[<< wikiquote] Werner Heisenberg
Werner Karl Heisenberg (5 December 1901 – 1 February 1976) was a German physicist, Nobel laureate, and one of the founders of the field of quantum mechanics.

== Quotes ==

The more precise the measurement of position, the more imprecise the measurement of momentum, and vice versa.
Initial statement of the Uncertainty principle in "Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik" in Zeitschrift für Physik, 43 (1927)
Variant translation: The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.
As quoted in "The Uncertainty Principle" at the American Institute of PhysicsLight and matter are both single entities, and the apparent duality arises in the limitations of our language. It is not surprising that our language should be incapable of describing the processes occurring within the atoms, for, as has been remarked, it was invented to describe the experiences of daily life, and these consist only of processes involving exceedingly large numbers of atoms. Furthermore, it is very difficult to modify our language so that it will be able to describe these atomic processes, for words can only describe things of which we can form mental pictures, and this ability, too, is a result of daily experience. Fortunately, mathematics is not subject to this limitation, and it has been possible to invent a mathematical scheme — the quantum theory —  which seems entirely adequate for the treatment of atomic processes; for visualisation, however, we must content ourselves with two incomplete analogies — the wave picture and the corpuscular picture.
"Introductory" in The Physical Principles of the Quantum Theory (1930) as translated by Carl Eckhart and Frank C. Hoyt, p. 10Every experiment destroys some of the knowledge of the system which was obtained by previous experiments.
"Critique of the Physical Concepts of the Corpuscular Theory" in The Physical Principles of the Quantum Theory (1930) as translated by Carl Eckhart and Frank C. Hoyt, p. 20; also in "The Uncertainty Principle" in The World of Mathematics : A Small Library of the Literature of Mathematics (1956) by James Roy Newman, p. 1051Die Quantentheorie ist so ein wunderbares Beispiel dafür, daß man einen Sachverhalt in völliger Klarheit verstanden haben kann und gleichzeitig doch weiß, daß man nur in Bildern und Gleichnissen von ihm reden kann.
Quantum theory provides us with a striking illustration of the fact that we can fully understand a connection though we can only speak of it in images and parables.
Der Teil und das Ganze. Gespräche im Umkreis der Atomphysik (1969); also in "Kein Chaos, aus dem nicht wieder Ordnung würde", Die Zeit  No. 34 (22 August 1969); as translated in Physics and Beyond : Encounters and Conversation (1971)Ein Fachmann ist ein Mann, der einige der gröbsten Fehler kennt, die man in dem betreffenden Fach machen kann, und der sie deshalb zu vermeiden versteht.
An expert is someone who knows some of the worst mistakes that can be made in his subject, and how to avoid them.
Der Teil und das Ganze. Gespräche im Umkreis der Atomphysik (1969); also in "Kein Chaos, aus dem nicht wieder Ordnung würde", Die Zeit  No. 34 (22 August 1969); as translated in Physics and Beyond : Encounters and Conversation (1971)In general, scientific progress calls for no more than the absorption and elaboration of new ideas — and this is a call most scientists are happy to heed.
Physics and Beyond : Encounters and Conversation (1971)There is a fundamental error in separating the parts from the whole, the mistake of atomizing what should not be atomized. Unity and complementarity constitute reality.
As quoted in Physics from Wholeness : Dynamical Totality as a Conceptual Foundation for Physical Theories (2005) by Barbara Piechocinska.
After these conversations with Tagore some of the ideas that had seemed so crazy suddenly made much more sense. That was a great help for me.
On conversations with Rabindranath Tagore, as quoted in Uncommon Wisdom: Conversations With Remarkable People (1988) by Fritjof Capra, who states that after these "He began to see that the recognition of relativity, interconnectedness, and impermanence as fundamental aspects of physical reality, which had been so difficult for himself and his fellow physicists, was the very basis of the Indian spiritual traditions."
Variant: After the conversations about Indian philosophy, some of the ideas of Quantum Physics that had seemed so crazy suddenly made much more sense.
As quoted in Pride of India (2006) by Samskrita Bharati. p. 56I think that modern physics has definitely decided in favor of Plato. In fact the smallest units of matter are not physical objects in the ordinary sense; they are forms, ideas which can be expressed unambiguously only in mathematical language.
Das Naturgesetz und die Struktur der Materie (1967), as translated in Natural Law and the Structure of Matter (1981), p. 34If nature leads us to mathematical forms of great simplicity and beauty—by forms I am referring to coherent systems of hypothesis, axioms, etc.—to forms that no one has previously encountered, we cannot help thinking that they are "true," that they reveal a genuine feature of nature... You must have felt this too: The almost frightening simplicity and wholeness of relationships which nature suddenly spreads out before us and for which none of us was in the least prepared.
Conversation with Einstein, as quoted in Bittersweet Destiny: The Stormy Evolution of Human Behavior by Del ThiessenOf course, we all know that our own reality depends on the structure of our consciousness; we can objectify no more than a small part of our world. But even when we try to probe into the subjective realm, we cannot ignore the central order…In the final analysis, the central order, or 'the one' as it used to be called and with which we commune in the language of religion, must win out.
Werner Heisenberg as quoted in Quirks of the Quantum Mind, p. 175, ICRL Press, ISBN 1936033062The great scientific contribution in theoretical physics that has come from Japan since the last war may be an indication of a certain relationship between philosophical ideas in the tradition of the Far East and the philosophical substance of quantum theory.
Quoted from F. Capra, The Tao of Physics.After a great war, history is written by the victors and legends develop which glorify them.
from p. 35 of "The Third Reich and The Atomic Bomb [Review of The Virus House by David Irving]" in The Bulletin of the Atomic Scientists (Pp. 34-35, June 1968), translated from the German by Margaret Seckel.

