Werner Heisenberg Quotes

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.

In classical physics, science started from the belief – or should one say, from the illusion? – that we could describe the world, or least parts of the world, without any reference to ourselves.

We may remark at this point that modern physics is in some way extremely near to the doctrines of Heraclitus. If we replace the word ‘fire’ by the word ‘energy’ we can almost repeat his statements word for word from our modern point of view. Energy is in fact the substance from which all elementary particles, all atoms and therefore all things are made, and energy is that which moves. Energy is a substance, since its total amount does not change, and the elementary particles can actually be made from this substance as is seen in many experiments on the creation of elementary particles. Energy can be changed into motion, into heat, into light and into tension. Energy may be called the fundamental cause for all change in the world.

Of 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.

Can you, or anyone else, reach the central order of things or events, whose existence seems beyond doubt, as directly as you can reach the soul of another human being? I am using the term 'soul' quite deliberately so as not to be misunderstood. If you put your question like that, I would say yes. ... the word 'soul' refers to the central order, to the inner core of a being whose outer manifestations may be highly diverse and pass our understanding.

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.

"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."

Cautious deliberation based on purely rational arguments can save us from many errors and dangers. ...But ...there will always be a fundamental complementarity between deliberation and decision. ...The decision finally... pushing away all the arguments... The decision may be the result of deliberation, but it is... complementary... it excludes deliberation. Even the most important decisions... contain this inevitable element of irrationality. ...[I]t cannot be avoided that some real or apparent truth form the basis of life; and this fact should be acknowledged with regard to those groups... whose basis is different from our own.

The ontology of materialism rested upon the illusion that the kind of existence, the direct 'actuality' of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible... Atoms are not things.

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.

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?

In a darkened world no longer illuminated by the light of this center [God], technical advances are scarcely more than despairing attempts to make Hell a more agreeable place to live in. This must be particularly emphasized against those who think that by spreading the civilization of science and technology even to the uttermost ends of the earth, they can furnish all the essential preconditions for a golden age. One cannot escape the Devil so easily as that.

[S]ets of concepts... defined in physics. ...[F]our systems... have ...attained ...final form.
The first ...Newtonian mechanics ...for the description of all mechanical systems, ...motion of fluids and ...elastic ..; it comprises , , aerodynamics.
The second closed system of concepts... the theory of heat. Though... connected with mechanics through... statistical mechanics, it... [is] not... a part of mechanics. ...[T]he phenomenological theory of heat uses ...[some] concepts that have no [physics] counterpart ...like: , specific heat, entropy, free energy, etc. ...[F]rom ...phenomenological ...to a statistical interpretation ...considering heat as energy, distributed statistically among ...many degrees of freedom due to ...atomic structure... heat is no more connected with mechanics than with electrodynamics or other ...physics. The central concept ...is ...probability, closely connected with ...entropy ...Besides this ...the statistical theory of heat requires the concept of energy. But any coherent set ...in physics will ...contain ...concepts of energy, and and the law that these ...be conserved. This follows if the ...set is ...to describe ...features ...correct at all times and everywhere; ...[i.e.,] features that do not depend on space and time ...[i.e.,] are invariant under arbitrary translations in space and time, rotations in space and the Galileo— or Lorentz—transformation. Therefore, the theory of heat can be combined with any of the other closed systems of concepts.
The third... electricity and magnetism... reached... final form... through... Lorentz, Einstein and Minkowski. It comprises electrodynamics, special relativity, optics, magnetism, and one may include the de Broglie theory of s of all different sorts of elementary particles, but not the wave theory of Schrodinger.
[F]ourth... the quantum theory... Its central concept is the probability function, or... "statistical matrix"... It comprises quantum and wave mechanics, the theory of atomic spectra, chemistry, and the theory of other properties... like electric conductivity, , etc.
...The first set is contained in the third as the limiting case where the velocity of light can be considered as infinitely big, and is contained in the fourth as the limiting case where of action can be considered as infinitely small. The first and partly the third set belong to the fourth as a priori for the description of the experiments. The second set can be connected with any of the other three sets without difficulty and is especially important in its connection with the fourth. The independent existence of the third and fourth sets suggests the existence of a fifth set, of which one, three, and four are limiting cases. This fifth set will probably be found someday in connection with the theory of the elementary particles.

What we observe is not nature itself, but nature exposed to our method of questioning.