What would a flat world be like?

[Skald the Rhymer]

Once upon a midnight clear, I wrote a fantasy story set, largely, in a flat (and magical) world. I won't go into any detail about the story, because this thread isn't about the story so much as about the idea of a flat planet.

Let's postulate the following:

The world in question is a disc of about the same surface areas as our Earth; the distribution of land and sea area is about the same as well. Its surface gravity is about the same as ours too, as its its the chemical composition of its atmosphere. It does not rotate; heat & light are provided by a sun that orbits it. Its crust is the same in chemical makeup as our world's; beneath it, though, is a base made of, oh, adamantium, one hundred miles thick. The planar Earth is surrounded by a clear dome, outside which the sun orbits. Said clear dome is made of unobtainium, which is transparent to EM radiation but impenetrable to any material object.

In what ways, both obvious & subtle, will such a place would differ from our world?

The first thing that occurs to me is that, unless the weather is always the same in all parts of this world, the sky will never be completely overcast.

Anybody else have any thoughts?

[panache45]

Gravity. It will pull straight down in the center, and almost horizontally near the edges. Because of this, there will be a central ocean surrounded by land . . . and lots of steps and ramps everywhere.

[ultrafilter]

Because the distance to the center of mass increases as you move away from the center of the disk, surface gravity can't be of the same magnitude everywhere. It also can't be of the same direction everywhere either; objects will fall towards the center of mass of the system, and at the edges that's not the direction that we would consider down.

I'm also pretty sure that you can't have a star orbiting a planet, but not quite confident enough to say that definitively. The only way that could happen is if the planet is much more massive than the star, but it's not clear how a small object could begin to produce fusion reactions while a larger object doesn't. Since the star has to be (much more) massive than the planet, the center of mass of the star/planet system--which is what both objects actually orbit--will be much closer to the star, if not actually inside it.

[Malleus, Incus, Stapes!]

Originally Posted by Skald the Rhymer

The world in question is a disc...

...supported on four elephants?

[Der Trihs]

No tides. Ships will fade into the distance instead of sinking over the horizon. Weather and ocean currents will be different; looking at Wikipedia it appears that you wouldn't get hurricanes on a non-rotating planet, and apparently a lot of other feature of climate/weather patterns depend on the Coriolis effect.

You could perhaps get around the gravity problem by changing the size of the disc, so that the edge effects are far away from the action. I like the Alderson disc, a vast disc with a star in the middle ( like an old style phonograph record ). Apparently on a disc, gravity is "down" except near the edges, so you'd want one bigger than Earth to provide an Earth's worth of living space.

As for the argument that you can't have a star orbiting a planet, since the whole system is clearly artificial, the obvious solution is that the sun isn't a star, but some sort of much less massive fusion device.

[Tapioca Dextrin]

Originally Posted by Skald the Rhymer

Anybody else have any thoughts?

Unless you want to say "wizards did it" to every problem, this scenario simply can't work.

How does the sun orbit this tiny planet? How does the disc remain stable if it doen't rotate? How can it have any topography if there's no mechanism to build mountains? How are you going to keep the glass shield free from meteorite dust build up?

[Skald the Rhymer]

Originally Posted by Der Trihs

No tides. Ships will fade into the distance instead of sinking over the horizon. Weather and ocean currents will be different; looking at Wikipedia it appears that you wouldn't get hurricanes on a non-rotating planet, and apparently a lot of other feature of climate/weather patterns depend on the Coriolis effect.

You could perhaps get around the gravity problem by changing the size of the disc, so that the edge effects are far away from the action. I like the Alderson disc, a vast disc with a star in the middle ( like an old style phonograph record ). Apparently on a disc, gravity is "down" except near the edges, so you'd want one bigger than Earth to provide an Earth's worth of living space.

As for the argument that you can't have a star orbiting a planet, since the whole system is clearly artificial, the obvious solution is that the sun isn't a star, but some sort of much less massive fusion device.

So we're clear, I'm not trying to get around the gravity or any other problems, as I'm not working on the story. My explanation when i wrote it was, of course, magic.

I was thinking the whole thing had to be artifically maintained; in fact, something I left out of the OP was the notion that, since this world in question is much, much less massive than Earth, its gravity is supplied by artificial-gravity generators, doubtlessly stolen from Jean-Luc Picard. The sun, likewise, is in orbit around the planar world because it is being artificially propelled.

