What experiment can I do to show that the Earth is a spheriod?
November 23, 2017 6:42 PM   Subscribe

Flat Earthers fascinate me. Mostly because it's such a pure conspiracy theory; it's good to see someone standing up to Big Sphere. What kind of experiment could I carry out for an open-minded Flat Earther that would demonstrate the Earth isn't a disk? There's the old "ship disappearing beyond the horizon" thing, but that's something you rarely (if ever) see with your naked eye. Presume that I'm willing to throw a little but of money into this.

One important constraint is that it can't rely on NASA or any other "suspicious" organization. It has to be some kind of experiment I could carry out. Any level of scientific sophistication is OK (I guess we're assuming a scientifically literate flat Earther), but simpler experiments are better.
posted by Betelgeuse to Science & Nature (40 answers total) 10 users marked this as a favorite
If you've got contacts at a decent enough distance, do it like Eratosthenes:

* establish the distance between the two sites
* arrange for two sites to communicate at a synchronised time, e.g. via skype or phone
* with a spirit level, establish a horizontal surface then set up a vertical stick
* measure the shadow cast at each location, then use trigonometry to find the angular difference between the two horizontal surfaces.
posted by Fiasco da Gama at 6:52 PM on November 23, 2017 [15 favorites]

Well, if you don’t have any tall ships sailing around at a convenient distance, you could start with Eratosthenes, and consider the difference in the angle of the Sun with latitude.
posted by Huffy Puffy at 6:54 PM on November 23, 2017

Yes. The Eratosthenes solution is great, but let's assume that I want to carry out the experiment in one location. I want something that "I can see with my eyes (or instruments)," and don't trust anyone other than myself making the observations.
posted by Betelgeuse at 6:57 PM on November 23, 2017

I guess that's the intellectually delightful thing about Flat Earth, that if you take it seriously with enough skepticism/imagination it's incredibly hard to disprove.

Why not use a balloon to near space with a camera?
posted by Fiasco da Gama at 7:14 PM on November 23, 2017 [8 favorites]

Well, you could use other solar system bodies as an analog, and ask why the Moon and planet Venus have phases. Or why Jupiter and Saturn appear to be disks, with Saturn’s rings changing in orientation over (long) time. If they’re all spherical, it seems odd that the Earth solely wouldn’t be.

Or consider why there is a horizon. And go up a mountain and consider why the horizon is so much farther away.
posted by Huffy Puffy at 7:25 PM on November 23, 2017 [2 favorites]

Or you could subscribe to DirecTV, and align your dish to a collection of satellites in geostationary orbit. Your TV signal is getting to you some sort of way, and it won’t work if you aren’t aimed right.
posted by Huffy Puffy at 7:28 PM on November 23, 2017

Unfortunately, Flat Earthers’ “evidence” of the Earth’s flatness tends to be stuff “I can see with my eyes,” which deliberately disregards whole schools of science and whole laws of physics. It’s like the “evidence” that a volcano’s ash cloud rises straight up, when “clearly” on a spinning sphere the cloud “should” be smeared across the atmosphere. So you’re looking to score points while letting the Flat Earthers define the game.

That said, you could use your little bit of money to travel to Antarctica with your Flat Earther friend and show them that Antarctica is not, in fact, a vast ice wall ringing the disc of the world.
posted by ejs at 7:34 PM on November 23, 2017 [15 favorites]

I googled Foucault's pendulum and found flat Earth theories about that, so I'm having a hard time imagining an "open minded flat Earther".
posted by bonobothegreat at 7:49 PM on November 23, 2017 [4 favorites]

Al-Biruni's method might be your best bet, so long as you have "a suitable mountain with a flat horizon in front of it" and an astrolabe.
posted by clawsoon at 8:26 PM on November 23, 2017 [3 favorites]

Taking a great circle route trans-Atlantic flight made it really obvious to me that the Earth is round, not that I ever doubted in the first place. I didn't find any good pictures on Google, but I remember seeing the curve of the earth pretty clearly, plus the whole light-dark-light thing in the course of about 10 hours. How much you can see might depend on the time of year, due to the jet steam. The flight I'm recalling was from Amsterdam to Vancouver in mid-December, which at one point was over 39000 ft.
posted by fiercekitten at 9:01 PM on November 23, 2017 [9 favorites]

Notw that Eratosthenes' measurement doesn't immediately prove a round Earth. If you assume the sun is close by then the changing angle to the sun can be explained with a flat Earth (assuming you are just taking measurements at two points).

I think objects going below the horizon is the best bet. How does a setting sun work on a flat Earth? The flay Earth assumes the sun will get close to the horizon.and smaller, not that it will go below the horizon.
posted by It's Never Lurgi at 9:04 PM on November 23, 2017

Watch the sun set over the ocean.

