One of the absolute rules I learned in the war was, don't know anything you don't need to know, because if you ever get caught they will get it out of you.

[Heisenberg's seminal 1925 paper initiating quantum mechanics marked] one of the great jumps—perhaps the greatest—in the development of twentieth century physics.

I spent every night until four in the morning on my dissertation, until I came to the point when I could not write another word, not even the next letter. I went to bed. Eight o'clock the next morning I was up writing again.

To make a discovery is not necessarily the same as to understand a discovery. Not only Planck but also other physicists were intially at a loss as to what the proper context of the new postulate really was.

To make a discovery is not necessarily the same as to understand a discovery.

Deliberately or not, every author is of course present in every book he or she writes - even in a scientific text.

One of the things I learned, one of the strangest things, is how to think. There was nothing else to do. I couldn't see people, or go for a walk in the forest. All I had was my head and my books, and I thought a lot.