An expert is someone who knows some of the worst mistakes that can be made in his subject and how to avoid them.

The one who insists on never uttering an error must remain silent.

It will never be possible by pure reason to arrive at some absolute truth.

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.

Modern physics has changed nothing in the great classical disciplines of, for instance, mechanics, optics, and heat. Only the conception of hitherto unexplored regions, formed prematurely from a knowledge of only certain parts of the world, has undergone a decisive transformation. This conception, however, is always decisive for the future course of research.

I 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.

Many people will tell you that an expert is someone who knows a great deal about the subject. To this I would object that one can never know much about any subject. I would much prefer the following definition: an expert is someone who knows some of the worst mistakes that can be made in the subject, and how to avoid them.