One should not be too distracted by definitions. Ideas transcend definitions.

If you're a scientist, and you have to have an answer, even in the absence of data, you're not going to be a good scientist.

To view space as, "Well, let's go to Mars now," or "Let's do this now," maybe we should rethink of space as our backyard and have a suite of launch vehicles that can enable any ambition a person has regarding space. It's the same way you can go to buy a car: I want to go offroading, I'll buy this model. I'm a city driver, that's this model. I want to use less fuel, well, that's this model. They're not selling you one car, you have options. So when I think of space, I think of having options.

I remain fearless of airplanes after 9/11. But during a trip to Los Angeles on a Boeing 767, I couldn't keep my mind from drifting: What's the largest piece of this airplane that could crash into the World Trade Center, explode out the other side, and survive intact? The landing gear? My computer battery? My belt buckle? My wedding ring?

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.

If an alien lands on your front lawn and extends an appendage as a gesture of greeting, before you get friendly, toss it an eightball. If the appendage explodes, then the alien was probably made of antimatter. If not, then you can proceed to take it to your leader.

The telescope... is a conduit to the cosmos.