The Hollow Earth is an idea that suggests Earth is completely empty inside or has a large space inside. This idea was first proposed in the late 1600s by Edmond Halley. Later, scientists Pierre Bouguer in 1740 and Charles Hutton in his Schiehallion experiment around 1774 showed that the idea was not true.
The concept was still supported by some people in the middle of the 1800s, such as John Cleves Symmes Jr. and J. N. Reynolds. However, by that time, it was no longer considered a valid scientific idea and was instead part of popular pseudoscience.
Today, the idea of a hollow Earth appears in folklore and in subterranean fiction, a type of adventure story set underground. It also appears in conspiracy theories and the cryptoterrestrial hypothesis. Some people believe the hollow Earth is home to mythical beings or political leaders.
History
In ancient times, people from many cultures believed there were lands hidden deep inside the Earth. These ideas appeared in myths, stories, and religious beliefs. Some cultures connected these underground places to the beginning of life or to afterlife locations. For example, the Greeks believed in the underworld, the Norse had a place called Svartálfaheimr, and the Christian religion describes Hell. Jewish traditions mention Sheol, and some Jewish religious texts, like the Zohar and Hesed L'Avraham, describe details about the inside of the Earth. Tibetan Buddhist beliefs also include a hidden city called Shamballa located inside the Earth.
The Ancient Greeks believed that caves led to the underworld. Specific caves in places like Tainaron, Troezen, and Herakleia were thought to connect to this hidden world. In Thracian and Dacian legends, a god named Zalmoxis was said to live in underground caves. In Mesopotamian religion, a story tells of a man who entered a subterranean garden after traveling through a dark tunnel in the mountain of "Mashu."
Celtic mythology includes a cave called "Cruachan," also known as "Ireland's gate to Hell," where strange creatures were said to emerge. Medieval knights and saints in Ireland visited a cave in Station Island, where they believed they traveled to a place called purgatory. In County Down, Northern Ireland, a myth says tunnels lead to the land of the Tuatha Dé Danann, a group believed to have brought Druidism to Ireland before returning underground.
In Hindu mythology, the underworld is called Patala. A version of the Hindu epic Ramayana describes how Rama and Lakshmana were taken to Patala by Ahiravan, the brother of the demon king Ravana. They were later rescued by Hanuman. The Angami Naga tribes of India believe their ancestors came from a subterranean land. The Taino people of Cuba claim their ancestors emerged from two caves in an underground mountain.
The Trobriand Islands' people believe their ancestors came from a subterranean land through a cavern called "Obukula." Mexican folklore mentions a cave near Ojinaga where devilish creatures are said to have come from inside the Earth.
During the Middle Ages, a German myth claimed that mountains near Eisenach and Gotha held a portal to the inner Earth. A Russian legend says the Samoyed people, an ancient Siberian tribe, lived in a cavern city underground. The Italian writer Dante described a hollow Earth in his work Inferno, where Lucifer's fall created a funnel and a mountain called Purgatory.
In Native American mythology, the Mandan people's ancestors are said to have emerged from a subterranean land through a cave on the Missouri River. A story from the San Carlos Apache Reservation describes a tunnel leading to a mysterious tribe underground. The Iroquois believe their ancestors came from a subterranean world, and the Hopi people believe a cave called Sipapu in the Grand Canyon leads to the underworld.
Brazilian tribes near the Parima River claim their ancestors came from an underground land, with many still believed to live inside the Earth. The Inca people's ancestors are said to have emerged from caves near Cuzco, Peru.
The idea of a hollow Earth was first proposed by Athanasius Kircher in his 1665 book Mundus Subterraneus, which suggested a network of underground caves and water channels connecting the Earth's poles.
In 1692, Edmond Halley used Newton's incorrect estimate of the Moon's density to suggest the Earth might be a hollow shell with inner layers, each with its own atmosphere and magnetic poles. He believed the inner Earth might be inhabited and that escaping gas caused the Northern Lights.
In 1781, Le Clerc Milfort claimed the Muscogee People believed their ancestors came from underground caves near the Red River. He said the caves could hold thousands of families.
Mathematician Leonhard Euler did not propose a hollow Earth but instead imagined an object falling through a hole drilled through the Earth's center.
In 1818, John Cleves Symmes suggested the Earth was a hollow shell with openings at the poles and multiple inner layers. He became a famous proponent of the hollow Earth theory, and a monument was later built in his honor in Ohio.
J. N. Reynolds promoted the idea of a hollow Earth and led an expedition to Antarctica. His ideas influenced others, including the author of NEQUA, an early feminist novel that mentioned Symmes' theory.
William Reed, a 20th-century writer, supported the hollow Earth idea but did not include inner layers or a sun. Other writers, like William Fairfield Warren, connected the hollow Earth theory to the idea that humans originated in a northern land called Hyperborea.
Contrary evidence
In 1735, Pierre Bouguer and Charles Marie de La Condamine organized an expedition from France to Chimborazo volcano in Ecuador. They reached the volcano in 1738 and performed an experiment to measure how gravity changed at different heights. This helped them understand how Earth’s mass affects gravity. In a paper written about ten years later, Bouguer noted that his findings did not support the idea that Earth is hollow. In 1772, Nevil Maskelyne suggested repeating the experiment to the Royal Society. That same year, the Committee of Attraction was created, and they sent Charles Mason to find a suitable place for the experiment. Mason chose Schiehallion mountain, where the experiment was conducted. The results confirmed earlier findings and provided stronger evidence against the Hollow Earth Theory.
