Thinking is to man what flying is to birds. Don’t follow the example of a chicken when you could be a lark.

I once thought that if I could ask God one question, I would ask how the universe began, because once I knew that, all the rest is simply equations. But as I got older I became less concerned with how the universe began. Rather, I would want to know why he started the universe. For once I knew that answer, then I would know the purpose of my own life.

The time comes in life when we have read enough. It's time to stop reading. It's time to lay down the books and write.

If only I had known, I should have become a watchmaker.

If people are good because they fear punishment, and hope for reward, then we are a sorry lot indeed.

The individual feels the futility of human desires and aims and the sublimity and marvelous order which reveal themselves both in nature and in the world of thought.

For every one billion particles of antimatter there were one billion and one particles of matter. And when the mutual annihilation was complete, one billionth remained - and that's our present universe.