The flat Earth is the post-truth landscape. As a group, its residents view themselves as staunch empiricists, their eyes wide open. The plane truth, they say, can be grasped in experiments that anyone can do at home. For instance, approach a large body of water and hold up a ruler to the horizon: it’s flat all the way across. What pond, lake, or sea have you ever seen where the surface of its waters curves? Another argument holds that, if Earth were truly spherical, an airplane flying above it would need to constantly adjust its nose downward to avoid flying straight into space. If, say, you flew on a plane and put a spirit level—one of those levels that you buy at the hardware store, with a capsule of liquid and an air bubble in the middle—on your tray table, the level should reveal a slight downward inclination. But it doesn’t: the level is level, the flight is level, the nose of the plane is level, and therefore the surface of Earth must be level. Marble performed this experiment himself, recorded it, posted it on YouTube, and a co-worker started a Reddit thread that linked to it. Soon Marble had twenty-two thousand followers and a nickname, the Spirit-Level Guy.

“We’re not trying to express any degree of intellectual superiority,” he said at the conference. “I’m just trying to wake people up to the idea that they’ve been lied to. It’s what you would do with any friend.”

https://www.newyorker.com/science/elements/looking-for-life-on-a-flat-earth