The Hollow Earth is a concept proposing that the planet Earth is entirely hollow or contains a substantial interior space.

Notably suggested by Edmond Halley in the late 17th century, the notion was tentatively disproven by Pierre Bouguer in 1740, and definitively by Charles Hutton in his Schiehallion experiment around 1774.

It was still occasionally defended through the mid-19th century, notably by John Cleves Symmes Jr. and Jeremiah N. Reynolds, but by this time it was part of popular pseudoscience and no longer a scientifically viable hypothesis.

The concept of a hollow Earth still recurs in folklore and as the premise for subterranean fiction, and a subgenre of adventure fiction.

In ancient times, the concept of a subterranean land inside the Earth appeared in mythology, folklore, and legends.

The idea of subterranean realms seemed arguable and became intertwined with the concept of “places” of origin or afterlife, such as the Greek underworld, the Nordic Svartálfaheimr, the Christian Hell, and the Jewish Sheol (with details describing inner Earth in Kabalistic literature, such as the Zohar and Hesed L’Avraham).

The idea of a subterranean realm is also mentioned in Tibetan Buddhist belief. According to one story from the Tibetan Buddhist tradition, there is an ancient city called Shamballa which is located inside the Earth.

According to the Ancient Greeks, there were caverns under the surface which were entrances leading to the underworld, some of which were the caverns at Tainaron in Lakonia, at Troezen in Argolis, at Ephya in Thesprotia, at Herakleia in Pontos, and in Ermioni.

In Thracian and Dacian legends, it is said that there are caverns occupied by an ancient god called Zalmoxis. In Mesopotamian religion, there is a story of a man who, after traveling through the darkness of a tunnel in the mountain of “Mashu“, entered a subterranean garden.

In Celtic mythology, there is a legend of a cave called “Cruachan“, also known as “Ireland’s gate to Hell“, a mythical and ancient cave from which according to legend strange creatures would emerge and be seen on the surface of the Earth.

There are also stories of medieval knights and saints who went on pilgrimages to a cave located in Station Island, County Donegal in Ireland, where they made journeys inside the Earth into a place of purgatory.

In County Down, Northern Ireland there is a myth which says tunnels lead to the land of the subterranean Tuatha Dé Danann, a group of people who are believed to have introduced Druidism to Ireland, and then went back underground.

In Hindu mythology, the underworld is referred to as Patala. In the Bengali version of the Hindu epic Ramayana, it has been depicted how Rama and Lakshmana were taken by the king of the underworld Ahiravan, brother of the demon king Ravana. Later on, they were rescued by Hanuman.

The Angami Naga tribes of India claim that their ancestors emerged in ancient times from a subterranean land inside the Earth. The Taino from Cuba believes their ancestors emerged in ancient times from two caves in a mountain underground.

Natives of the Trobriand Islands believe that their ancestors had come from a subterranean land through a cavern hole called “Obukula“. Mexican folklore also tells of a cave in a mountain five miles south of Ojinaga, and that Mexico is possessed by devilish creatures who came from inside the Earth.

A Russian legend says the Samoyeds, an ancient Siberian tribe, traveled to a cavern city to live inside the Earth. The Italian writer Dante describes a hollow earth in his well-known 14th-century work Inferno, in which the fall of Lucifer from heaven caused an enormous funnel to appear in previously solid and spherical earth, as well as an enormous mountain opposite it, “Purgatory“.

Native American mythology

In Native American mythology, it is said that the ancestors of the Mandan people in ancient times emerged from a subterranean land through a cave at the north side of the Missouri River.

There is also a tale about a tunnel in the San Carlos Apache Indian Reservation in Arizona near Cedar Creek which is said to lead inside the Earth to a land inhabited by a mysterious tribe.

It is also the belief of the tribes of the Iroquois that their ancient ancestors emerged from a subterranean world inside the Earth. The elders of the Hopi people believe that a Sipapu entrance in the Grand Canyon exists which leads to the underworld.

