The Hollow Earth is an idea that suggests Earth is completely empty inside or has a large space within. This idea was first proposed in the late 1600s by Edmond Halley. Later, scientists Pierre Bouguer in 1740 and Charles Hutton in 1774 through his Schiehallion experiment proved this idea was not true.

Although the idea was disproven, some people still believed in it during the middle of the 1800s, including John Cleves Symmes Jr. and J. N. Reynolds. By this time, the Hollow Earth was considered part of unscientific ideas and no longer a serious scientific theory.

The concept of a hollow Earth continues to appear in stories, myths, and fictional books about underground worlds. It is also found in conspiracy theories and ideas about hidden beings. Some claim the hollow Earth is home to mythical creatures or important people.

History

In ancient times, people believed there was a hidden land deep inside the Earth. This idea appeared in stories, myths, and religious beliefs from many cultures. These beliefs often connected the hidden land to places of origin or the afterlife, such as the Greek underworld, the Nordic Svartálfaheimr, the Christian Hell, and the Jewish Sheol. Some religious writings, like the Zohar and Hesed L'Avraham, described details about the inside of the Earth. Tibetan Buddhist traditions also mention a hidden city called Shamballa located inside the Earth.

The Ancient Greeks believed that caves under the Earth 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 told of a man who traveled through a dark tunnel in the "Mashu" mountain and entered a subterranean garden.

Celtic mythology describes a cave called "Cruachan," sometimes called "Ireland's gate to Hell." Strange creatures were said to come from this cave. Medieval knights and saints in Ireland visited a cave on Station Island, believing it led to a place of purgatory. In Northern Ireland, a myth says tunnels connect 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 Ramayana tells of Rama and Lakshmana being taken by Ahiravan, the brother of the demon king Ravana, but later rescued by Hanuman. The Angami Naga people of India say their ancestors came from a hidden land inside the Earth. The Taino people of Cuba believe their ancestors emerged from two underground caves.

The Trobriand Islanders claim their ancestors came from a subterranean land through a hole called "Obukula." Mexican folklore mentions a cave near Ojinaga, Mexico, where devilish creatures are said to have come from underground.

During the Middle Ages, a German myth said some mountains between Eisenach and Gotha held a portal to the inner Earth. A Russian legend claimed the Samoyed people, an ancient Siberian tribe, lived in a cavern city underground. In Dante’s 14th-century work Inferno, he described a hollow Earth formed by Lucifer’s fall, creating a funnel and a mountain called "Purgatory."

In Native American mythology, the Mandan people’s ancestors emerged from a cave on the Missouri River. A San Carlos Apache Reservation story says a tunnel near Cedar Creek leads to a land inhabited by a mysterious tribe. The Iroquois and Hopi tribes also believe their ancestors came from a subterranean world. Brazilian Indians near the Parima River claim their ancestors emerged from an underground land, with some still living inside the Earth. The Inca people are said to have come from caves east of Cuzco, Peru.

In 1665, Athanasius Kircher wrote Mundus Subterraneus, suggesting a network of underground caves and water channels connecting the Earth’s poles. In 1692, Edmond Halley proposed the Earth might be a hollow shell with inner layers, explaining unusual compass readings. He imagined the inner Earth as luminous and possibly inhabited, with gas escaping to cause the Aurora Borealis.

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. In 1818, John Cleves Symmes suggested the Earth was a hollow shell with openings at the poles. He became famous for his ideas, and a monument was built in his honor in Ohio.

Other figures, like J. N. Reynolds and Sir John Leslie, also proposed hollow Earth theories. William Fairfield Warren believed humans originated in a northern land called Hyperborea. In the early 20th century, William Reed wrote about a hollow Earth without inner suns or shells. These ideas influenced stories and scientific debates about the Earth’s structure.

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 at two different heights to study how local mass differences affected gravity. About ten years later, Bouguer wrote a paper stating that his findings had shown the Hollow Earth Theory was incorrect. In 1772, Nevil Maskelyne suggested repeating the experiment to the Royal Society. That same year, the Committee of Attraction was formed, and they sent Charles Mason to find a suitable location for the experiment. Mason identified Schiehallion mountain, where the experiment was conducted. The results supported the earlier Chimborazo findings and provided stronger evidence.

In 1798, Henry Cavendish published a calculation of Earth’s density using a torsion balance. These results were later used to determine the gravitational constant.

