Saturday, August 22, 2020

Flat Earth “Science”: Wrong, but not Stupid

I, as many people in science communication, am fascinated with flat earthers. Here you have a group of people steadfastly rejecting evidence that’s right in their face. Today, I want to tell you why I nevertheless think flat earthers are neither stupid nor anti-scientific. Most of them, anyway. More importantly, I also want to explain why you should not be embarrassed if you can’t remember how we know that the earth is round.

But first I have to tell you what flat earthers actually believe and how they got there. The most popular flat earth model is that of a disk where the North pole is in the middle and the south pole is an ice wall on the edge of the disk. But not all flat earthers sign up to this. An alternative is the so-called bipolar model where both poles are on the disk, surrounded by water that’s held by a rim of something, maybe ice or rocks. And a minority of flat earthers believe that earth is really an infinite plane.

They mostly agree though that gravity does not exist, and that the observations we normally attribute to gravity come instead from the upward acceleration of the flat earth. As a consequence, the apparent gravitational acceleration is the same everywhere on earth. I explained last week that this is in conflict with evidence – we know that the gravitational acceleration is most definitely not the same everywhere on earth.

The idea that gravity is due to upward acceleration also causes other problems. For example, you have to assume that the moon and the sun accelerate along with the flat earth so we don’t just run into them. That’s an ad-hoc assumption which disfavors the flat earth hypothesis against models where the orbits of the moon and the sun can be calculated from the gravitational law.

But that’s not the only problem. You also have to get the moon and the sun to somehow circle around over the disk to explain day and night and the phases of the moon. To get the day-night cycle to be noticeable, you have to shrink the sun and move it closer to the earth. 

You also have to somehow get the radiation of the sun to be directional. That’s many more ad hoc assumption. But even with those assumptions, the size of the sun will change during the day more than we observe. And no one has ever successfully predicted solar eclipses on a flat earth, or calculated the observed motions of the planets.

The bottom line is: it’s not easy to improve on today’s scientific standard. It was for good reasons that the hypothesis of a flat earth was abandoned more than two thousand years ago.

Some people suggested to me that flat earthers do not actually believe the earth is flat, they are just mocking people who take scientific evidence on trust. And that, let us to be honest, is something we all do to some extent every now and then. And it is probably the case that some flat earthers are indeed just pretending. But I find it exceedingly implausible they are all just faking it. 

To begin with, they would all have to be excellent actors. Just look at some of the videos on YouTube. Also, they’re putting quite some time and, in some cases, money behind their conviction. And that’s while most of them full well know coming out as flat earther will make others doubt their sanity. All that makes it unlikely they are just in for the fun.

Now, you may want to discard flat earthers as conspiracy theorists, which some fraction of them arguably are. But I think that would be somewhat unfair to most of them. To understand why, it helps to have a look at the history of the flat earth society.

The flat earth society goes back to an Englishman by name Samuel Rowbotham, who lived in the 19th century. He was a medical doctor who believed he had proved that the earth is flat and then complained for the rest of his life that the supposed scientific authorities ignored him. He referred to his methodology as “Zeteticism” after the Greek word zeteo, “to seek”. 

By “Zeteticism” he meant an extreme version of the philosophy of empiricism. Rowbotham’s philosophy, which is still the philosophy of flat earthers today, is that if you want to understand nature, you should only rely on information from your own senses. You can for example read on the website of the flat earth society:
“The world looks flat, the bottoms of clouds are flat, the movement of the Sun; these are all examples of your senses telling you that we do not live on a spherical heliocentric world. This is using what’s called an empirical approach, or an approach that relies on information from your senses. “
That flat earthers insist on evidence from your own senses only really is key to understanding their problem; I will come back to this. But first, let me tell you the rest of their history.

After Rowbotham’s death in 1884, the flat earth idea was carried forward by another British guy, Samuel Shenton, who once explained to a journalist:
“No man knows the ultimate shape of the earth, but that portion we life on is definitely flat. No one will ever know what the whole complexity is like, I suppose, because it goes beyond his sphere of observation, investigation and comprehension.”
Again, note the emphasis on personally collected evidence. In 1954, Shenton created the International Flat Earth Society. Few people cared. He died in 1971.

After his death, the Flat Earth Society was taken over by the US-American Charles Johnson. But even after the advent of the internet, flat earthers did not attract much attention. Johnson died in 2001, at which point the flat Earth society had 3500 or so members. The job then fell to another American, Daniel Shenton, who is not related to the earlier Shenton but whose logic falls right in line. He said in an interview with the Guardian in 2010:
“I don't think there is solid proof. I'm not intentionally being stubborn about it, but I feel our senses tell us these things, and it would take an extraordinarily level of evidence to counteract those. How many people have actually investigated it? Have you?”
Shenton had the idea to set up a wiki page for the flat earth community. Still no one cared. But in 2016, everything changed.

What happened in 2016 is that a few devout flat earthers put up videos, here, on YouTube. And that really got things going, by way of recruiting new believers. These videos have meanwhile been watched by millions of people. And that had consequences: In a 2018 poll in the United States, two percent of the respondents said they believe the earth is flat, while another 5 percent are not quite sure. 

Reliable numbers are hard to come by, but we are meanwhile probably talking about more than ten-thousand people in the developed world who reject science that was settled by the middle ages. Let that sink in for a moment.

How does someone end up rejecting something as scientifically well-established as the fact that the earth is round? 

There is not only one reason, of course. Some flat earthers find the idea is appealing for religious reasons, others are of the crowd who think NASA is evil, space a fake, and the moon landing didn’t happen. But mostly it’s because they think they are merely being rational skeptics. They have not themselves been able to prove the earth is round, so they believe they are only reasonable when they request evidence. CNN for example reports from a flat earth conference:
“Like most of the speakers at the event CNN spoke to, he was convinced after he decided he couldn’t prove the Earth’s roundness.”
I want to leave aside here that, of course, you cannot strictly speaking prove any empirical fact; you can only prove mathematical identities, so more precisely we should speak of seeking evidence that disfavors the hypothesis that the earth is flat. Of which there is plenty, starting with the historical evidence about how stellar constellations shift if you travel, how the length of shadows changes, to Newton’s 1/R2 force law that is the law for a sphere, not a disk, not to mention Einstein and gravitational redshift and the perihelion precession of mercury, and so on, and so forth.

