Sargent could arguably be regarded as the godfather of the modern flat-Earth movement. "If you got into flat Earth, there's a really high chance you read into my stuff first," he tells CNN.

But he had help -- it was the advent of YouTube that gave him a platform to spread his own views, which he says the movement "wouldn't exist without."

"Flat Earth was a binge watch on YouTube," he adds, aided by algorithms and personalized recommendations that turned flat earth research into a never-ending rabbit hole.

Earlier this year, YouTube started burying those videos and reducing recommendations of "borderline content," but video makers like Sargent feel it no longer makes much difference. "Anything on social media is always going to be helpful if it goes viral, right?" adds Davidson. "Well flat Earth has gone viral."

CNN has contacted YouTube for comment.

But the alleged rapid growth of a movement so enthusiastically rejecting fundamental scientific beliefs does have some worried.

"It seems that increasingly, people don't trust scientists and experts, or their motives," Douglas says. "More research needs to be done in this area, and I'm sure there are some positive consequences to believing in conspiracy theories, but early indications suggests that they are more harm than help."

"I don't say this often, but look -- there is a downside," admits Sargent, reflecting on the movement he helped encourage. "There's a side effect to flat Earth ... once you get into it, you automatically revisit any of your old skepticism."

"I don't think they're just linked," Sargent says of flat Earthers and populists. "They kind of feed each other ... it's a slippery slope when you think that the government has been hiding these things. All of a sudden, you become one of those people that's like, 'can you trust anything on mainstream media?'"

For Davidson, the next stage is to debate leading members of the scientific community, but "they just laugh at us and say, 'you guys are dumb.'"

But he's not deterred.

"It's touching everyone ... it's not going away, and it's not going to slow down," Davidson says of the movement. "This thing is out of the can."

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