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How to debate a flat-Earther

In a new study, researchers found that, over 20 years, ozone increased in Earth's lower atmosphere over the Northern Hemisphere.
(Image: © NASA)

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space

A number of ancient cultures believed that the Earth was flat because, simply, they didn’t know any better. But today, there remain people who still believe that the Earth is flat, despite centuries of evidence proving the contrary. 

So, why do people believe this, and is it even worth getting into a debate over? 

Surprisingly, while there are mountains of proof, the discussion around the idea of a "flat Earth" has nothing at all to do with evidence at all.

Related: How Big Is Earth?

Looking around

To put it bluntly, we know more about the curvature of the Earth than almost any other topic in the realm of physical science. There are so many experiments, observations and demonstrations that have, time and time again, revealed the curve of the Earth.

And it all starts with the horizon.

As objects recede from you, they begin to look smaller and slowly disappear in a very unique way: first their bottoms become hidden, and then their tops. If you’ve ever watched a ship on the horizon, you’ve seen this for yourself. Similarly, from a great distance the tops of tall objects, like mountains, are visible well before their bases.

Earth's atmosphere is capable of playing funny tricks on our eyes, with different layers of air bending light into interesting directions. This phenomenon, a side effect of Earth's curvature, isn't a sure-fire guarantee of our planet's curve, but it’s a start.

But, even if you can’t look to the horizon for evidence, you can look up.

Different stars are visible from different parts of the Earth, in two very peculiar ways. First, there is the division between the northern and southern hemispheres. So, you can see Polaris, the star nearly directly above the north geographic pole of the Earth quite easily in northern latitudes. 

But, as you travel south, approaching the equator, Polaris sinks lower and lower toward the horizon. Once you’ve crossed that boundary, you can’t see it at all — it’s blocked by the curve of the Earth in that direction.

Similarly, as you travel south, new constellations await your delighted gaze; ones that would be completely obscured by Earth's curve if you stayed up north.

There’s another trick you can play, too. If you live in an especially flat area, you’ll be able to see stars down to the horizon, but no further (because the Earth is in your way). But if you travel up, say to the top of a mountain, you get a better vantage point and can see stars further down than when you could before. 

In fact, the ninth century Abbasid Caliph al-Ma-mun sent an expedition to do exactly that, and used those observations to measure the circumference of the Earth.

Relative: Earth's Atmosphere: Composition, Climate & Weather

Circles everywhere

You might not be able to mount such a scientific investigation to your nearest mountain peak. But there is something you can do to witness the curvature of the Earth in the comfort of your own backyard, You just have to be lucky.

During a lunar eclipse, the Earth passes between the sun and the moon, allowing the Earth to cast its shadow on the moon. That shadow is always, always always a circle, no matter where you are on the planet, no matter the timing of the eclipse. Always..

The only way to always cast a circular shadow is if the thing casting the shadow — in this case, the Earth — is a globe. It’s just a matter of geometry.

And that’s not to mention the countless photographs taken of Earth by orbiting satellites and eyewitness testimonies from astronauts hailing from dozens of different countries, space programs and private organizations.

Our curved Earth also aligns perfectly with all of physics.. Additionally, all of the other planets ever discovered also appear round, because that’s how gravity likes things. 

If you use gravity to, say, trust your GPS to give you accurate positions and calculate trajectories, then that same force will form material the size of the Earth into a ball.

Related: What Is the Temperature on Earth?

Arguing from evidence

However, I don’t think this discussion is really about the actual evidence or the scientific process. 

People who believe that the Earth is flat aren’t coming to that conclusion from the same types of observations. They, instead, believe that we are being misled and lied to, that scientists (including me) want you to believe that the Earth is round, despite its flatness.

So the question isn’t "why do people believe in a flat Earth" but rather "why do people believe in a conspiracy?" And the answer is the same reason it always is: a lack of trust.

Many people don’t trust the society around them, most notably the representatives of that society. That trust often falls even further when it comes to elite representatives of that society, which includes government officials, members of academia and scientists like me.

By claiming that the Earth is flat, people are really expressing a deep distrust of scientists and science itself.

So, if you find yourself talking to a flat Earther, skip the evidence and arguments, and ask yourself how you can build trust.

