We account for all the matter and energy that we're familiar with, measure up how much gravity it should have, it's one-sixth of the gravity that's actually operating on the universe. We call that dark matter. It really should be called dark gravity. We don't know what that is.

The theory of evolution, like the theory of gravity, is a scientific fact.

Curiosity is a self-driven motivation to explore and to learn. Learning is like... you know, you have to take your medicine. And that is what it has become. And that's unfortunate.

In five billion years, the sun will expand and engulf our orbit as the charred ember that was once Earth vaporizes. Have a nice day

I have thoughts every day that are themselves tweets.

Let us not fool ourselves into thinking we went to the Moon because we are pioneers, or discoverers, or adventurers. We went to the Moon because it was the militaristically expedient thing to do.

I think we are all the sum of that which has happened in our lives. And if you're successful, it would be wrong to think that you'd be more successful had something been easier. That's not a given.