=== The Development of Quantum Mechanics (1933) ===
 Nobel lecture (11 December 1933) Full text online (PDF) 
The interest of research workers has frequently been focused on the phenomenon of regularly shaped crystals suddenly forming from a liquid, e.g. a supersaturated salt solution. According to the atomic theory the forming force in this process is to a certain extent the symmetry characteristic of the solution to Schrödinger's wave equation, and to that extent crystallization is explained by the atomic theory. Nevertheless this process retains a statistical and — one might almost say —  historical element which cannot be further reduced: even when the state of the liquid is completely known before crystallization, the shape of the crystal is not determined by the laws of quantum mechanics. The formation of regular shapes is just far more probable than that of a shapeless lump. But the ultimate shape owes its genesis partly to an element of chance which in principle cannot be analysed further.However the development proceeds in detail, the path so far traced by the quantum theory indicates that an understanding of those still unclarified features of atomic physics can only be acquired by foregoing visualization and objectification to an extent greater than that customary hitherto. We have probably no reason to regret this, because the thought of the great epistemological difficulties with which the visual atom concept of earlier physics had to contend gives us the hope that the abstracter atomic physics developing at present will one day fit more harmoniously into the great edifice of Science.

=== Physics and Philosophy (1958) ===
 Physics and Philosophy: The Revolution in Modern Science (1958) Lectures delivered at University of St. Andrews, Scotland, Winter 1955-56 
We have to remember that what we observe is not nature herself, but nature exposed to our method of questioning.
This has also appeared in the alternate form: "What we observe is not nature itself, but nature exposed to our method of questioning."The atoms in the philosophy of Leucippus do not move merely by chance. Leucippus seems to have believed in complete determinism, since he is known to have said: "Naught happens for nothing, but everything from a ground and of necessity." The atomists did not give any reason for the original motion of the atoms, which just shows that they thought of a causal description of the atomic motion; causality can only explain later events by earlier events, but it can never explain the beginning.
In the philosophy of Democritus the atoms are eternal and indestructible units of matter, they can never be transformed into each other. With regard to this question modern physics takes a definite stand against the materialism of Democritus and for Plato and the Pythagoreans. The elementary particles are certainly not eternal and indestructible units of matter, they can actually be transformed into each other. As a matter of fact, if two such particles, moving through space with a very high kinetic energy, collide, then many new elementary particles may be created from the available energy and the old particles may have disappeared in the collision. Such events have been frequently observed and offer the best proof that all particles are made of the same substance: energy.But the resemblance of the modern views to those of Plato and the Pythagoreans can be carried somewhat further. The elementary particles in Plato's Timaeus are finally not substance but mathematical forms. "All things are numbers" is a sentence attributed to Pythagoras. The only mathematical forms available at that time were such geometric forms as the regular solids or the triangles which form their surface. In modern quantum theory there can be no doubt that the elementary particles will finally also be mathematical forms but of a much more complicated nature.The Greek philosophers thought of static forms and found them in the regular solids. Modern science, however, has from its beginning in the sixteenth and seventeenth centuries started from the dynamic problem. The constant element in physics since Newton is not a configuration or a geometrical form, but a dynamic law.The equation of motion holds at all times, it is in this sense eternal, whereas the geometrical forms, like the orbits, are changing. Therefore, the mathematical forms that represent the elementary particles will be solutions of some eternal law of motion for matter. Actually this is a problem which has not yet been solved.There is an enormous difference between modern science and Greek philosophy, and that is just the empiristic attitude... Since the time of Galileo and Newton, modern science has been based upon a detailed study of nature and upon the postulate that only such statements should be made, as have been verified or at least can be verified by experiment. The idea that one can single out some events from nature by an experiment... to find out what is the constant law in the continuous change, did not occur to the Greek philosophers. Therefore, modern science has from its beginning stood on a much more modest, but at the same time much firmer, basis than ancient philosophy. Therefore, the statements of modern physics are in some way meant much more seriously than the statements of Greek philosophy.[I]n the Copenhagen interpretation of quantum theory we can indeed proceed without mentioning ourselves as individuals, but we cannot disregard the fact that natural science is formed by men. 