Why do people believe the Earth is flat? How do we know it’s curved? Is a debate even worth it? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
Yes. The Earth is round. And, yes, some people believe that it's flat. Why do they believe it's flat? Well, if you ask them, they'll start talking about conspiracies and elites and scientists and so on.
They they might or might not have very sophisticated arguments. They might or might not have diagrams and plots and good looking math to back up their claim. And when they're done making their case after you've had this conversation where you say, why do you think they're this flat? And then they just go on and they're done. They'll look at you.
What do you say? Do you call them stupid? Do you say you're wrong? Do you say no? Come on.
The Earth is round. Don't don't stop kidding around. Do you try to make a case? Well, I think the Earth is round because blah blah blah blah. Or do you walk away?
But here we are. You know that the Earth is round. Right? But but how do you know that it's round? Do you believe it because some random guy on a random podcast told you it is?
That's not much different than the person saying it's flat. So here's a good opportunity for some self reflection and self edification. Not with the goal of winning an argument. I'll I'll get into debates with flat earthers later, but for increasing your own sophistication, which isn't a bad thing. Right?
Right. First off, the earth is flat, at least locally. In your backyard or even your city or even your country, the earth is flat enough that you can just go ahead and pretend it's flat per for purposes of walking around or urban planning or agriculture or civil engineering, you know, everyday life. Yes, there are hills and valleys in general topography, but for purposes outside of that, you can just go ahead and assume of it's flat for most of your everyday life. It's only on global scales that the curvature of the Earth even becomes an issue, which explains why most of our ancestors assume that the Earth was flat because they had no reason to think otherwise.
Right? If all of your everyday experiences can work just fine if you assume that the Earth is flat, then it will never even enter your consciousness that the earth could be around. What's the point? There's no reason for that thought to even occur to you, but it occurred to the Greeks. It may have occurred to other people throughout time, throughout human history, but they didn't record it.
They didn't study it a lot. They didn't preserve it. They didn't make a solid case for it. The Greeks were the first to do it in this way. Even with contemporary cultures to the ancient Greece.
We're talking, like, twenty five hundred years ago when they started thinking these kinds of thoughts. Even cultures that were alive and kicking and thriving back then weren't thinking along the same lines. The Greeks had their philosophy and their thinking and their mathematics and their general time on their hands, and they began to wonder if something else was going on. And they had a few reasons to wonder if something else was going on when it came to the shape of the Earth. First is the nature of horizons.
When something goes away from you, it gets smaller. That's just basic geometry perspective, the usual. But if you're watching something get farther away from you, say, looking out over a flat ocean, not only will it get smaller, but then the bottom of it will disappear, and then the middle, and then the very last thing to disappear will be the top. And similarly similarly, if you're on the ocean, you're and you're approaching land, you will see the tippy top of a mountain first, the peak, and then you'll see the middle parts, and then you'll see the bottom in the coastline. Last.
That seems interesting. If it was just far away, you should be able to see a tiny little mountain and a tiny little coast all at the same time, and then as you got closer, it get bigger and bigger. But you see the top first and then the bottom last as you're approaching, and the first thing to disappear when something is going away is the bottom part. This makes sense with a curved Earth because with the curvature of the Earth, the Earth is in the way of seeing the bottom parts, but you can still get a perspective. You can still see the top parts.
This is generally true, but it's relatively unreliable. You can't just point to this and say that the Earth is curved, and that's because we have an atmosphere. And, yes, the atmosphere is great for a few wonderful things like breathing. It's also really annoying for a few other things like, astronomy in general, and for trying to determine the curvature or flatness of the Earth, and that's because the atmosphere can have different layers of cold air and hot air, and cold air and hot air will hot air will have different densities, and different densities of air will bend the path of light in different ways. So you can get interesting, effects because of the temperature in layers of air.
So you can get images of distant objects that are inverted, are upside down, are all wibbly wobbly that disappear with gaps because the air between you and the object is interfering with the light and making it weird. So you can see a distant mountain on the horizon appear upside down because the air is messing with the light and making it appear upside down. So it's not generally useful. Like, it's not pinpoint 100% accurate, but on a calm day with calm air, this is what will happen, and this is what the Greeks noticed. That, yes, there can be weird things.
