> According to a 1716 paper mentioned in the book, Hollow Earth: The Long and Curious History of Imagining Strange Lands, Halley devised the Hollow Earth theory as a way to explain strange disturbances in the magnetic field that were connected to the aurora borealis — Earth’s natural light show. Halley was right about the magnetic field, but not so much about Hollow Earth..
> Years later, War of 1812 veteran and explorer, John Cleves Symmes, seized on the Hollow Earth theory.. to justify American expansionism.. into Antarctica. Similar to Halley, Symmes believed that the Earth was made of a hollow shell 800 miles thick, but he added his own twist: there were openings to Earth’s hollow core at both the North and South Pole. These he called “Symmes holes.” There, he believed that light — and human explorers — could descend underneath the surface into the hollow core.
There was also a German sci-fi novel "Two Planets" by Kurd Lasswitz (1897), which influenced a young Werner von Braun who would later contribute to German rocketry and American space program, and write his own sci-fi novel about Mars exploration, https://news.ycombinator.com/item?id=39571588
So, I happen to know a bit about this because his cult compound is a state park in Florida, in Bonita Springs. Highly recommend visiting! Say hi to the loose big turtles!
The park is presented as a lovely old commune with vintage bungalows, a rare place where women actually ran things in the late 1800's and had a lot of freedom within the community to create art, plays, and raise their kids. A lot of the women were widows and this was basically the only option for them aside from marrying their dead husband's brother, or some other arcane ritual of the day. They paid for the upkeep and food for the "commune" by staging plays, and the men dealt with the outside world and negotiated for such transactions (to keep up external appearances of a patriarchy, something that was totally expected back then.)
My wife and I were touring the place, having a good old time, and when we entered the community gathering hall/church, my wife started slapping my arm repeatedly to get my attention. She's gasping for air in an almost shocked laughter. She pointed to the giant model of the split-open Earth as interior, like the one shown at the top this article. The whole commune were hollow Earthers!!
Of course, the bloom was then very much off the rose. A few things to know about Teed, in addition to the hollow Earth stuff, which we subsequently learned by reading more deeply into the interpretive museum text, therein:
1: Teed believed he was Jesus Christ, or at least, that he would come back with Christ. When he died, the cult left him on the porch for a few weeks, waiting for him to get back up. The Sheriff had to come and demand they bury him, because the stink was so bad from the rotting corpse in the hot Florida sun. A testament to the power of belief, or delusion, you decide.
2: The last Koreshanty-ist (As they were called) born and living on the Florida property admitted she was wrong about the Earth when she watched the moon landing on TV in 1969 in her bungalow.
3: Teed believed his theory was true because he said if you walked in a flat, straight line in any direction, you would eventually hit an incline. This was absolutely true! BECAUSE THEY LIVED IN A SWAMP.
4: Of course, 100% as expected, despite the ladies running the cult via committee and being very free in the cult society... All men except Teed were to remain celibate, but--OMG!-- there were plenty of babies! Teed 100% did the cult leader thing and had relations with every woman on the property. That's the real reason he built the cult.
But shouldn't the planet start with a small, solid core (which would have always been solid due to the immense pressure), surrounded by the liquid magma, which is then in turn surrounded by the solid layer of crust (which solidified due to being exposed to the rest of the space to cool)? Then, as the Earth continues to cool down, the liquid part would also start to turn solid, starting from the near the core/crust, and therefore reduce its volume so... if the crust is sturdy enough, it will all end up as the small, solid core surrounded by the lot of empty space surrounded by the outer crust?
Like, that's also a pretty ridiculous scenario of planetogenesis, but it's at least somewhat plausible.
1. The empty space between the crust and the mantle isn't going to fill up with air. If the mantle cools and shrinks, it's going to pull the crust inwards because there's nothing to expand to fill a potential void.
2. There's no hard line where the crust becomes mantle. The rock gets gooey in a gradient.
3. If there was a void filled with gas, the gas would desperately want to escape. There's a tremendous amount of pressure down there, and the gas would fart out to the surface as volcanic activity at the first chance it got. Tectonic plates move fast enough that even if such a bubble did form, the gas would escape relatively quickly.