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 nature of questioning. This was a possibility of which Descartes could not have thought, but it makes a sharp separation between the world and the I impossible.If one follows the great difficulty which even eminent scientists like Einstein had in understanding and accepting the Copenhagen interpretation... one can trace the roots... to the Cartesian partition....it will take a long time for it  [this partition]  to be replaced by a really different attitude toward the problem of reality.Modern positivism...expresses criticism against the naïve use of certain terms... by the general postulate that the question whether a given sentence has any meaning... should always be thoroughly and critically examined. This... is derived from mathematical logic.  The procedure of natural science is pictured as an attachment of symbols to the phenomena. The symbols can, as in mathematics, be combined according to certain rules... However, a combination of symbols that does not comply with the rules is not wrong but conveys no meaning.The obvious difficulty in this argument is the lack of any general criterion as to when a sentence should be considered meaningless. A definite decision is possible only when the sentence belongs to a closed system of concepts and axioms, which in the development of natural science will be rather the exception than the rule. In some case the conjecture that a certain sentence is meaningless has historically led to important progress... new connections which would have been impossible if the sentence had a meaning. An example... sentence: "In which orbit does the electron move around the nucleus?" But generally the positivistic scheme taken from mathematical logic is too narrow in a description of nature which necessarily uses words and concepts that are only vaguely defined.The words "position" and "velocity" of an electron... seemed perfectly well defined... and in fact they were clearly defined concepts within the mathematical framework of Newtonian mechanics. But actually they were not well defined, as seen from the relations of uncertainty. One may say that regarding their position in Newtonian mechanics they were well defined, but in their relation to nature, they were not. This shows that we can never know beforehand which limitations will be put on the applicability of certain concepts by the extension of our knowledge into the remote parts of nature, into which we can only penetrate with the most elaborate tools. Therefore, in the process of penetration we are bound sometimes to use our concepts in a way which is not justified and which carries no meaning. Insistence on the postulate of complete logical clarification would make science impossible. We are reminded... of the old wisdom that one who insists on never uttering an error must remain silent.The law of causality is no longer applied in quantum theory and the law of conservation of matter is no longer true for the elementary particles. Obviously Kant could not have foreseen the new discoveries, but since he was convinced that his concepts would be "the basis of any future metaphysics that can be called science" it is interesting to see where his arguments have been wrong.Any concepts or words which have been formed in the past through the interplay between the world and ourselves are not really sharply defined with respect to their meaning: that is to say, we do not know exactly how far they will help us in finding our way in the world. We often know that they can be applied to a wide range of inner or outer experience, but we practically never know precisely the limits of their applicability. This is true even of the simplest and most general concepts like "existence" and "space and time". Therefore, it will never be possible by pure reason to arrive at some absolute truth.  The concepts may, however, be sharply defined with regard to their connections. This is actually the fact when the concepts become  part of a system of axioms and definitions which can be expressed consistently by a mathematical scheme.  Such a group of connected concepts may be applicable to a wide field of experience and will help us to find our way in this field. But the limits of the applicability will in general not be known, at least not completely.The existing scientific concepts cover always only a very limited part of reality, and the other part that has not yet been understood is infinite.Whenever we proceed from the known into the unknown we may hope to understand, but we may have to learn at the same time a new meaning of the word "understanding." 
The physicist may be satisfied when he has the mathematical scheme and knows how to use for the interpretation of the experiments. But he has to speak about his results also to non-physicists who will not be satisfied unless some explanation is given in plain language. Even for the physicist the description in plain language will be the criterion of the degree of understanding that has been reached.I remember discussions with Bohr which went through many hours till very late at night and ended almost in despair; and when at the end of the discussion I went alone for a walk in the neighbouring park I repeated to myself again and again the question: Can nature possibly be so absurd as it seemed to us in these atomic experiments?

