EXCERPT: . . . In [German physicist Johann] Zöllner’s view, based on his readings of the German philosopher Immanuel Kant and the German mathematician Carl Gauss, the fourth dimension was as real as the three dimensions of space. Due to their prejudices, Zöllner thought, most people don’t perceive the fourth dimension, but they could if they were properly trained [...]
Zöllner had ample precedent for reaching this seemingly audacious conclusion. The roots of connecting higher dimensions with a transcendental realm date back at least to Plato’s cave allegory, in which prisoners confined to a cavern observe two-dimensional shadows on a wall while being unaware of the three-dimensional world outside that produced them. But although Plato implied that we three-dimensional beings might be likewise oblivious to a greater reality, he didn’t explicitly argue that there was an actual fourth dimension.
A more immediate antecedent to Zöllner’s hypothesis is found in The Unseen Universe, a popular book published anonymously in 1875, and later revealed to have been co-authored by the Scottish mathematical physicists Balfour Stewart and Peter Guthrie Tait (a lifelong friend of Maxwell). The treatise speculates about links between scientific concepts such as conservation of energy and spiritual questions such as the persistence of life after death. In one brief passage, it connects the fourth dimension with an unseen realm:
Just as points are the terminations of lines, lines the boundaries of surfaces, and surfaces the boundaries of portions of space of three dimensions: so we may suppose our (essentially three-dimensional) matter to be the mere skin or boundary of an Unseen whose matter has four dimensions.
Zöllner knew enough about optical illusions to posit similarly that space’s restriction to three dimensions could simply be a persistent mirage. Perhaps, then, the world of the spirit, including all manner of psychic occurrences, had a perfectly natural explanation in a hitherto unexplored dimension. Goaded by the widespread interest in spiritualism at the time, Zöllner delved into connections between higher dimensions and the occult with greater gusto than anyone prior to him had dared. It was high time, he concluded, for the study of four-dimensional phenomena to be part of science.[...] In the mid-1880s, despite [...] the prominence of quasi-mystical groups [...] several mathematicians published works trying to explain four-dimensional realms as realistic possible extensions of the known physical world. Their writings drew heavily on an analogy by Gauss, who imagined how a bookworm confined to flat pages would perceive the three-dimensional world as ‘unreal’ until informed otherwise.
[...] Other late-19th-century mathematicians began to imagine the fourth dimension as something far more familiar: the passage of time. The pages of Nature and other scientific journals featured speculations about a four-dimensional amalgam of the three-dimensions of space along with an additional dimension of time. These notions eventually received a concrete mathematical treatment in Einstein’s general theory of relativity, which enabled physicists to reclaim higher dimensions from the spiritualists. Long before then, though, they left their own imprint on popular culture.
[...] As the concept of spacetime became an integral part of physics, the fourth dimension began to lose its spooky edge. Scientists began to turn their attention to the realistic possibility of a fifth dimension. Nevertheless, higher dimensions continued to appear as common elements of horror stories and pop mysticism....
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