5 ms·

I have seen a very similar (incorrect) argument used to justify the idea of a flat earth. A builder on youtube made the argument (with a similar out of scale d

I have seen a very similar (incorrect) argument used to justify the idea of a flat earth. A builder on youtube made the argument (with a similar out of scale drawing of the earth) that if he drops a plumb bob and makes a right angle so he has a straight horizontal line and then goes across that line for a bit and drops another plumb bob, the two lines he has dropped are parallel, "proving" that the surface of the earth must be parallel to the horizontal line and therefore flat and not curved. If the earth's surface was actually curved he argued then the two lines he has dropped should tilt slightly inward towards each other. Which of course they do. The earth is just much much much bigger than in the diagram so the effect is within the margin of error for the measurement he was taking. As a meta point, our intuition often fails us hilariously when we are dealing with stuff that is out of the scale we have commonly seen in our lives. We joke about LLMs hallucinating but I'm not convinced we are so superior when we are outside our personal "training data".

munch117 2y ago
Ah, but would they actually be parallel on a flat earth? Say the earth is disc-shaped. Then the center of gravity is only directly beneath you if you're standing at the exact center. You get ever-so-slightly not parallel lines, just like on a round earth. The fun part of a disc-shaped earth comes as you move towards the sides, and gravity, still pointing towards the center, makes you stand at an increasingly acute angle to the surface. The ground beneath you will then appear like one big endless mountainside, with an increasingly steep slope the further away from the center that you get.
- jimmaswell 2y ago
  I'm considering what flat-surfaced shape you could construct with equal gravitational pull at all points. Maybe something where the center is thin as a point, the edges have a lot of depth, and they curve towards the center either convex or concave. Might run some calculus to figure it out.
  - t_mann 2y ago
    That way you should be able design a disc-shaped earth with constant strength of the gravitational force on the whole surface. But it would still have a center of mass (likely lying outside the shape you're describing, in the void beneath the center point), and the direction of the force should still be pointing towards that center, no? So the problem the GP has described, that you're starting to tilt as you move towards the edge, should remain in principle.
    - benterris 2y ago
      I believe the strength of gravitational force would not be constant either, as your center of mass would still have a fixed location, so every point on the disc have different distances to that center of mass (in addition to not being orthogonal to the surface). But maybe it might be approximated with an infinitely long cylinder, so the center of mass is infinitely far away below the surface ?
      - t_mann 2y ago
        The thinking in the other post, that the mass increases as you move away from the center, in a manner that the two effects cancel out, intuitively seems like it should be feasible. Remember that the center of mass is just an abstraction, you need to take the full integral over all mass to get the force vector at each point. And if you're closer to more mass further away from the center, which a shape like the one described above should give you, it might work. But one would have to do the math to be sure. Edit: come to think of it, maybe that effect would let you adjust the direction of the force, too. Thinking about center of mass can be treacherous with more complex shapes...
  - somat 2y ago
    yes, we call it a sphere. I am just joking with you, I know what you mean, however the fruit was hanging too low not to pick.
    - t_mann 2y ago
- thombat 2y ago
  Standard flat-earther response is to scornfully deny the existence of gravity. It's all density/buoyancy you see... Gravity is a hoax promulgated by the notorious cabalist Newton, in service to his Illuminati/Papal masters, etc, etc.
  - mp05 2y ago
    Why do we still talk about these people? The more we stand in awe of their calculated ignorance, the more satisfied they are. I feel like there are better things to do with my time than be as fascinated by it as some people.
    - thombat 2y ago
      I periodically suffer the delusion that some of the nonsense-adjacent people may benefit from seeing that sensible answers can be found. Of course there's effectively no chance of reaching the proudly loudly ignorant, wearing their refusal of any good-faith discussion as a shibboleth, but perhaps their recruitment can be stayed.
