Carl Sagan Explains How the Ancient Greeks, Using Reason and Math, Figured Out the Earth Isn’t Flat, Over 2,000 Years Ago

The denial of science has entered the highest levels of government, and no matter what the data says, the U.S. promises to cease all efforts to curtail, or even study, climate change. Astrophysicist Katie Mack calls this retrenchment a form of "data nihilism," writing in an exasperated tweet, "What is science? How can a thing be known? Is anything even real???" Indeed, what can we expect next from what Isaac Asimov called the United States’ anti-intellectual “cult of ignorance”? A flat earth lobby?

Welp… at least a couple celebrity figures have come out as a flat-earthers, perhaps the vanguard of an anti-round earth movement. First Cleveland Cavaliers guard Kyrie Irving made the claim on a podcast, insisting, Chris Matyszczyk writes, that “we were being lied to about such basic things by the global elites.”  Then, no less a basketball worthy than Shaquille O’Neal weighed in with his own belief in flat-earthism.




Is this a joke? I hope so. Neil DeGrasse Tyson—who hosted the recent Cosmos remake to try and dispel such scientific ignorance—replied all the same, noting that Irving should “stay away from jobs that require… understanding of the natural world.” The weird affair has played out like a sideshow next to the mainstage political circus, an unsettling reminder of Carl Sagan’s prediction in his last book, The Demon Haunted World, that Americans would soon find their “critical faculties in decline, unable to distinguish between what feels good and what’s true.”

Sagan devoted much of his life to countering anti-science trends with warmth and enthusiasm, parking himself “repeatedly, arguably compulsively, in front of TV cameras,” writes Joel Achenbach at Smithsonian. We most remember him for his original 1980 Cosmos miniseries, his most public role as a “gatekeeper of scientific credibility," as Achenbach calls him. I think Sagan may have chafed at the description. He wanted to open the gates and let the public in to scientific inquiry. He charitably listened to unscientific theories, and patiently took the time to explain their flaws.

In the very first episode of Cosmos, Sagan addressed the flat-earthers, indirectly, by explaining how Eratosthenes, a Libyan-Greek scholar and chief librarian at the Library of Alexandria, discovered over 2000 years ago that the earth is a sphere. Given the geographer, mathematician, poet, historian, and astronomer's incredible list of accomplishments—a system of latitude and longitude, a map of the world, a system for finding prime numbers—this may not even rank as his highest achievement.

In the Cosmos clip above, Sagan explains Eratosthenes' scientific method: he made observations of how shadows change length given the position of the sun in the sky. Estimating the distance between the cities of Syene and Alexandria, he was then able to mathematically calculate the circumference of the earth, as Cynthia Stokes Brown explains at Khan Academy. Although “several sources of error crept into Eratosthenes' calculations and our interpretation of them,” he nonetheless succeeded almost perfectly. His estimation: 250,000 stadia, or 25,000 miles. The actual circumference: 24,860 miles (40.008 kilometers).

No, of course the Earth isn’t flat. But Sagan’s lesson on how one scientist from antiquity came to know that isn’t an exercise in debunking. It’s a journey into the movement of the solar system, into ancient scientific history, and most importantly, perhaps, into the scientific method, which does not rely on hearsay from “global elites” or shadowy figures, but on the tools of observation, inference, reasoning, and math. Professional scientists are not without their biases and conflicts of interest, but the most fundamental intellectual tools they use are available to everyone on Earth.

via 9Gag

Related Content:

Carl Sagan Predicts the Decline of America: Unable to Know “What’s True,” We Will Slide, “Without Noticing, Back into Superstition & Darkness” (1995)

Hear Carl Sagan Artfully Refute a Creationist on a Talk Radio Show: “The Darwinian Concept of Evolution is Profoundly Verified”

Carl Sagan Presents His “Baloney Detection Kit”: 8 Tools for Skeptical Thinking

Josh Jones is a writer and musician based in Durham, NC. Follow him at @jdmagness


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  • Mike Lowery says:

    Just to give you an update on the flat earth thing; Shack has already admitted it was a joke and people should not be so gullible.

    Kyrie Irving is doing this for several reasons;
    1. To make fun of this caricature of people that don’t put a lot of belief into science.
    2. To make fun of people who are so gullible and make such a big deal on social media about this stuff.
    3. To show how something as insignificant, as someone’s opinion, can be so newsworthy.
    4. To get his name out there; any publicity is good publicity, right? Seriously, most people had never heard of him before this. Plus, his shoe is now the top selling in the Nike line! lol

    So I guess he did a great job of getting what he wanted because you can pretty much check each one of these off of the list.

  • Gwil says:

    The far sighted Carl Sagan. I watched him week in and week out on TV. His series was wonderful. Sadly there are billions in the world who still live in darkness.

  • E. Derksen says:

    Walker Percy has a very insightful comment about Carl Sagan’s approach to “science”, one worthy of consideration:
    What is to be deplored is not Sagan’s sophomoric scientism — which I think better than its counterpart, a sophomoric theism which attributes the wonders of the Cosmos to a God who created it like a child with a cookie cutter — no, what is deplorable is that these serious issues involving God and the nature of man should be co-opted by the present disputants, a popularizer like Sagan and fundamentalists who believe God created the world six-thousand years ago. It’s enough to give both science and Christianity a bad name.

  • Josh Jones says:

    @Mike: Figured as much. Some smooth trolling, and a great excuse to talk about ancient Greek science.

  • mike hire says:

    As a true skeptic I must ask if the character Eratosthenes ( supposed geographer, mathematician, poet, historian, and astronomer -really ? ) isn’t the figment of “scientistic believers” wishful thinking- indeed, purely made up like the ‘flying saints’ and miracle workers of religious believers.

  • mike hire says:

    And do we really know if Mike is telling the truth about Shaq – he gave no source ?

    lately I’ve been wondering about all the false ‘facts’ everywhere from the past-in books and newspapers full of BS – made up just to sell papers ….. not unlike today’s TV

    yep, I can make up words like they make up facts ….

    The Truth is hard to find ….

  • Dario says:

    @mike Hire: consider that the term “scientist” did not mean the same thing in ancient times as today. As shown in Sagan video, Heratostenes simply had a genial idea and the will to prove it. No training, no instruments nor theories were needed: just basic math and genius.
    Aristotle was a biologist, psychologist, sociologist, theater critic, logician, grammarian.
    Plato poet, mathematician, politician, psychologist, literary critic.
    Actually even in more recent times Descartes, Leibniz, Vico were all polymaths.
    This is just to say that ordinary (scientific) skepticism shouldn’t go as far as to deny the data and the world, otherwise it plays against and not for reason.
    Radical skepticism (solipsism, transcendental phenomenology, Cartesian doubt) would not question empirical and mundane matters as the existence of Heratostenes, because it would deny the relevance of such questions themselves: Heratostenes, be one or many, would be an illusion anyway.

  • Jose A Amoros says:

    The early Greek philosophers–the atomists–had great faith in the existence of the atom, without seeing them and without empirical evidence too.

  • Jose A Amoros says:

    Ironically that this article starts by asking philosophical questions and then goes into quoting Neil DeGrasse Tyson, who has disparaged philosophy, while trying to understand the “natural” world.

  • Ifianassa Karabatsou says:

    Eratosthenes, a Libyan-Greek ????how did you end up in this ??there was no Libya that time mister !! all around Mediteranen sea were ancient Greek colonies ,and the knowledge was written in GREEK ,,THANKS TO MY ANCESTORS .DR IFIANASSA KARA

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