The U.S. was once the undisputed front-runner, but since the Great Recession, our pace (read: investment) has slumped, Simon says. That’s not unique to the U.S.; investment has slowed worldwide. But “computing transforms itself on an exponential timescale. If you sleep for three years, you’re two generations behind,” he says. “We slept for five years.” Now China might be on track to beat us to exascale by the early 2020s.