- tempestn 2y ago
  Depends what causes things to stick to the flat Earth. IIRC flat earthers have various explanations for gravity, including the disc continuously accelerating upward; in that case you'd experience the same force everywhere on it.
  - munch117 2y ago
    If this mysterious disc-accelerating force also accelerated the people and things on the surface, we'd all be weightless. I guess it must be a pushing force from below. So, who's doing the pushing? I'm thinking a big turtle.
    - nkrisc 2y ago
      They mean it is actually accelerating constantly. My math might be wrong, but if we were accelerating at 9.8m/s/s for at least 4000 years (roughly as long as we have continuously recorded history and the minimum time “gravity” has been observed) then we ought to currently be traveling through space at over 1,000,000,000,000m/s. Now I’m no physicist, but I reckon that might end up violating causality.
      - jbeninger 2y ago
        Nah, when you move that fast, further acceleration stops increasing speed and starts squishing time instead, so you asymptotically approach C. So I guess what I'm saying is I see absolutely no problem with the flat earth arguments?
        bryanrasmussen 2y ago
        wait, is the flat earth theory going to make me immortal?
        lukan 2y ago
        Only if you truly believe in it. Then you create a belive field, shaping your reality in any form you desire.
- rendaw 2y ago
  Doesn't the flat earth extend infinitely in all directions?
- phkahler 2y ago
  Even physicists have a hard time with disks and gravity. I can't tell you how many times I've seen them use the shell theorem on galaxies (does not apply). The only dark matter is in their head ;-)
- Someone 2y ago
  > and gravity, still pointing towards the center, makes you stand at an increasingly acute angle to the surface. The ground beneath you will then appear like one big endless mountainside That’s why you never hear of people who went to the edge of that dis: they slid down that mountainside, and dropped off :-) Alternatively, you can postulate that disc to be arbitrarily thick. That will decrease the deviations. If that’s not enough to make them immeasurable, postulate that the stuff “deeper down” has higher density. In the limit, just postulate that there’s an enormous black hole millions of light years below the center of the earth. Flat-earthers probably won’t accept Newton’s theory of gravity, however, so you can make up anything.
userbinator 2y ago
The earth is just much much much bigger than in the diagram so the effect is within the margin of error for the measurement he was taking. It's actually measurable on a human scale: https://www.mathscinotes.com/2017/01/effect-of-earths-curvature-on-suspension-bridge-dimensions/ https://www.mathscinotes.com/2017/01/effect-of-earths-curvat... 1 5/8" difference over 693', or slightly less than 1 part in 5 thousand --- definitely measurable on a smaller scale with accurate machinists' tools.
- pvillano 2y ago
  One can also watch a boat leaving shore descend "under" the horizon with a telescope
  - sigmoid10 2y ago
    You don't even need a boat or a telescope. Just watch the sun set on the ocean while lying down at the beach just in front of the water. The moment it disappears completely, stand up. You'll see part of it again. If you measure the time it takes disappear completely again and know your own height, you can even get a rough estimate of earth's radius.
    - yen223 2y ago
      Unless I'm picturing it wrong, wouldn't this still happen even if the world were flat?
ben_w 2y ago
> We joke about LLMs hallucinating but I'm not convinced we are so superior when we are outside our personal "training data". Every time I see the phrase "common sense", I expect to see an example of the human failing you describe.
jerf 2y ago
"We joke about LLMs hallucinating but I'm not convinced we are so superior when we are outside our personal "training data"." In all seriousness one of the things about LLMs that most impress me is how close they get to human-style hallucination of facts. Previous generations of things were often egregiously and obviously wrong. Modern LLMs are much more plausible. It's also why they are correspondingly more dangerous in a lot of ways, but it really is a legitimate advance in the field. I observe that when humans fix this problem, we do not fix it by massive hypertrophy of our language centers, which is the rough equivalent of "just make the LLM bigger and hope it becomes accurate". We do other things. I await some AI equivalent of those "other things" with interest; I think that generation of AI will actually be capable of most of the things we are foolishly trying to press hypertrophied language centers into doing today.