Learn more by listening to the episode "How do we know the Earth is curved?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Asher F. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

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  • rod
    My observation. This space.com report discusses briefly *evidence* based observations supporting the spherical Earth. However, what about reports like this using QM? https://forums.space.com/threads/new-quantum-paradox-throws-the-foundations-of-observed-reality-into-question.33556/#post-524588
    It would seem that *objective reality* cannot be determined then, thus flat earth folks can have a seat at the place of science too :)---Rod
    Reply
  • LijeBaley
    Probably the best way to debate a flat-Earther would be to send one up to the ISS and let them tell you what they see with their own eyes.
    Reply
  • rod
    LijeBaley, consider the space.com report on QM universe I cited in post #2 where apparently there is no objective reality. Your proposed evidence for the flat earther to see, assumes that there exist in nature an objective reality that can be clearly defined. Yet space.com report undermines such a concept in science. Applying QM universe rules to the ISS and view from the ISS, that suggest the ISS may not be real and what is seen below may not be real too. A flat earther could simply cite this now and ask that the flat earth be taught in sciences classes now in public schools as an example. Also the Sun could be moving above the flat disk earth too, a form of geocentric astronomy that can be valid because there is no objective reality now in science, apparently.
    Reply
  • LijeBaley
    Oh please, enough with the quantum voodoo. I read the same article and it’s just another possible theory put forth by theoretical physicists, no different than the theory that the universe is a digital simulation. Creative thinking at best. I’ll stick with the “I think therefore I am” version of reality that says the Earth is a sphere.
    Reply
  • rod
    LijeBaley, I point out the *quantum voodoo* as a philosophy of interpreting nature, seems to appear more and more in QM reports. If I apply this approach to the macro universe, the cat is dead or alive also leads to the earth is flat and round too. Your version of reality is yours, flat earth folks will have another version of reality and no one can define a standard of verification that works for all to accept it seems. In my opinion, the scientific method breaks down and replaced with a different definition of reality, based upon different views and needs. I see this as the direction that science is taking today - my opinion. I do not agree with this but it looks like that to me---Rod
    Reply
  • Helio
    QM describes the sub-micro world. Extrapolating by factors of billions doesn't work, else GR would look a lot different, and so would we.

    The Flat Earth belief seems to me another case of solipsism. Perhaps it's that our tendency to believe what we want to believe and, in this case believing in excess, that appearances are deemed satisfactory, whereby objective evidence becomes dismissed.

    Apparently, those that hold the flat earth view aren't all conspiracy advocates. That's a little surprising.
    Reply
  • rod
    Helio, in your post #7, I know some flat earth folks. Conspiracy can play a role but for many, flat earth is empirical too. I have studied flat earth videos on measuring the distance to the Moon using telescopes, angles obtained, and plane trigonometry vs. spherical trigonometry. FE folks are correct like the Flat Earth Society. The Moon will always be much closer to the flat disk earth using plane trigonometry. At most the Moon is about 3400 miles away and about 0.5 degrees angular size, so much smaller in size too.

    However, I stand by what I said about QM philosophy interpretation of nature. Applying to the macro universe leads to no objective reality and the space.com report does suggest this to me.
    Reply
  • COLGeek
    Never let science, or facts, get in the way of a good argument. :rolleyes:

    Some folks' opinions will never be swayed, regardless of the facts before them. Many in the FE camp are of this ilk.
    Reply
  • Helio
    rod said:
    Helio, in your post #7, I know some flat earth folks. Conspiracy can play a role but for many, flat earth is empirical too. I have studied flat earth videos on measuring the distance to the Moon using telescopes, angles obtained, and plane trigonometry vs. spherical trigonometry. FE folks are correct like the Flat Earth Society. The Moon will always be much closer to the flat disk earth using plane trigonometry. At most the Moon is about 3400 miles away and about 0.5 degrees angular size, so much smaller in size too.
    I don't know the trig approach they use, nor care to spend time on it, but the parallax would be 75x greater for a 3400 mile distance than actual. Two telescopes relatively close together could see this. Only one falsification is needed to debunk their model, but hundreds exist. Finding one element to be correct and hundreds false is not a scientific model, even if one element is found.

    It won't shock me if most flat earthers are nice folks. But when worldviews allow the scrutiny of science due to an overlap with it, then it is subject to the test of science.

    However, I stand by what I said about QM philosophy interpretation of nature. Applying to the macro universe leads to no objective reality and the space.com report does suggest this to me.
    If you remove the teeth from a dog then it won't bite. Redefining objectivity changes things. Objectivity is simply repeating tests by many others and agreeing on the results. And it helps to remember that not agreeing on results for clearly understood reasons, is what scientists look forward to, unlike many philosophies and religions.
    Reply
  • Russ Kincade
    LijeBaley said:
    Probably the best way to debate a flat-Earther would be to send one up to the ISS and let them tell you what they see with their own eyes.
    I like the idea of letting them build their own rockets instead like Mike Hughes did:

    https://www.bbc.com/news/world-us-canada-51602655
    The people who are incapable of critical thinking (like anti-vaxers and supporters of lying politicians) and believe what they want to believe are a danger to society.
    Reply