The nuclear approach I'm involved in is called a traveling-wave reactor, which uses waste uranium for fuel. There's a lot of things that have to go right for that dream to come true - many decades of building demo plants, proving the economics are right. But if it does, you could have cheaper energy with no CO2 emissions.

In fact, that's where my vision of the coming digital opportunity is somewhat different from other people's. I divide it into three parts. One is the office. That's the one I'm most excited about and is the most concrete.

Vaccines are extremely well tested; their safety is well understood. The false allegations about vaccines causing autism have been disproven. But there are still echoes out there confusing people.

Every three years, we have to go to the governments and say, okay, you know you're saving millions of lives and even though your budgets are tight, helping Africa avoid this disaster really is a priority.

Learning from mistakes and constantly improving products is a key in all successful companies.

Flying cars are not a very efficient way to move things from one point to another.

Melinda [Gates] has been my partner in raising the kids and I went from before I met her, intentionally having an unbalanced life, to having a more balanced life with all sorts of fun things that she and I do together.