# You mean the Earth isn't flat?

Forgive me if this has been answered, but I did a quick search and came up with nothing so I figured I would ask the question.

A coworker of mine just came to me with a problem. His daughters friends’ mother seriously believes the Earth is flat. “Its the most logical answer, think about it!” she told him last night and he wasn’t pulling his leg. So, he came to me wondering if I could come up with some easy fact/question he could throw at her to make her realize the error of her ways.

The first thing I could think of was “Why can’t you see cities or towns that are 100 miles away?” but I realized visibilty/haze would be her response.

Can someone give me some ideas?

Thanks!
Eric

The explanation I always heard was the curved shadow that the earth throws on the moon was proof that it was round. Or you could just put her in a boat and tell her to find the edge.

From the archives: You say the earth is round? Prove it.

My first thought is, if the Earth is flat, how come our geography is “closed”, i.e., if you keep travelling you end up where you start? A more ancient proof is, look at the moon when it’s in a crescent or gibbous phase. Why is the shadow of Earth curved? Also, if she travels in a ship, she’ll see that the sea is curved – she’ll see the tops of buildings in whatever harbor she’s approaching before she sees the rest.

Well, those are the “easiest” I can think of.

Uhhh… Does she think photos of the Earth taken from space are fake? My, what a conspiracy we would have on our hands!

An easy proof is that if you go to the ocean and watch a boat sail away, if the Earth were flat, you should see it become smaller and smaller indefinately. But it doesn’t. You can clearly see the boat dissapearing “over” the horizon. Also, if you are on a boat sailing towards land, you’ll see the tops of mountains and buildings before the ground, another impossibility if the Earth were flat. By the way, you won’t convince her. Flat-earthers are nutball conspiracy types who only believe that tripe because it adds substance to their pathetic lives.

The easiest thing I can think of is to put her in a 747 and hope for a clear day flying. From that height the curvature of the earth becomes noticeable.

Actually, you can discern (if barely) the curvature of the earth from the top of a mountain or even the observation deck of the Sears Tower or World Trade Center on a clear day.

The 747 would give the best view however (IIRC 747’s generally fly higher when cruising than most other commercial airliners).

I shudder at the thought that people like this vote and are on juries.

My argument to her would be that she is obviously an ignoramus and would do well in trusting more knowledgeable people. Nobody has proved to me many things I believe. I just choose who to trust. some people believe HIV is not the cause of AIDS but I choose to believe otherwise even though it has not been conclusively proven to ME.

Thanks for the link, I will check it. As for the shadow and such, I don’t think she doubts much that its shaped as a “circle” but not a “sphere-ish” object, if that makes sense.

As for ending up where you started, I agree. But that wouldn’t be easy enough to prove to her.

Thanks

It’s not a simple explanation, but proof that the Earth is both spherical and that it rotates can be found using a pendulum. Since it’s too hard to tell with most pendulums, the general term for a pendulum that can clearly display this is “Foucault’s Pendulum” after the man who discovered (or at least explained) the concept .

To see what happens, your pendulum must be suspended at one point. The easiest place to observe is at the North or South Pole. As the earth rotates, it essentially rotates under the pendulum. If you draw a line on the floor where the pendulum swings, the pendulum’s arc will appear to rotate around that line once a day. This proves the earth’s rotation.

The sphericity of the earth is proven in the way the period of the pendulum changes depending on latitude. I don’t think that another shape would yield the same results.
Umberto Eco’s book Foucault’s Pendulum by the way, is about “nutball conspiracy types” and secret societies.

I think Friedo’s last two sentences are the best reply so far. That said, I don’t know how you’d have different time zones on a flat Earth. That’s something I’ve experienced directly.

On the other hand, you might have better success just saying “Look at a globe! Of course it’s a sphere!” Whatever she says in rebuttal, just keep repeating “But look at a globe.” Note that success here is defined as not stressing yourself out, and possibly having some fun in the process.

Foucault’s Pendulum? That sounds like more of that fuzzy math Bush has been talking about.