They didn't understand the physics of refraction, but they could tell that most of the time, the bottoms disappear first or arrive last, and that's maybe the curvature of the Earth has something to do with them. Maybe it's not so flat. The second thing they noticed was the, lunar eclipses. This is when the Earth passes directly between the sun and the moon, and the Earth shadow gets casted onto the moon, and a lunar eclipse will last a few hours. No long events.
They make the moon look really dark and creepy and cool, and the shadow of the Earth is always a circle. It doesn't matter when the lunar eclipse happens. It doesn't matter how long it lasts. It doesn't matter where on the surface of the Earth you are. No matter what, from beginning to end over the course of hours, that shadow of the Earth is always a circle.
And the only shape that always makes a circle shadow is a sphere, a ball. Try it. Get out anything else. Get out a coin. Cast a shadow.
Yeah. You can make a circle, but as soon as you start moving the light around or moving the coin around, you get different shapes. But if you have a ball, it doesn't matter where you point that light. The shadow will always be a circle. There is simply no way to arrange this with any other geometric object, and the Greeks noticed it.
And the last thing they noticed was the visibility of stars. They knew living in Greece that there were some stars and constellations that they were very familiar with, that they saw regularly season after season after season. But they knew that their friends down in Egypt saw some stars that they couldn't see from Greece, and that the stars that the Egyptians saw appeared in different positions on the sky than what they saw. And they talked occasionally to the weird barbarians to the North, and the weird barbarians to the North talked about stars that the Greeks couldn't see reliably. This is very interesting.
We can expand this. They they had a even with that limited picture, even that with that Mediterranean picture of the world, they were able to determine that different parts of the Earth see different chunks of sky. This only works on a curved Earth. On a flat Earth, we should all see the exact same sky. In fact, we should see it the same sky every single night.
But the fact that the sky is different as you move north and south is a big deal and only possible with the curved Earth because the Earth is in the way of you seeing some stars. If you want an awesome demonstration of this, it this is awesome. Look at the constellation names. In the Northern hemisphere, we get our constellation names from the Greek and Roman and Persian tradition. So they have all sorts of cool stories.
There's like Orion and Pegasus and Hercules and Gemini and, Cassiopeia, like, so many cool stories, so much mythology, so much richness to the Northern Hemisphere constellations. And then look at the list of the official Southern Hemisphere constellations. Those constellations are boat or sail or bird or, oh, cross. They're lame. They're lame.
There's no stories. There's no mythology. It's just objects. Objects that have a rather nautical theme, and that's because we and we, I mean, in the sense of Europeans and the official constellations, they don't take the constellation names from the cultures that lived in the South and came up with rich mythologies about the stars. They got it from sixteenth and seventeenth century explorers from Europe who were exploring those oceans for the first time, and were charting those constellations and those stars for the first time.
They were naming it, and they were not a very creative bunch. And so the Northern Hemisphere stars are rich and have awesome constellations. The Southern Hemisphere is boring, at least when it comes to the European tradition, and that's because the Europeans didn't have access to those stars until they started making boats capable of going South Of The Equator reliably. They just couldn't do it. If the Earth were flat, they would have been able to see those stars and give those stars rich names and constellations.
Take the North Pole, Polaris. As you move north or south, its position on the sky changes. And once you cross the Equator, you can't see it anymore. It's as simple as that. There's another way that the Greeks didn't know about that you can use the positions of stars to determine that the Earth is around.
And that's if you go out on a flat plane, you can see down to your horizon a certain number of stars. Then if you hike up a nearby handy mountain, you have a better vantage point. You can see over the curvature of the Earth a little bit more, and you can see stars even more down looking in the direction now. Like, you can see you have a wider field of view than you do on a flat plane. You can see more of the dome of the sky.
This only works with the curved Earth because when you're on the ground, the curvature of the Earth blocks you. The dirt and sand and mud and ocean gets in the way of seeing the star. You go up onto the mountain. You can see over the curve a little bit and see a few more stars. The Persians in the ninth century launched an expedition to measure this and use this fact to measure the curvature of the Earth, and they did it, and they got to within 10% of the modern value.
But even without that, just the Greeks looking at horizons, looking at the shadow of the moon, looking at the visibility of stars figured out that the Earth is round, and that was thousands of years ago. So far, in fact, the Eratosthenes, an ancient Greek, was able to measure the curvature of the Earth because he waited for the summer solstice to appear in Cyrene, Egypt. That's when the sun is directly overhead at noon. And at the exact same day, at the exact same time, he was living a few hundred miles away in the city of Alexandria. The sun was not directly overhead.
