For the last 15 years, I've worked as a scholar of science denial, studying the mistakes and biases used by ideologues—and sometimes the truly confused—to engage in the kind of faux-skepticism that allows them to preserve their own beliefs, no matter the scientific evidence.

But it's one thing to study this, it's another to see it in action, so in November, 2018, I found my way to the Flat Earth International Conference (FEIC 2018) in Denver, Colorado.1 It wasn't quite what I expected. The mood was celebratory. Even jubilant. Of course, no one self-identified as a “science denier.” They thought that they were more scientific than the scientists, that the 600 people in that room had somehow discovered a truth that the rest of the scientific world had somehow missed—or been complicit in covering up. The Earth is flat.

What really surprised me, though, is that they claimed their views were based on evidence. Using just the first-person evidence that came to them through their senses they could tell that water was always level, that we are not moving, and that the stars aren't really very far away. With the assistance of some tools, they also claimed to be able to perform some experiments. One “experimentalist” reported that he'd flown to the conference with a carpenter's level on the tray table in front of him and—since the bubble only moved during takeoff and landing—he had direct evidence that the Earth was flat.

Oh boy… some of the claims were so easy to refute, I could bat them down myself. (Or could if the Flat Earthers believed in gravity, which they do not.) But you'd be wrong to think that all their claims were simple. Some of the thought experiments and experimental puzzles were actually quite hard, not because they were right, but because they were so intricately wrong. As a philosopher of science, rather than a physicist, I was also handicapped by my dim recollection of such topics as the Coriolis effect.

The rumor at the convention was that there was a conference of physicists up the street, who never showed up to refute them. This led them to crow about scientific cowardice which was, in their minds, the ultimate sign that they were right.

It is of course easy to laugh at such ignorance and hubris and you may think that this is all really quite harmless. But I think that the Flat Earthers are actually dangerous. For one thing, the public flaunting of such a basic form of science denial is evidence that the problem of public ignorance and disrespect for science is growing. The Flat Earthers may not be hurting anybody directly but the confusion and doubt they spread helps to create a culture of denial that could cost lives indirectly by affecting congressional decisions about climate change and family decisions about vaccination.

I propose that scientists need to take a more active role in pushing back against science deniers. Of course some have already tried this, but just think about how these encounters usually go. Someone says that climate change isn't “settled science” or that evolution is “just a theory,” and so we offer them some evidence. Those who are more studious or better trained force us to admit that our scientific claims are not “proven,” for scientific claims are always at the risk of new data. Through that small opening of uncertainty, they drive trucks of antiscientific nonsense. We know, and we need them to know, that there is nothing wrong with uncertainty; it is the backbone of how scientists learn from new evidence. Scientists work not with certainty but with probability.

When I was at the Flat Earth convention, I had one memorable conversation, over dinner, with one of their guest speakers. He kept wanting to present me with his evidence (even as he rejected all of mine), until I finally decided to channel my inner philosopher. “OK,” I said. “If your view is based on evidence, then answer me this: what evidence would it take to prove to you that your view was wrong?”

For a moment he went silent. Finally, he suggested he'd have to go out in space and see the global Earth for himself. But a minute later he ruled that out. “The windows in the space ship might be curved,” he said.

“Ok,” I offered. “How about we take a trip together over Antarctica. You guys think it's not a continent, right? That the ‘mountains of Antarctica' are spread out as an ice wall at the perimeter of the disk of the flat Earth. That means, according to you, it's tens of thousands of miles long. But I think it's only a few thousand miles long. So let's fly over it and see how long it takes.”

“There aren't any flights over Antarctica.”

“Oh no?” I said. I was ready with a sheet of paper in my back pocket, which offered a commercial flight from Santiago, Chile, to Auckland, New Zealand.

“Have you been on that flight?” he said.

“No, and neither have you. So let's go.”

He shook my hand, but then something occurred to me.

“Wait,” I said. “We have to have some sort of criterion to measure who is right. I don't want to spend all this time and effort, and then have you say it was somehow flawed. So how about this: If Antarctica is tens of thousands of miles long we'd have to stop to refuel. But if I'm right, and it's only a few thousand miles wide, we won't. So can we make that the criterion?”

“Sure.” He shook my hand again, but then something occurred to him.

