Ancient Origins and Folklore

• 💡 The Hollow Earth hypothesis proposes that Earth is either entirely hollow or contains a significant interior space, a notion dismissed by science but recurring in folklore and fiction.
• 🌍 Ancient myths from Greek, Nordic, and Buddhist traditions describe subterranean realms like the underworld, Asgard, hell, and the city of Shambhala.
• 🗺️ Legends from various cultures, including Celtic, Indian (Ungawa Naga), Taino, and Mexican folklore, speak of ancestors emerging from or creatures originating from subterranean lands and caves.
• 🇮🇪 Irish myths mention tunnels leading to the land of the Tethra and a purgatorial place within the earth, while medieval legends describe journeys into underground chambers.

Early Scientific and Pseudo-Scientific Theories (17th-19th Centuries)

• ⚛️ Edmund Halley proposed in 1692 that Earth consisted of a hollow shell with inner concentric shells and an inner core, each with its own atmosphere and magnetic poles, to explain anomalous compass readings.
• ☀️ Leonard Euler is sometimes credited with a Hollow Earth idea involving an interior sun, though this is debated, and Sir John Leslie expanded on this with two interior suns.
• 🏞️ Leclerc Mill for led a journey in 1781 where Creek Indian ancestors were believed to have emerged from caverns near the Red River.
• 🧭 John Cleves Symmes Jr. famously proposed in 1818 that Earth was hollow with openings at the poles, advocating for an expedition to the North Pole hole.
• 🗣️ Jeremiah Reynolds lectured on the Hollow Earth and agitated for expeditions, though he missed joining a major US expedition to Antarctica.

20th Century Developments and Fiction

• 💡 William Reid supported a Hollow Earth without interior shells or an inner sun, while Walburga Lady Padgett claimed cities exist beneath the desert where Atlanteans moved.
• 🚀 Marshall Gardner wrote about humanity originating from the Earth's interior via a North Pole entrance and built a working model of a Hollow Earth with an interior sun.
• 👽 Ferdinand Ossendowski reported tales of a subterranean kingdom known to Buddhists as Agharti, and Peter Colosimo linked UFOs to subterranean tunnels and activities.
• 📖 The Shaver Mystery, published in Amazing Stories, claimed a superior prehistoric race built caves inhabited by degenerate descendants who tormented surface dwellers.
• 🗺️ David Hatcher Childress defended the Hollow Earth idea based on alleged tunnel systems beneath South America and Central Asia.

Variations and Scientific Rebuttals

• 🌐 Some theories propose concave Hollow Earths, where humans live on the inside surface of a hollow sphere, with the universe existing within its interior.
• 🔬 Scientific evidence, particularly from seismic waves, directly contradicts the Hollow Earth theory, indicating Earth is composed of solid mantle, liquid outer core, and solid inner core.
• ⚖️ Gravity explains that massive objects like planets tend to form solid spheres to minimize gravitational potential energy; a hollow shell of planetary size would collapse under its own gravity.
• 📉 Based on Earth's size and gravity, its average density is significantly higher than surface rocks, necessitating a dense interior like nickel-iron alloy, not a hollow space.
• 🕳️ The deepest drilled hole is only about 12 km, far from proving or disproving a hollow interior, but seismic data and gravity provide strong counter-evidence.
• 📚 The Hollow Earth concept remains a popular element in fiction, appearing in novels, films, games, and comics, exploring themes of subterranean worlds, lost races, and hidden civilizations.