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Episode 33: Flat Earth

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Recap: It might be a parody these days, but there are websites out there that claim Earth is flat. Learn some "do-it-yourself" ways to figure out that it's round.

Solution to Episode 31's Puzzler: Trebor posted a YouTube video that shows exactly what I was after for this puzzler. (Note: It does have background music. Other Note: The shutter speeds that Trebor reports is about a factor of 10 faster than I usually use to photograph the Moon. If your ISO is set to around 100 or 200, then start photographing at around 1/200 sec and see how you do for the Moon.

(Best seen full screen in 720p)

Puzzler: Can two different objects, when illuminated by a single distant light source, ever cast non-parallel shadows? If you can take a photo to support your answer, that would be best.

Q&A: Gary S. from Israel asks: "I've heard all you debunking of the Planet x nuts, but I'm reading Bill Bryson's A Short History of Nearly Everything, which is NOT a nut-job, and I came across this paragraph: A few astronomers continue to think there may be a Planet X out there—a real whopper, perhaps as much as ten times the size of Jupiter, but so far out as to be invisible to us. (It would receive so little sunlight that it would have almost none to reflect.) The idea is that it wouldn't be a conventional planet like Jupiter or Saturn—it's much too far away for that; we're talking perhaps 4.5 trillion miles—but more like a sun that never quite made it. Most star systems in the cosmos are binary (double-starred), which makes our solitary sun a slight oddity. Is there anything in what these "few astronomers" think?"

The short answer is "yes."

The longer answer is also "yes." It's entirely possible that there *is* another object in the far outer solar system, well beyond Pluto, that could be several times Earth's mass. There is an observed phenomenon called the "Kuiper Cliff" where we observe Kuiper Belt objects until about 50 times the Earth-Sun distance. Some have suggested that a large, unseen planet-sized object is sweeping this area clean of objects, though it has yet to be observed.

So, as I said, it's possible, and there may be ancillary evidence that one exists. It's just when you claim that it's going to come by in 7 months but no one's seen it yet that we get into the pseudoscience.

New News from a Future Episode (#56)

  • The Skeptoid podcast run by Brian Dunning just put out a Flat Earth "Theory" as episode #338. He doesn't go too much into showing why Earth is actually spherical, but it's a pretty good episode on the history of the idea, which is something that I didn't really go into in my episode on the topic.

Additional Materials:


History: Perhaps we should start with some of the claimed history for the idea the Earth is flat.

Just Look Around: One can start with the basic idea of, "Just look around." If you grew up in an isolated part of the world, away from any modern civilization, knowledge, modes of transportation, or anything else, how would you know Earth was round? You would know that it had some topography, ups and downs, but in isolation, it would be difficult to really tell that you lived on a sphere rather than a plane. It takes some experimentation, larger perspective imagery, or some other science measurements to tell from the ground that Earth is round.

It's often believed that ancient Greeks and Romans thought Earth was flat. To the contrary, at least some of them knew Earth is a sphere and had a pretty good estimate of its circumference. I'll talk more about that later, but it bears mentioning for historic purposes in this historic discussion.

Christian Bible: Moving forward, no discussion of flat Earth would be complete without a brief discussion of the Christian Bible. Since, like it or not, this one collection of works held significant sway over much of the world for many centuries, how people interpreted it is important.

First, there are many passages in the Bible that say Earth is immobile. Psalm 96:10, for example, reads, "He has fixed the earth firm, immovable." Other parts talk about the sky as being a vault that covers Earth, or that it is a fixed entity, such as Isaiah 48:13, "...with my right hand I formed the expanse of the sky."

Other parts imply if not actually state Earth is flat. Daniel 4:10-11 talks about a tree that's so tall it's visible from all parts of Earth. If Earth is round, then that's impossible; it's only possible if Earth is flat.