“Wait,” he said. “What if the whole thing is a hoax?”

I knew what was coming, since I knew the patterns of conspiracy theorists.

“Maybe airplanes don't have to refuel,” he said. “Maybe they can get anywhere on Earth on one tank of gas. This could all be a set up.”

This was the pinnacle of a two-hour argument, so the stakes were high. He looked uncomfortable, but I didn't want to let him off the hook.

“Are you saying that the entire history of aviation, since before you and I were born, has been a sham… where planes have been landing to pretend to refuel even when they didn't need to… all to condition us to believe that planes actually need to refuel when they don't? And that all of this was done against the day when you and I would be sitting here now making this agreement, so that I could fool you into giving up your belief in Flat Earth?”

“Yes,” he said.

Before this he had proven himself to be an articulate, intelligent, debating partner, but this was one of the worst forms of reasoning I'd ever witnessed. At that point, our discussion was basically over. I paid the check, and we parted as friends.

In this encounter, it is obvious that I revealed a flaw in the Flat Earther's reasoning. Long ago, philosopher Karl Popper has suggested that if nothing can ever disprove a theory, then it isn't really a scientific theory. It's not just that their “evidence” was bad, but that they weren't reasoning about evidence in a scientific way.

Back in the ballrooms, speakers were still up on stage, blathering on about why there were no flights over Antarctica, why the Sun and Moon shouldn't appear in the sky at the same time if the “globalists” were right, and their other favorite hoaxes,2,3 that were all perfectly explicable with a little knowledge of physics. But how many folks at the Flat Earth convention had taken any physics? How many of the people that they were trying to recruit on the street (or over YouTube videos) knew the first thing about gravity, or optics, or whatever.

These topics are child's play for physicists. So why not play a little? Why not show up to the Flat Earth convention, take their arguments seriously, and disprove them? Of course, you will never convince a hard-core science denier (witness my conversation above), but what about their audience? If every lie has an audience—but they never hear from the “other side” who is too busy to bother with such charlatans—then, the circle of denial grows.

I understand not wanting to dignify outrageous claims with a response. Or to give ignorance a platform in “debate.” Maybe it's not worth the time to talk to someone who is irrational, especially when the best evidence (such as photos of the Earth from space) will be dismissed as fake and part of a conspiracy.

But that attitude of disengagement is a losing one in the war for science. When roused, perhaps scientists will show up for another “March for Science,” but by then it may already be too late. After science marchers went back to their labs denial became mainstream. Indeed, climate change denial has now made its way to Congress, and even the White House.

If it hasn't already, it's also coming to a community near you.

The anti-vaxx crisis erupted into American consciousness in the last few months as over a thousand measles cases broke out in 28 states. Why the sudden jump? Parents who have questions about the safety of vaccines are often scolded by their physicians and told they're being irrational. This turns them away, and sometimes they look for alternative places to get their questions answered, like the Internet or an anti-vaccine conference. Here they are presented with the worst forms of misinformation and disinformation, which can radicalize them so far that it is almost impossible to bring them back.

But some are trying. In response to the measles crisis in Clark County, Washington, the state sent out a team of public health officials to engage with anti-vaxxers. They held workshops. They brought white boards. They talked to some people one on one and answered all of their questions. It started to work.4 You present the evidence in a calm and respectful way, to show that someone other than the science deniers are listening to their concerns. But first you have to show up!

This November I'm going back to FEIC 2019 (this time in Dallas, Texas) to continue my efforts. My hypothesis is that if we can learn how to fight back against this most elemental form of science denial, we can learn how to confront all the others as well. Back in 2007, Mark and Chris Hoofnagle5 suggested that there were five basic traits behind all science denial: belief in conspiracy theories, cherry picking evidence, embracing impossible standards for what science had to show, relying on fake experts, and making logical errors. The reasoning strategy used by science deniers has started to come into focus, and I'm now thinking more about how to respond to it. But I could use the help of a panel of physicists to handle the evidential questions. Mythbusters anyone? Hey, we have to start somewhere.

How hard could it be for a physicist to give simple, straightforward answers to refute the “evidence” for Flat Earth, answers that are comprehensible to a general audience? Or even better, come with me to FEIC 2019 and do it in person.

Who's with me?