When we see the shadow on our images, are we seeing the time 11 minutes ago on Mars? Or are we seeing the time on Mars as observed from Earth now? It's like time travel problems in science fiction. When is now; when was then?

There is no debate in the scientific community...We need [Congress] to change things, not to deny what's happening.

History is but the record of the public and official acts of human beings. It is our object, therefore, to humanize our history and deal with people past and present; people who ate and possibly drank; people who were born, flourished and died; not grave tragedians, posing perpetually for their photographs.

You stop planetary exploration, those people who do that extraordinary work are going to have to go do something else.

For me, the meaning of life is pretty clear: Living things strive to pass their genes into the future.

We should educate more women and girls. Because that is the surest route to controllably, manageably reducing the human population. Educated women have fewer kids. And the kids they do have are better cared for and are more successful. As I like to say, it's not one thing that we need to focus on. It's everything all at once.

I often reflect on what an extraordinary time (pun intended) it is to be alive here in the beginning of the twenty-first century. It took life billions of years to get to this point. It took humans thousands of years to piece together a meaningful understanding of our cosmos, our planet and ourselves. Think how fortunate we are to know this much. But think also of all that's yet to be discovered. Here's hoping the deep answers to the deep questions-from the nature of consciousness to the origin of life-will be found in not too much more time.