One of the many pseudoscientific ideas about Earth’s form size and shape. Some hollow Earth theories suppose Earth to be flat like a flapjack, and others suppose it to be spherical. But the most bizarre theory must be that we humans, along with the flora and fauna, are living on the inside shell of a huge sphere that looks inwards toward the whole universe, which occupies the central hollow. Most Hohlweltlehre are of the 19th century.
In early history before global travel, many people envisaged the world to be flat and worried about going too far afield for fear of falling off the edge. Today in the United States there are still adherents to this theory, probably followers of Wilbur Glenn Voliva of the Church of Zion, who propounded the idea that the Earth was shaped like a flapjack, with the North Pole in the center and the South Pole spread around the circumference. If this can be believed today and it still is how much more difficult must it have been in the past to abandon notions of what seemed to be quite obviously a flat earth, in order to think of it as a giant ball, with we mortals living all around its surface. It must have been like replacing an apparently plausible theory by an impossible one. In the 16th century, Martin Luther argued that the “underside” of such an Earth could not be habitable, because God would not have allowed so many people to be disadvantaged, by hiding from their view Christ’s descent from heaven at his Second Coming.