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Yes, we can easily explain to all intelligent adults why the Earth looks flat, when it is actually round. But my question is, how can we explain this fact, that the Earth is round, to those people who will not accept new data, which contradicts their knowledge, by providing them with some proper facts?

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marked as duplicate by Kyle Kanos, ja72, Brandon Enright, BMS, David Z Apr 3 '14 at 19:13

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

What proper facts tell that Earth is flat? – evil999man Apr 3 '14 at 11:25
Earth looks flat only when you're looking at short distances. As soon as you look at long distances, it doesn't look flat - the classic example was looking at distant ships in the ocean with a spyglass where the curve would obscure half of ship; nowadays you can see the curve by looking from a high-flying plane on a cloudless day. – Peteris Apr 3 '14 at 11:51
Firstly there are similar questions already available…. Second this question queaation seems to be off topic, it is a hypothetical question. If someone does not believe in practical and experimental data then... Phys.SE is not a place for him. – user Apr 3 '14 at 13:37
if a ship appears on the horizon, first you see the sails, then the rest of the ship. – weberik Apr 3 '14 at 14:36
The question is "how can I convince people to believe something who refuse to be convinced of anything they don't already believe?" You can't, by the premise of the question. You could also ask "how can I convince people to buy me lunch who refuse to ever buy me lunch under any circumstances?" You can't, by the premise of the question. This isn't a physics question. – Eric Lippert Apr 3 '14 at 16:04

10 Answers 10

If showing them a picture taken from space won't convince them, I doubt there is anything you can do about it.

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A time lapse video of the Earth making a few full rounds could be more convincing. – user1306322 Apr 3 '14 at 11:38

Tell them to take a flight to the edge. And call us there when they reach it.

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You can't call from a plane :p But seriously, who would actually fly "to the edge" just because some guy said it's a proof of a concept that isn't even vital to understand to go on living as always? If I were those people, I'd rather look for a less effortsome way to understand how the Earth is spherical. – user1306322 Apr 3 '14 at 14:04
@user1306322 actually you can call from a plane – kaptan Apr 3 '14 at 17:29
@kaptan but you can't call from the edge! – Volker Siegel Apr 4 '14 at 3:31

Think of a circle first. So if you look at the whole circle you see it as round. Now just zoom into a small part of that circle. Now you don't see the whole cricle any more. But still you see a curvature. Similarly you making the cirlce larger and look into the same point. When the circle get large the difference between one point and the next point looks (gets) lower. Now think in 1000 km scale

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If the landscape in front of you and your sceptical 'other people' is very flat, some curvature is still perceptible (but only just). Standing at a higher vantage point will increase your ability to see the curvature. I see this regularly near where I live, as I drive to the top of an escarpment and look down at the very flat Vale of York. This effect will only increase as you go higher up. If you can get your sceptics to the top of any sort of mountain, they will see it for themselves, and measure it by holding a long (meter or longer) straight edge up to the horizon. Going up in a plane above 20000m should clinch it, but could be an expensive proof!

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The simplest thing to do would be to point them to the sun and show a person that it's round. Also point out that how could sun move below horizon if it was flat?

And one thing more, you could achieve with a clock. Get a clock and travel 3000 miles and ask a person why did the sun rised later/sooner, while the clock is moving at constant speed.

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Use Google Earth:

  • Start at high zoom level at your location, or anywhere — so that Earth would actually feel flat, as it does normally
  • Use middle mouse button to rotate camera to get view parallel to Earth or similar
  • Gradually zoom out showing how the curvature becomes more and more apparent as you go deeper to space
  • Finally you are looking at the Earth from space. Now let the person you're trying to convince rotate it and play with it in other ways.

After that show several images of the Earth taken from space to confirm that what one sees in Google Earth is what the astronauts see.

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The problem here is that one could argue Google Earth is simply perpetuating the round-Earth myth by mapping the surface to a sphere. :P – cHao Apr 3 '14 at 14:02
They would say that google earth is developed by evil scientists to feed false information to the masses. – user42733 Apr 3 '14 at 14:17

Possible options

  1. Show them picture of earth (taken from space)

  2. If the guy believes in Mathematics , ask him to measure distance between two far separated points. ( The metric of sphere will serve the purpose and not the Euclidean one)

  3. Go for a straight nose tour along any direction till you come at the same point. ( nothing as such can happen in a flat space)

  4. There is a famous shadow and stick experiment.

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Simple, empirical questions to ask a person who believes the earth is flat:

  • If the earth is flat, there must be countries that live on the edge, literally. In this day and age, why haven't we seen any videos from these spectacular sites?
  • Why haven't we heard of any accidents where a person got drunk and fell off the edge? Better yet: would such a person actually fall off? Where does the attractive force keeping us on the ground come from according to you? If it comes from the plane that is the earth in your view, would they not simply swivel down and end up on the other side of the earth? But then we would have heard stories from such people, going over the edge and coming back.
  • Also: why do we have oceans? If there were an edge, the water would flow off the edge and soon all be gone (or transfer violently to the other side of the earth). We don't see this happening either.

I wouldn't bring in things like the rotation of the earth or photographs from space because it's easy to dismiss things like that. Any argument you give yourself is probably easy to dismiss for such people. However, when you ask the right questions, they might come to the understanding that they can't satisfactorily answer them. They might experience that "hey, I hadn't thought of that!"-feeling.

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Fly in a plane with that person. With enough fuel one day you guys shall reach at where you had started. This will prove that earth is round.

Response to comments:
All material objects apply the gravitational force on all other material objects. The earth is made up of atoms,molecules etc, all these constituent particles exert force on each other.

All the heavenly bodies in the universe are more or less spherical in shape. This is due to the fact that any material object of a given mass has least surface area if it is spherical in shape, lesser the surface area lesser the potential energy more the system becomes stable. So for a given mass the object tends to become spherical in shape.

What would happen if earth becomes cylindrical?
Then all the objects placed on the curved surface of the cylinder near the edge will fall towards the centre until the Earth becomes spherical because of the gravity. In fact every system tends to go from higher potential to lower potential state.

Why some meteorites are not of spherical shape?
This is only the case for meteorites of small size. As the size grows the meteorites becomes more an and spherical. The small sized physical objects does not have enough gravity to change their shape.

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Ok, earth is not flat... but it is cylindrical, I know it! – Volker Siegel Apr 4 '14 at 3:35
@VolkerSiegel Earth's cylindrical!, this is beyond the scope of my knowledge. Would you explain how or if you could give me a link(refer) for further info. – user Apr 4 '14 at 10:18
"I just know it" - that's the point! – Volker Siegel Apr 4 '14 at 10:37
@VolkerSiegel I have edited my answer. you are terribly misinformed that earth is cylindrical. I do not know where do you live. It is well known across the world. that Earth is spherical. – user Apr 4 '14 at 11:10
Ok, I admit earth is spherical here too. It was meant as a "devils advocate" comment - it somebody is 'crazy' enough to assume the earth is flat, he could well be crazy enough to assume the earth is cylindrical. An if you prove to him that the earth in not flat, as you can go around in one direction (as in the answer to the time I made the comment), he could still claim that the earth is cylindrical. He would basically say "Hmm, ok, I accept yaou have shown the earth is not flat... Ha! But in this directioin only!" And then he claims that it it still flat in the orthogonal directon... – Volker Siegel Apr 4 '14 at 11:20

Show them a lunar eclipse. A flat earth would not always cast a round shadow on the moon.

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