Why People Believe the Earth Is Flat

Ask most people when humanity believed the Earth was flat and they will say the Middle Ages. That answer is itself a myth. Educated people have known the Earth is a sphere since ancient Greece, and organised flat Earth belief is a nineteenth-century invention that found a second life on YouTube.

So the interesting question is not whether the Earth is round. It is why a small but persistent number of people today are sure it is not, and what evidence anyone can use to check for themselves.

Older than the Middle Ages: the round Earth

The earliest written mentions of a spherical Earth come from Greek philosophers around the fifth century BC. By the third century BC, Hellenistic astronomers had established the planet's roughly spherical shape and calculated its circumference; Eratosthenes made his famous estimate around 240 BC. The voyage of Magellan and Elcano, between 1519 and 1522, demonstrated the shape in practice by sailing all the way round.

Later measurements refined the picture rather than overturning it. Isaac Newton described the Earth as slightly flattened at the poles in the seventeenth century, and the modern World Geodetic System, in use since the 1960s, puts that flattening at close to 1 part in 298.

The myth about the myth

Historians are clear that educated Europeans in the Middle Ages did not think the Earth was flat. Most European and Middle Eastern scholars accepted a spherical Earth in the Early Middle Ages, and belief in a flat Earth among educated Europeans was almost non-existent from the late Middle Ages on. The historians David Lindberg and Ronald Numbers wrote that scarcely a Christian scholar of the period failed to acknowledge the sphericity of the Earth.

The idea that they did came largely from the nineteenth century. Washington Irving's romanticised 1828 biography of Christopher Columbus invented a scene in which scholars raised biblical objections to a round Earth. Writers such as John William Draper and Andrew Dickson White then used the story to argue that religion had always fought science. In reality, the dispute over Columbus's voyage was about the size of the Earth, not its shape, and Columbus was the one who got it wrong: he underestimated the circumference by about a quarter.

Where modern flat Earth belief began

The modern movement started with Samuel Rowbotham, who in 1849 published Zetetic Astronomy under the pen name Parallax. It rested on his Bedford Level experiment of 1838, in which he claimed to see a distant object along a straight stretch of canal that should have been hidden by the curve of the Earth. In 1870 the naturalist Alfred Russel Wallace repeated the experiment, allowed for the bending of light near the water's surface, and found the curvature the globe predicts.

In 1956 Samuel Shenton founded the International Flat Earth Research Society, better known as the Flat Earth Society. Under his successor Charles K. Johnson it reported about 3,500 members, but a house fire in 1997 destroyed its records and the society faded until it was relaunched in the 2000s.

The YouTube revival

Belief has grown again since about 2015, carried mostly by social media and YouTube videos. A flat Earth conference in North Carolina in November 2017 drew more than 500 paying attendees. Polls vary: a 2018 YouGov poll found about 4 percent of Americans believed in a flat Earth, a 2019 YouGov survey found about 3 percent of Britons, and a 2020 Datafolha poll found 7 percent of Brazilians.

When believers test it themselves

The 2018 documentary Behind the Curve followed believers who set out to prove their case. One group used a ring laser gyroscope, which detected the rotation of the Earth; they put the result down to interference. A test with lasers over water showed the surface curving by several feet; they called it inconclusive. The experiments worked, and the beliefs survived them.

Why the belief holds

Researchers who have studied the movement point to several things at once. Some come from how we reason: overconfidence about what our own eyes tell us, misreading simple observations, confirmation bias and the habit of seeing conspiracies. Others are about trust, with deep distrust of governments, scientists and space agencies, and in some cases religious motivation.

Belonging may matter most. Believers can lose friends and family outside the community and find companionship inside it, which makes changing one's mind socially expensive. That is a pattern well beyond flat Earth, and it explains why evidence alone rarely settles these arguments.

Evidence you can check yourself

You do not need a space agency to test the shape of the Earth. During a lunar eclipse, the Earth's shadow on the Moon is always round. The stars visible at night change as you travel north or south. And distant objects disappear from the bottom up: one series of photographs in the Strait of Magellan showed a tanker 186 metres long rising over the horizon, its lower part hidden by about 23 metres of curvature at a distance of about 18 kilometres.

For a general method that works on this claim and many others, see our guide to evaluating a claim, and for why broad scientific agreement deserves weight without being treated as infallible, read what scientific consensus means.