The Earth is a sphere. This is a simple fact that humans have known for thousands of years; it was incontrovertibly confirmed as soon as the Soviet Union launched the Sputnik 1 satellite in 1957 and it went … you know ... around the globe.
Nevertheless, a small but vocal group of people who insist that the world is flat — so-called flat-Earthers — have emerged online in recent years, and they seem to be sowing doubt about this most basic aspect of reality. Many flat-Earthers put a great deal of effort into concocting alternative explanations for why the world behaves as if it's round when it's actually flat — even though a spherical Earth clearly fits the observations humans have made about the planet over the last few millennia.
However, if Earth, somehow, were truly flat, it would not behave much like the planet we know today. In fact, humanity (and everything else) would be very, very dangerous.
To shape a cosmic body into a disk (rather than a sphere), you've got to spin it very fast, says David Stevenson, a planetary scientist at Caltech in Pasadena, California. This would, unfortunately, destroy the planet by tearing it into tiny particles. In the 1850s, astronomer James Clerk Maxwell showed mathematically that a solid, disk-like shape isn't a stable configuration in the cosmos, in work he conducted regarding Saturn's rings. Maxwell's research predicted that Saturn's rings would be made of lots of small, unconnected particles; he turned out to be right. His math also explains why there are no planet-size disks floating around the galaxy.
To flatten Earth without spinning it very rapidly, you'd need magic, or perhaps a galactic panini press. At any rate, a stamped-flat Earth wouldn't last for long. Within a few hours, the force of gravity would press the planet back into a spheroid. Gravity pulls equally from all sides, which explains why planets are spheres (or nearly so – depending on the speed of a planet's rotation, those forces may work against gravity to create a bit of a bulge at the equator). A stable, solid disk-like Earth just isn’t possible under the actual conditions of gravity, as Maxwell’s math showed.
And once you get rid of gravity, everything about our planet rapidly stops making sense.
The atmosphere? Gone, because it's held to the planet by gravity. Tides? Gone. They're caused by the gravitational pull of the moon, which tugs on the oceans and causes them to subtly bulge out as it swings bAlso gone, since every explanation of the moon's existence involves gravity. In the most widely accepted scenario, the moon was created when a giant, planet-size body crashed into the early Earth; debris from the crash was captured by Earth's gravity. Another scenario suggests that the moon formed at the same time as Earth did (again, thanks to gravity). Or, Earth's formidable gravity attracted and snagged the traveling hunk of space rock as it went hurtling by.
