Carl took on the military-industrial complex. He campaigned around the world for an end to the production of weapons of mass destruction. To him it was a perversion of science.

And what greater might do we possess as human beings than our capacity to question and to learn?

The way he treated me & the way I treated him, the way we took care of each other & our family, while he lived. That is so much more important than the idea I will see him someday.

I remember that one time Carl Sagan was giving a talk, and he spelled out, in a kind of withering succession, these great theories of demotion that science has dealt us, all of the ways in which science is telling us we are not who we would like to believe we are. At the end of it, a young man came up to him and he said: "What do you give us in return? Now that you've taken everything from us? What meaning is left, if everything that I've been taught since I was a child turns out to be untrue?" Carl looked at him and said, Do something meaningful.

For most of the history of our species we were helpless to understand how nature works. We took every storm, drought, illness and comet personally. We created myths and spirits in an attempt to explain the patterns of nature.

It takes a fearless, unflinching love and deep humility to accept the universe as it is. The most effective way he knew to accomplish that, the most powerful tool at his disposal, was the scientific method, which over time winnows out deception. It can't give you absolute truth because science is a permanent revolution, always subject to revision, but it can give you successive approximations of reality.

The greatest thing that science teaches you is the law of unintended consequences.