I hadn't thought about tides. That is a good one. If I write a sequel to the tale I'll mention that. The ships-not-thinking bit was one of my first thoughts, though; it was how the visitor from our world realized that the people on the plane weren't full of shit when they said their world was flat.

[dracoi]

How much pseudo-scientific hand-waving do you want in the explanation?

If you permit artificial gravity, for example, you've solve a lot of the issues right there.

One thought about the star rotating around the planet: you could theoretically have a binary star/black hole system. The star and black hole would have to be the same exact mass and period of rotation so that they could rotate around each other with a fixed common center in which the flat world would lie. They couldn't see the black hole and thus would think there was only the sun. I suppose a black dwarf or cold neutron star might also fit the bill. This kind of system would make planets and moons either impossible or highly erratic in their movements.

As far as weather goes, I'm not sure how much weather you'd have at all. The Earth's rotation and its roundness both contribute significantly to weather and you wouldn't have either on a flat world. You might have small weather effects like air rising in the day and sinking at night, but there'd be nothing to drive larger weather patterns.

We don't know the properties of a clear unobtanium dome, but my guess is that it would be pretty cold being exposed to space. Rising humid air would probably condense on it and either turn to frost or form droplets that trickle down the sides. Either way, it would be pretty hard to see through and might mean that rain as we know it is impossible. (Even if the dome is a hundred miles high in the middle, condensation would still be a problem on the edges).

[Skald the Rhymer]

Originally Posted by dracoi

How much pseudo-scientific hand-waving do you want in the explanation?

An infinite amount, obviously! I want one pseudo-scientific handwave for each irrational number in the set of real numbers.

[JFLuvly]

It would be different cause you could watch your dog run away for three days!

[dracoi]

Originally Posted by Skald the Rhymer

An infinite amount, obviously! I want one pseudo-scientific handwave for each irrational number in the set of real numbers.

I'll get to work on that, but it might take a while.

[Sage Rat]

With no timezones, possibly no such thing as magnetic poles, navigation during the day would be quite different.

[Lemur866]

One difference is that the stars don't move across the night sky. All stars are fixed except the "sun" and any other bodies orbiting the disk. So nightime navigation is easy. Since the stars never move you can pick a bright star in the direction you want to travel and always keep it in the same position and you'll travel in a straight line.

[Lamia]

Originally Posted by Skald the Rhymer

I was thinking the whole thing had to be artifically maintained; in fact, something I left out of the OP was the notion that, since this world in question is much, much less massive than Earth, its gravity is supplied by artificial-gravity generators, doubtlessly stolen from Jean-Luc Picard. The sun, likewise, is in orbit around the planar world because it is being artificially propelled.

I hadn't thought about tides. That is a good one. If I write a sequel to the tale I'll mention that. The ships-not-thinking bit was one of my first thoughts, though; it was how the visitor from our world realized that the people on the plane weren't full of shit when they said their world was flat.

You may want to read Terry Pratchett's early (pre-Discworld) novel Strata. It's about a team of engineers who visit an Earthlike but flat planet that turns out to be the product of technology (not magic, as in the Discworld series). IIRC, the first people they meet are some Vikings who are sailing off from their homeland in search of new land...and either nearly or actually sail right off the edge of the planet.

[Sage Rat]

Originally Posted by Lemur866

One difference is that the stars don't move across the night sky. All stars are fixed except the "sun" and any other bodies orbiting the disk. So nightime navigation is easy. Since the stars never move you can pick a bright star in the direction you want to travel and always keep it in the same position and you'll travel in a straight line.

Why do you say that? I can take a coin and spin it in air just fine.

[Randy Seltzer]

Originally Posted by Sage Rat

Why do you say that? I can take a coin and spin it in air just fine.

But won't the non-round planet quickly become tidally locked with the sun? Which would mean that there would be perpetual dusk on the flat surfaces, and either fiery inferno or freezing wasteland on the edges.

[sunacres]

Originally Posted by Skald the Rhymer

It does not rotate; heat & light are provided by a sun that orbits it. Its crust is the same in chemical makeup as our world's; beneath it, though, is a base made of, oh, adamantium, one hundred miles thick. The planar Earth is surrounded by a clear dome, outside which the sun orbits.

