The world the authors describe may be unsettling, but it is a world that we would all recognize and will likely live to see. A very different—indeed startling—vision of the future comes from George Mason University professor and economist Robin Hanson in “The Age of Em.” He believes that an age of brain emulations— “ems”—will soon make mere augmentation obsolete.

To make an em, he writes, “scan a human brain at a fine enough spatial and chemical resolution . . . combine that scan with good enough models of how individual brain cells achieve their signal processing functions, to create a cell-by-cell . . . model of the full brain in artificial hardware, a model whose . . . behavior is usefully close to that of the original brain.”

These emulations, Mr. Hanson writes, will at first be unleashed to perform tasks too tedious, odious or dangerous for us to do. But like any of us (since they are us), the emulations will go on to do some things that interest them and we just can’t squeeze into our lives, such as taking flying lessons, lounging on a beach in Bermuda or having sex with super-attractive partners. I wouldn’t mind having a cloned brain balance my checkbook for me every month. But I imagine that in this Hansonian future balancing checkbooks will seem as foreign as shoeing a horse does to us now—a quaint, vague memory of something other people used to do.