Seeing time as the fourth dimension made sense of Einstein's special relativity. The German mathematician Theodor Kaluza had even grander designs. In 1919, he sent a paper to Einstein in which he argued that by adding a fifth dimension to space-time, it was possible to show that gravity and electromagnetism were two aspects of one and the same force.
A few years later a Swedish mathematician, Oskar Klein, took Kaluza's idea and ran with it. He countered the obvious objection to the existence of a fifth dimension - that it is not immediately apparent - by showing it could be tiny and curled up at every point in our four-dimensional space-time. Thus began the trend of searching for the unification of forces in the hidden dimensions of hyperspace that continues today in string theory.
Perhaps, however, the fifth dimension is not as tiny as Klein suggested. Using string ...
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