- Go to a beach that has an unobstructed view of the horizon.
- Watch the sunset while lying down.
- Just when the sun sinks below the horizon, stand up, and you can watch the sun go down again because by raising the height of your field of view you can see further round the curve of the earth.

Princeton explains it better.
posted by His thoughts were red thoughts at 9:17 PM on November 23, 2017 [41 favorites]

What exactly is an open-minded Flat Earther? That argument was settled 500 years ago.
posted by Kwadeng at 9:36 PM on November 23, 2017 [13 favorites]

They have an open mind about whether the earth is flat or round. Saying that an argument is settled is close-minded. Sometimes, as in this case, there's nothing wrong with being close-minded; the argument is, indeed, settled. The only thing you miss by being close-minded in this case is that you have less (intellectual) fun.
posted by clawsoon at 9:56 PM on November 23, 2017

What kind of experiment could I carry out for an open-minded Flat Earther that would demonstrate the Earth isn't a disk?

I think your main problem here is going to be finding a genuinely open-minded Flat Earther, as opposed to one with a completely rigid devotion to Maintaining The Controversy.

Having overcome that difficulty, take your OMFE to a west coast beach with a cliff behind it, and sit with them as they watch the horizon's shadow climb the cliff at sunset. Or if you're nearer an east coast you can watch the horizon's shadow come down a cliff at sunrise.

Both of these effects demonstrate conclusively that the sun must genuinely be sinking below the horizon as it sets. But if it were to do that on a flat Earth, the entire Earth would experience night at the same time. It demonstrably doesn't do this, because time zones are a thing.

The only way for a FE to wriggle out of this conundrum is via handwaving about "perspective", none of which they will be able to illustrate with anything like a plausible diagram.
posted by flabdablet at 10:45 PM on November 23, 2017 [7 favorites]

Perhaps you're asking because you already listened, but Oh No Ross and Carrie just did three episodes talking (under cover) with a flat earther group on California and a convention. They discuss what things would convince them - most of it is severely expensive and they each must see it with their own eyes. (And agreed that they aren't actually open minded and lean toward a lot of conspiracy theories and don't generally think out the whole "flat earth" conspiracy - at least that group. Note I haven't listened yet to the recent episode from the conference.)
posted by Crystalinne at 12:28 AM on November 24, 2017 [5 favorites]

Popular Science has a pretty lighthearted article about it here: https://www.popsci.com/10-ways-you-can-prove-earth-is-round

they also mention what I was thinking about which was: if the earth is flat why can't we see every country when we photograph the Earth from the moon or an even further distance?
posted by alchemist at 1:29 AM on November 24, 2017 [6 favorites]

why can't we see every country when we photograph the Earth from the moon or an even further distance?

Because it's NASA that takes those photos and therefore they're all fake, duh.
posted by flabdablet at 2:11 AM on November 24, 2017 [6 favorites]

A classic, which apparently used to be demonstrated in schools before we had satellite images, is the Bedford Level Experiment.

Your flat-earth friend needs to agree that, generally, a body of water will find a level surface. On a flat earth the surface of a lake will be flat, on a curved earth the surface of a lake will be curved. This is consistent with most flat earthers' ideas, from what I've read.

Then it's just a matter of demonstrating that the surface of a lake or river is curved. Find a long, still or slow-flowing body of water (a canal is ideal) and have three friends hold or plant a measuring stick at your position, two miles away, and four miles away. Using a telescope or a theodolite, sight a line from 1m above water level at your position to 1m above water level 4 miles away. If the surface of the water is flat, the intermediate 2-mile marker should be exactly on this sight-line. If the surface of the water is curving with the earth, the 2-mile marker will be higher than this sightline.

A simple bit of trig will let you estimate the radius of the earth based on how far off the sightline the marker is, plus their distances apart.

This isn't a trivial experiment logistically - you need friends with waders, and to travel to a suitable body of water - but it's something that can be seen with one's own eyes, and explained with a simple line drawing.

