Travel in one direction until you end up where you start. (Unless you think the flat Earth was Pacmanesque warp points?)

great idea! What's your preferred method of guaranteeing you're travelling the same direction? Even a slight angle off from 'straight' could lead you in a circle on a flat earth.

Measure the length of a sundial's shadow at noon at different latitudes.

Shoot a laser horizontally across a large still lake to measure the curvature of the lake's surface. There was a documentary on flat earthers (I think on Netflix) where this was done, but the flat earthers dismissed the results falsifying a flat earth.

First, we can take the claim of scientists and experts and test them ourselves. We can test with measuring shadows like in ancient Rome. We can test by finding flat land and assessing when the visibility of distant objects should vanish according to predicted angles. We can attempt to travel around the world ourselves.

The question of "Pondering flat Earthers" can be more abstractly applied to, "How can we verify our trust in authority?" Good authority will tell you how they arrived at their conclusions and let you test it yourself. Bad authority will refuse to divulge their methods, or proper testing will reveal flawed results.

We can test by finding flat land and assessing when the visibility of distant objects should vanish according to predicted angles — Philosophim

The weird thing I've discovered with this is that there's actually a bit of an unexpected result here (at least, unexpected to me) -- you can actually see a little bit more than you would expect if you just considered the geometry of the globe. Have you heard of this?

https://sciencemeetsfiction.com/2020/12/22/flat-earth-challenge-follow-up-refraction/

prove yourself that the earth is round — flannel jesus

The earth's curvature is visible wherever there's a visible horizon. What's an example of a place from which the Earth could appear flat? Is there good reason to doubt that the curvature that we can see does not imply a round shape?

The earth's curvature is visible wherever there's a visible horizon — jkop

That's not my experience. Go to the beach, look out to sea, it looks pretty flat to me. Take a photo, I'm pretty sure it's not visibly curved.

Does this look curved to you? It doesn't to me.

1 Go up in one of those tourist rockets or even a good airplane. It gets high enough to see the curvature.

2 Learn ocean navigation. One can tell where one is on a globe given visibility to sun/starts and a good clock. Can't do any of that on a flat Earth. It was the sea people that first knew the Earth was round, and also how big it was. Interesting that Columbus, the original BS artist, had to convince those loaning him his boats, that it was smaller than what was measured. He knew his stuff, but he was looking for somebody with boats but without the smarts. Yay Portugal!

3. Not a personal test, but look at airplane schedules. Surely the guys in it for a buck are not in it to perpetuate the hoax.

Tourist rockets? Like the one jeff bezos went up in? Is there something affordable for a normal person?

Have you heard of this? — flannel jesus

Sure, I'm quite sure the specifics of it are going to be slightly different from my example. My point is the same: Look at how the experts formed their answer, then try it yourself.

Absolutely. It's just interesting that, if the earth were the size oficially claimed, you would actually expect to see less than you do - that's something that a lot of flat earthers notice, it gives them ammo. "I can see more of chicago than I geometrically should if you were right". They're actually right about that.

Tourist rockets? Like the one jeff bezos went up in? Is there something affordable for a normal person? — flannel jesus

It costs about the price of a normal house. I could afford it if I had different criteria about how my earnings are best spent.

No comment on the other two? Both are pretty easy and less expensive.

definitely less expensive. I don't think sailing around the world is easy!

I don't think sailing around the world is easy! — flannel jesus

Don't need to. Just be in a few different places, enough to show the curvature. You do need to leave home, something not necessary for option 3.

Absolutely. It's just interesting that, if the earth were the size generally claimed, you would actually expect to see less than you do - that's something that a lot of flat earthers notice, it gives them ammo. "I can see more of chicago than I geometrically should if you were right". They're actually right about that. — flannel jesus

Ever heard of the saying, "Enough knowledge to be dangerous?" The problem with the flat Earthers is they're only taking one part of the equation and not factoring in refraction. Here's an example:

I believe I can't survive under water for more than 10 minutes. I go to a deep diving class and read up to the point that says, "Deep sea divers can survive anywhere from 30-60 minutes underwater..." "Rubbish!" I say. I hold my breath until I pass out. I cite scientific information about brain damage from patients who lack oxygen for 15 minutes. But what I didn't do was continue to read the rest of the sentence on the scuba diving page. "...with a working air tank and diving gear."

Yes, I'm right that people cannot survive 60 minutes without air. But I'm not right people with proper air tanks can't survive underwater for 60 minutes. So again, the flat Earthers are either being willfully ignorant, or refusing to understand the entire justification of the argument for why the Earth is round when observed from X distance away.

What's your preferred method of guaranteeing you're travelling the same direction? — flannel jesus

Try lots of times, and if you never find the edge of the world... (It's not practical anyway, since you need to fly. This means you need to make a pilot license, and then you'd need to trust your instruments...)

