.The first person to add a fifth dimension to Einstein's general relativity was German mathematician Theodor Kaluza in 1919. The reason for the unobservability of the fifth dimension (its compactness) was suggested by the Swedish physicist Oskar Klein in 1926 (see Kaluza–Klein theory). These predictions would set the foundation for string theory by introducing the concept of extra dimensions
http://en.wikipedia.org/wiki/String_theory#History


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