Werner Heisenberg

We are both spectators and actors in the great drama of existence.

The most striking feature of the new quantum theory is that it does not deal with the behavior of objects, but with our knowledge of them.

The observer plays a decisive role in the description of atomic events.

The atom is not a billiard ball.

In the strict 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 premises.

The world is complicated, and so is physics.

Peace cannot be kept by force; it can only be achieved by understanding.

The human race has today the means for annihilating itself—either in a fit of complete lunacy, i.e., in a big war, or by disrupting its very being by the consequences of its own madness.

Every scientific concept is limited and approximate.

The search for the fundamental laws of nature is a search for the harmony of the universe.

I have tried to be a philosopher; but cheerfulness keeps breaking through.

The future belongs to those who prepare for it today.

Knowledge is a process of discovery.

The essence of knowledge is to understand the structure of reality.

In quantum mechanics, the observer is part of the system.

The probability wave is not a physical entity but a mathematical tool.

We must learn to live with uncertainty.

The beauty of physics lies in its simplicity.

Life is a journey through uncertainty.

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.