Of course, you'd need the people holding the measuring sticks to be people you both trust, to save you from accusations that e.g. the person at 2 miles swapped their stick for a slightly longer one to fake the experiment's results. You'll also need to repeat it in a lot of different locations and directions, to demonstrate that it's not due to e.g. an upwelling making the water level higher at the centre point. And lots of other things that I haven't thought of but a flat-earther, who is necessarily very skilled at finding justifications for ignoring evidence, will.
posted by metaBugs at 2:19 AM on November 24, 2017 [17 favorites]

Find a tall skyscraper that has an observation deck in the nearest big city. Wait until the end of December o r beginning of January and sit outside in front and watch the sun set. As soon as it gets dark, race up to the observatory with your flat-earth friend and watch the sun set again. It's an impressive sight, with the city below in darkness while it is still day up at the top where you are. No way to explain that with flat earth "theory".
posted by ambulocetus at 4:59 AM on November 24, 2017 [6 favorites]

Pffft. Everybody knows that light rays can only travel a limited distance before they stop. The top of the building is just closer to the receding sun than the bottom, is all.
posted by flabdablet at 5:12 AM on November 24, 2017

Ask your interlocutor this simple question: If the earth is not round, how does DigitalGlobe do what they do? Where are these pictures of places planes do not fly coming from?
posted by wierdo at 5:23 AM on November 24, 2017

I've read that (some of) the ancients knew the world because the shadow of the earth on the moon during a lunar eclipse is circular.

You can see the "ship below the horizon" observation at a fairly short distance if you lower your height of eye to a foot or so. If you have a body of water a mile across with trees or buildings visible on the far side, you might be able to see a difference between a picture taken at ground level and one taken at 6 ft high.

The fact that days/nights have different durations at different latitudes is due to the shape of the earth. But, to be honest, you would have to compare that to the precise model of the sun and seasons proposed by the flat earthers, if they have one, which they probably don't because it would be easily disproved.
posted by SemiSalt at 5:27 AM on November 24, 2017

Find a place with dark night skies and watch the stars over the course of several hours and over a range of seasons. It helps if you learn the constellations. It will soon become obvious that the sky is a sphere, turning on its polar axis around you [relative to your reference frame of course]. Now travel to a sufficiently different latitude (at least 5 degrees; the more the better) and go watch the night sky. It will be viscerally obvious that the ground beneath you is at a different angle relative to the axis of the sphere of the sky.

Honestly though? Flat earthers are just trolling you.
posted by heatherlogan at 7:13 AM on November 24, 2017 [4 favorites]

I've also been listening to the Oh No Ross and Carrie investigation and there are people actually saying they'd believe the earth was round if they saw a photo of it, but there are no photos of it! (There are many, many photos of it.) Flat Earth seems to be the terminus of all conspiracy theories. Once someone reaches Flat Earth Station, they've already passed through anti-vaxx, pizzagate, chemtrails, Infowars, David Icke, and every truther/false flag conspiracy. So, like, get a GoPro and send it up in a weather balloon, but it's not going to make a dent.
posted by soren_lorensen at 8:24 AM on November 24, 2017 [5 favorites]

get a GoPro and send it up in a weather balloon

But those photos look like a disc, no? I guess it'd have to hover there for a while to watch the Earth rotate...
posted by Pig Tail Orchestra at 8:51 AM on November 24, 2017

Here is a satellite video of rotating earth at night from a geostationary position.

Another showing the motion of earth while also showing the motion of the sun!! Cool stuff starts at 17.00 of the video.
posted by indianbadger1 at 9:38 AM on November 24, 2017 [1 favorite]

Buy an around-the-world airplane ticket. You keep going in one direction and end up where you started.
posted by JackFlash at 10:25 AM on November 24, 2017 [1 favorite]

A question I've always wanted a an answer to from a flat-earther is: which map projection is correct?

I mean, if the world is flat, exactly one of them is. Please enlighten us!
posted by dmd at 11:18 AM on November 24, 2017 [10 favorites]

On a clear day, from Indiana Dunes National Lakeshore, one can see the Chicago skyline with the naked eye, ~25 mi. away.

From lake level at Warren Dunes State Park, ~50 mi. away, you may be able to make out the tops of the tallest buildings in Chicago. Climb one of the dunes and you can see more of the skyline.

From Muskegon State Park, ~115 mi. away, the Chicago skyline cannot be seen, even with binoculars.

All of these are across open water.

Substitute any city skyline which would have views across open water from various distances — but keep in mind that atmospheric effects may cause a skyline to be visible from a greater distance than it would on an airless world. (Muskegon is far enough from Chicago that Chicago is unlikely to be visible even with weird atmospheric effects.)
posted by DevilsAdvocate at 11:25 AM on November 24, 2017 [2 favorites]

Speaking of large lakes...
posted by Huffy Puffy at 12:43 PM on November 24, 2017 [6 favorites]

How do they explain why the Soviets didn't expose NASA's duplicity?
posted by GhostintheMachine at 7:26 PM on November 24, 2017

You don't. You put the onus on the Flat Earther to prove to your satisfaction that the Earth is flat. They have to spend the time and money doing so, not you. This will require the patience of a saint, and the ability to keep sharp/heavy objects out of reach for the duration, though.

