One, remember to look up at the stars and not down at your feet. Two, never give up work. Work gives you meaning and purpose and life is empty without it. Three, if you are lucky enough to find love, remember it is there and don't throw it away.

A theory is a good theory if it satisfies two requirements. It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.

The Universe in a Nutshell.

Today, we commit to this next great leap into the cosmos because we're human, and our nature is to fly.

The eventual goal of science is to provide a single theory that describes the whole universe.

I believe the universe is governed by the laws of science. The laws may have been decreed by God, but God does not intervene to break the laws.

I believe in the possible. I believe, small though we are, insignificant though we may be, we can reach a full understanding of the universe. You were right when you said you felt small, looking up at all that up there. We are very, very small, but we are profoundly capable of very, very big things.