For the last several years, the U.S. military has observed an increase in what it calls "unexplained aerial phenomena." The rest of us may know them by their more common name — unidentified flying objects — and we should all strive, as the navy is doing, to take these reports more seriously.
Sometimes, according to The Washington Post, well-trained military pilots "claimed to observe small spherical objects flying in formation. Others say they've seen white, Tic Tac-shaped vehicles. Aside from drones, all engines rely on burning fuel to generate power, but these vehicles all had no air intake, no wind and no exhaust." They also appear to exceed all known aircraft in speed and have been described by a former deputy assistant secretary of defense as embodying a "truly radical technology."
Meanwhile, Avi Loeb, chair of the Harvard astronomy department, recently suggested that a passing object in space, named Oumuamua, might be a light sail from an advanced alien civilization, as evidenced by its apparently strange movements.