Most ancient cultures believed that the Earth was flat. The idea that it might be spherical was first posited by the Greek philosopher Pythagoras in the sixth century BC. In the third century BC, it was widely adopted in ancient Greece. Gradually, over the early modern period, astronomy supported the idea of a spherical Earth. While this was adopted as fact at different times in different world cultures, most scientific historians are agreed that the debate was laid to rest entirely around five centuries ago.

It is odd, then, that it has resurfaced this year. Bobby Ray Simmons Jr, better known as B.o.B, is an American rapper and music producer. In January, he posted a series of tweets proclaiming his belief that the world is flat. “a lot of people are turned off by the phrase ‘flat earth’ … but there’s no way u can see all the evidence and not know… grow up,” read one.

“No matter how high in elevation you are… the horizon is always eye level … sorry cadets… I didn’t wanna believe it either,” said another. He argued that if the Earth was curved, distant cities would be hidden from view, and we would be able to see the curvature in the horizon.

American astrophysicist and cosmologist Neil deGrasse Tyson soon joined the fray, poking holes in BoB’s argument. “Being five centuries regressed in your reasoning doesn’t mean we all can’t still like your music,” he tweeted. Appearing on late-night TV to discuss the issue, Tyson distilled the argument: “Listen, B.o.B – once and for all. The earth looks flat because 1) You’re not far enough away at your size 2) Your size isn’t large enough relative to Earth to notice any curvature at all.”

The rapper is not the only Flat Earther out there; according to recent media reports, the movement, which began in the 19th century, is on the rise. A recent online petition demanded: “We ask Google to recognise this movement, which has trended over 600% in just the past 12 months, by marking 01/01/2016 as the anniversary of the Flat Earth Movement and changing the Google Doodle image appropriately.”

Beyond the clearly apparent silliness lies a deep distrust of government and of science. Many arguing against Flat Earth theory simply point to NASA’s satellite images of Earth, which clearly show it as a sphere. Yet for adherents to this theory, that is not proof. NASA is part of the establishment, a co-conspirator to the lies fed to us for millennia, and is therefore not to be trusted.

It is easy to prove that the earth is round: just point to time zones, the differences in seasons across the world, the effectiveness of GPS. What is more difficult is understanding why some people reject these basic facts about the world they live in.

A version of this article appears in the Witness section of the Spring 2016 issue of the New Humanist. Subscribe today.