I don't think that kids know enough about the people who are doing the medical breakthroughs. Hepatitis C went from being a terrible liver disease that is likely to kill you—now we have not one but multiple cures for that. The heroics and amazing work in the biology space, including medicines for poor countries and rich countries, I don't think those get the visibility they should. But there are plenty of scientists and others that have taken on those causes.

For the young people right now, they probably know the historic figures better than they know the present-day innovators.

In the letter, you mention that The Martian was your favorite movie last year. What in particular did you like about it?

I thought it was pretty educational, and the science- related aspects were fun. Unlike a lot of science things, they struck me as actually realistic. Usually, movies dumb down the book so much that you are almost disappointed when you see the movie. It didn't have the full content of the book, but I thought they did a good job.

How do you stay optimistic?

Our deep scientific understanding of how to design alloys, how to pick catalysts on a rational basis—our ability to do science is accelerating. Science has taken us from a situation where more than a third of all kids died to a situation where 5 percent of kids die. In the next 15 years, if we do our job right, we will get that down to 2.5 percent.

If you zoom out a little bit, and you look at the acceleration of science over the past 100 years, and the basic understanding we have gained and the tools we have, and the percentage of people in the world getting literate and getting engineering degrees, those numbers are on the constant rise.

I think it is irrational not to be optimistic, but I admit I am disposed to be optimistic. So maybe I would misconstrue the facts if they were against me. But I think, honestly, you have to be optimistic. Look at what we are doing with food production. Look at what we are doing with health. Would you rather have cancer 10 years ago or 10 years from now?

My favorite book is The Better Angels of Our Nature by Steven Pinker. As he says, there is only one thing that has gone down faster than violence, and that is our tolerance for violence. Ironically, at the period where violence is lower than ever, our disgust to how much violence there is at an all-time high.

When the U.S. was poor, we polluted our rivers so badly. We made such a mess of this country. And then we got rich and said, "Oh God, we have to clean up the Potomac. We even have to clean up the stupid Hudson." I mean, my God, we're getting so picky.