Ever heard of the saying, "Enough knowledge to be dangerous?" — Philosophim

Indeed! There's just a bit of a trap around the hole 'seeing stuff beyond the curve' question because of this. If you went in not knowing about refraction, you would think you've just proven that the earth is flat.

And if we're not relying on expert opinions, we might have to prove refraction too. I'm not sure how that proof would go.

The earth's curvature is visible wherever there's a visible horizon — jkop


That's not my experience. Go to the beach, look out to sea, it looks pretty flat to me. Take a photo, I'm pretty sure it's not visibly curved. — flannel jesus

Dan Olson has done the test for you:

that is over an hour long. I assume I don't have to watch over an hour of content to find out if the horizon of the sea visually looks flat or not. Do you have a timestamp to the part you think is relevant?

That covers the whole flat earth cultural thing. He made a companion piece just about the experiment:

That covers the whole flat earth cultural thing — Srap Tasmaner

Ah okay, the context you quoted made it seem like there was some specific claim in the video about the (un)flatness of the horizon.

This isn't that, this video is more a general reply to the op.

this video is more a general reply to the op — flannel jesus

And a reply to things "looking pretty flat."

Dan Olson happens to live not too far from a perfect spot to test whether the earth is curved or flat, a very long straight lake. He's just an ordinary guy who makes videos and is capable of being careful and thorough. More or less exactly what you said you wanted.

He looked. The earth is not flat. Case closed.

so he does disprove that the horizon looks visibly flat to the naked eye in that video? So... where's the time-stamp for that?

However, I believe the question of the shape of the earth is one where we can actually kinda go along with the flat earthers in rejecting expertise entirely, and say "no, no really, how can I personally demonstrate the shape of the earth?" Not all questions are within the grasp of the average person — flannel jesus

Yes it is, you can test it yourself. You can just walk the footsteps of everyone who was able to measure the curvature of earth before we had rockets that went into space. You can use telephoto lenses yourself etc. Without it being out of reach for a common citizen. The folding ideas video is a good example of this.

I think the major problem with all this is that people aren't questioning or are critical of scientific facts because they've measured anything. Their beliefs are rooted in the laziness of never looking for actual answers and facts themselves.

They operate on pure belief, no different from religion.

The reasons for them doing so comes not from a genuine interest of what is true or not, but the emotional foundation of wanting to be better than others. And without education or intellectual capacity, they are jealous of scientists and experts. So they form a cognitive bias in which they manifest a truth of their own making that contradicts what experts say about some specific thing, in order to feel like they're the ones in the know and everyone else is stupid.

It's basic Dunning Kruger biases forming.

It is never about earth being flat, it is about people feeling lost in a world in which experts dominate the consensus of truth. These kinds of cognitive limitations are the basis for all forms of populism, it's the basis for MAGA and other extreme movements around the world (pun intended). People find a family and social structure within these groups as they don't feel welcome anywhere else.

so he does disprove that the earth looks visibly flat to the naked eye in that video? So... where's the time-stamp for that? — flannel jesus

I recommend watching it in its entirety. It's very thorough about the whole thing and the people believing earth is flat.

Yes it is, you can test it yourself. You can just walk the footsteps of everyone who was able to measure the curvature of earth before we had rockets that went into space. You can use telephoto lenses yourself etc — Christoffer

Judging by how you cut off my quoted post, and your subsequent response, I think you missed the part where I explicitly said that THIS question is within the realm of a normal person. I think you got mixed up in what I said there.

I recommend watching it in its entirety. It's very thorough about the whole thing and the people believing earth is flat. — Christoffer

I would love to, it looks like a really interesting video. It was linked in a very specific context though - the context was, someone claimed that the horizon is visibly curved, and I'm doubting that.

I'm 100% sure that the video is a great reply to the OP. What it ISN'T a great reply to, is the quote of the conversation it was given as a reply to, which was specifically about the apparent visibility of the curve of the horizon.

Judging by how you cut off my quoted post, and your subsequent response, I think you missed the part where I explicitly said that THIS question is within the realm of a normal person. I think you got mixed up in what I said there. — flannel jesus

Oh, sorry, my bad. However, the rest of my answer is about why they don't do it.

For the second video I posted, the first five minutes goes over his camera setup and the math he is going to be checking. He explains exactly what measurements he will confirm or disconfirm in the video. The entire rest of the video is just a whole bunch of the footage he shot for the first video.

If you watch for a few minutes, you can see the curvature of the earth perfectly clearly.

I'm 100% sure that the video is a great reply to the OP. What it ISN'T a great reply to, is the quote of the conversation it was given as a reply to, which was specifically about the apparent visibility of the curve of the horizon. — flannel jesus

I'm just giving a note on that. I've seen the whole thing and it's a really good video. All of Folding Ideas' videos are masterfully done arguments.