The economy in the next 20 to 25 years is going to change more than they did in the last 20, 25 years. And that's because exponential trends are affecting a bigger and bigger share of the economy. So we have some huge disruptions in store, and I can't predict exactly what the innovations are going to be. If I did, I would have already invented them. But I think they'll be comparable to the innovations we saw in the past 20, 25 years if not greater.

Electricity is an example of a general purpose technology, like the steam engine before it. General purpose technologies drive most economic growth, because they unleash cascades of complementary innovations, like lightbulbs and, yes, factory redesign.

G.D.P. is not a measure of how much value is produced for consumers. Everybody should recognize that G.D.P. is not a welfare metric.

Technology is not destiny. We shape our destiny.

Now comes the second machine age. Computers and other digital advances are doing for mental power - the ability to use our brains to understand and shape our environments-what the steam engine and its descendants did for muscle power.

Going a little further into the future, we'll start literally connecting to machines. Some of my colleagues at MIT here - some of them are working on a neural mesh that connects directly to your brain, and they've already done it with some disabled people and allowed them to move objects just by thinking.

In the global millennium goals, we're on track to beat and eliminate severe poverty. So there are lots of positive trends. I think the world in 25 years could be a much better version of the world we have today. But the role of humans would still be fundamentally at the center of that.