He's able to measure the length of the shadows, do some trigonometry, and calculate the circumference, and he got to within 15% of the modern value. And just so I can name drop the correct names, it was the ninth century Abbasid caliph Al Mamun. It was an Arab caliph, that sent the expedition to explore the mountain top and measure the curvature of the Earth. Then centuries later, there's the whole circumnavigation thing in all sorts of directions. You can circumnavigate the globe by going through the North Pole, by going through the South Pole, by going around the middle, by doing some combination of thereof.
You can pick any direction you want as long as you work hard enough, you will end up in the position you started, and there's more. There's more than that. Like, that's what the ancient Greeks had. That's what our ancestors have. Today, we have know about things like the Coriolis effect.
The Coriolis effect is a tendency if if you're on something that is spinning or rotating, it will make you want to rotate in very interesting and fun ways. The Coriolis effect is what's responsible for hurricanes being how they are. The fact that hurricanes spin one direction in the Northern Hemisphere and another direction in the Southern Hemisphere can only work on a curved surface. Because if everything were a disc and spinning, we would have a coral Coriolis force, but the Coriolis force would be the exact same direction no matter where it is on the Earth. The fact that it changes directions north to south can only happen if you have a curved world.
The fact that you can measure the Coriolis effect and see how it strengthens as you change latitude and then reverses direction once you crosses the Equator, that can only happen on a curved earth. The whole Foucault's pendulum, you know, this classic science demo that sits in almost every science museum in the world where you get to watch over the course of a day this pendulum knocked down pegs due to the the rotation of the Earth. The fact that those pendulums act differently at different latitudes is an indication of a curved Earth. The fact that there are different sunrise and sunset times around the globe, both as a function of latitude and as longitude, the fact that the both sun and moon appear as full discs no matter where you are on the earth, the fact that the sun and moon are always the exact same size no matter where you are on the earth, the fact that Patreon exists, go to patreon.com/pmsutter to to keep this show going and to demonstrate the curvature of the Earth. A great circle is great circles.
This is awesome. If you want to go between two distant cities, and you are looking at a flat map, your first inclination is it wanna say you want to spend as little money as possible, as little fuel as possible. You draw a straight line between those cities. That will be not the shortest path. Because the earth is curved, that straight line on the flat map is going to be wrong.
Instead, you have to draw a curved path between the cities to represent the actual curvature of the Earth. These are called great circle roots and you can do it if you have a couple planes handy. Draw, take a map, take a flat map, draw a straight line between two cities, and then draw the great circle routes between those two cities. Mark all the landmarks and cities on the two routes so you know how to how to guide yourself. Then get in those two planes.
Go at the exact same speed following those two routes, the straight line route on the flat map will not get you there sooner. The great circle map, the curved path will because that's what accurately represents the curvature of the Earth itself. But wait, there's more. The concept of a round Earth fits neatly with everything else we know about the universe. The other planets are all round.
The sun is round. We understand the gravitational force. We understand how it works, how it pulls objects in closer and closer, and how it pulls uniformly in all directions. We understand the formation of the solar system and how the earth formed and the differentiation of the elements in the generation of our magnetic field because of our molten spinning core. We have satellites in orbit.
We have spacecraft in orbit. We have eyewitness testimony. We have human beings who have gone up high enough to witness the curvature of the Earth with their own eyes. They've taken pictures of it. They've taken videos of it.
They've come back down to Earth to tell us what they saw. All of space flight relies on assuming that the Earth is curved. If you assume that it is flat, your satellites will crash into the ground. Could the Earth be flat? Sure.
It could be, but so far no evidence whatsoever aligns with that idea. If you want to say that the Earth is flat, you have to account for a huge variety of experiments and observations all disconnected from each other. The satellites that we have in orbit, totally disconnected from the Coriolis effect, totally disconnected from the observations of stars at different latitudes, Totally disconnected. All disparate, and they all point. It would only take one of those to indicate that the Earth is round, but we have all of them.
