So, yes, I am optimistic. It does bother me that most people aren’t.

Maybe you have successful person’s bias?

Of course, we have to factor that in. In my own life I’ve been extremely lucky. But even subtracting out my personal experience, I think the big picture is that it’s better to be born today than ever, and it will be better to be born 20 years from now than today.

One of the technologies on your list is lab-grown meat, which is still very tentative and expensive. Why did it make the cut?

Part of the reason I picked it is to remind people that clean energy does not solve climate change. Only about a quarter of emissions come from electricity generation. This is a category that people weren’t paying much attention to as a greenhouse-gas problem. And yet I think the path to solve it is clearer than in, say, cement or steel or other materials.

Another of your picks is the reinvented toilet, which you call the biggest advance in sanitation in 200 years. Why?

Building sewers, using clean water, having a processing plant—that’s the paradigm in rich countries. In low-income countries, the capital cost of a sewer system is just unattainable. This toilet takes the human waste, liquid and solid, and in most cases does some type of separation. The solids you can essentially burn. The liquids you can filter. That’s a huge effect on quality of life, in terms of both disgust and disease, in an increasingly urbanized world. The Gates Foundation has given out $200 million in grants to try to get this technology going. It’s not there yet.

Three of your picks are about reducing greenhouse-gas emissions. You lead a $1 billion investment fund, Breakthrough Energy Ventures. But it feels like there are already a lot of technological solutions to climate change. Do we really need more? Isn’t the biggest problem political?

No, the problems are when you say to India, “Provide electricity to everyone to have things we take for granted—heating, air conditioning.” Their path is to build more coal plants. That’s the cheapest form of electricity for them. In France they were asked to pay a 5% increase on their diesel price, and even that was unacceptable.

The politics is where you decide how much you’re going to put into basic research or how you’re going to make things attractive for innovative companies. But if we freeze technology today, you will live in a 4 °C warmer world in the future, guaranteed.

One of those picks is nuclear fusion. That’s something that’s always seemed just around the corner. What makes you optimistic about it?

The company that Breakthrough put money into, Commonwealth Fusion Systems—the methods they’re using allow you to get a dramatic reduction in the size and therefore the capital cost. It’s very impressive. There are over 10 companies pursuing fusion in different ways. Most of them will not work. But these projects certainly will make a big contribution. So I think it’s important we back fusion.