munch117 2y ago

Ah, but would they actually be parallel on a flat earth? Say the earth is disc-shaped. Then the center of gravity is only directly beneath you if you're standing at the exact center. You get ever-so-slightly not parallel lines, just like on a round earth. The fun part of a disc-shaped earth comes as you move towards the sides, and gravity, still pointing towards the center, makes you stand at an increasingly acute angle to the surface. The ground beneath you will then appear like one big endless mountainside, with an increasingly steep slope the further away from the center that you get.

jimmaswell 2y ago
I'm considering what flat-surfaced shape you could construct with equal gravitational pull at all points. Maybe something where the center is thin as a point, the edges have a lot of depth, and they curve towards the center either convex or concave. Might run some calculus to figure it out.
- t_mann 2y ago
  That way you should be able design a disc-shaped earth with constant strength of the gravitational force on the whole surface. But it would still have a center of mass (likely lying outside the shape you're describing, in the void beneath the center point), and the direction of the force should still be pointing towards that center, no? So the problem the GP has described, that you're starting to tilt as you move towards the edge, should remain in principle.
  - benterris 2y ago
    I believe the strength of gravitational force would not be constant either, as your center of mass would still have a fixed location, so every point on the disc have different distances to that center of mass (in addition to not being orthogonal to the surface). But maybe it might be approximated with an infinitely long cylinder, so the center of mass is infinitely far away below the surface ?
    - t_mann 2y ago
      The thinking in the other post, that the mass increases as you move away from the center, in a manner that the two effects cancel out, intuitively seems like it should be feasible. Remember that the center of mass is just an abstraction, you need to take the full integral over all mass to get the force vector at each point. And if you're closer to more mass further away from the center, which a shape like the one described above should give you, it might work. But one would have to do the math to be sure. Edit: come to think of it, maybe that effect would let you adjust the direction of the force, too. Thinking about center of mass can be treacherous with more complex shapes...
- somat 2y ago
  yes, we call it a sphere. I am just joking with you, I know what you mean, however the fruit was hanging too low not to pick.
  - t_mann 2y ago
thombat 2y ago
Standard flat-earther response is to scornfully deny the existence of gravity. It's all density/buoyancy you see... Gravity is a hoax promulgated by the notorious cabalist Newton, in service to his Illuminati/Papal masters, etc, etc.
- mp05 2y ago
  Why do we still talk about these people? The more we stand in awe of their calculated ignorance, the more satisfied they are. I feel like there are better things to do with my time than be as fascinated by it as some people.
  - thombat 2y ago
    I periodically suffer the delusion that some of the nonsense-adjacent people may benefit from seeing that sensible answers can be found. Of course there's effectively no chance of reaching the proudly loudly ignorant, wearing their refusal of any good-faith discussion as a shibboleth, but perhaps their recruitment can be stayed.
tempestn 2y ago
Depends what causes things to stick to the flat Earth. IIRC flat earthers have various explanations for gravity, including the disc continuously accelerating upward; in that case you'd experience the same force everywhere on it.
- munch117 2y ago
  If this mysterious disc-accelerating force also accelerated the people and things on the surface, we'd all be weightless. I guess it must be a pushing force from below. So, who's doing the pushing? I'm thinking a big turtle.
  - nkrisc 2y ago
    They mean it is actually accelerating constantly. My math might be wrong, but if we were accelerating at 9.8m/s/s for at least 4000 years (roughly as long as we have continuously recorded history and the minimum time “gravity” has been observed) then we ought to currently be traveling through space at over 1,000,000,000,000m/s. Now I’m no physicist, but I reckon that might end up violating causality.
    - jbeninger 2y ago
      Nah, when you move that fast, further acceleration stops increasing speed and starts squishing time instead, so you asymptotically approach C. So I guess what I'm saying is I see absolutely no problem with the flat earth arguments?
      - bryanrasmussen 2y ago
        wait, is the flat earth theory going to make me immortal?
        lukan 2y ago
        Only if you truly believe in it. Then you create a belive field, shaping your reality in any form you desire.
rendaw 2y ago
Doesn't the flat earth extend infinitely in all directions?
phkahler 2y ago
Even physicists have a hard time with disks and gravity. I can't tell you how many times I've seen them use the shell theorem on galaxies (does not apply). The only dark matter is in their head ;-)
Someone 2y ago
> and gravity, still pointing towards the center, makes you stand at an increasingly acute angle to the surface. The ground beneath you will then appear like one big endless mountainside That’s why you never hear of people who went to the edge of that dis: they slid down that mountainside, and dropped off :-) Alternatively, you can postulate that disc to be arbitrarily thick. That will decrease the deviations. If that’s not enough to make them immeasurable, postulate that the stuff “deeper down” has higher density. In the limit, just postulate that there’s an enormous black hole millions of light years below the center of the earth. Flat-earthers probably won’t accept Newton’s theory of gravity, however, so you can make up anything.

userbinator 2y ago

The earth is just much much much bigger than in the diagram so the effect is within the margin of error for the measurement he was taking. It's actually measurable on a human scale: https://www.mathscinotes.com/2017/01/effect-of-earths-curvature-on-suspension-bridge-dimensions/ https://www.mathscinotes.com/2017/01/effect-of-earths-curvat... 1 5/8" difference over 693', or slightly less than 1 part in 5 thousand --- definitely measurable on a smaller scale with accurate machinists' tools.

pvillano 2y ago
One can also watch a boat leaving shore descend "under" the horizon with a telescope
- sigmoid10 2y ago
  You don't even need a boat or a telescope. Just watch the sun set on the ocean while lying down at the beach just in front of the water. The moment it disappears completely, stand up. You'll see part of it again. If you measure the time it takes disappear completely again and know your own height, you can even get a rough estimate of earth's radius.
  - yen223 2y ago
    Unless I'm picturing it wrong, wouldn't this still happen even if the world were flat?

ben_w 2y ago

> We joke about LLMs hallucinating but I'm not convinced we are so superior when we are outside our personal "training data". Every time I see the phrase "common sense", I expect to see an example of the human failing you describe.

jerf 2y ago

"We joke about LLMs hallucinating but I'm not convinced we are so superior when we are outside our personal "training data"." In all seriousness one of the things about LLMs that most impress me is how close they get to human-style hallucination of facts. Previous generations of things were often egregiously and obviously wrong. Modern LLMs are much more plausible. It's also why they are correspondingly more dangerous in a lot of ways, but it really is a legitimate advance in the field. I observe that when humans fix this problem, we do not fix it by massive hypertrophy of our language centers, which is the rough equivalent of "just make the LLM bigger and hope it becomes accurate". We do other things. I await some AI equivalent of those "other things" with interest; I think that generation of AI will actually be capable of most of the things we are foolishly trying to press hypertrophied language centers into doing today.