I recently read an article on the BBC’s website about “flat-earthers”, i.e. people who believe that the Earth is flat. The article investigates why people with access to so much knowledge to the contrary can actively believe that the Earth is flat. Among other things, they believe that the moon landings were faked, as were any photos of the Earth ever taken from space. They also believe that the governments (yes, all of them) are engaged in a massive cover-up to prevent us from learning the Earth’s true shape. Why would our government (or much less anybody) want to do this? Your guess is as good as mine.

Of course, ‘flat Earth theory’ (and I’m being incredibly generous by calling it a theory) has some rather large theoretical gaps that extend far beyond visual horizon lines and photographic evidence of the Earth’s shape. For example, it cannot account for the concepts of sunrise, sunset and different time zones. Even if we were to assume that the Earth orbited the Sun (or vice versa) in such a way that the Sun wasn’t always positioned directly above the Earth, sunrise would occur everywhere at the same time. Furthermore, every part of the Earth would experience the same amount of daylight, regardless of time of year or geographic location. That means that if you’re living by the equator, you’re going to experience the same amount of daylight as people in the Arctic Circle. However, unless everybody else in the world is also in on the conspiracy, this would appear not to be the case. Sunset also wouldn’t look nearly as pretty without our curved atmosphere absorbing only certain wavelengths of light.

Of course, gravity would also be a huge theoretical hurdle to any flat earth theory. Anybody with a telescope, or even a pair of binoculars, can observe other spherical astronomical bodies in our solar system. We know that gravity would not be conducive to the formation of a planar (or ovoid) bundle of rocks and gasses. How a flat planet would be able to retain an atmosphere is equally mysterious. Gravitational physics also wouldn’t work the same way on a body that isn’t round, as certain parts of the planet would be much further away from the Earth’s center of gravity than others’, and so we would observe a rather large change in Earth’s gravitational field, depending on where on the planet we were. But even with all of these theoretical problems, flat-earthers differ from other conspiracy theorists in one other important way.

Most conspiracy theories are based on perceived anomalies in data – data that cannot be observed or collected firsthand. All that we have of the moon landings is a bunch of well-documented evidence (photos, videos, samples, etc.) and firsthand testimony, which to a normal person would be enough to conclusively show that we went to the moon, but does not allow people to personally observe the fact that astronauts walked on the surface of the moon. At most, they saw a video feed showing astronauts walking around on the moon. We know that videos can be faked, even if there’s good reason to believe (and corroborating evidence to prove) that this one was not. The reason that people can believe in this conspiracy theory is that they weren’t there, and so have no way of personally verifying whether or not the event occurred. However, this is not the case with the belief that the Earth is flat. We don’t have to rely on pictures from space or the word of our government in order to arrive at the conclusion that the Earth is not flat. Belief in a flat Earth requires you to shut down your own powers of observation.

To prove that the Earth is (roughly) the shape of a globe, all you have to do is go outside and look for a horizon; you’ll notice that you can’t see to the end of the Earth, but rather only a certain distance ahead of you – regardless of how clear of a day it is. Similarly, you could go outside and look at the moon during a lunar eclipse, and you’ll see something like this:

You might notice that the shadow that the Earth casts on the moon is a round one, and ask how a flat Earth could cast a rounded shadow. Even if you believed that the Earth was the shape of a flat disc, in order for the Earth to cast such a shadow it would have to be oriented such that (as discussed above) everybody on Earth was experiencing night at the exact same time. It would also mean that everybody on the world should be able to see at least a partial eclipse, every time an eclipse occurs. Not to mention that your view of the sky and stars would be exactly the same no matter where you are on the planet. It makes you wonder if people who believe in a flat Earth have ever looked to the skies¹.

In conclusion,

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• BBC.co.uk: Do they really think the earth is flat?