Brazilian Indians, who live alongside the Parima River in Brazil, claim that their forefathers emerged in ancient times from an underground land and that many of their ancestors still remained inside the Earth. Ancestors of the Inca supposedly came from caves which are located east of Cuzco, Peru.

17th and 18th centuries

Edmond Halley in 1692 put forth the idea of Earth consisting of a hollow shell about 800 km (500 mi) thick, two inner concentric shells and an innermost core. Atmospheres separate these shells, and each shell has its own magnetic poles.

The spheres rotate at different speeds. Halley proposed this scheme in order to explain anomalous compass readings. He envisaged the atmosphere inside as luminous (and possibly inhabited) and speculated that escaping gas caused the Aurora Borealis.

De Camp and Ley have claimed (in their Lands Beyond) that Leonhard Euler also proposed a hollow-Earth idea, getting rid of multiple shells and postulating an interior sun 1,000 km (620 mi) across to provide light to advanced inner-Earth civilizations but they provide no references; indeed, Euler did not propose a hollow-Earth, but there is a slightly related thought experiment.

De Camp and Ley also claim that Sir John Leslie expanded on Euler’s idea, suggesting two central suns named Pluto and Proserpine (this was unrelated to the dwarf planet Pluto, which was discovered and named a century later).

Leslie did propose a hollow Earth in his 1829 Elements of Natural Philosophy (pp. 449–53) but does not mention interior suns. Jules Verne alludes to the Pluto-Proserpine theory, which he attributes to “an English captain“, in Journey to the Center of the Earth.

Le Clerc Milfort in 1781 led a journey with hundreds of Creek Indians to a series of caverns near the Red River above the junction of the Mississippi River. According to Milfort, the original Creek Indian ancestors are believed to have emerged out to the surface of the Earth in ancient times from the caverns. Milfort also claimed the caverns they saw “could easily contain 15,000 – 20,000 families.

19th century

In 1818, John Cleves Symmes, Jr. suggested that the Earth consisted of a hollow shell about 1,300 km (810 mi) thick, with openings about 2,300 km (1,400 mi) across at both poles with 4 inner shells each open at the poles.

Symmes became the most famous of the early Hollow Earth proponents, and Hamilton, Ohio, even has a monument to him and his ideas. He proposed making an expedition to the North Pole hole, thanks to the efforts of one of his followers, James McBride.

Jeremiah Reynolds also delivered lectures on the “Hollow Earth” and argued for an expedition. Reynolds went on an expedition to Antarctica himself but missed joining the Great U.S. Exploring Expedition of 1838–1842, even though that venture was a result of his agitation.

Though Symmes himself never wrote a book about his ideas, several authors published works discussing his ideas. McBride wrote Symmes’ Theory of Concentric Spheres in 1826. It appears that Reynolds has an article that appeared as a separate booklet in 1827: Remarks of Symmes’ Theory Which Appeared in the American Quarterly Review.

In 1868, professor W.F. Lyons published The Hollow Globe which put forth a Symmes-like Hollow Earth hypothesis but failed to mention Symmes himself. Symmes’s son Americus then published The Symmes’ Theory of Concentric Spheres in 1878 to set the record straight.

William Fairfield Warren, in his book Paradise Found–The Cradle of the Human Race at the North Pole, (1885) presented his belief that humanity originated on a continent in the Arctic called Hyperborea. This influenced some early Hollow Earth proponents. According to Marshall Gardner, both the Eskimo and Mongolian peoples had come from the interior of the Earth through an entrance at the North pole.

20th century

The spiritualist writer Walburga, Lady Paget in her book Colloquies with an unseen friend (1907) was an early writer to mention the hollow Earth hypothesis. She claimed that cities exist beneath a desert, which is where the people of Atlantis moved. She said an entrance to the subterranean kingdom will be discovered in the 21st century.

