I hope this doesn’t seem to stupid, but what if the earth was flat?
How thick would it have to be to support vegetation?
What about the gravity, especially near the edges?
I don’t think the Earth would have to be too thick to support vegetation. The tillable soil layer is a few feet deep at most, and the crust of the Earth is only 20 miles (32 km) thick, if you believe geologists and other purveyors of the myth of the spherical Earth. 
People who beleive that the Earth is flat don’t tend to have a very good understanding of Newtonian gravity, either. I recall Charles Johnson, the president of the International Flat Earth Society, stating that his wife, who is from Australia, can testify that she did not hang upside down when she lived there. Therefore, the Earth is not a sphere. Q.E.D.
As far as the edges go, IIRC, they say that the Earth is like a pancake with the north pole at the center and the south pole at the outer edge. They claim that no on has really been to the south pole, or they’d have found the edge of the world.
I don’t know if the IFES is still functioning. Don’t confuse it with “The Flat Earth” society, which is a joke, whereas the IFES is deadly serious.
How do flat earthers explain that you can call someone long distance and have it be day where you are and night where they are?
Back to the OP:
Try an article by Larry Niven called “Bigger Than Worlds” in A Hole in Space (New York: Ballantine Books, 1974) ISBN # 0-345-30051-3.
If you build an extremely large, flat structure, gravity will be perpendicular to the surfaces. On the edges, gravity will have a perpendicular component, but the net direction will be toward the structure.
Gravity will tend to pull the structure into a spherical shape, so if you want it to stay flat, you have to build it out of some substance that is much stronger than anything known to exist in the real world.
Any Dopers remember the Sunday comic strip “Little Iodine”?
One week her class was assigned to make maps of the earth at home, from common household objects. Kids used basketballs, ping-pong balls, oranges, and other spherical objects.
Not Little Iodine. She made her map in a disk shape; on a phonograph record. She said, “This is a map of the world in 1491; the world was flat in those days, y’know!” 
lumpy wrote:
I believe most modern flat-earthers allow for different time zones, although I’m not quite sure how.
This may be so, but as an Aussie Flat-Earther, I have to add that our footwear industry is the world’s largest consumer of Velcro.
I just read – either in Discover or Natural History – the maximum size an asteroid can be before its own gravity forces it into a roughly spherical shape. Unfortunately I’m moving at the end of the month, and these references have already been packed away…
It’s around 100-1000 km in radius. Depends on the density.
This may be a hard question to answer, but I must ask it anyway. Recently my brother and I got into an arguement that he, if he lived back before “Columbus sailed the ocean, blue”, he would’ve believed the world was flat like everyone else did. I know that he would’ve believed it was flat, but it is hard to pound anything into his head once he has his mind set on it. Does anybody have any suggestions about what might be a good arguement for me?
Actually, if a European of the Middle Ages had at least some formal education (putting him in the top 1/10 of 1% of the population, I guess), he would have learned the Earth was a sphere, located at the immobile centre of the universe.
Alternately, if he had been one of the great uneducated mass, it would have been an achievement for him to even THINK or CARE about the shape of the world.
jrd
I hate to resurrect a dead thread, but I just heard that Charles Johnson has died. Here’s an obituary at the LA Times.
http://www.latimes.com:80/news/state/20010325/t000025955.html
It addresses one of vanilla’s original questions:
Endless huh? How did he explain the sun coming up every morning?
Remember, he put the North Pole at the center of the Earth, and the South Pole along the outer edge of expored territory.
He thought the Sun was small, and only a few miles up. I guess its motion would describe a circle above the disk, roughly above the equator.
- Ships sailing away sink into the horizon, indicating that they are going down (relative to you) on a spherical surface.
- The earth always casts a curved shadow on the moon during an eclipse.
Educated folx knew the earth was round in Columbus’s time. The argument was over the size, not the shape.
The producers of Fox’s Moon Landing Hoax show missed a good thing with Charles Johnson. In the LA Times article on his death is the following:
With this kind of endorsement the whole thing would have been more believable. :rolleyes:
In the documentary on King Arthur we learn that their knowledge was different:
If only Monty Python’s editing wasn’t so tight we would know the scientific reasoning behind this.
Sorry