The problem that flat earthers have is that they cannot do most of these observations themselves. So if you buy the idea that it’s only your personally collected evidence that you should accept, then it seems you cannot refute the idea that the earth is round, and so flat earthers philosophy forbids them to accept scientific fact. 

Needless to say, if you want to hold on to your convictions it helps if you refuse to do observations that could speak against them. There are actually many ways to convince yourself that the earth is round which are not that technically difficult. Buy a telescope and try to explain the motions of the moons of Jupiter, for example.

So what’s wrong with flat earther’s attitude? Isn’t it asking for evidence exactly what rational thinkers should do? Sure, evidence is key to scientific progress, but flat earthers’ philosophical approach by which they reject certain types of evidence is inconsistent and, ultimately, logically wrong. 

See, the only evidence anyone ever has of anything is evidence you collect with your own senses. Except, as Descartes pointed out, evidence of your own ability to think, but this is not relevant here. Relevant is that the distinction which flat earthers are trying to draw between different types of evidence does not exist.

All evidence you have is sensory input. If you hear an explanation of someone else’s experiment, if you read a paper laying out someone else’s argument, that’s your own sensory input. A distinction which does exist, however, is that some of our sensory input requires very little decoding, while some requires a lot. Flat earthers’ problem is that they refuse to decode difficult sensory input.

A good example for the need to decode sensory input by conscious thought are optical illusions. Your brain tries to interpret visual input in ways that sometimes gives a misleading result as in this example. You almost certainly think square A is darker than square B. It is not. 

To understand your sensory input correctly you need to draw on other information, in this case your knowledge about optical illusions. Your brain interprets this image as if it was a natural, 3-dimensional scene, and therefore calculates back to the original color of the squares taking into account what appears to be a shadow. This is the wrong interpretation if you want to know the actual color of pixels on the screen. The lesson is, if you do not think about your sensory input, if you do not properly decode it, you arrive at a wrong conclusion.

Flat earthers similarly arrive at the wrong conclusion by failing to decode evidence, indeed by simply ignoring a lot of evidence that their own senses deliver. This is evidence about how society and science works.

Whether we are scientists or not, we all constantly use this evidence to navigate life. And I am sure flat earthers are no exception. Just consider going to the supermarket and buying canned soup. Do you have evidence that what’s in the can is edible? Probably not. For one, the can’s closed. And if you are anything like me, you probably have no idea how or where or by whom it was produced. Why then are you not afraid of eating canned soup? Isn’t this entirely irrational?

No, because you do have evidence that canned soup is edible. You know how the legal system in your country works, you know that there are regulations on what can be sold as food in a supermarket, you know that if what’s in that can was harmful to you, then a lot of people along the food chain would be punished for their mistake, and they don’t want that. Your trust in canned food is an entirely reasonable inference from evidence, evidence that you collected with your own sense, because what else could you possibly have collected it with?

Now let’s come back to flat earthers. Most of you don’t have a physics degree and chances are that after learning in school how we know the earth is round you didn’t think much about it ever again. By and large you are probably confident it’s correct because what you learned in school was plausible, and you know it is widely taught to children, and you know that your government strives to give children in your country a scientifically accurate education. So you have good reason to think the knowledge you were taught is backed by solid scientific evidence.

There is no appealing to authority here. You have totally yourself collected all this evidence about how society works. You have also yourself collected lots of evidence that science works. Any airplane, any laptop, any pair of glasses is evidence that science works. It’s evidence that the system works. It’s evidence for how the whole world works.

So, if you cannot recall just what experiments demonstrate that the earth is not flat, or if you cannot immediately figure out what’s wrong with flat earther’s arguments, there’s no shame in rejecting their claims, because your rejection is based on evidence, evidence that science works.

What’s wrong is that flat earthers’ claim they are leading a scientific argument. But there is no scientific argument about whether the earth is flat. This argument was settled long ago. Instead, flat earthers’ argument is about whether you should trust evidence that other people have collected before you. And it’s an important argument because this trust is essential for society and science to progress. The only alternative we have is that each and every one of us has to start over from scratch with birth. You see, flat earthers would eventually figure out the earth is round. But it might take them a thousand years until they’ve reinvented modern science.

This is why I think scientists should take flat earthers’ philosophical problem seriously. It’s a problem that any scientifically advanced society must address. It is not possible for each and every one of us to redo all experiments in the history of science. It therefore becomes increasingly important that scientists provide evidence for how science works, so that people who cannot follow the research itself can instead rely on evidence that the system produces correct and useful descriptions of nature.

To me, therefore, flat earthers, are a warning sign that scientists should take seriously. The more difficult scientific experiments and arguments are to follow for non-experts, the more care we must take to explain how we lead those arguments.


  1. Mother Earth is round where she is supposed to be round and dented where she is supposed to be dented. Beauty lies in the eye of the beholder.

  2. The first concrete evidence for spherical surface to Earth was found by Eratosthenes. At the summer solstice a southern region along the Nile gave no shadow to a pole, while in Alexandria it did. Reasoning the angle of the shadow with the distance to this southern region provided not only evidence of sphericity, but a way to calculate the size of the Earth. This meant not only was the world round, but demonstrating such could be used to calculate something.

    That the popularity of flat Earth began in 2016 is I think evidence of this hypermanic social shift, where this corresponds to the election of the biggest idiot and sociopath to ever head a democracy or republic. I am sure we all know who that is. It is my observation or sense that something in the American mind, and I think this flat Earth flap-doodle is largely in the US, has gone horribly wrong. There was evidence of this prior to 2016, but with that year a lot of things became “legit,” from some of the most appalling bigotry to the most absurd conspiracies. Now we have a host of these ideas, from Covid vaccine conspiracies to QAnon.

