Above all, I regret that scientific experiments—some of them mine—should have produced such a terrible weapon as the hydrogen bomb. Regret, with all my soul, but not guilt.

I looked for it [heavy hydrogen, deuterium] because I thought it should exist. I didn't know it would have industrial applications or be the basic for the most powerful weapon ever known [the nuclear bomb] ... I thought maybe my discovery might have the practical value of, say, neon in neon signs.
[He was awarded the 1931 Nobel Prize in Chemistry for discovering deuterium.]

Life is not a miracle. It is a natural phenomenon, and can be expected to appear whenever there is a planet whose conditions duplicate those of the earth.
[Stating his belief that planets supporting life cannot be rare.]

[My study of the universe] leaves little doubt that life has occurred on other planets. I doubt if the human race is the most intelligent form of life.

[Pure research] is worth every penny it costs.