Oh. I guess you're not talking about A.K. Dewdney's The Planiverse:

http://en.wikipedia.org/wiki/The_Planiverse

[Markxxx]

There's a good book called "Flatland," about a two demensional world. Not the same thing exactly but kind of in the same line

[Sage Rat]

Originally Posted by Randy Seltzer

But won't the non-round planet quickly become tidally locked with the sun? Which would mean that there would be perpetual dusk on the flat surfaces, and either fiery inferno or freezing wasteland on the edges.

I dunno about quickly. Eventually maybe, but eventually the Moon is going to crash into the Earth, doesn't mean I'm worried. The total mass of water on the disk planet is probably a fairly insignificant value on a planetary scale and we don't know how long this planet has been like this or how it's powered.

Or heck, you could spin the whole thing like a top. That would cause the sky to rotate and produce no discernible tide.

Originally Posted by ultrafilter

I'm also pretty sure that you can't have a star orbiting a planet, but not quite confident enough to say that definitively. The only way that could happen is if the planet is much more massive than the star, but it's not clear how a small object could begin to produce fusion reactions while a larger object doesn't. Since the star has to be (much more) massive than the planet, the center of mass of the star/planet system--which is what both objects actually orbit--will be much closer to the star, if not actually inside it.

You could have a dual-star system where one of them is a black hole and there's a disk planet between the two.

Though I'm not sure if you can do that and get the bodies far enough away from one another to not have the planet be too hot.

[Alex_Dubinsky]

Surprised noone's mentioned the Flat Earth Society yet.

[Tom Tildrum]

Why wouldn't there be tides, if the sun is rotating around this earth?

[Ohime_Rose]

Originally Posted by Randy Seltzer

But won't the non-round planet quickly become tidally locked with the sun? Which would mean that there would be perpetual dusk on the flat surfaces, and either fiery inferno or freezing wasteland on the edges.

Hey, I pretty sure that the tides are caused primarily by the MOON.
So depending where it was, you'd be getting flooded every other day if it still rotated aroung us.

But that wouldn't matter, 'cos all the extra water would just dropp of the edge of the earth, la dee da...

[Randy Seltzer]

Originally Posted by Sage Rat

I dunno about quickly. Eventually maybe, but eventually the Moon is going to crash into the Earth, doesn't mean I'm worried. The total mass of water on the disk planet is probably a fairly insignificant value on a planetary scale and we don't know how long this planet has been like this or how it's powered.

Originally Posted by Ohime_Rose

Hey, I pretty sure that the tides are caused primarily by the MOON.
So depending where it was, you'd be getting flooded every other day if it still rotated aroung us.

But that wouldn't matter, 'cos all the extra water would just dropp of the edge of the earth, la dee da...

The tidal locking I'm talking about has nothing to do with water. See here. There's no water on our moon, and it is tidally locked with Earth.

Non-spheres (like disk worlds) would have a greater tendency to become tidally locked with other bodies because of torque from bulge dragging.

[Snickers]

What would a flat world be like? Iowa.

[Tapioca Dextrin]

The "front" and "back" are going to be pretty unpleasant places. Since the dome transmits UV light, they're gonna be fried. Come to think about about it, that's going to be the case pretty much everywhere at dawn and dusk, unless a passing wizard puts a heavy UV filter around base of the glass dome.

[Lemur866]

Look, you guys are still thinking that the "sun" is a star. It's pretty clear the sun cannot be a star. It's some other type of object. It seems to me that if it orbits around the disk every 24 hours and appears to be about the same size as Sol from Earth, the "sun" has to be smaller than the Moon, and closer to the disk than the Moon is from Earth. If it was about the same size as the Moon, it would have to be about the same distance from the Disk as the Moon is from Earth, and that would mean it would orbit the Disk in about 30 days. So--let's call it "Helios"--Helios has to orbit the disk in 24 hours. Assuming the Disk has about the same mass as Earth, that means Helios has to be about the same distance from the Disk as a geostationary orbit.

On Earth geostationary orbits are 36,000 km above sea level. Add in another 6000 km for the radius of the Earth, and we see that geostationary orbits around an Earth-massed object are ~42,000 km from the center of gravity.

[Lemur866]

Couple more things.

Somebody is going to have to work out how large Helios must be if it's 42,000 km above the center of gravity of the Disk and appears to be the same size as Sol. It's going to be a pretty small object, much smaller than the Moon.

