Werner Heisenberg

The word 'reality' is also a difficult word, and we must be careful with it.

The atomic bomb is a paper tiger which the American reactionaries use to scare people. It looks terrible, but in fact it isn't.

In the history of human thinking the most fruitful developments frequently take place at those points where two different lines of thought meet.

The problems of quantum theory are not problems of physics but problems of philosophy.

The development of atomic physics in the last fifty years has taught us that we must be very cautious in the use of ordinary language when we speak about atomic phenomena.

The decision to use the atomic bomb against Japan was a terrible one, but it was made by men who were convinced that it would save more lives than it would take.

The path of science is paved with the corpses of discarded theories.

The history of physics is not only a story of discoveries, but also a story of the changing concepts of reality.

We have to remember that what we observe is not nature in itself, but nature exposed to our method of questioning.

The most important new result of nuclear physics was the recognition that the atomic nucleus is not an elementary particle but a composite system.

The world is not a collection of objects, but a web of relationships.

The development of quantum mechanics has forced us to give up the idea of a completely objective description of nature.

The uncertainty principle refers to the fact that we cannot know both the position and the momentum of a particle with absolute precision.

The idea of a 'real' world, independent of our observation, is a philosophical prejudice.

Science is made by men, not by machines.

The most important task for physics in the coming decades will be to understand the elementary particles.

The world of atoms is not a world of things, but a world of possibilities.

The concept of 'causality' is not applicable in the atomic realm in the same way as in the macroscopic world.

The progress of science depends on the courage to ask new questions and to challenge old assumptions.

The language of mathematics is the only language that can adequately describe the atomic world.