120 Quotes by Werner Heisenberg

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.

The ‘path’ comes into existence only when we observe it.

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 is impossible, however.

Whenever we proceed from the known to the unkown we may hope to understand, but we may have to learn at the same time a new meaning of the word ‘understanding’

It is probably true quite generally that in the history of human thinking the most fruitful developments frequently take place at those points where two different lines of thought meet.

Both matter and radiation possess a remarkable duality of character, as they sometimes exhibit the properties of waves, at other times those of particles. Now it is obvious that a thing cannot be a form of wave motion and composed of particles at the same time – the two concepts are too different.

I believe that the existence of the classical “path” can be pregnantly formulated as follows: The “path” comes into existence only when we observe it.

Nature allows only experimental situations to occur which can be described within the framework of the formalism of quantum mechanics.

The solution of the difficulty is that the two mental pictures which experiment lead us to form – the one of the particles, the other of the waves – are both incomplete and have only the validity of analogies which are accurate only in limiting cases.