People who believe in and promote a flat Earth seem to enjoy, and maybe this is an unfair characterization, they seem to enjoy making flowery descriptions of their ideas. They seem perfectly happy to have explanations at the ready for any rebuttal. So if you were to come up and present anything that I've just told you, if if they they're really into this flat earth thing, they will have an answer for you. Oh, their pictures taken above the Earth's atmosphere? Well, lenses on cameras are curved and cause that distortion at at big angles.
Oh, the the Coriolis force well, I have no idea what their answer is to that, but I'm sure they'd have some answer. Oh, oh, the sun and the moon being the same size? Oh, they're spotlights. They're discs that appear, and and there's very complicated interactions. Oh, oh, oh, horizons.
Well, there here's some geometry and some plots on a page to show you how how it doesn't work, etcetera, etcetera, etcetera. But people who believe in the flat earth don't make a critical next step. They don't take their own ideas seriously. Once you have a new idea in science, you have to flesh it out. You have to make it real.
You have to find a new way to test it, and you'll have to go out and test it. Okay. The Earth is flat. The sun and the moon are discs. Okay.
What does that mean? What force is responsible for keeping us pinned to the ground on a flat earth? Stars have visible in some places from the earth and other places not visible, or you get a different set of stars. Whatever explanation you have for that, what's a prediction you can make? What is the responsible thing?
Okay. Saturn and Jupiter are round, but Earth is not. Why? What what's the physics behind that? What generates our magnetic field in the Earth?
Why do hurricanes flip directions once you cross the Equator? On and on and on and on. You have to actually test these ideas. It's not enough. You can come up with whatever fancy idea you want, but you have to take it seriously.
You have to flush it out all the way, and then you have to test it. If you don't test it, you are just making up stories, and this is what sets science apart from other ways of investigating the universe is the essential critical role of observations and of testing. You can tell whatever story you want, but you have to test it. And people who believe in the flat earth don't take that next step. Some flat earthers have attempted to measure things, to test things.
And when you run into when you believe something strongly enough and you run into tests that fail, that go against what you believe, I don't know how you reconcile that, but somehow they're able to. Many people are. And if at any point in the discussion or the analysis or the explanation, the word conspiracy arrives, then you're just running in circles. Because we have all this evidence. And then when something doesn't add up or a test fails or something doesn't make sense and you say, well, it's just a conspiracy.
Where are we supposed to go from there? I wanna talk about conspiracies a little bit more in a little bit. First, I wanna mention that there is an issue with all the lines of evidence that I presented for a curved Earth. And there's a lot. There's a lot.
There's centuries, millennia of evidence, data that back up that the Earth is curved. But all these lines of evidence are largely inaccessible to everyday experience. Like I said, most of your life, you will just go on living on a flat Earth. This whole thing about other stars as a position of latitude or height, if you wanna do that right, if you really wanna test it, it requires extensive travel, detailed measurements. That's not something we have in our everyday lives.
Lunar eclipse, again, careful observations and measurements and, you know, lucky timing. You wanna do a circumnavigation, you need, I don't know, a boat. This stuff is hard to do. This isn't stuff you can do from your backyard. This isn't stuff you can do on your own.
I haven't performed any of these experiments. I have performed a lot of experiments in science, both as part of my education and as part of my research, but I haven't performed these. Likely, you haven't either. So how do we trust that? I'm asking you to trust me.
I am trusting the work of all previous and current scientists because I trust science. I trust the infrastructure, the system of science to produce reliable results. I have not personally tested the germ theory of disease, but you know what? I'm gonna get vaccinated, and I'm gonna take my antibiotics because I think that's the best way to stop being sick because I trust medicine and biology. I even personally tested outside of some classroom laboratory experiments the atomic theory of matter, but I'm gonna use the atomic theory of matter in all my work.
I'll tell you about the atomic theory of matter. I have not performed you have not performed the vast majority of experiments that led to how we know things in science, but we explicitly designed the institution of science to be trustworthy because it always points to the evidence, because it's been fact checked and peer reviewed, because it's falsifiable, because it's provisional, because we're always learning. We designed it to be trusted, but some people don't trust it. That's why I never ever recommend getting in an argument with someone about the curvature of the earth because it isn't a debate about the evidence or logic or reason. A true believer in flat earth will at some point just claim conspiracy and end it there.