Seriously, how hard would it be to doctor one of those up to give you the rate of rotation you wanted?

It’s been awhile since I’ve been there but I believe the Museum of Science and Industry in Chicago has one of these. The pendulum is suspended some 30 feet or so to the roof with a quite large brass sphere at the end. The period has to be something like 10 seconds for a complete swing. On the floor they setup little pegs in a circle around the pendulum that get knocked over as the earth rotates under the pendulum. If you wait long enough (a day) you can see the pendulum eventually cross all points on the circle.

Of course, proving to her that the earth is rotating under the pendulum and not that someone is merely swinging the pendulum slowly in different directions may be another chore.

Good point. And when you think about it, we label many things as “fact” when in actuality we simply believe them.

For example: your birth certificate says you were born on such-n-such a date (September 28th, 1967, for example). But can you prove it? How do you know you weren’t actually born on September 26th, 1967? Or two weeks before??

In reality, you believe you were born on September 28th, 1967, because that’s what your parents told you, and that’s what your birth certificate says. But you can’t prove it…

Thinking on this and what I wrote in my post I’m not sure you could doctor a pendulum to change the direction of its swing (assuming the pendulum hangs from a rope and not a stiff arm the the pendulum on a clock).

If you walk around the pendulum will continue to swing on the same plane (as is the premise of Foucault’s Pendulum except the earth is doing the walking). If you give the rope a good twist or shake the pendulum will go haywire and start swinging in circles or spirals.

With a decent amount of weight (say a bowling ball) you might be able to prove to her satisfaction that someone can’t change the direction of the pendulum without it being obvious that something else is going on.

Hijack
That reminds me of a story about Mario Cuomo. Once he was out shaking hands and saw a little boy and his mother, so he asked the little boy how old he was. When the boy said “Six”, Cuomo asked, “How do you know you’re six? Is it just because your mother said so, or do you “feel six”? What is it like to be “six”?”
Supposedly, the boy started crying…

You could ask her what evidence she has that the Earth is flat, especially taking into account gravity. Wouldn’t gravitational forces cause the edges to warp? Also, if the Earth is flat, what would the composition of the “bottom” of the earth be? Is it livable? Is their life down there? Can a person travel to the other side of the earth?

The phases of the Moon are not caused by the shadow of the Earth! If they were, how would the Earth cast a crescent-shaped shadow onto the gibbous moon? The Moon changes phase because it’s a sphere illuminated by the Sun, moving around the Earth.

The shadow that the Earth casts on the Moon during a lunar eclipse, however, is an excellent demonstration that the Earth is round.

D’oh! Thanks Podkayne. Of course, it’s eclipses I should’ve been thinking of.

scratch1300 wrote:

I’m afraid you’re mistaken about the causes of a crescent or gibbous moon. The reason for that is that only half of the moon is lit by the sun at any given time, and it’s not always the half pointing toward the earth. This does suggest the moon is a sphere, but doesn’t really address the earth. The shadow of the earth argument is a good one, but when the shadow of the earth obscures the moon it’s called a lunar eclipse. Lunar eclipses only occur when the moon is full, so looking at a crescent or gibbous moon will never show you the shadow of the earth.

The ancient Egyptians determined the radius of the earth to within a few thousand miles with the following method:
At noon on a particular day, it was known that the sun shone directly down to the bottom of a particular deep, straight well. This showed them that the sun was directly overhead at that location. On that same day at noon, hundreds of miles north, the length of the shadow of a tall,straight obelisk was measured. Since the height of the obelisk was known, simple geometry enabled them to determine what the angle was between the two locations, and the distance between the two locations gave them the radius of the earth.

I have personally travelled around the world: starting in HongKong, westward to Europe, America and back to HK. Does this prove anything? The earth could be flat and I was just being taken for a ride. I did lose a solar day in the process but it could be that I was just told that when I woke up and the entire world was part of the joke.

I just talked to my friend in HK on the phone this morning and she told me it was night there and she was getting ready to go to bed. But I wonder if the entire world is just playing a joke on me.