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Kaluza-Klein theory
A model that seeks to unite classical gravity and electromagnetism by resorting to higher dimensions. In 1919 the German mathematician Theodor Kaluza (1885-1954) pointed out that if general relativity theory is extended to a five-dimensional spacetime, the equations can be separated out into ordinary four-dimensional gravitation plus an extra set, which is equivalent to Maxwell's equations for the electromagnetic field, plus an extra field known as the dilaton. Thus electromagnetism is explained as a manifestation of curvature in a fourth dimension of physical space, in the same way that gravitation is explained in Einstein's theory as a manifestation of curvature in the first three.
In 1926 the Swedish physicist Oskar Klein (1894-1977) proposed that the reason the extra spatial dimension goes unseen is that it is compact – curled up like a ball with a fantastically small radius. In the 1980s and 1990s, Kaluza-Klein theory experienced a big revival and can now be seen as a precursor of string theory.
Related categories
• SPACE AND TIME
• PARTICLE PHYSICS
• COSMOLOGY
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