"History teaches that one kind of relatively easy call about the future involves realizing that something looks theoretically possible according to the laws of physics, and predicting that eventually someone will go do it. Heavier-than-air flight, weapons that release nuclear energy, rocket that go to the Moon with a person on board: these events were called in advance, and for the right reasons, despite pushback from skeptics who sagely observed that these things hadn’t yet happened and therefore probably never would."