The tidal effects of Helios are going to be the same as Sol, assuming Helios has a similar density to Sol. If Sol were as dense as the Moon, it would exert the same tidal force. But since Sol is mostly hydrogen gas it is much less dense than the Moon and so has a much smaller tidal force. Therefore, if Helios has a similar composition as Sol, since it looks to be about the same size it would cause the same tides.

How those tides would work on a disk is hard to say exactly. And I agree that the disk is going to start spinning in sync with the orbit of Helios fairly quickly. The Earth won't become tidally locked to the Moon or the Sun within the lifetime of the Earth, because it's so massive in comparison to the tidal forces. But that disk is going to create huge tidal gradients. Maybe you'll have to make Helios nearly massless

About the disk itself rotating with regard to the fixed stars, that's certainly possible. You could give the disk any rotation you like. But then you screw up the notion that Helios is orbiting the Disk, because then the spin of the disk has to sync with the motion of Helios. And you don't even have to spin it like a spinning coin, you can spin it like a record player, or some combination.

But this is nonsense. The whole point of a flat earth is that it doesn't move. Do you feel any motion? No. Therefore, the earth doesn't move. Period, end of story.

If the disk has a spin then you're pretty much going to have to put Helios on tracks that run on top of the dome rather than try to orbit it because otherwise things get screwy.

[Alex_Dubinsky]

Yes. And isn't all this an exercise in suspension of disbelief? The question wasn't, "how would it be possible from a physics/geophysics/astronomy pov." This isn't science fiction. The question is what would it be like, assuming that it's just the way things were.

Never having a completely overcast sky (light almost always coming in from the edges) is a good start. You could also perhaps see lightning flashes at night from very, very far away, if you were reasonably high up. Also no timezones. Very simple astronomical calcs (not the very complex stuff that ancient civilizations loved spending time figuring out). The same stars in the same positions no matter your latitude (very unfortunate for navigation). And you couldn't estimate the size of the earth the way the Greeks and others had done (so the most educated philosophers probably wouldn't think it's nearly as large as it actually is).

[drastic_quench]

Not having a molten core at the planet's center generating sufficient magnetic fields would be the death of your world as solar winds would simply blow any habitable atmosphere off into space.

[Lemur866]

No it won't, because the light source for this world is not a star. It's something else, something that is small enough to orbit the disk in ~24 hour and from the surface of the disk looks about the same size and puts out as much light as the Sun from Earth. Therefore, it has to be very small. Much smaller than the disk itself. Therefore, it's not going to blast the atmosphere away into the void.

And besides, the disk has a transparent unobtanium dome over it, so the question is moot anyway.

Oh, and if we're assuming that the disk gets its gravity from the 100 mile thick incredibly dense adamantium center of the disk, then both sides of the disk can be landscaped and you get twice as much habitable surface for almost the same cost. If you use artificial gravity then you don't need the adamantium in the first place. Therefore, since we know that the disk WAS built with an adamantium core that is pretty good evidence that The Ancients didn't use artificial gravity in the construction of the disk.

[Alex_Dubinsky]

Please, let's stop talking about the light source and the dome and the molten core and the cost of the thing This isn't an engineering project. This isn't even science fiction. This is just an imagining of what would things be like if the earth was flat like some ppl had assumed in the past.

[Lumpy]

The problem with having the sun be small and close is that then different parts of the disc are appreciably closer to the sun than others. Near the edges you'd have north and south "poles" that never get as warm as the rest of the disk, while the easternmost and westernmost edges would have extreme temperature fluctuations. Either this would be part of your setup, or else the sun would have to emit light and heat unsymmetrically, to make up for the geometry.

[Lemur866]

If you want an actual star, then the suggestion of just spinning the disk is a good one. The sun doesn't orbit the disk, the disk just spins on it's axis every 24 hours, and then you have day and night cycles just like on the earth.

But again, the problem with this is that the disk is spinning. A flat earth shouldn't move. It should be imobile. This is the number one aesthetic reason to have a flat earth. Therefore all the other physics of the system depend on the disk not having any spin. Therefore the sun has to move around the disk. And if you want it to orbit, it's got to be very small and very close. If you don't like that, you've got to move the sun across the sky in some other way--on a chariot pulled by flaming swans is in fashion this epoch, I believe.