They'll say, oh, they don't want the or the earth is really flat, but they don't want you to know it. Why? Because it's a conspiracy. Because at some point, the evidence requires a certain amount of trust in scientists, and either you trust in scientific methods and centuries of evidence or you don't, which is what I believe is the real motivation behind things like the flat earth movement. It's not about science itself or evidence.
I mean, the same people who believe that satellite imagery are a hoax are more than happy to use satellites for global communication or GPS. It's about trust. And you know what? Scientists themselves can be at fault for that. Scientists have misled people.
Scientists have deliberately perpetrated falsehoods. Scientists have aligned or supported narratives that have oppressed people. Some groups, some people have a reason to be suspicious of authority figures and scientists are authority figures. How many times have scientific results been used as an excuse to put people down or to screw people over? And then there's the whole science journalism thing, which is it.
If you wanna know what my beef is with science journalism, I truly do believe that science journalism is doing a disservice and it's broken, but that's a whole other episode. Feel free to ask if you want my thoughts and opinions on science journalism and how to do it better. The question if you ever encounter someone who believes in a flat earth, say at a gathering or with your family, the question isn't why does this person believe that the earth is flat. The question is why does this person believe in a conspiracy? And the answer why people believe in conspiracies is a lack of trust.
How do you debate someone who believes in the flat earth? You don't. Because a debate will never win. A day debate will go back and forth, back and forth, back and forth. And at the end of the day, the flat earther will say, you trust science?
I don't. You trust what all these people you trust with that guy on that podcast told you about some observations made two thousand years ago and great circles and and hurricanes and and satellites and visibility of stars and sunrise and sunset times. I don't trust him. And I don't trust what he represents. I don't trust the system.
I don't trust the authority figures. It's not about the flat earth. It's about trust in science. And you arguing by quoting scientists or quoting experiments or quoting anything, any tool or product of science isn't going to change. Why do people get attracted to flat earth movements?
Why do people get attracted to conspiracies? There's that's a whole sociology question. My take on it is that these are people who have been disenfranchised, people who have been marginalized, people who have been oppressed by authorities, by systems, by political structures, by economics, by life, and scientists are a part of the system that oppress them. Scientists are a part, deservedly or not, a part of the system that marginalized them, that disenfranchised this them that took away their power, that took away their agency, that took away their voice. They don't trust the government.
They don't trust authority figures. They don't trust scientists. Scientists are like the ultimate authority figure. We come in and we tell you how reality works, and our methods are inscrutable and full of jargon, and we live in ivory towers. And we say this is the way the world works and this is how and then a lot of scientists take the next step and this is how you should live your life now that we know better.
People who join flat earth movements are isolated, disenfranchised, marginalized, and looking for a community, looking for a group of people who wanna stick it to the man and scientists are the man. It's not about the curvature of the Earth. It's about science and authority and institutions. How's that change? It's not gonna change by quoting scientists or evidence or reason.
I did this episode too. You can personally understand how we know that the Earth is curved. None of this is gonna work with the flat earther because it's about something else. Talk about something else then. Talk about the weather.
Talk about relationships. Talk about that Netflix show that everyone else is talking about. Build that relationship. Build trust. I have met many flat earthers in a variety of settings.
I don't debate about the flat earth. I just talk to them like people. Yes. I think they're wrong. I've met a lot of people in my life that I think are incorrect about things.
That doesn't stop me from talking to them, listening to them. If I'm ever asked how I got my information or what I believe I share, I hope I'm listened to in those moments. If I'm not, then I just stop the conversation. I honestly believe that science as an institution suffers a deficit of trust in modern times. It may have suffered a deficit of trust ever since it originated.
The only way I believe the only way to build trust is by building one on one relationships to repair that trust, to construct that trust. If someone can trust me as a person, that might be a gateway, a doorway into trusting the institution of science that I represent. Maybe not. It's worth a shot. It's hard.
It's slow. It's not fun. It's way more fun to just get in an argument and get someone mad and you get mad and start debating the evidence. It's a lot harder to listen, to empathize, to try to understand why this person believes rather than focus on what they believe and try to build their trust again in science one step at a time. I'd like to thank Asher f for asking the question that led to this episode.
If you haven't got my new book, How to Die in Space, now is a good time. It's available in bookstores nationwide and on Amazon. Feel free to leave leave a review on Amazon. That helps get get grow the visibility and get the word out. Really appreciate it.
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