Never forget that Wallace ultimately lost the wager with Hampden over the Bedford Levels experiment.
posted by scruss at 7:05 AM on November 25, 2017 [3 favorites]

I think at this point in history, finding an 'open-minded Flat Earther' is very improbable and maybe impossible. The history of the conflict between science and religion has shown us that it's impossible to prove something to someone if they are determined to never believe it. People would rather get violent than admit that their dearly-held belief is wrong. Especially when their eyes are telling them that they're wrong.

So your experiment is impossible (or dangerous, if you try it on a regular flat-earther) for that reason. You could add time travel and pull some poor sap from the uneducated classes of the Middle Ages but that person would, by definition, be scientifically illiterate.

One way around this problem is to posit a hypothetical person raised in seclusion by flat-earther parents and taught scientific literacy EXCEPT about anything that could prove a round earth. And, also, they'd have to have already come to a point in their life where they are questioning what their parents taught. This person could work for your purposes... but I don't know if they exist anywhere.

Maybe I'm ruining the question by overthinking it, and you just want to do some hands-on science for your own amusement. The most fun idea I can come up with is going to Nevada and climbing some buttes. The taller the mountain / butte, the better, but you also have to have good atmospheric visibility which is why the desert is ideal. Bring binoculars and a sketchbook, and as you go up and down stop at various heights to draw the horizon and the landmarks you can see as accurately as possible. As you draw the horizon over and over at the different heights you'll start to see it really clearly.

It'll work best if you do the hike several times to refine your ability to draw accurately. It's kind of like the sunset/skyscraper thing, or the ship/horizon thing, but it doesn't require such good timing. And taking a vacation to go hiking and drawing in the desert seems like a lot more fun to me. If your drawings are detailed and accurate enough — big sheets of graph paper would help — you could even try to figure out the math for the distances between the landmarks, or how high they are. Just like old-timey explorers did when they didn't have elevation maps.
posted by it's FuriOsa, not FurioSA at 8:43 AM on November 25, 2017

A paper about how children learn to conceptualize a spherical earth posted in a related thread has an interesting idea from Aristotle: When you travel north and south, the angle of the North Star changes. Every 69 miles or so north that you travel will change the angle of the North Star by about 1 degree.

This could also be partially explained by a North Star which is close to earth. You could address that in a couple of ways:

Keep travelling north. With a spherical earth and a distant North Star, the angle change will remain consistent: For every 69 miles, the angle will change by 1%. With a flat earth and a close North Star, the angle change for every 69 miles will keep getting larger. I haven't done the math to figure out how far you'd have to travel to make it obvious, but the calculation should be straightforward trig.

Travel in a perfectly straight line east and west. If the North Star is distant, it should always remain at the same angle with respect to your east-west line. If the North Star is close, its angle should observably change with respect to your east-west line.
posted by clawsoon at 10:30 AM on November 25, 2017 [2 favorites]

Have them try to recreate moon phases with a tennis ball, a ping pong ball, and a flashlight. Then swap out the tennis ball for a coaster and ask them to do it again.
posted by ananci at 1:09 PM on November 25, 2017 [3 favorites]

Most projections of the flat earth show the center at the north pole and Antarctica as a giant circular ice mass. A flight from Johannesburg to Sao Paolo is just about the same length of time as a flight from JFK to Moscow. Now, either the flights in the southern hemisphere somehow manage to travel faster than the speed of sound, or there is a problem with the projection. Play around with google flights and take a look at non-stop flights from various locations to other locations. The timing of flights just doesn't work unless either: a.) the airlines intentionally delay or speed up flights to make it look like it is a round earth, thus burning extra fuel and somehow hypnotizing everyone in the flight paths to make them ignore the supersonic planes overhead or b.) the earth actually is round.
posted by Hactar at 3:55 PM on November 25, 2017 [1 favorite]

Y'all are way underestimating the batshitness of the average flat earther. Many of them actually think the sun literally moves along a literal track in the sky. The phases of the moon? Engineered by "them" to perpetuate the spherical lie. No, really.
posted by soren_lorensen at 4:32 PM on November 25, 2017

A question I've always wanted a an answer to from a flat-earther is: which map projection is correct?

I mean, if the world is flat, exactly one of them is. Please enlighten us!

The only correct map is this one. Shows the ice wall and everything.

What's a "projection"?
posted by flabdablet at 6:37 PM on November 25, 2017

A variation on the Foucault pendulum is this pair of videos observing the Coriolis effect in the US and in Australia in identical kiddie pools. Both pools spontaneously develop vorticity, but in opposite directions.
posted by fantabulous timewaster at 8:47 AM on December 5, 2017 [2 favorites]

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