There have been lots of theories saying the Earth is hollow, but I know only one that could be true.
Edmond Halley, the guy who discovered the famous comet, had a theory where Earth consists of a hollow shell about 800 kilometers thick, two smaller shells nested inside, and a ball in the middle - all separated by atmospheres and rotating at different speeds! It sounds nutty, but Halley was trying to explain the Earth's rather complicated magnetic fields: each of his shells was magnetic.
People sometimes accuse Leonhard Euler, the famous mathematician and physicists, of believing the Earth was hollow. But that's not true. In fact, all Euler did was propose a famous thought experiment:Puzzle:
If you could drill a hole all the way through the Earth, and drop a stone in, what would happen?
With the passage of time, scientists have been learning more about geology, so the remaining people who believe in hollow Earth theories get crazier and crazier. For example, the neo-Nazi Ernst Zündel wrote a book entitled UFOs - Nazi Secret Weapons?
claiming that Hitler and his men had boarded submarines at the end of the war, escaped to Argentina, and then established a base for flying saucers in a hole leading to the inside of the Earth at the South Pole. Zündel also suggested that the Nazis had originated as a separate race that had come from inside the Earth.
My favorite hollow Earth theories are the ones that say we are actually inside!
That's right: all of outer space fits inside an Earth-sized ball, while rocks
fill the infinite outside of the universe! Or maybe the outside is outer space too... but we're stuck on the inside.
I'm not sure what this theory is supposed to accomplish, but it's fun to think about. What you think are stars may actually be lights from cities on the other side of the Earth! When the Sun sets.... well, there are different ideas about where it goes. Perhaps it goes into a hole? Or perhaps its light bends
in such a way that only half the Earth gets sunlight at any one time.
In fact, if you change enough laws of physics, the inside-out Earth theory becomes hard to refute. It's becomes our usual theory of the universe described in "inside-out coordinates", so it becomes equivalent
to our usual ideas - except perhaps for one tiny point, which I'll mention later.
There's an Egyptian mathematician Mostafa Abdelkader who actually took this line of thought seriously. According to Martin Gardner, this guy claimed that light rays travel in circular paths, and slow as they approach the center of the spherical star-filled hollow Earth. Everything shrinks and slows down as it gets close to the center, so nothing can ever get there. On the other hand, a drill would get longer as you used it to dig outward into the rock.
This theory gets a bit freaky if you drill all the way through the Earth
. At some point your drill tip has to suddenly appear on the opposite side of the Universe!
But if you allow this, there's not much difference between the inside-out Universe and ours. True, it's missing one point
compared to our usual Universe - namely, the point right at the center of the Earth! But to make up for this, it has an extra point, namely the "point at infinity", in the center of this inside-out Universe.
In fact, if we include both
these points, the Universe itself becomes a "3-sphere", which has two "hemispheres", namely the inside and the outside of the Earth. One is solid rock, the other empty space. And in fact Dante describes this cosmology in his Divine Comedy
. He was a smart dude.
It's a fun exercise in the philosophy of science to figure out why a theory that makes almost identical predictions to our usual theories is nonetheless considered much worse.
For more on hollow Earth theories, try:https://en.wikipedia.org/wiki/Hollow_Earth
For more on the myth that Euler believed in a hollow Earth:http://eulerarchive.maa.org/hedi/HEDI-2007-04.pdf
The nice mathematical way to turn space inside out is called conformal inversion
. It sends straight lines and circles to straight lines and circles, and it preserves angles. You can read more about it here:https://en.wikipedia.org/wiki/Inversive_geometry
And here's the webpage where I got this marvelous picture:http://aetherforce.com/the-hollow-earth-in-science-by-duane-griffin/
Here is seems that the 'point at infinity' is contained inside a glowing octahedral Heaven, the Moon is bowl-shaped, the Sun's light bends, and there's a hole in the North Pole, leading... where?
Zündel, by the way, was jailed several times for publishing books like The Hitler We Loved and Why
and Did Six Million Really Die?