Mad scientist Maxwell Scheinst gives a science writer a paradox: If time travel is possible, then where are all the time travelers? Scheinst also provides an answer: They haven’t arrived yet because nobody has built a receiver . . . until now!

Mathematician Fred Galvin from Kansas University pointed us to this gem, which also got us wondering who was the first to pose the paradox. Both Clarke and Hawking have mentioned the problem, but where did it originate? We’re working on tracking that down. Let us know if you have any leads!