With no gravitational force to work against, your body not only doesn't need the same amount of muscle and bone, it starts breaking them down. As on Earth, so in space: use it or lose it. And exercise may not solve the problem.

All tweets are tasty. Any tweet anybody writes is tasty. So, I try to have each tweet not simply be informative, but have some outlook, some perspective that you might not otherwise had.

Astronauts are the only kind of celebrity I know who can have a line of people waiting for their autograph, even if the line of people does not know in advance the astronaut's name.

We have people who believe they are scientifically literate but, in fact, are not.

For centuries, magicians have intuitively taken advantage of the inner workings of our brains.

The tenacity of life is mind-boggling. We keep finding it where no one thought it could be.

I'd go back and hang out with Isaac Newton. I'm torn between do I hang out with him or do I bring him into the present to hang out with me. See, that might be terrifying because his head will just explode once he sees everything that was derived from his discoveries, but I'd spend more time with someone who I think is one of the most brilliant minds our species has ever known.