For most people, being described as a "flat Earther" is an insult. The idea of the Earth being flat is considered not only wrong, but a model of wrongness, the gold standard of being incorrect about something.
This being so, oddly enough, most people described pejoratively as "flat Earthers" do not actually believe that the Earth is flat. "Flat Earther" is simply a scientifically seasoned variation of "idiot".
For a recent example, US President Barack Obama recently expressed impatience with the persistent objections put forward by climate change deniers by saying: "We don't have time for a meeting of the Flat Earth Society."
In a subsequent move that one can read as either very fortunate or very unfortunate, the real Flat Earth Society issued a statement in support the hypothesis of anthropogenic climate change.
What do we do, then, when someone actually does believe that the Earth is flat, as the American rapper B.o.B expressed recently? The usual path seems to be blocked; it's difficult to insult someone with a term that they themselves happily adopt.
Edge of the world
But what exactly is a "flat Earth theory"? In fact, there never has been anything called "the flat Earth theory". Different cultures at different times have posited a staggeringly diverse array worldviews which cannot easily be summed up with the phrase "flat Earth." Nor is the idea of a flat Earth something that is exclusive to the Western world.
Even the most cursory historical survey shows that the idea that the Earth is flat has been a notion shared by an extraordinarily wide range of cultures and tied to vastly different metaphysical systems and cosmologies.
It was a common belief in ancient Greece, as well as in India, China and in a wide range of indigenous or "pre-state" cultures. Both the poets Homer and Hesiod described a flat Earth. This was maintained by Thales, considered by many one of the first philosophers, Lucretius, an avowed materialist, as well as Democritus, the founder of atomic theory.
The ancient Greek conception, in turn, has some parallels with that of early Egyptian and Mesopotamian thought, with both thinking that the Earth was a large disc surrounded by a gigantic body of water. The ancient Chinese were also virtually unanimous in their view of the Earth's flatness, although – in this system – the heavens were spherical and the Earth was square.
A number of ancient Indian conceptions, common – with some degree of variation – to ancient Hinduism, Jainism and Buddhism, tie their cosmography to botanical images, with the earth being comprised of four continents surrounding a mountain, akin to the way petals encircle the bud of a flower. Ancient Norse thought postulated a circular flat Earth surrounded by a sea inhabited by a giant serpent.
Others, like the Mountain Arapesh people of Papua New Guinea, envisage a world which ends at the horizon, the place where giant clouds gather. But even where commonalities exist across these traditions, vastly different metaphysical and cosmological narratives are at stake.
And, to complicate matters, to these we must add cultures and intellectual traditions for whom the shape of Earth is of no interest whatsoever. Many tribal or pre-state societies, for instance, have little concern for what might be considered cosmography.
Turtles all the way down
However, from at least the 6th century BCE, the theory of the flat Earth began to fall out of favour. By the time we get to Aristotle in the 4th century BCE, the idea of a spherical Earth is commonplace, at least among the educated classes. And by the 1st Century BCE it is considered an uncontroversial truth. Having said that, the theory of a flat Earth has continued as a minor tradition in thought, like a handful of theories in science, such as Lamarckianism and vitalism.
Despite the historical tide having long turned, the mid 20th century saw the establishment of the Flat Earth Society, started in 1956 by Samuel Shenton, whose work was continued by the retired aircraft mechanic, Charles K. Johnson, in 1972.
From California (where else?), Johnson functioned as president for The International Flat Earth Society. As its spokesman, he made a series of claims that have now become widespread outside the flat Earth community: the Apollo moon landings were faked, and that the correct view of the world is the traditional Christian one of the earth being flat.
Johnson, interestingly enough, didn't get only his cosmology wrong, he got his history and theology wrong as well. Orthodox Christian thinkers, at least since 5th century on, have supported the idea of a spherical Earth, from Bede through to Thomas Aquinas.
Indeed, as the University of California historian Jeffrey Burton Russell has argued, very few educated people in the West after the 3rd century BCE thought that the world was flat. This goes directly against the common belief that most people in medieval times believed the Earth was flat.
How unenlightened they were
But, if the flat Earth serves as a kind if myth or fantasy for those who believe in it, there are also myths about the flat Earth that are just as widespread.
One of the most widely propagated myths in the contemporary world is the belief that Columbus was advised by the Catholic Church to abandon his journey on the basis that he risked falling off the edge of the world.
It's source is the 19th century writer, Washington Irving, author of other rigorous historical accounts such as The Legend of Sleepy Hollow and Rip Van Winkle.
What this suggests is that we are sometimes overly keen to enlist the past – or our version of the past – in our attempts to feel better about how enlightened we are and how benighted were our predecessors.
That, of course, does not mean that nobody believed the Earth was flat in the middle ages; nor does it entail that nobody believes it today. Mohammed Yusuf, the founder of Boko Haram, famously claimed to not believe in a whole series of modern ideas which he though were contrary to Islam – including the spherical shape of the Earth.
If there is anything truly astounding about BoB's improbable cosmographical musings, it's that the battle between him and Neil deGrasse Tyson is, at this stage at least, being carried out only through the medium of rap. That could be a historical first for cosmography.
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