WHEN I give public astronomy talks, I’m often asked about unidentified flying objects (UFOs). Now, over the last 20 years, mobile phone cameras everywhere have shown us that funny cats and abusive police are not as rare as we once wanted to believe, but we have not seen a parallel explosion of credible UFO sightings. Either there’s a successful global conspiracy to suppress the truth, or there are no UFOs. Yet UFOs continue to fill the dark corners of the internet.

As it happens, many of the most ardent UFO fans are highly trained engineers. (They’re often the same people who have abandoned religion because “it’s irrational”.) Likewise, I have found such engineers are also great believers in the Face on Mars (an optical illusion in the shadows of a rocky outcrop on Mars), the Flat Earth, and many other popular conspiracy theories. Why are such highly educated people susceptible to such lunacy?