretically, to measure the position and momentum of an electron with equal precision.
The position of a body is known only when the light falling on it is reflected back to the observer. Light consists of electromagnetic waves of different wavelengths, each wavelength corresponding to a different color and amount of energy. There is more energy in light of smaller wavelengths. The precision of measurement depends upon the wavelength of the light used; smaller the wavelength, greater is the resolution and accuracy. Therefore, accurate localization of a small particle like an electron would require light of extremely small wavelength. But these waves would have greater amount of energy and they would affect the velocity or momentum of the electron on striking it. Thus the attempt at having greater accuracy in measuring the position of the electron results in the sacrifice of precision in measuring the momentum. If light of greater wavelength, and hence lesser energy, is used so as to measure the momentum more precisely, the position cannot be known as accurately.
The simultaneous measurement of the two conjugate variables necessarily involves imprecision; the more precise is the measurement of position, the less precise is the measurement of momentum, and vice versa, i.e. the uncertainties are dependent on each other. This uncertainty in making measurements at the atomic or micro-mechanical level arises because in making measurements, the system has to be disturbed. Heisenberg showed the classical belief that the precision of any measurement was limited only by the accuracy of the instruments to be wrong. The uncertainty is a fundamental consequence of the properties of the physical universe; it becomes overtly visible only when we deal with the micro-world. Hence a particle can be described only in terms of probabilities.
The mathematical formulation of the uncertainty principle is
Delta(p) Delta(q) > h / 4p
Delta(q) is the uncertainty of the position,
Delta(p) is the uncertainty of the momentum,
h is Planck's constant and p (p or pi) is also a constant, therefore the right-hand term h / 4 p is a constant and has an extremely low value.
The equation implies that Delta(q) and Delta(p) are inversely related. When one of these uncertainties approaches zero so that the measurement of the quantity is more exact, the uncertainty in the other quantity approaches infinity resulting in that quantity becoming undefined.
Implications of the Uncertainty Principle
Classical physics assumes that there exists a real external objective world independent of observers. Heisenberg asserted that the distinction between the observer and the observed vanishes in the act of observing atomic processes, and that things cannot have meaning beyond the precision with which they can be observed. This was contrary to what was considered to be the basic supposition of science.
The developments in classical physics since the time of Galileo and Newton led to a deterministic world-view – that there is a law of causality, i.e. every effect is preceded by a cause, and that the knowledge of the present would enable us to predict the future. The uncertainty principle challenges this notion by stating that exactitude is impossible; at the most one can have the probabilities of possible results. Since the present itself cannot be known completely, the future remains even more obscure.
The whole superstructure of modern physics and philosophy has been built upon the uncertainty principle. Its influence on modern culture can be gauged from the bumper stickers that became very popular at one time. They proclaimed ‘Heisenberg may have slept here’.
• Die physikalischen Prinzipien der Quantentheorie, 1928
• The Physical Principles of the Quantum Theory
• The Physicist's Conception of Nature
• Physics and Philosophy, 1962
• Physics and Beyond: Encounters and Conversations, 1971
• An expert is someone who knows some of the worst mistakes that can be made in his subject, and how to avoid them.
• The space in which man has developed as an intellectual being has more dimensions than that of the single direction in which he has moved during the last few centuries.
• We will have to abandon the philosophy of Democritus and the concept of elementary particles. We should accept instead the concept of elementary symmetries.
•The more precisely the position is determined, the less precisely the momentum is known, and conversely.
• What we observe is not nature itself, but nature exposed to our method of questioning.
• The atom of modern physics can be symbolized only through a partial differential equation in an abstract space of many dimensions.
• Every word or concept, clear as it may seem to be, has only a limited range of applicability.
• Every tool carries with it the spirit by which it had been created.
• Even for the physicist the description in plain language will be a criterion of the degree of understanding that has been reached.
• I wished to procure for science some right to take the initiative in public affairs.
• Natural science does not simply describe and explain nature; it is part of the interplay between nature and ourselves; it describes nature as exposed to our method of questioning.
• Of those early days at the Gymnasium I recall that both my interests in languages and in mathematics were awakened rather early.
• Others, including myself, had been working two years earlier as farm hands on farms in the Bavarian Highlands. So the raw wind was no longer alien to us; and we were not afraid to form our own opinions on the most difficult problems.
• From Sommerfeld I learned optimism, from the Göttingen people mathematics, and from Bohr physics.
• All of my meager efforts go toward killing off and suitably replacing the concept of the orbital path which one cannot observe.
• The more I think about the physical portion of Schrödinger's theory, the more repulsive I find it.….What Schrödinger writes about the visualizability of his theory 'is probably not quite right,' in other words, it's crap.
• In the summer of 1939, 12 people might still have been able, by coming to mutual agreement, to prevent the construction of the atom bomb.
• We regard quantum mechanics as a complete theory for which the fundamental physical and mathematical hypotheses are no longer susceptible of modification.
• Think of the time after the catastrophe, Planck had said, and I felt he was right.
• I believe that the existence of the classical "path" can be permanently formulated as follows: The "path" comes into existence only when we observe it.
• In the sharp formulation of the law of causality-- "if we know the present exactly, we can calculate the future"-it is not the conclusion that is wrong but the premise.
• You can say, well, this orbit is really not a complete orbit. Actually, at every moment the electron has only an inaccurate position and an inaccurate velocity, and between these two inaccuracies there is this uncertainty relation.
• One can’t get anywhere in philosophy now without knowing something about modern physics.
HONORS
• Received the 1932 Nobel Prize for Physics.
• Honorary doctorate of the University of Bruxelles.
• Honorary doctorate of the Technological University, Karlsruhe.
• Honorary doctorate of the University of Budapest in 1964.
• Recipient of the Order of Merit of Bavaria.
• Received the Grand Cross for Federal Services with Star of Germany.
• Fellow of the Royal Society of London.
• Knight of the Order of Merit, Peace Class.
• Received the Max Planck Medal.
• Honored with the Matteucci Medal.
• Awarded the Barnard College Medal of Columbia University.
• Member of the Academies of Sciences of Göttingen, Bavaria, Saxony, Prussia, Sweden, Rumania, Norway, Spain, The Netherlands, Rome (Pontifical), the German Akademie der Naturforscher Leopoldina (Halle), the Accademia dei Lincei (Rome), and the American Academy of Sciences.
President of the Deutsche Forschungsrat (German Research Council) during 1949-1951.
President of the Alexander von Humboldt Foundation from 1953 to 1975.
