In 1692, Edmond Halley, of the comet, proposed in a Royal Society paper that Earth consists of concentric spheres around a small central sun, with luminous, possibly inhabited atmospheres between them, an attempt to explain the drifting magnetic poles. The theory died by measurement: the 1774 Schiehallion experiment weighed the Earth against a Scottish mountain and found the planet nearly twice as dense as surface rock, too heavy to be hollow. Newton's shell theorem finishes the job: inside a hollow shell, gravity nets to zero. Nobody inside could stand up.
Disproof never stuck. Symmes revived it in 1818, occultists gave it a king by 1886, pulps gave it dinosaurs by 1914, and UFO culture gave it a space program by 1950. Each generation hollowed the Earth again for its own reasons: exploration when the map had blanks, escape when the surface got crowded, conspiracy when the institutions lost trust. The theory is less a claim about geology than a recurring vote of no confidence in the surface.
The claim: hollow earth belief spikes precisely when real frontiers close, 1890s pole races, 1940s post-war unease, now the fully-satellited planet, because a mapped world with no unknowns is intolerable to a species built by exploring. Verdict: the timing correlation is real and the psychology is plausible, but it explains the belief's persistence, not its content. The interior was always where cultures put what the surface could not hold: the dead, the treasures, the exiles, and the better versions of us.
Every culture dug an underworld. Why did only the moderns demand coordinates?