To be fair, this only rules out the hollow earth scenario. It says nothing about whether there are large (artificial?) caverns that may be large on a human scale but small on a planetary scale. To detect those, one would look for small variations in the surface gravity; the surface gravity would be stronger where dense, solid rock is underneath and weaker where porous rock or a cavity is underneath. Geologists working for petroleum companies use this method to look for rock that might contain oil or gas. This is how Glen Penfield found the Chicxulub crater.

Well, we’ve been drifting off topic here, but no, my refutation is entirely sound. All it needs is the inverse square law for gravity, which certainly works on the scale of the earth. (Some people suspect that “dark matter” may be a problem with our understanding of gravity on the scale of thousands of light-years, but they are a minority.) If we didn’t understand gravity pretty well, we wouldn’t be able to dock with the ISS, for example, or send a probe to the asteroid Vesta. It’s even been tested down to distances of well less than a centimeter, in the vain hope of providing evidence of “large” hidden dimensions. So we can state with confidence that if the earth were hollow, with all its mass concentrated in a thin shell, the gravitational forces would cancel out and you would have weightlessness inside the shell. If there were an “interior sun” that (for some unknown reason) kept at the center the earth, it might pull things into it; it would not help keep Nazis and Atlantian hippies stuck to the shell. The centrifugal pseudoforce might, but it would be a tiny effect — much, much smaller than the moon’s surface gravity, which already was enough to interfere with normal walking. This is backed up by the fact that our apparent weight does not much vary with latitude.

Here are a few sites that describes the analogous situation for electric forces (because they are also inverse-square):

Electric Field of a Spherical Conducting Shell
More on Gauss’s Law
Gauss’s Law
A proof of Gauss’s Theorem (in the generic case) can be found on pages 7 and 8 of Fundamental Theorems of Vector Calculus

I was just expressing my belief that your refutation was not as sound as you appear to think it is.

Well, certainly the idea of a hollow earth goes back centuries, so there has long been a story looking for someone to attach itself to. Likewise, Admiral Byrd has been dead for about 56 years now, so it’s had plenty of time to spread, mutate, adapt, and implant itself in the culture. I strongly suspect it to be an urban legend.

Well, if you don’t like the gravity argument, you can use at least two more. One is that we can use seismic waves from earthquakes to probe depths all the way down to the core. This should be impossible if the earth is hollow. Another one deals specifically with the many entrances that are said to exist, for example at Mt. Shasta, at the Great Pyramid, and in Mammoth Cave, KY. Well, if you go any deeper in Mammoth Cave than the current level of the Green River, you’ll hit water. That’s how the cave was carved over time. Yes, the cave has been mapped for more than 350 miles, but those are 350 miles of branches and turns, not 350 miles in a straight line (as many people seem to think) and certainly not 350 miles down.

So, sorry, Lord of Gravity, I am unable to help either one of us, and only willing to help one.

@Goodfoot

There are web pages that claim Admiral Byrd as a believer in their claims, but these are … questionable sources. Can you point to something a bit more tangible? Something like an unambiguous statement in support of the hollow earth theory in a book written by Admiral Byrd and published during his lifetime (so no, The Missing Diary of Admiral Richard E. Byrd, published 35 years after his death, does not count), or an interview in a major newpaper — something that would indicate this is not an urban legend about what he allegedly wrote in his unpublished diary?

There are many problems with the hollow earth idea. One is that it is an undergraduate exercise to show (using Gauss’s Theorem) that gravity would not hold people against the inner wall, where peaceful communes of technically and spiritually advanced hippies are said to live. Gravity does not work that way! Good night!

YOU tell him he’s not; I’m not having anything to do with it.

Just sayin’.

The photo was taken about a month ago at the Austin, Texas-based “Museum of the Weird.” If you ever get chance, you should check it out. It’s a very cool place!