== Quotes about Heisenberg ==

Heisenberg's name will always be associated with his theory of quantum mechanics, published in 1925, when he was only 23 years old. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen, Heisenberg was awarded the Nobel Prize for Physics for 1932.His new theory was based only on what can be observed, that is to say, on the radiation emitted by the atom. We cannot, he said, always assign to an electron a position in space at a given time, nor follow it in its orbit, so that we cannot assume that the planetary orbits postulated by Niels Bohr actually exist. Mechanical quantities, such as position, velocity, etc. should be represented, not by ordinary numbers, but by abstract mathematical structures called "matrices" and he formulated his new theory in terms of matrix equations.
Official Biography at the Nobel Prize site, from Nobel Lectures, Physics 1922-1941 (1965)When he arrived he looked like a simple peasant boy, with short, fair hair, clear bright eyes and a charming expression. He took his duties as an assistant more seriously than Pauli and was a great help to me. His incredible quickness and acuteness of apprehension has always enabled him to do a colossal amount of work without much effort; he finished his hydrodynamic thesis, worked on atomic problems partly alone, partly in collaboration with me, and helped me to direct my research students.
Max Born, My Life: Recollections of a Nobel Laureate (1978), p. 212We gaze continually at the world and it grows dull in our perceptions. Yet seen from the another's vantage point, as if new, it may still take our breath away. Come... dry your eyes, for you are life, rarer than a quark and unpredictable beyond the dreams of Heisenberg. Come, dry your eyes. And let's go home.
Alan Moore, in lines for "Doctor Manhattan" in Watchmen (1987)In 1925, the world view of physics was a model of a great machine composed of separable interacting material particles. During the next few years, Schrodinger and Heisenberg and their followers created a universe based on super imposed inseparable waves of probability amplitudes. This new view would be entirely consistent with the Vedantic concept of All in One.
Walter J. Moore in Schrödinger: Life and Thought (1989)  ISBN 0521437679 In  1929, Heisenberg  spent  some  time  in  India  as  the  guest of  the  celebrated  Indian  poet  Rabindranath  Tagore,  with  whom he  had  long  conversations  about  science  and  Indian  philosophy. This  introduction  to  Indian  thought  brought  Heisenberg  great comfort,  he  told  me.  He  began to  see  that  the  recognition  of  relativity,  interconnectedness,  and  impermanence  as  fundamental aspects  of  physical  reality,  which  had  been  so  difficult  for  himself  and  his  fellow  physicists,  was  the  very  basis  of  the  Indian spiritual  traditions. “After  these  conversations  with  Tagore,” he said, “some  of  the  ideas  that  had  seemed  so  crazy  suddenly made much more sense. That was a great help for me.”
Fritjof Capra, Uncommon Wisdom, 1988, p.43

== External links ==

Brief biography at the official Nobel prize site 
Brief biography at the MacTutor archive (University of St Andrews, Scotland)
About Werner Heisenberg
Heisenberg - his life & work  - The American Institute of Physics History Center
Critical Resources: Heisenberg Uncertainty Principle
The Nobel Prize in Physics 1932
Niels Bohr Archive's 2002 release of Bohr-Heisenberg letters