Is digital technology destroying middle-class jobs? Does it exacerbate income inequality? Does it boost economic growth and productivity — without creating the jobs that ought to come with economic growth?

Last month I gave space to a book titled “Who Owns the Future?” by the computer scientist Jaron Lanier. His answer was an unequivocal yes. He tellingly compared the great photography company of the analog age, Kodak, with the hot photography company of the moment, Instagram. At its peak, Kodak employed 140,000 people; Instagram had only 13 employees when it was bought by Facebook (for $1 billion!) in 2012.

Lanier isn’t the only one to have noticed the Kodak-Instagram example. So have Erik Brynjolfsson and Andrew McAfee, two economists from the Massachusetts Institute of Technology, whose newly published book is titled “The Second Machine Age.” As they put it, “Rapid and accelerating digitization is likely to bring economic rather than environmental disruption, stemming from the fact that as computers get more powerful, companies have less need for some kinds of workers.”

In some ways, “The Second Machine Age” is an odd book. For the most part, its tone is one of sunny optimism about all the wonderful things technology will soon bring us, from driverless cars to more powerful forms of artificial intelligence. “Innovation,” they write, is the “most important force that makes our society wealthier.” The authors believe that we are at a moment when technological innovation is about to accelerate, and make the world much wealthier, just as the Industrial Revolution did 250 years ago.