The problem with debating a flat-Earther is that they didn’t arrive at their conclusions from the weight evidence, so using the evidence isn’t going to work to change their minds.

That said, the evidence for the curved Earth is abundant. Besides the enormous body of photographic documentation, it’s even possible to do the experiment yourself. For example, I recently flew from New York City to Doha, from there to Singapore, then to Brisbane, then to Dallas, then back home. I followed an eastward course for my entire journey, and ended up back where I started. That’s only possible on a globe.

On that journey I got to enjoy plenty of views of the night sky, and one of the most striking features was that the sky was different. On a flat Earth, everyone would get the same view of the sky, but there were stars that I could only see at home and couldn’t on my trip, and vice versa.

And lastly, during a lunar eclipse the shadow of the Earth passes over the Moon. That shadow is always a circle, and only spheres are capable of casting circular shadows 100% of the time, regardless of angle.

But like I said, it’s not about the evidence. People who believe that the Earth is flat think that we are being lied to by scientists and political leaders. Many people don’t trust their society, and especially leaders of that society. And most especially elite leaders of that society. Scientists are indeed elite leaders of the government, academia, and other powerful institutions. By claiming that the Earth is flat, people are really expressing a deep distrust of scientists and science itself.

Distrust in science is a deep, thorny issue. But one way to rebuild trust is to simply listen. I know it sounds counter-intuitive, but studies have shown that people tend to trust other people, not necessarily the facts. So if you encounter a flat-Earth, as I have many times, don’t bother getting in a debate. Instead, change the subject so that you focus on something you find wonderful or extraordinary about the universe or about science. Maybe it’s an exciting new observation, or a clever experimental result, or an example of a real-world impact from scientific learning.

By building bridges based on shared wonder, awe, and curiosity, we can defuse the tension, moving around the flashpoint caused by a triggering proclamation and instead focusing on common ground. That’s the only place where trust can take root. And once trust is established, the question of the geometry of the Earth simply fades into the background.