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.

Knowing how to keep someone motivated and how to keep a connection are skills humans have learned and evolved over hundreds of thousands of years. A robot can't figure out whether you can do one more push-up, or how to motivate you to actually do it.

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.

There are lots of examples of routine, middle-skilled jobs that involve relatively structured tasks, and those are the jobs that are being eliminated the fastest. Those kinds of jobs are easier for our friends in the artificial intelligence community to design robots to handle them. They could be software robots; they could be physical robots.

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.

Technology is always creating jobs. It's always destroying jobs.

Computers get better faster than anything else ever. A child's PlayStation today is more powerful than a military supercomputer from 1996.