In 1798, Henry Cavendish used a special tool called a torsion balance to measure Earth’s density. This measurement later helped scientists calculate the gravitational constant.
Based on Earth’s size and the strength of gravity on its surface, Earth’s average density is about 5.515 grams per cubic centimeter. Surface rocks are much less dense, averaging about 2.75 grams per cubic centimeter. If Earth were hollow, its average density would be much lower than surface rocks. For Earth to have the gravity it does, denser materials must be present deep inside. Nickel-iron alloy, which is expected to exist in Earth’s interior, has a density between 10 and 13 grams per cubic centimeter. This helps explain Earth’s observed density.
Studies of seismic waves show Earth’s structure is not hollow. Seismic waves travel through Earth in ways that do not match a hollow sphere. Evidence suggests Earth is mostly solid rock (mantle and crust), liquid nickel-iron alloy (outer core), and solid nickel-iron (inner core).
Other scientific reasons argue against a hollow Earth. Gravity pulls matter together, forming solid, non-hollow objects like planets. A hollow shape would not be stable under gravity’s force. Ordinary materials cannot support a hollow structure the size of Earth against its own gravity. A hollow shell with Earth’s crust thickness would collapse.
Drilling does not prove Earth is not hollow. The deepest hole drilled is the Kola Superdeep Borehole, reaching about 12 kilometers (7.5 miles) deep. However, Earth’s center is nearly 6,400 kilometers (4,000 miles) away.
In fiction
The idea of a hollow Earth is a common theme in fiction. It first appeared in Ludvig Holberg's 1741 novel Nicolai Klimii iter subterraneum (Niels Klim's Underground Travels), where the main character, Nicolai Klim, falls through a cave while exploring and lives for years on a smaller globe inside the Earth and on the inside of the Earth's outer shell.
Other early examples include Giacomo Casanova's 1788 work Icosaméron, a 5-volume, 1,800-page story about a brother and sister who fall into the Earth and discover a utopian underground world called the Mégamicres, inhabited by multicolored, hermaphroditic dwarves. Another example is Symzonia: A Voyage of Discovery (1820), which reflects the ideas of John Cleves Symmes, Jr. Edgar Allan Poe's 1838 novel The Narrative of Arthur Gordon Pym of Nantucket also includes this concept. Jules Verne's 1864 novel Journey to the Center of the Earth describes a subterranean world filled with prehistoric life. George Sand's 1864 novel Laura, Voyage dans le Cristal features giant crystals inside the Earth. Sir Edward Bulwer-Lytton's 1871 novel Vril: The Power of the Coming Race and the 1895 science-fiction story Etidorhpa also explore subterranean themes. The 1908 novel The Smoky God suggests the North Pole is the entrance to a hollow planet.
In William Henry Hudson's 1887 novel A Crystal Age, the main character falls into a Utopian paradise, which some classify as a hollow Earth story. The character believes he may have traveled forward in time by thousands of years.
Edgar Rice Burroughs used the hollow Earth idea in his seven-novel Pellucidar series, starting with At the Earth's Core (1914). Using a mechanical drill called the Iron Mole, the heroes David Innes and Professor Abner Perry discover a prehistoric world called Pellucidar, 500 miles below the surface. This world has a constant inner sun, prehistoric people, dinosaurs, mammals, and the Mahar, who evolved from pterosaurs. The series continued with six more books, ending in 1963 with Savage Pellucidar. The 1915 novel Plutonia by Vladimir Obruchev also uses the hollow Earth concept to explore different time periods in Earth's history.
In recent decades, the hollow Earth idea has appeared in many science fiction and adventure stories, including films like Children Who Chase Lost Voices, Ice Age: Dawn of the Dinosaurs, Aquaman, and MonsterVerse; TV shows like Inside Job, Slugterra, and parts of Sanctuary; role-playing games such as Hollow World Campaign Set for Dungeons & Dragons and Hollow Earth Expedition; and video games like Torin's Passage and Gears of War. The concept also appears in Marvel Comics through a subterranean realm called Subterranea. The SNES game Terranigma includes this idea in its opening and closing scenes.
The Hollow Earth is a central location in Legendary Pictures' MonsterVerse franchise, where it is the origin of the Titans and the creatures of Skull Island. It was first hinted at in Kong: Skull Island and Godzilla: King of the Monsters, and a full exploration of the Hollow Earth is a main focus in Godzilla vs. Kong, its sequel Godzilla x Kong: The New Empire, and the TV series Monarch: Legacy of Monsters.
Owen Egerton's book Hollow: A Novel uses the hollow Earth concept, including a journey to find an entrance to the hollow Earth led by a con artist. The title also serves as a recurring metaphor for grief and despair.
In popular art
In 1975, Japanese artist Tadanori Yokoo created the cover art for jazz musician Miles Davis's album Agharta. He used ideas from the Agartha legend and other myths about underground places to show an advanced civilization. Tadanori said he was inspired by reading Raymond W. Bernard's 1969 book, The Hollow Earth.