According to the ancient astronaut writer Peter Kolosimo a robot was seen entering a tunnel below a monastery in Mongolia. Kolosimo also claimed a light was seen from underground in Azerbaijan. Kolosimo and other ancient astronaut writers such as Robert Charroux linked these activities to UFOs.

A book by a “Dr. Raymond Bernard” which appeared in 1964, The Hollow Earth, exemplifies the idea of UFOs coming from inside the Earth and adds the idea that the Ring Nebula proves the existence of hollow worlds, as well as speculation on the fate of Atlantis and the origin of flying saucers.

An article by Martin Gardner revealed that Walter Siegmeister used the pseudonym “Bernard“, but not until the 1989 publishing of Walter Kafton-Minkel’s Subterranean Worlds: 100,000 Years of Dragons, Dwarfs, the Dead, Lost Races & UFOs from Inside the Earth did the full story of Bernard/Siegmeister become well-known.

Hollow Earth proponents have claimed a number of different locations for the entrances which lead inside the Earth. Other than the North and South poles, entrances in locations that have been cited include Paris in France, Staffordshire in England, Montreal in Canada, Hangchow in China, and the Amazon Rainforest.

Concave Hollow Earths

Instead of saying that humans live on the outside surface of a hollow planet—sometimes called a “convex” Hollow Earth hypothesis—some have claimed humans live on the inside surface of a hollow spherical world so that our universe itself lies in that world’s interior. This has been called the “concave” Hollow Earth hypothesis or skycentrism.

Cyrus Teed, a doctor from upstate New York, proposed such a concave Hollow Earth in 1869, calling his scheme “Cellular Cosmogony“. Teed founded a group called the Koreshan Unity based on this notion, which he called Koreshanity.

The main colony survives as a preserved Florida state historic site, at Estero, Florida, but all of Teed’s followers have now died. Teed’s followers claimed to have experimentally verified the concavity of the Earth’s curvature, through surveys of the Florida coastline making use of “rectilineator” equipment. Additionally, the divergence of long plumb lines at the Tamarack Mine is also claimed as experimental evidence.

Several 20th-century German writers, including Peter Bender, Johannes Lang, Karl Neupert, and Fritz Braut, published works advocating the Hollow Earth hypothesis, or Hohlweltlehre.

It has even been reported, although apparently without historical documentation, that Adolf Hitler was influenced by concave Hollow Earth ideas and sent an expedition in an unsuccessful attempt to spy on the British fleet by pointing infrared cameras up at the sky.

The Egyptian mathematician Mostafa Abdelkader wrote several scholarly papers working out a detailed mapping of the Concave Earth model.

In one chapter of his book On the Wild Side (1992), Martin Gardner discusses the Hollow Earth model articulated by Abdelkader. According to Gardner, this hypothesis posits that light rays travel in circular paths, and slow as they approach the center of the spherical star-filled cavern. No energy can reach the center of the cavern, which corresponds to no point a finite distance away from Earth in the widely accepted scientific cosmology.

A drill, Gardner says, would lengthen as it traveled away from the cavern and eventually pass through the “point at infinity” corresponding to the center of the Earth in the widely accepted scientific cosmology. Supposedly no experiment can distinguish between the two cosmologies. Gardner notes that:

“most mathematicians believe that an inside-out universe, with properly adjusted physical laws, is empirically irrefutable”.

Gardner rejects the concave Hollow Earth hypothesis on the basis of Occam’s razor.

Purportedly verifiable hypotheses of a “Concave Hollow Earth” need to be distinguished from a thought experiment that defines a coordinate transformation such that the interior of the Earth becomes “exterior” and the exterior becomes “interior”.

The transformation entails corresponding changes to the forms of physical laws. This is not a hypothesis but an illustration of the fact that any description of the physical world can be equivalently expressed in more than one way.

*This article uses material from the Wikipedia article Hollow Earth, which is released under the Creative Commons Attribution-ShareAlike License 3.0 (view authors).