Convincing a Flat Earther: Proving the Earth is Spherical

[jim77]

Because I must be a masochist I would like to know how I could convince a flat earther that the Earth is a sphere. The way I've chosen to do it is the following. I live in Honolulu and the person I am trying to convince lives in south america. At an agreed upon time we both take a 50 cm stick outside and measure the angle of the shadow and its offset from magnetic north. Knowing the position of the sun at that time will give us both right triangles so we add 90 degrees to the angle we measured and subtract that from 180. then we'll add both of the remainders together. His measured angle plus mine plus the sum of the two remainders will add up to 180 if the Earth is flat and something other if the world is round. Do I have this correct? Is there any advice you can give me to make it as simple as possible with as small a possibility for error as can be? It seems like with the internet this should not be an issue so I am hoping that this simple math experiment will show them that they are mistaken. (Unlesss of course you astronomers have actually been tools of the underground global authority and forbidden to tell us the truth that the sun is actually only 35 miles up like they say, You arent part of a global conspiracy here are you? I didnt think so but thought I'd ask :)

 

[fresh_42]

Here are a few opinions: https://www.physicsforums.com/threads/i-want-to-prove-that-the-earth-is-round.926515/

 

[Borg]

This is my favorite proof:

 

[fresh_42]

Mine is this:

 

[nikkkom]

Because I must be a masochist I would like to know how I could convince a flat earther that the Earth is a sphere.

Make a video chat call to, say, three people on different continents, some in the daytime, others at nighttime, others at e.g. sunset. Ask them to show the sky.

Of course, a sufficiently stubborn insanity can refuse to be convinced by anything.

 

[russ_watters]

At an agreed upon time...

Isn't that enough evidence on its own?

...we both take a 50 cm stick outside and measure the angle of the shadow and its offset from magnetic north. Knowing the position of the sun at that time will give us both [different] right triangles...

This too.

so we add 90 degrees to the angle we measured and subtract that from 180. then we'll add both of the remainders together. His measured angle plus mine plus the sum of the two remainders will add up to 180 if the Earth is flat and something other if the world is round. Do I have this correct?

I really don't see what you are trying to do with that math (it isn't clear to me which angles you are using), but honestly, is he really going to accept anything? If he already knows about time zones (the first quote), isn't that enough evidence that the Earth must at least be a cylinder?

Or start a chat with him just before sunset and ask him what it looks like from where he lives.

Or when you put the stakes in the ground and measure the angles are different in both axes, just knowing that they are different tells you the Earth is curved in both directions, doesn't it?

You could use a modification of Eratosthenes' method to calculate the Earth's circumference:
https://www.windows2universe.org/citizen_science/myw/w2u_eratosthenes_calc_earth_size.html

Each of you measure the angle of the sun at local noon. Subtract the two angles and you should get the difference between your latitudes. If you want to take it further you can measure on a map how far south he is from you and multiple by 360/that angle.

 

[at94official]

Why would you even waste your time arguing with these kind of people?

 

[jim77]

Or when you put the stakes in the ground and measure the angles are different in both axes, just knowing that they are different tells you the Earth is curved in both directions, doesn't it?

Brilliant! thanks for the responses. Especially the cat one.

 

[newjerseyrunner]

Or when you put the stakes in the ground and measure the angles are different in both axes, just knowing that they are different tells you the Earth is curved in both directions, doesn't it?

Not necessarily, If you put two stakes on a flat surface and move the light itself around, you will get different angles. Science isn't about a individual pieces of evidence that may have multiple solutions, it's about coming up with a theory that explains ALL evidence. You could easily replicate almost all types of ancient measurement with a flat plane and clever geometry. It's things like the fact that you can't see the bottom few tens of feet of Chicago from Canada, or simply that we've been high enough to see the Earth as a ball that can't be explained by anything other than a great science conspiracy.

I think it's best to simply one-up the conspiracy nut with something even more ludicrous:
"The sun's shadows can easily be created on a flat plane"
"Pffft, you believe in the sun?"

 

[russ_watters]

Not necessarily, If you put two stakes on a flat surface and move the light itself around, you will get different angles.

Not if the light is far away and the angles are measured at the same time.