Where did the concept of "without borders" come from? No one had that concept until you saw Earth from space, illustrated not by a mapmaker who's color-coding political boundaries; it's illustrated by nature itself and there's land, there's ocean, there's atmosphere.

When I needed to overcome the low expectations of others or the bias that would be expressed in one circumstance or another, I'd keep on keeping on. And I climb over the obstacle, go around it, dig under it, fly over it. That's what kept me going. Otherwise I would have never been an astrophysicist.

My only hope is that every other alien civilization isn't doing exactly what we are doing because then everybody would be listening, nobody would be receiving, and we would collectively conclude that there is no other intelligent life in the universe.

I'm often asked whether I believe in Global Warming. I now just reply with the question: "Do you believe in Gravity?"

You could do math early, but there are no brilliant 16-year-old novelists. They don't know the human condition yet.

When I was a kid, I thought that if everyone looked up the way I did then everyone would want to study the universe just like me - how could they not? This naiveté is what tells me that my interest was more a calling than a rational comparative assessment about what to be when I grew up.

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.