    The idea of a flat Earth in some sense does come from the senses. The Bible does make mention of what amounts to a Sumerian cosmogony. This has repeated, but infrequent references, where in Ezekiel there is mention of an “iron dome,” translated from Hebrew, that covers the Earth. Any idea why the Israelis called an anti-missile system Iron Dome? The creation myth of B’raysheet (aka Genesis) has references to the Sumerian worldview. The God Marduk slays Tiamut, a dragon from the deep (reference to the leviathan in Genesis), and uses the body to create the Earth with a dome that prevents the water from entering. The Story of Noah has God opening windows to let the water in etc. Ok sure enough, if one looks out the view is split in two between the ground and the sky. The two appear equal in extent and the Earth by all appearances is really huge.

    It is of course a denial of science to say claimed evidence that is not confirmed directly by senses can’t be relied upon. This reminds me of the Amazonian culture that denies any sort of abstract concept and only admits what is directly experienced. It is a step back.

    1. Did Eratosthenes's observation actually provide evidence of sphericity? Surely the same effect could be observed from a flat surface. It gives you the radius, if you make the assumption.

    2. He calculated the radius of the Earth.

    3. He treated the earth was a sphere, based on whatever evidence and beliefs he had, to calculate the radius. If he had assumed the earth to be flat, he could have calculated the distance to the sun. There is nothing in the experiment to discern between those two interpretations.

    4. Hi Lawrence! I'm a Christian (almost as bad as a Flat Earther in the opinion of many) but ALSO a cultural historian from a long string of fairly smart engineers and a dad who was an aeronautical engineer and a great inventor. I really appreciate your deconstruction of Sumerian cosmology and find most Christians oddly unable to consider the origins of our peculiar faith, and I love science which due to my dad's wanderlust and sheer curiosity about the world I never got to study in depth (on average one school per year for 13 years - I could wing English and Ancient History and indeed intuit some Maths and Science but they need more than that). I wish I'd paid more attention to gravity though, not just as something an aeroplane engine has to overcome. It occurs to me that despite themselves Flat Earthers may be more accurate than we realise, though not in ways they'd appreciate being told about. You know those newish models of how we interact with the world around us, where everything appears 3-D but is actually our senses doing a little sleight-of-hand so we can interact with/operate in our environment fairly efficiently? Gives me a kind of smothers feeling though of course Zen practitioners figured out the perceived world was an illusion a long time ago!

    5. I think you're a bit unfair to Macron here..

  3. Agree completely, FWIW. To add, I think we have to be specially careful because requiring diffeomorphism invariance of the dynamics is a central idea in the physics of GR. Indeed the mathematical idea of a manifold depends on introducing an atlas of maps from what is an ostensibly curved space-time to regions of a 4-dimensional Euclidean space. If we work with a weird map the dynamical equations may look weirder than if we choose some different map, but that doesn't speak to whether any coordinatization is "true". Applied to flat earth, the equations that describe the geometry and fields that apply at different points may be more complicated if we insist on a stereographic or similar projection of the surface of the earth to a flat plane as a subspace of a 4-dimensional Euclidean space, but they are no less an instance of Einstein's equations. This may be giving more sophistication than flat earthers give, but diffeomorphism invariance is strong sauce.

    1. Ah I'm convinced , it means there earth is neither flat nor sprerical , its a matter of convention . let us not be lost in math as our great proffesor say.

    2. You said it better . had a similar idea. It is a matter of convention to choose either hypothesis. The earth is neither spretical Nor flat . coordinazation is completely arbitrary . how come Sabine misses this point im not sure

    3. No, it's not a matter of convention. Switch on your brain.

  4. I never realized they believed gravity came from the Earth accelerating. Where does the energy for that acceleration come from? And if we've been accelerating at 1G all this time, how fast are we going by now?

    1. You might just as well ask the same questions relating to dark energy, the first now, the second at some arbitrarily distant time in the future.

  5. Everyone believes that the sun that sets in the East is the same that rises in the West. That suggests that the earth cannot be an infinite in extent and nor infinite in depth - otherwise the sun couldn't traverse the earth.

    This then suggests that the earth hangs, contra the senses, in space. Then when we look up at the sky we see other bodies hanging in space, the sun and the moon. So this notion is not against nature. It also suggests that the earth, in some sense, is like them. And given that they are both round, this suggests that maybe, just maybe, that the earth is round...and moving in space ...

    1. "Everyone believes that the sun that sets in the East is the same that rises in the West."

      What planet do you come from?

  6. Sabine,

    Regarding the impact of YouTube and the internet on flat-earth beliefs, I hope you don’t mind if I talk a bit about the impact of networking on cognition in general.

    The first point is to emphasize just how unique this networking moment is in history.

    Function-encoding digital data is an extremely old invention, having first appeared billions of years ago in RNA and DNA. For most of that time the many clever problem solutions (e.g. photosynthesis) encoded in DNA have largely remained isolated within the individual branches of the tree of life. It has only been in the last century that digital data escaped this isolation and began interacting combinatorially. This cross-linking was enhanced and accelerated by the invention of technologies that free digital data from biomolecules, making possible the entirely new type of sharable problem solutions that we call software.

    Think of it this way: Given that the highly isolating tree-like model of digital function encoding has held absolute sway for several billion years, what are the odds that you, right now, would be alive during the very first century in which that tree model was upended by the almost unimaginably more powerful combinatorics of a fully networked model? Not very high, I’d say!

    Networking also plays a huge role in human intelligence.

    Networking in fact helps explain why human intelligence is so oddly tricky to define. There are individual bonobos who are just as good — probably better — at raw problem-solving than most humans. However, bonobos lack both the internal linguistic scaffolding needed to name, store, and build on such solutions, as well as the external linguistic transfer mechanisms by which to share such solutions with other bonobos. Human language capabilities in contrast allow us to internally organize and externally share solutions in ways that make us look and feel a lot smarter than we really are. The assertion that be stand on the shoulders of those who came before us goes deeper than we realize! Furthermore, since human intelligence is itself highly networked, the expanded data sharing of the internet unavoidably has a profound impact on both community and individual human intelligence.

    To understand that impact, here is the second piece to consider:

    The boundary between high intelligence and insanity is disturbingly thin, since both depend on the ability to create imaginary mental worlds that are almost completely severed from immediate sensory reality. Such imaginary worlds enable exploration of possible futures, but they also create a high level of risk, since bad models can lead to severe misunderstandings of reality. How we accept, discard, and interpret sensory inputs within such cognitive models is also profoundly dependent on the models that have been handed to us, often unconsciously, by the human communities in which we are nurtured.

    Here’s the scary part: Since so much of human cognition is networked and thus dependent on external contributions, allowing ourselves to become dependent on models of perception from unknown sources means we are also handing over part of our sanity to such sources. At both the group and individual levels, perceptive priority models that are severely anomalous, whether by accident or design, can result in perceptive psychosis, an inability to perceive reality well enough to survive within an uncaring universe.

    Or, more bluntly: If sanity is defined as the ability of communities and individuals to take the actions that keep them alive in the presence of profound threats, then relying unquestioningly on the internet can drive you perceptively insane.

    If that sounds a bit extreme, I assure you it is not. Just take a look at the late August 2020 figures on the ratios of daily COVID deaths between the USA and the similarly-size European Union, and then probe the underlying causes of that ratio.

    1. Totally agree. Beliefs are information stored in a brain. There's absolutely no deep reason for such information to correspond to reality; it's just a practical matter of what is acquired. Science is a slow, careful and biologically expensive process which has had game-changing success but it requires a level of economic surplus that has only existed recently. It's an "unnatural" state. We are wired to absorb what comes for free or at low cost, and for solid evolutionary reasons and, worse still, optimise for social signalling as much as anything.

    2. I just read a short piece on a proof of the Keller conjecture on tiling of space. The proof had been found for all dimensions except 7. This problem was converted into a graph, which is a standard procedure for looking at honeycombs and lattices of polytopes, and reduced to 2^{30} cases. This was then solved by computer and the output "proof" was then checked by a proof checking algorithm. I would presume that in the sense that if all the parts in this chain of reasoning are operating right then we have some confidence in the whole. It is though taking us a bit beyond the standard college or grad level mathematics course where we learned to prove things.

      There is a sort of dialectic here. If I understand something in its entirety because it has some simplicity, even if abstract or elegant, that is more satisfying than multi-100 page proof of something or one that requires computing. This tendency to use numerics started with the proof of the 4-color problem by Hecke, and even manual proofs are turning into these enormous tomes. I read Perelman’s proof of the Poincaré conjecture, but it has loads of difficult lemmas that I either glossed over or skipped. I simply concentrated on the main idea and results. As a result, I defaulted to an assumption the details I skipped over are correct. This becomes even more the situation where we let a machine work a vast number of cases we cannot possibly work. From a physics perspective this is a bit similar to working in Feynman’s idea of “Babylonian math.”

      We humans have a sort of meta-scaffold in our social ordering. We require the activities of millions of other people to understand things, and far more to work the “conveyors and feeders” that keep us alive. There is a crisis of confidence in things, particularly in the United States. I mention the “conveyors and feeders” because there are in addition the preppers, who work to stock up to survive an impending collapse. I know somebody who dove into that reality, and it is a bit extreme with ideas of God, guns and guts. There are with many things these growing doubt gaps, where data from NASA, say images from Mars, are doubted as studio or photoshop fakes. Of course, the same people are using internet and smartphones with all the satellite feeds etc. Interestingly, these types of people are potentially the ones most likely to bring about this collapse some of them worry about. As our scientific understanding becomes more abstract and complex, fewer people are able to understand any subject in detail or have an overview of things on a broader scope. This leaves many outside the loop, and I think many have then latched onto easy to grasp ways of thinking. These may be religious, or they might involve tunnel vision into quirky things, such as flat-Earth, Sasquatch or big foot, UFOs or conspiracy ideas such as the lizard-men.

      Back in the 1930s a man and woman pair, Baxter and Whitaker, formed a political consulting firm. They operated by extending the Ed Bernays idea of public relations, where they formed messages that appealed not to argumentation or reason, but to emotional reaction and impression. This proved to be wildly successful and was a leading trend to the largely Republican domination of the state of California that was at the same time centrist to liberal based on demographics. This has taken the nation as a whole. This is to be contrasted to the Lincoln-Douglass debates in 1859-60 that were exercises in rhetorical treatises. This has unfortunately framed the American mind, and minds in much of the world. These types of media clever modes of presentation have come to dominate things.

    3. Cont: The flat-Earth idea has come at a time of perceived crisis in the world order. There is also the emergence of a new technology in communications, where in previous such revolutions there have also been social upheavals. This in part occurred with the election t’Rump, where this crisis was fueled by a lot of extremist ideas in the media, such as the conspiracy laden production of Alex Jones’s Infowars and prior to that birthers, teaparty conspriacies, climategate and so forth. These were promoted to impede developments deemed “unAmerican” by various right winged organizations that operated by the Baxter and Whitaker rules of influence. The problem is they let a genie out of the bottle, and now things have gone nonlinear. Now almost half of Americans think the Covid vaccine is a conspiracy to control us by chip implants and 2 to maybe 10% of American think the Earth just might be flat.

      Is this development of computer based communication really progress over the old method of books and print?

    4. If you look over the history of print you'll see that there was an awful lot of silliness printed. It took time for how the print media managed authority and trust.

      No doubt, social media will have to take on similar institutional roles. At present, they aren't interested as it has far more costs associated with it than profits. However, they do have a much larger playing field to survey. Whereas print media probably had hundreds of publishing firms to consider, and thousand of writers ... now we have millions of them, if not tens and hundreds of millions.

      Personally, I think the social media companies could have done a lot more earlier, but we gave them a free pass by simply allowing them to be taken at their own valuation as not publishing firms when that is the model that is most applicable to them and so at one stroke denying ourselves the most effective legal instrument in regulating them. In other words, we allowed them to be irresponsible. What respectable bookstore today would have given shelf-space to neo-nazis, child sex rings, holocaust denial, macabre real life violence? Yet we've allowed this to happen right under our noses on a vast industrial scale all under the rubric of so-called 'free speech'. This is patent rubbish. Zuckerberg is interested mainly in one thing, and that is to make as many squillions as he can whilst he can.