Based on Earth’s size and surface gravity, the planet’s average density is 5.515 g/cm³. Typical surface rocks have about half that density (2.75 g/cm³). 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 make up most of its interior. Nickel-iron alloy, found in a non-hollow Earth, has densities between 10 and 13 g/cm³. This explains Earth’s observed density.

Studies of seismic waves show Earth’s structure is not hollow. The time seismic waves take to travel through Earth contradicts the idea of a fully hollow planet. Evidence suggests Earth is mostly solid rock (mantle and crust), liquid nickel-iron (outer core), and solid nickel-iron (inner core).

Scientific arguments against a hollow Earth or any hollow planet come from gravity. Large objects naturally form solid spheres, like stars and planets, because this shape minimizes gravitational energy. A hollow shape is not stable under gravity. Ordinary matter cannot support a hollow structure of planetary size. A hollow Earth with the known thickness of its crust would collapse under its own weight.

Drilling does not prove Earth is not hollow. The deepest hole drilled is the Kola Superdeep Borehole, reaching about 12 km (7.5 mi) deep. However, the distance to Earth’s center is nearly 6,400 km (4,000 mi).

In fiction

The idea of a hollow Earth is often found in stories, appearing as early as Ludvig Holberg's 1741 novel Nicolai Klimii iter subterraneum (Niels Klim's Underground Travels), where the character Nicolai Klim falls through a cave during an exploration and lives for years on a smaller globe inside the Earth and within the Earth's outer shell.

Other early examples include Giacomo Casanova's 1788 work Icosaméron, a five-volume, 1,800-page story about a brother and sister who fall into the Earth and discover a utopian underground world called the Mégamicres, a group of colorful, hermaphroditic dwarves; Symzonia: A Voyage of Discovery (1820), which reflected the ideas of John Cleves Symmes, Jr.; Edgar Allan Poe's 1838 novel The Narrative of Arthur Gordon Pym of Nantucket; Jules Verne's 1864 novel Journey to the Center of the Earth, which describes a subterranean world filled with prehistoric life; George Sand's 1864 novel Laura, Voyage dans le Cristal, where giant crystals are found deep within the Earth; Sir Edward Bulwer-Lytton's 1871 novel Vril: The Power of the Coming Race, published anonymously; Etidorhpa, an 1895 science-fiction story with major underground themes; and The Smoky God (1908), which includes the idea that the North Pole is the entrance to a hollow planet.

In William Henry Hudson's 1887 novel A Crystal Age, the main character falls down a hill into a perfect world; since this world is reached by falling, the story is sometimes considered a hollow Earth tale. However, the character believes he may have traveled forward in time by thousands of years.

The idea was used by Edgar Rice Burroughs in the seven-book "Pellucidar" series, starting with At the Earth's Core (1914). Using a mechanical drill called the Iron Mole, the characters David Innes and Professor Abner Perry discover a prehistoric world called Pellucidar, 500 miles below the surface, lit by a constant inner sun. They find prehistoric people, dinosaurs, mammals, and the Mahar, a group that evolved from pterosaurs. The series continued with six more books, ending with Savage Pellucidar (1963). The 1915 novel Plutonia by Vladimir Obruchev uses the hollow Earth concept to explore different time periods in Earth's history.

In recent years, the hollow Earth idea has become common in science fiction and adventure stories. It appears in films such as Children Who Chase Lost Voices, Ice Age: Dawn of the Dinosaurs, Aquaman, and MonsterVerse; television shows like Inside Job, Slugterra, and the third and fourth seasons of Sanctuary; role-playing games such as the 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, where a subterranean realm called Subterranea exists beneath the Earth. The Super Nintendo Entertainment System (SNES) game Terranigma includes the hollow Earth idea in its opening and closing scenes.

The Hollow Earth is a central location in Legendary Pictures' MonsterVerse franchise, serving as 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 of Godzilla vs. Kong, its sequel Godzilla x Kong: The New Empire, and the Monarch: Legacy of Monsters TV series.

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 in a story about grief and despair.

In popular art

In 1975, Japanese artist Tadanori Yokoo used parts of the Agartha legend and other myths about underground places from Eastern cultures to create the cover art for jazz musician Miles Davis's album Agharta. He said he was partly inspired by reading Raymond W. Bernard's 1969 book The Hollow Earth.