If you can't explain what you are doing to a nine-year-old, then either you still don't understand it very well, or it's not all that worthwile in the first place.

You teach me baseball and I'll teach you relativity...No we must not. You will learn about relativity faster than I learn baseball.

To my mind, to kill in war is not a whit better than to commit ordinary murder.

How was I able to live alone before, my little everything? Without you I lack self-confidence, passion for work, and enjoyment of life--in short, without you, my life is no life. [Written to his wife, Mileva]

People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.

I want to know God's thoughts.

What is the meaning of human life, or of organic life altogether? To answer this question at all implies a religion.