      Perhaps in line with how slowly people began to recognise that large firms dumping their rubbish wherever (I was surprised to learn the the UK had not one - until recently - river of swimmable quality due to dumping of raw sewage) was not free of costs, and in fact had a huge and increasing cleanup cost associated with polluting the environment. A recent IMF report put it at some huge number which they warned when it catches up with the global economy will make past recessions look like a storm in a teacup.

      We should also recognise that the social and public sphere can also be polluted by bad thinking, spite and stupidity and that this can happen both individually and in concert, that is in an organised manner; and also that this has very real, very tangible, and large costs associated with it which social media firms - being the main instigators of, and the main beneficiaries of, should be made to pay for.

  7. I don't know if this is real or not, but as the saying goes, if not true, then it is well told:

    1. You actually find this mentioned on the website of the flat earth society where they claim it's a mock screenshot.

  8. "The first concrete evidence for spherical surface to Earth was found by Eratosthenes. At the summer solstice a southern region along the Nile gave no shadow to a pole, while in Alexandria it did. Reasoning the angle of the shadow with the distance to this southern region provided not only evidence of sphericity, but a way to calculate the size of the Earth. This meant not only was the world round, but demonstrating such could be used to calculate something."

    Not really. You have to assume that the Sun is very far away. If the Earth were flat, and the Sun not so far away, then the angle at which sunlight strikes the Earth would also vary with position. The ancient Chinese had this conception.

    Observing the shadow of the Earth on the Moon during a solar eclipse provides good evidence that the Earth is round and, since the geometry is not always the same, a sphere fits the bill. This was known to the ancient Greeks.

    1. "Observing the shadow of the Earth on the Moon during a solar eclipse"

      Should be: Observing the shadow of the Earth on the Moon during a lunar eclipse

    2. Eratosthenes I think provided the first approach that gave a method of calculation.

  9. Excellent! They are canaries in our mine.

  10. A nice note, Sabine. I suggest that you watch Clark's 2018 documentary on flat earthers - Behind the Curve - if you haven't already. It's quite revealing, in particular, how a radical, and I think obtuse misreading of "freedom" leads individuals to believe that the achievements of the giants of the past, are as molehills in their sight. They should "trust their senses," not realizing, as you put, that so much is beyond what we can easily souse out for ourselves, by ourselves.

    I would also refer you to the "Dunning-Kruger effect," a cognitive bias in which people believe themselves smarter and more capable than they actually are. Unwarranted confidence permits easily such dismissive behaviors as seen in Behind the Curve. Humility in the fact of knowledge does not.

  11. Most prominent flat earth youtubers have this sensory decoding difficulty as the foundation of their belief.
    All of them appeal to their senses, and declare that only their senses should be trusted, unconditionally. The true rational thinker should question one own's senses to begin with, and they do not, refusing decodification as a principle of their dogma.

    Optical illusions are the quoted example and more than one time I have thought that, following a flat earther's approach, all magicians and illusionists should be beings with god like powers, should I believe my own senses.
    In the end, their approach is completely incoherent, refusing to interpret how their sensory inputs interact with reality, and at the same time accepting other statements with unquestioning loyalty (like the strictly literal interpretation of ancient religious texts, in most cases).

    Ironically, the "free thinking" flat earthers are among the best exaples of judging a book by its cover while boasting a self attributed, and non existing, open mindedness.

  12. Hi Sabine,
    Yesterday, I sent twice a comment (first time the Browser showed an error, the second was OK) but it doesn't appear on yours Blog.

    Please could you check it.

    1. This is the only comment I got from an account by name "RFI". There is nothing in the spam queue either.

    2. I would like to share with you and everybody that I just created my first Blog called "Reaction Force Inversion" (Check my Profile).

      No moderation will apply as also the Blog supports LaTeX along with plain text for the comments.

      The subject of the first post is named "Collinear vs Induced Internal Forces". Here may one discover for the first time there are induced forces in classical mechanics.

      Feel free to drop a comment!

      P.S. I changed the displayed Profile name from "John" to "RFI" (Blog's initials).

  13. Anyone who watches a sailing ship approach from sea can get immediate and direct evidence of the earth's curvature. First you see only the top of the mast, and gradually more of the mast, and finally the ship's hull.

  14. Dr. Hossenfelder,

    To paraphrase Pauli, flat-Earthism is not even unscientific. It is simply mad.

    I take the point that you are trying to make, and it is correct, though narrow and, in my view, irrelevant.

    In today's circumstances, in effect, what you are doing is making excuses for emotional illness; and that is the last thing that ought to be done.


    1. Narrow? I think it is the opposite of that and very relevant to a big scope of problems

      You made up your own explanation of those people and also made up a possible "bad consequence" of Prof. Sabine's post

      (and also made up an idea that there is a really better thing to be done by her)

    2. Interpreting Dr. Hossenfelder's remarks and drawing connections to related topics is my job. It's called "conversation".

      Flat-Earth-ism is a form of magical thinking. The purpose of magical thinking is to evade responsbility. To each scientific question that has been made here, the flat-Earther will respond, "It's magic!" Subtext: if it is magic, then no one can possibly understand it, therefore I am not under any obligation to try to understand it.

      This is why magical thinking is unacceptable. There are three things you can do with unacceptable behavior: it can be normalized, criminalized, or medicalized. I declare it a form of emotional illness and thereby I medicalize it.

      This, if any, is the "big scope", and it is why any discussion of any specific form of magical thinking, as opposed to the general problem, is narrow and without purpose. Attempting to engage with the "merits" of it is a mug's game. You cannot win the game, because your opponent is playing a different game and, more importantly, does not accept the legitimacy of any rules, including their own.

      You may or may not be aware of how emotional illness is treated in the U. S. Most of its victims are thrown onto the street, where they are not safe and where they very severely degrade the quality of everyone else's life. Most -- but a tiny, select handful are elevated to positions of power. One imagines (perhaps only fondly) that this is handled better in most other places in the world. Anyone who had not been here and seen it with their own eyes would not believe it.

      Another aspect of the infantility of American discourse is that only the tone of any discussion is absorbed, not its substance. From that standpoint, the tone of the original post would be interpreted as endorsing a "fair" attitude towards flat-Earthers. (Again, the word "fair" has a special meaning to Americans that is unknown even among other Anglophone communities. Here, it means "unaccountable".)

