What do you mean: “If …”? Chriskiy
Terry Pratchett would have been the winner of a Nobel prize for physics. Alan Williams-Key, Sudbury
In the entire history of Guardian comments, can the invitation in this little box here to “Join the disc-ussion” ever have been so delightfully apt? ThereisnoOwl
We’d have a load of conspiracy theorists trying to convince people of a globular Earth. lexicon_mistress
Fairly sure the rotational forces needed to shape/flatten matter into a disk rather than an ovoid are so extreme that they inevitably tear the disk apart before it can stabilise completely. So … the Earth wouldn’t be here if it were flat. Thomas1178
There wouldn’t be much left on a flat Earth after the cats had flicked everything off it. Bokalok
If the Earth was flat, mountaineering would be a lot safer. Jerry144
There could be no plate tectonics, therefore no mountain ranges. All land would eventually be eroded and you would be left with a shallow sea covering the entire disc. RogerMusson
The most obvious differences would be:
Gravity would work very differently. Assuming uniform density, it wouldn’t merely pull “downwards”, it would pull much more strongly towards the centre of the flat structure. If you tried to travel towards the edge, you’d be pulled back the middle again. (Unless, of course, the flat disc is rotating at such a speed that centripetal acceleration cancels out the effect.)
There would be no time zones, as the sun would rise and set at the same time across the entire face of the world.
There would be no difference in climate between the “poles” and the “equator”.
Coriolis forces would work differently, so weather systems in the “southern” “hemisphere” wouldn’t rotate in the opposite direction.
There would be no horizon as such; if you could get high enough to see over any intervening hills (or waves), you could see clear to the edge of the world.
It’s unlikely that the Earth would have a magnetic field. Our magnetic field depends on a combination of the Earth rotating and there being a liquid core that conducts electricity. This would mean we would all be dead from solar or cosmic radiation. Shasarak
Can a flat Earth exist? No. Planets are round because their gravitational field acts as though it originates from the centre of the body and pulls everything towards it. With its large body and internal heating from radioactive elements, a planet behaves like a fluid, and over long periods of time succumbs to the gravitational pull from its centre of gravity. The only way to get all the mass as close to a planet’s centre of gravity as possible is to form a sphere. The technical name for this process is “isostatic adjustment”.
With much smaller bodies, such as the 20km asteroids we have seen in recent spacecraft images, the gravitational pull is too weak to overcome the asteroid’s mechanical strength. As a result, these bodies do not form spheres. Rather they maintain irregular, fragmentary shapes.
Gravity, inevitably, will crush a non-spherical object into a spherical one assuming it has enough mass and weight. An object with the mass of the Earth that is flat would inevitably break up into fragments due to the gravity of the Sun, then accrete into an object and pull itself into a spherical object. Only in a universe where there is no gravity could a flat Earth exist. But no gravity means neither matter nor energy can exist. So, no life, no planets, no stars. Nothing. We’re stuck with spherical worlds no matter what. Tiberius123
If the Earth were flat but there were still three spatial dimensions, then the likelihood is that this discussion would be taking place between bacteria living on the side of a piece of wombat dung (which is famously cuboid). Although it might seem unlikely, this offers a better explanation for how the UK ended up with Boris Johnson as PM than any other that I’ve come across. BlueThird
Christopher Columbus would never have returned. Nor would Leif Erikson. MyOtherNameIsReal
It would have to rest on the backs of four elephants who themselves stand on the back of a giant turtle … and Sir Terry Pratchett would still be alive. Skydancer1
Brexit would have turned out to be a great idea after all. Styggron
Let’s allow that gravity, magnetism, daylight etc are all unchanged (perhaps this flat Earth has been faked up by aliens who enjoy watching us scampering in our playpen). So, perhaps, for many people, especially those near the centre, life would be basically unchanged.
The one huge difference that cannot be ignored is the edge. Whether it’s implemented as a cliff edge, or a wall, or an invisible force field, it would have profound effects on society. Perhaps religion would step in to prevent people approaching it. Perhaps we would throw criminals over it, or our rubbish. Perhaps explorers would attempt to scale it. paulreilly
If the Earth were flat, we would find that we cannot account for anything we see in the sky, especially the sun, moon and planets. We would have to accept that these are just “luminaries”, which are mysteriously unknowable to us. We would be happy in this unknowing, for it is clearly what God intends.
Until we got the telescopes out, of course, and had a really good look. Then we would see that the moon is obviously a globe, as are Jupiter, Mars, Saturn and Venus. We’d see that Jupiter has its own moons, happily orbiting away. We would notice sunspots and see how they move across the surface of the sun, showing that it is also a rotating globe. Sorry, God.
Pretty soon, some clever clogs would figure out how the same force that causes apples to fall from trees also causes the movement of the planets; not long after that, someone else would work out that all objects over a certain size tend to form themselves into globe shapes because of this force.
After that, it is only a matter of time before someone realises that an object the size of the Earth can be only one shape – and it isn’t flat.
I could be wrong, of course. It might be that some much earlier clever clogs experiments with the length of shadows cast by sticks at midday and notices that they are longer if you travel farther north; someone that clever might be able to understand the shape of the Earth long before telescopes.
To summarise: it can only be a flat Earth until you start thinking about it. ThatBlokeBruce
Our measurements of the motions of the planets, and our observations of the way the sunlight hits them, prove that the sun is the centre of the solar system. So, if the Earth was flat and did not spin, it would either always have sunlight on the top or underneath, in which case the part we live on would either be totally frozen or too hot for water to be liquid, or it would spin on a horizontal axis, in which case we would have days and nights but all the water would slide off the sides away from the axis due to Coriolis forces. So we would never have evolved. It’s highly, highly unlikely that any life would have begun. And that’s just the beginning of the problems. EdgarCarpenter
A lot of these answers approach the question from a physics perspective. I’ve enjoyed thinking about it from a more mathematical point of view: how to map points on the surface of a sphere in 3D to points on a plane?
One way might be to map the points to a planar annulus (that’s the region defined in 2D space by two concentric circles). I think that might work, although it yields very weird results for great circles. If you walked around the annulus world starting out due west, it could take 1,000 times as long as it would if you headed due north. AlCramer
We should ask what a flat Earther would make of the M25 orbital, as the road seems to go in a straight line when driving on it and yet after several roadblocks and long queues you reach the same starting point. If we get some sort of sensible answer, which I doubt we will, we can then try to extrapolate it to the third dimension. Wishful thinking, I know. cycling_uk
If the world was flat, we would be blissfully out of contact with billionaire space tourists for half the time they were orbiting the planet. Richard Simmons
If the Earth was flat, we would not have to cycle up hill. I’ve already given this too much thought. Dae Pandy, Wales
Road signs such as “The end is near”, “Dead end ahead” and “The end of the line” would sound more ominous. Richard Orlando, Quebec
We would have to deal with the unbearable smugness of the flat Earthers being right … Dave Smith