books.google.com - In physics, the idea of extra spatial dimensions originates from Nordstöm s 5-dimensional vector theory in 1914, followed by Kaluza-Klein theory in 1921, in an effort to unify general relativity and electromagnetism in a 5 dimensional space-time (4 dimensions for space and 1 for time). Kaluza Klein...http://books.google.com/books/about/Extra_Dimensions_In_Space_and_Time.html?id=fFSMatekilIC&utm_source=gb-gplus-shareExtra Dimensions In Space and Time
