In whatever you choose to do, do it because it's hard, not because it's easy. Math and physics and astrophysics are hard. For every hard thing you accomplish, fewer other people are out there doing the same thing as you. That's what doing something hard means. And in the limit of this, everyone beats a path to your door because you're the only one around who understands the impossible concept or who solves the unsolvable problem.

Never presume that just because you disagree with an idea that you must be correct.

In modern times, if the sole measure of what’s out there flows from your five senses then a precarious life awaits you.

I am convinced that the act of thinking logically cannot possibly be natural to the human mind. If it were, then mathematics would be everybody's easiest course at school and our species would not have taken several millennia to figure out the scientific method.

We went to the moon using just Newton's laws of motion and gravity. Newtonian dynamics we call it. So then we find out, "Well, this works because there's certain regimes we've never tested it in." Had we done so, we would show that it didn't work: For example, at very high speeds, very high gravity, Newton's laws fail. They just fail. You need Einstein's laws of motion and gravity. Those would be his special theory of relativity and general theory of relativity. Now you invoke those and it works.

Ignorance is a virus. Once it starts spreading it can only be cured by reason. For the sake of humanity, we must be that cure.

If you find life on Europa [Jupiter's moon], like, what would you call it? Would it be, like, Europeans?