If A is a success in life, then A equals x plus y plus z. Work is x; y is play; and z is keeping your mouth shut

Nobody knows how the stand of our knowledge about the atom would be without him. Personally, [Niels] Bohr is one of the amiable colleagues I have met. He utters his opinions like one perpetually groping and never like one who believes himself to be in possession of the truth.

Every serious scientific worker is painfully conscious of this involuntary relegation to an ever-narrowing sphere of knowledge, which threatens to deprive the investigator of his broad horizon and degrades him to the level of a mechanic.

I am not a Jew in the sense that I would demand the preservation of the Jewish or any other nationality as an end in itself. Rather, I see Jewish nationality as a fact and I believe that every Jew must draw the consequences from this fact.

It is an outcome of faith that nature-as she is perceptible to our five senses-takes the character of such a well formulated puzzle.

The important thing is not to stop questioning. Curiosity has its own reason for existing. One cannot help but be in awe when he contemplates the mysteries of eternity, of life, of the marvelous structure of reality. It is enough if one tries merely to comprehend a little of this mystery every day. Never lose a holy curiosity.

... on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality the very opposite happens. It is the theory which decides what we can observe.