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(Investigator 99, 2004 November)

Edmond Halley (1656-1742), English astronomer and mathematician, thought that planet Earth consists of several concentric spheres around an inner solid core.

He speculated that Earth's interior supported life and had a luminous atmosphere that bathed it in continuous light.

John C Symes an American army captain in the war of 1812 claimed that Earth consisted of five concentric spheres. He added that there was a huge hole or entrance, hundreds of miles wide, at the north and south poles. Symes is the probable author of Symzonia: A Voyage of Discovery (1820) which describes a Utopian civilization inside the hollow Earth.

Various fiction writers took up the idea. Jules Verne (1828-1905) wrote Journey to the Centre of the Earth (1864). This was made into a movie of the same name.

In 1920 M B Gardner also wrote about the hollow Earth but rejected the idea of five concentric spheres. He claimed the interior is lighted and warmed by a miniture sun.

Refutation came in 1926 and 1929 when American aviator/explorer Richard E Byrd (1888-1957) made flights over the North and South Pole but did not see any openings. When the Space Age came, satellite photos likewise showed no openings.

Some objections to the Earth being hollow are:

The reduced mass would mean low gravity – the atmosphere and oceans would have boiled away into Space;

Low gravity also implies a low escape velocity – anyone who pole-vaulted or even jumped might fly off into Space;

Low gravity also means that the Moon would be much further away;

A hollow Earth would have no magnetic field because this is generated by the iron centre;

Plate tectonics and mountain-building could not occur, and therefore erosion would have reduced the continents to flat plains;

There would be no major volcanism and lava flows;

The Moon is believed to have formed from debris thrown into Space when a Mars-size object collided with Earth. If the Earth were hollow, such a collision would have shattered it;

Subject to the thickness surrounding the alleged hollow, the impacts of large asteroids in Earth's early history might also have shattered the Earth;

The planets formed by the accretion of clouds of gases and dust revolving around the Sun – a process that would not form concentric spheres separated by hollows;

Studies of Earth's interior via seismic waves, show the Earth solid or filled, not hollow.