  15. "Watch a ship's mast as a ship sails away. The mast is last to be seen, which is impossible on a flat earth. An observation which is inline with their philosophy of only accepting data from personnal observations."

    I assume a flat-earther would retort that they have never seen a masted sailing ship sail over the horizon, nor have you, nor has anyone within the last hundred years.

  16. In the model having the sun circle over the flat earth, with directional light providing daytime only for spots under or nearly under the sun, there should never be a sunset or sunrise.

    In flat earth models in which the sun dips below the flat surface and travels underneath at night, the sunrise should occur at the same time for all. A simple phone call across several time zones should be enough to disprove that. Stronger evidence - in this model it should never be daylight in one place and nighttime in another. Have a flat-earther in Japan (assuming there is one) make a phone call to a fellow flat-earther in NY.

  17. Well if flat-earthers aren't stupid they are doing a great imitation of it.

    In addition to the points raised by previous commenters (masts or smoke stacks at sea, trees or tall buildings or telephone poles on a flat plain or seen from the sea, lunar eclipses, etc.), the vastness of the conspiracy that would be involved is not credible.

    You can find lots of statellite pictures of the Earth online, and zero photos showing the earth as a disk with an edge. Globes are sold in roughly every city in the world. You can use Google Earth to traverse the Earth in all directions and always arrive back at your starting point. School texts all over the world proclaim a roughly-spherical Earth and Newton's Law of Gravity. You can see satellites crossing the sky at night, launched by engineers who used Newton's law to calculate their orbits. The world is divided into different time zones, and you can gain or lose a day by crossing the International Dateline. Latitude and longitude are used to navigate.

    For the Earth to be flat, all this has to be part of a giant conspiracy, costing trillions of euros (or other currency) to maintain, and for what gain?

    Even if you restrict your attention to a small local area and refuse to believe the rest of the world exists, you should have access to newspapers, a library, school texts, and the Internet. Even on a local level the conspiracy would be consuming a lot of time, energy, and resources for no apparent purpose.

    As for the local evidence of the senses, as a philosopher once pointed out, everything we see is exactly what we would see if the Earth is a large sphere which rotates about an axis and orbits around the Sun.

    I vote for "stupid", with the caveat that no one is immune to being fooled on every matter all the time.

  18. I've occasionally participated in the flat earth topic on Quora. To me, the focus on scientific refutation is an unnecessary complication. I usually describe a counterexample that is much simpler (at least simpler given access to modern conveniences).

    Have a friend or co-worker fly to some place that "ball-earthers" say is on the "other side" of the ball-earth. Now open a video call with them. If it's light where you are, it will be dark where they are; if it's dark where they are, it will be light where you are.

    In times before Covid, my company flew members of my team (i.e. people I've known for a very long time and trust) from my location near Portland, Oregon to central India, which ball-earthers say is on the other side of the earth.

    We had multiple video calls. And guess what? When it was morning in Portland, it was evening in Bangalore!

    How do flat-earthers explain this?

    1. If the Earth really is ball shaped, wouldn't the people on the video call appear up-side down to each other? But they don't! Ah hah! Explain that!

      (Sad that it needs to be said, but I am joking.)

  19. I don't think this is a case of only trusting evidence you see for yourself, as it is so easy to disprove Flat Earth theories by simple naked-eye observations. For example, simply noting that the apparent diameter of the Sun never changes disproves this idea of the sun circling above a flat Earth, as does simply observing the sunset. After numerous fruitless debates on this topic, I've concluded that we are dealing with a bona fide cognitive deficit here: Flat Earthers appear to have almost no geometric intuition.

  20. Faith (on some basic and reasonable assumptions) is the ground for science... Without the act of faith on the real existence of the world outside you, there would no be any kind of knowledge nor science.

  21. One of my fond memories growing up in the American south is the Arkansas preacher who predicted doomsday. He told all his parishioners to sell all their worldly goods, come to the church on the appointed day, and pray for salvation. Somehow he collected all the cash and absconded to where ever. I grew up in Tennessee. We considered people from Arkansas just a bunch of rubes.

    The Flat Earth Society is a nice little hobby scam. Send $10.00 and become a member. It falls right in line with many bigger scams on the American gullible. Sometimes it seems like that's about 40% of the population over here. The Build the Wall scam which resulting in the recent arrest of one of its founders for absconding with over a million dollars is one of our big time scams.

    The denial of science and expertise is just another scam. In messed up times its understandable that emotion might overcome reason and people want quick and simple relief from their misery. There will always be someone somewhere willing to offer fake relief, false hope, and bogus salvation for a buck.

    Anyway, thanks Sabine for the excellent meditation on pseudoscience.

  22. I suspect that most flat earthers are of the zealot variety who would not alter their opinion regardless of the evidence presented. It reminds me of Moore's paradox: "It is raining outside but I do not believe it."

  23. It is about a rejection of "experts". Support for FE is a shorthand way to say "I reject the prognostications of my betters" for those who haven't the time or education to articulate what has gone wrong.

  24. If the earth was flat then the sun would rise and set at the same time for all obsevers.

    1. Did you read what I wrote? Did you watch the video? If not, why are you wasting our time with your comment?

  25. Thanks for the explanation of the flat earth theory. I thought this was merely a put down for anyone who disagreed. However I will wager that the vast majority who use the term "flat earther" as a pejorative, have now idea that there actually is some reasoning, even if incorrect, behind the position.

    As a general position, people, regardless of their level of education, accept a certain narrative as the Truth. Science, by its iconoclastic nature, must challenge the narrative. In so challenging, the narrative is either proven true or proven false. If proven false, it should change. This usually takes a generation, as "science advances one death at a time".

  26. Dear Sabine,
    Not a flatearther in any way but one question keeps bugging me.
    In every video, the space is always depicted as empty, a vacuum with almost nothing in between heavenly objects. Then again we have an atmosphere around our globe. And vacuum versus our atmosphere and there is no veil in between. Should the atmosphere not fade away into space? Entropy? If you say the gravity keeps it around the globe, still there should be some molecules leaking slowly.

