The opening chord to “A Hard Day’s Night” has reached an almost mythical status. For years, no one knew what it actually was. People would come close, through trial and error, watching Ed Sullivan performances, and studying advanced music theory, but no attempts ever quite captured the exact chord.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.