But really, consider that if the center of the earth is liquid and cooling, that'll shift the center of gravity in the direction the mantle moves in (same mass, now more dense). That direction is... towards the opposite side of the planet, where there's uncooled liquid mantle, which in turn would just squish back around in time. Cooling the whole mantle evenly around the world enough to decrease the circumference of it such that there's an appreciable void is an unimaginable amount of cooling.
As you said, the crust would need to be extremely sturdy, and at that point tectonics would close up those voids pretty quickly.
I'm no geologist but I would think it would be hard for the outer layer to stay stable enough to harden to that degree, while the inner part is still liquid and cooling. On our own planet the crust is incredibly thin compared to the other layers, even while the mantle is cooled enough to be solid, and the solid mantle still moves around enough to break apart the crust constantly. Seems impossible for the hollow eggshell of the crust to not break and crumble into the retreating center at some point.
Hallow Earth, perhaps with dinosaurs still living there is, of course, BS. However, it may not be all barren in there either, e.g. this report from 2006 talking about bacteria nearly 2 miles in: https://www.princeton.edu/news/2006/10/20/two-miles-undergro....
So, as a Friday afternoon thought, one can hypothesize the existence of large-ish (~hundreds of meters) empty cavities within the mantle with some simple animal life (worms, insects?), which doesn't sound totally off the rails to me. I wonder if our current seismic analysis technology can detect such cavities (chatGPT says waves to propel core have wavelengths on the order of kilometers).
No, "within the mantle" is definitely off the rails. It's really hot down there, way hotter than cooking temperatures. A few highly specialized microbes can survive conditions like that, but not animals. Also the pressure is high enough that rock acts like liquid. Large cavities cannot survive. I think this started to be a problem even for the Kola borehole, the walls of the hole just started squishing in.
The Kora Borehole got to 12,262 metres deep, and was stopped due to a lack of funds.[1]
"""
Drilling penetrated about a third of the way through the Baltic Shield of the continental crust, estimated to be around 35 kilometres (22 mi) deep, reaching Archean rocks at the bottom.[13] Numerous unexpected geophysical discoveries were made:
During the drilling process, the expected basaltic layers at 7 kilometres (4.3 mi) down were never found, nor were basaltic layers at any depth.[14] There were instead more granites, deeper than predicted. The prediction of a transition at 7 kilometres was based on seismic waves indicating discontinuity, which could have been caused by a transition between rocks, or a metamorphic transition in the granite itself.[14]
Water pooled 3–6 kilometres (1.9–3.7 mi) below the surface,[14][15] having percolated up through the granite until it reached a layer of impermeable rock.[16][17] This water did not naturally vaporize at any depth in the borehole.[15]
The drilling mud that flowed out of the hole was described as "boiling" with an unexpected level of hydrogen gas.[18]
Microscopic plankton fossils were found 6 kilometres (3.7 mi) below the surface.[1]
"""
I thought maybe it would get into how different hollow Earth theory played into Nazi cosmology. This is the best source I can find, though it does blather a bit about falsifiability, so feel free to skim. https://aeon.co/essays/how-the-hollow-earth-hypothesis-illum...
I think a lot of people didn't read past the first paragraph because of the paywall, but this is actually about Edmund Halley (the comet Halley), and his attempt to explain the wandering of earth's magnetic field by positing that the earth was full of rotating spheres with magnetic material in the middle, which was _wrong_, but not _that_ far off, all things considered.
> According to a 1716 paper mentioned in the book, Hollow Earth: The Long and Curious History of Imagining Strange Lands, Halley devised the Hollow Earth theory as a way to explain strange disturbances in the magnetic field that were connected to the aurora borealis — Earth’s natural light show. Halley was right about the magnetic field, but not so much about Hollow Earth..
> Years later, War of 1812 veteran and explorer, John Cleves Symmes, seized on the Hollow Earth theory.. to justify American expansionism.. into Antarctica. Similar to Halley, Symmes believed that the Earth was made of a hollow shell 800 miles thick, but he added his own twist: there were openings to Earth’s hollow core at both the North and South Pole. These he called “Symmes holes.” There, he believed that light — and human explorers — could descend underneath the surface into the hollow core.