    1. Don't know what you mean by "fade away". The atmosphere doesn't just stop at some point, it becomes gradually thinner. It doesn't fly off because gravity. Pls don't ask me how flat earthers want to deal with that.

      Btw, this is why small stellar objects have no or pretty much no atmosphere: They're just not large enough to keep it gravitationally bound. It's somewhat of a matter of definition though exactly what you mean by atmosphere. The moon, eg, is leaking some traces of gases, which creates a thin layer that's sometimes called an atmosphere.

    2. Molecules of air have a distribution in velocity, but high velocities are exponentially surpressed. The average velocity is about 400 m/s or about 1400 km/h. the escape velocity is about 40,000 km/h, so only a tiny fraction will have escape velocity. Also, tons of material per day are collected by the Earth, some of which we see as meteors.

    3. My bad about "fade away". I meant the gases in atmosphere in time should "fly away" until nothing is left behind. Every now and then a molecule should have enough energy to leak out into so-called empty space. Think of it as two gas chambers. One has a gas and a volume and the other one has nothing and infinite volume. Who wins that?

    4. Hi again,

      Oh, I see, sorry for the misunderstanding. I think atmospheric molecules can "fly away" but (as Phillip points out) in the case of Earth it's not a lot of them that manage to escape. Again, you can see this happening on smaller objects where the escape is more substantial (depending on temperature, solar wind, mass of the moon, etc). I'm not sure how long it would take for Earth to entirely lose its atmosphere. I would guess not before the sun runs out of fuel anyway.

    5. Thnx Philip, this makes sense now. I sleep well tonight.

  27. Usually I don't know enough on the topic to dare to contradict you, but in this case I have to: Flat-earthers are STUPID.

  28. Quote: The more difficult scientific experiments and arguments are to follow for non-experts, the more care we must take to explain how we lead those arguments.
    I am asking myself how much care scientist will take in order to explain to non-experts that astrobiology is a serious natural science and not a hope-driven philosophy?

    Why do scientists 'believe' that the laws of life, psychology and sociology are universal in their nature?
    Have you ever seen a funghi traveling through space and time on an asteriod?
    Have you ever seen a human being walking on Mars and doing farming there?

    Isn't Astrobiology a flat-earth society of its own who's supporters simply deny the fact that planet earth is very likely the only planet in the universe that contains life?

    1. I responded to this in the post by Benjamin below.

  29. It's utterly preposterous to state in your preamble "flat earthers are...[not] anti-scientific" and then spend a healthy portion of your article describing, using scientific principles, how they reject "science that was settled by the middle ages". Perhaps you're confused by the likely probability that a flat-earther will go to a doctor, thus allowing you to see them as believeing medical science. You should reconcile that conflict.

    1. While I do not give SETI great odds, it is by no means determined that we are the only intelligent life in the universe. I suspect that maybe the nearest ETI that is on our past light cone is 10s of millions of light years away on some other galaxy and to far away to ever detect. I suspect, I do not know.

  30. Dr. Hossenfelder,

    I find this post to be just outstanding for so many reasons. If I may add an observation of mine that goes with how I view the overall message of your post;

    The Higgs Field, the 21st Century Luminiferous Aether.

  31. My brother in law is a fundamental Christian. Like the rest of us he has some flaws but is basically a decent person. He rejects evolution and believes the Earth is only 5,000 years old. He rejects the science of evolution and geology because those things are less basic to who he is than his fundamental Christian beliefs. For him, accepting science requires rejecting the literal truth of the bible. So he chooses the bible over science.

    The same thing applies to flat earthers. The science doesn't carry enough weight to overcome whatever emotional or psychological need a flat earth theory fulfills. That's why appeals to scientific evidence don't work for them.

  32. It is not a luminiferous aether. The Higgs field does not couple to photons. It is a vacuum condensate, which has maybe aether-like qualities to it. Also the aether of the 19th century was erected as an ad-hoc assumption. Maxwell' theory has no need of this, even though JC Maxwell appealed to aether-gears and the like. However, even then the aether could have been stripped away with no loss of real physics. The Higgs field has far more substantial reasons for existing.

    1. I know it is not a luminiferous aether,just like we all know the earth is not flat, you missed my point. In fact, you have supported my point and the point of Dr. Hossenfelder's piece.

  33. "Instead, flat earthers’ argument is about whether you should trust evidence that other people have collected before you."
    "To me, therefore, flat earthers are a warning sign that scientists should take seriously."

    Yes, for a number of reasons. Nevermind the flat earthers. It doesn't take a fringer to doubt what we hear from "science". I use quotes because of course "science" does not collect evidence and make conclusions. Scientists do. There are a lot of them and inevitably some are a little nutty, some let their politics pollute their research, some are just incompetent. But the more sensational and outlandish claims often get the most minutes in the evening news. Scientists need to do a better job of policing their own. This means that journal editors need to actually read the papers they publish and be unafraid to reject papers that are obviously garbage; it means publicly rebuking scientists who allow their politics to blatantly skew their research; and it means acknowledging the limits of science, not pretending the question is settled when it really isn't. I'm older now, but my brain still works, and that means I'm old enough to remember that what passed for fact 40 years ago is often now considered just plain silly. Yet, we act like now, this time, we've got it right! No way we could be wrong. BS

    When so many peer reviewed papers are garbage (there's plenty of data on just how bad the situation is), science clearly is in a crisis. It could solve that problem with higher standards, greater rigor, and a big dose of humility. But the academic establishment has an awful lot to lo$e, so don't expect any of that soon.

    1. Yes, I agree with that. And of course a lot of people understand that just as fine, consciously or unconsciously. So how is it surprising that some fraction of them just call bullshit on everything? Yet scientists can't be bothered to get their act together.

  34. This was wonderfully well written. It’s an argument that I give people. “Don’t be so smug- there is a lot we should all learn from flat earthers”. You said it better than I have , though.


  35. A nice subject where the senses on the rotation of the earth are forcing the Flat Earthers to rely on the evidence of many, many other people are the tides. The flat earth universe has no gravity and should, therefore, have no tides.

    To get around the fact that the 12 hour cycle of the tides is linked to the revolving earth AND adapts to the position of the moon, the flat earthers go to all kinds of maps of tidal nodes and reports of old explorers that visited the North Pole.

    But if I cannot trust anything but my own senses, why should I trust some unconfirmed reports from old explorers and tidal node maps from scientists? Others do not buy that, and resort to Electro-Magnetic energy to explain the tides.

    Unsurprisingly, these explanations also are not verifiable using your own senses. Why trust some people on EM energy I cannot sense myself, and not others on gravity I cannot sense myself?

    On the other hand, visiting a nearby Foucault Pendulum shows you the rotation of the earth before your very eyes, in lockstep with the tides. There is one within travel distance to everyone (see Wikipoedia: Foucault pendulums).

    And a last easy to check (geometric) point. Just travel to two places on the equator, or call two Flat Earthers that live on distant parts of the equator. Ask them to measure the angle between the direction to the (magnetic) north pole and the line between East-West, or sun-rise and sun-set. On a flat earth, the sum of these two angles should be considerably less than 180 degrees. On a round earth, these two angles are both 90 degrees.

    But alas, the documentary Behind the Curve already showed what happens when Flat Earthers do experiments, the simply deny the results.

  36. Excellent article Sabine!

    I had put in my head that the whole Flat Earth movement suddenly appearing was a test run of a massive disinformation campaign, but it turns out that reality is often far better than fiction. Thank you for the history.

    Is there any chance that you'll activate community translations on the youtube video? I wanted to sub it in Portuguese, if that's ok.

    1. Hi Yuri,

      I have turned community contributions on for this video. I got a note the other day from YouTube that said that the feature will go away though, apparently there aren't enough people using it. It's a shame, if you ask me. I think the major reason there are few people using it is that few people know about it. In any case, the existing subtitles will remain, so please don't hesitate. Best,


    2. Sabine,

      Yeah, the latest victim the long Google tradition of sunsetting their useful-but-not-making-much-money features... I have added the subs, should be OK if they stick around after the deadline. I will try to add them for some other videos later too.

      Thanks for everything!

    3. Hi Yuri,

      Thanks, I have published those. Here is the Google announcement that they are discontinuing the community contributions.

  37. The simplest proof to flat earthers is takes only a telescope and a boat with a tall mast. As the boat goes over the horizon, the mast can still be seen. Hard to explain if the earth is flat 🤷

  38. To all the people who have commented that a boat going over the horizon proves that the earth is flat (and all similar comments): General Relativity is perfectly happy with a coordinate system in which the earth's surface is flat, except at one point. If we adopt such a coordinate system, the *metric connection* becomes such that light rays and all other lines we might draw become curved in just the right way in that coordinate system. Then we can happily transform back to a coordinate system in which the earth is a sphere and the metric connection is curved in just the right way to look like a pervasive force of gravity. That's what GR does: it keeps the accounting well-managed even under nonlinear coordinate transformations. That can mean that straight lines may be nonlinear, even extremely weirdly, so that it looks like the sailboat goes over an horizon, but again, that accounting is what the math of GR keeps straight.
    This brings up one aspect of the video that made me curious: do the different flat earth systems talk to each other (that is, is there an atlas of conversions between different flat earths?), or are the different flat earthers really at each others throats because one is right and the others are wrong?

    1. Hi Peter,

      Needless to say, flat earthers have an answer to the sinking ship observation, which is either that the ocean can bulge upwards or that it's an optical illusion or such. You see, there's an answer to everything. (Let us not ask what it takes for the ocean to bulge upwards in the required amount or what other evidence there is for the supposed optical effect.)

      It is correct of course that you can project the surface of a sphere onto a plane if you leave out one point, and that's how maps of the earth (or sky, for that matter work). Alas, this has absolutely nothing to do with observables, which are independent on the choice of coordinate system.

      I have not come across a set of equivalences between different falt earth models. For all I can tell they actually think of them as different. Then again, I may just have missed that. It's not like I aspire to become the world-expert on flat earth models ;)

  39. I've always thought the simplest way to deal with Flat Earthers is to ask them the question: "Well, what would it look like if the Earth was round?".

  40. Explain, using flat earth theory, why in the southern hemisphere (going towards south in case earth is flat) the moon is seen upside-down as opposed to when it's observed from the northern hemisphere :).

    1. "Explain, using flat earth theory, why in the southern hemisphere..."

      Even nicer point, why do people close to the rim (Australia, South Africa, Tierra del Fuego) see different constellations of stars than those North of the equator? But they do not see the Pole star which should be visible from everywhere on a flat earth.

      Also people in the North see the stars revolve around the Pole star, but people in the South see it revolve around a point in the Southern sky

      That is very easy to check, actually, you cannot miss it when you visit any of these places and look up at night.

      Conclusion, flat earthers do not travel far, or they never look up when they do travel. (As this apocryphal man who refused to look in Galileo's telescope)

    2. And the southern celestial pole is so well known that several southern hemisphere countries put the constellation that points to it, the Southern Cross, on their flags. Even if a flat earther has never crossed the equator themselves to see, they are effectively saying hundreds of millions of southern hemisphere inhabitants are in on a gigantic hoax.

  41. "going towards south in case earth is flat"

    South == Rimwards
    T. Pratchett

    1. "South == Rimwards"

      Nice to hear from a fellow software dev. :)

  42. You say " know that your government strives to give children in your country a scientifically accurate education." That might be true in Germany. Where I live, in the USA, it is certainly not true. In most if not all places in the USA the education of children is the responsibility of local government. So, there is a wider variety in the quality of primary and secondary education depending on the both the wealth and politics of the community.

  43. I like this article, because it is not about whether Earth is flat or round, but mainly about whether one should trust established science or not. It is about the conditions under which one should trust established knowledge. The problem is not new. It has been debated thoroughly by scientists and philosophers in the past. For people who are not afraid of reading (as opposed to watching short videos), I would suggest reading "The Ethics of Belief”, published in 1877 by Cambridge mathematician and philosopher William Kingdon Clifford. It addresses the problem with remarkable clarity. It can be found here:

  44. Sabine,

    You seem to have a kindred soul in astrophysics , when it comes to denouncing the occurrence of cognitive biases in physical science :




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