I'll link up to a page that presents these arguments and others in the shownotes, but suffice to say, if someone is Christian and wants to believe in a flat planet, they can easily find Bible verses that will support their position. And it also bears mentioning that, despite many hard-core Christians today stating that the Bible must be read literally with no exceptions, they still reinterpret these passages to NOT mean Earth is flat.

Modern Flat Earth Society

With that brief history out of the way, there is a modern Flat Earth Society. It's honestly hard to tell if these people really believe Earth is flat or whether this falls under Poe's Law. Poe's Law being, in my words, that some claims that people believe are so incredibly stupid that a made-up parody is indistinguishable from the claims people really believe.

The proposed model is a cylindrical Earth with a flat surface. The cylinder is tall enough for there to still be what they call a core which is what they say creates volcanism. The map of the surface is claimed to look like the UN flag, with the north pole in the center and all the continents spread out radially from it, with the continents near Antarctica all squished up. The claim is that Antarctica is really a wall of mountains that are covered in ice that keep the oceans from falling off.

Gravity is caused by a constant acceleration upwards, and they have various models for how the atmosphere stays here, including a great dome or a dark energy field.

The sun and moon orbit above us in a circle. Each is 32 miles (50 km) across and orbit 3000 miles (5000 km) above sea level. Stars are another 100 miles above that. As I said, this could be Poe's Law in the works, but on the FAQ on their wiki, the first answer is, "This site is not a joke. There are people who seriously believe the Earth is flat. However, there are also people who do not."

The Flat Earth Society website presents a few reasons for believing Earth is flat. I'm only going to go briefly into two of them.

First is Earth can't orbit the Sun because there's no way for it to maintain its velocity over billions of years, and because when you orbit an object, there's an acceleration and any object "ahead" gets squished and "behind" would float away.

I want to talk about this one because it raises two basic physics concepts. The first part of this is really Newton's First Law -- The velocity of an object remains constant unless the body is acted on by an external force. Yes, there have been tiny perturbations to Earth's orbit due to external forces over the œons, but in general there has been no significant velocity change, no dying down of our orbital speed through time because there has not been any sort of frictional force to slow us down.

The other part of this has to do with reference frames and acceleration versus velocity. Our reference frame is effectively a moving object. To us, this object is stationary for all practical considerations. Our motion is completely relative to Earth because it is the dominant gravitational field that affects us. So, it doesn't matter if you're temporarily on the leading or trailing side of the planet, you are not going to get squished or fall off.

The next claim is related: Objects on a curved surface would fall off, sliding "down" until they reached the bottom and then fall off.

The misconception here is the concept of "down." Again, in our reference frame, "down" is towards Earth's center of gravity, which is within the core of the planet. No matter where you are on any point on the surface, you will always be pulled towards the center of the planet as opposed to an arbitrary "down" point like the south pole and then fall off.

Independent Ways to Show the Earth is Round

With all that said, there are many, many ways to demonstrate Earth is round, especially in this day and age. Not the least of which are photos from space, circumnavigation, and other things. Predictably, the Flat Earth people generally just say that it's all a vast conspiracy and none of it is real.

So in the place of modern techniques, I'm going to describe two different ways that really anyone can use if they wanted, and they're both ways that people hundreds or thousands of years ago used.

The first was figured out by the Greek Eratosthenes, which I alluded to in the quick history lesson at the beginning. Eratosthenes figured that if Earth is round then shadows cast by the same height object at different latitudes on Earth at the same time of day would be different. With some trigonometry, you can calculate the circumference of the planet. If Earth were not round then the shadow lengths should be the same.

Eratosthenes did this experiment and was able to calculate the circumference of Earth to within 2% of the value that we have today. Pretty darn good for a guy who lived 2200 years ago.

The other method is one that was supposedly used by Galileo. If Earth were flat, then the shadow cast by it on the moon during a lunar eclipse would be flat, too. It's not. Since Earth is round, then its shadow - regardless of what part of Earth is facing the moon - is also round.

And that's about all I wanted to say about the flat Earth idea.

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