Carl Sagan Describes How The Ancient Greeks, Using Reason & Mathematics, Discovered That the Earth Wasn’t Flat 2,000 Years Ago
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Carl Sagan Describes How The Ancient Greeks, Using Reason & Mathematics, Discovered That the Earth Wasn’t Flat 2,000 Years Ago

Science denial pervades American society, and no matter what the data says, some conservative forces reject attempts to limit, or even study, climate change. Astrophysicist Katie Mack calls this thriftiness a form of “data nihilism,” she writes irritated tweets, “What is science? How can something be known? Is anything real???” Indeed, what can we expect next from what Isaac Asimov calls the United States’ anti-intellectual “cult of ignorance”? Flat earth lobby?

Welp… at least there are some celebrities who appear as flat earthers, maybe the pioneers of the anti round earth movement. Especially, [Dallas Mavericks] guard Kyrie Irving made the claim on the podcast, insisting, Chris Matyszczyk writes, that “we’re being lied to about basic things like that by global elites.” Is it a joke? I hope so. Neil DeGrasse Tyson—who hosted the show recently Cosmos remake to try and dispel such scientific ignorance—answering all the same, noting that Irving should “stay away from work requiring…an understanding of nature.” The strange affair has played out like a sideshow alongside the main stage political circus, a disturbing reminder of Carl Sagan’s prediction in his last book, The World Haunted by Satanthat Americans would soon find their “critical faculties declining, unable to tell the difference between what feels good and what is right”.

Sagan devoted much of his life to fighting anti-science trends with warmth and enthusiasm, parking himself “repeatedly, you could say compulsively, in front of TV cameras,” wrote Joel Achenbach in Smithsonian. We remember it best for its 1980 original Cosmos miniseries, his most public role as “the gatekeeper of scientific credibility,” as Achenbach called it. I think Sagan might be offended by the description. He wanted to open the gate and let the public conduct scientific investigations. He generously listens to unscientific theories, and patiently takes the time to explain his shortcomings.

In the first episode of Cosmos, Sagan addressed flat earthers, indirectly, by explaining how Eratosthenes (276-194 BC), a Libyan-Greek scholar and chief librarian at the Library of Alexandria, discovered more than 2000 years ago that the earth was round. Given the impressive list of accomplishments of geographers, mathematicians, poets, historians, and astronomers—systems of latitude and longitude, maps of the world, systems for finding prime numbers—this may not even be his crowning achievement.

In Cosmos In the clip above, Sagan explains Eratosthenes’ scientific method: he made observations of how the length of a shadow changed given the sun’s position in the sky. Estimating the distance between the cities of Syene and Alexandria, she was then able to calculate the circumference of the earth mathematically, as Cynthia Stokes Brown explains at Khan Academy. Although “several sources of error have crept into Eratosthenes’ calculations and our interpretation of them,” he still succeeded almost flawlessly. The estimate: 250,000 stadia, or 25,000 miles. Actual circumference: 24,860 miles (40,008 kilometers).

No, of course the Earth is not flat. But Sagan’s lesson about how a scientist from ancient times knew that was no exercise in disproving. It is an excursion into the movement of the solar system, into ancient scientific history, and most importantly, perhaps, into the scientific method, which relies not on the hearsay of the “global elite” or shadowy figures, but on the tools of observation, inference, reasoning, and math. Professional scientists are not without bias and conflicts of interest, but the most basic intellectual tools they use are available to everyone on Earth.

Note: A previous version of this post appeared on our site in 2017. This version has been slightly edited and updated.

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

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