Ever since Plato first told his students the allegory of the cave, people have wondered whether dimensions exist beyond the three we immediately perceive. An extra dimension—time—played a role in Einstein's work, although he saw it only as a necessary evil to get his equations to work.
Other scientists were more receptive: mathematical physicists Oskar Klein and Theodor Kaluza made higher dimensions an integral part of their attempts to discover a "theory of everything" that would tie together strong and weak nuclear forces, electromagnetism and gravity. Halpern explains that over the past century gravity has been the shadow flickering on the walls of the cave hinting at other realms.
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