There was also a German sci-fi novel "Two Planets" by Kurd Lasswitz (1897), which influenced a young Werner von Braun who would later contribute to German rocketry and American space program, and write his own sci-fi novel about Mars exploration, https://news.ycombinator.com/item?id=39571588
The park is presented as a lovely old commune with vintage bungalows, a rare place where women actually ran things in the late 1800's and had a lot of freedom within the community to create art, plays, and raise their kids. A lot of the women were widows and this was basically the only option for them aside from marrying their dead husband's brother, or some other arcane ritual of the day. They paid for the upkeep and food for the "commune" by staging plays, and the men dealt with the outside world and negotiated for such transactions (to keep up external appearances of a patriarchy, something that was totally expected back then.)
My wife and I were touring the place, having a good old time, and when we entered the community gathering hall/church, my wife started slapping my arm repeatedly to get my attention. She's gasping for air in an almost shocked laughter. She pointed to the giant model of the split-open Earth as interior, like the one shown at the top this article. The whole commune were hollow Earthers!!
Of course, the bloom was then very much off the rose. A few things to know about Teed, in addition to the hollow Earth stuff, which we subsequently learned by reading more deeply into the interpretive museum text, therein:
1: Teed believed he was Jesus Christ, or at least, that he would come back with Christ. When he died, the cult left him on the porch for a few weeks, waiting for him to get back up. The Sheriff had to come and demand they bury him, because the stink was so bad from the rotting corpse in the hot Florida sun. A testament to the power of belief, or delusion, you decide.
2: The last Koreshanty-ist (As they were called) born and living on the Florida property admitted she was wrong about the Earth when she watched the moon landing on TV in 1969 in her bungalow.
3: Teed believed his theory was true because he said if you walked in a flat, straight line in any direction, you would eventually hit an incline. This was absolutely true! BECAUSE THEY LIVED IN A SWAMP.
4: Of course, 100% as expected, despite the ladies running the cult via committee and being very free in the cult society... All men except Teed were to remain celibate, but--OMG!-- there were plenty of babies! Teed 100% did the cult leader thing and had relations with every woman on the property. That's the real reason he built the cult.
Like, that's also a pretty ridiculous scenario of planetogenesis, but it's at least somewhat plausible.
1. The empty space between the crust and the mantle isn't going to fill up with air. If the mantle cools and shrinks, it's going to pull the crust inwards because there's nothing to expand to fill a potential void.
2. There's no hard line where the crust becomes mantle. The rock gets gooey in a gradient.
3. If there was a void filled with gas, the gas would desperately want to escape. There's a tremendous amount of pressure down there, and the gas would fart out to the surface as volcanic activity at the first chance it got. Tectonic plates move fast enough that even if such a bubble did form, the gas would escape relatively quickly.
But really, consider that if the center of the earth is liquid and cooling, that'll shift the center of gravity in the direction the mantle moves in (same mass, now more dense). That direction is... towards the opposite side of the planet, where there's uncooled liquid mantle, which in turn would just squish back around in time. Cooling the whole mantle evenly around the world enough to decrease the circumference of it such that there's an appreciable void is an unimaginable amount of cooling.
As you said, the crust would need to be extremely sturdy, and at that point tectonics would close up those voids pretty quickly.
So, as a Friday afternoon thought, one can hypothesize the existence of large-ish (~hundreds of meters) empty cavities within the mantle with some simple animal life (worms, insects?), which doesn't sound totally off the rails to me. I wonder if our current seismic analysis technology can detect such cavities (chatGPT says waves to propel core have wavelengths on the order of kilometers).
""" Drilling penetrated about a third of the way through the Baltic Shield of the continental crust, estimated to be around 35 kilometres (22 mi) deep, reaching Archean rocks at the bottom.[13] Numerous unexpected geophysical discoveries were made:
During the drilling process, the expected basaltic layers at 7 kilometres (4.3 mi) down were never found, nor were basaltic layers at any depth.[14] There were instead more granites, deeper than predicted. The prediction of a transition at 7 kilometres was based on seismic waves indicating discontinuity, which could have been caused by a transition between rocks, or a metamorphic transition in the granite itself.[14]
Water pooled 3–6 kilometres (1.9–3.7 mi) below the surface,[14][15] having percolated up through the granite until it reached a layer of impermeable rock.[16][17] This water did not naturally vaporize at any depth in the borehole.[15]
The drilling mud that flowed out of the hole was described as "boiling" with an unexpected level of hydrogen gas.[18]
Microscopic plankton fossils were found 6 kilometres (3.7 mi) below the surface.[1] """
[1] https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole