Kaluza–Klein theory (KK theory) is a classical unified field t | DailySciencePost

Kaluza–Klein theory (KK theory) is a classical unified field theory of gravitationand electromagnetism built around the idea of a fifth dimension beyond the common 4D of space and time and considered an important precursor to string theory. Gunnar Nordström had an earlier, similar idea. But in that case, a fifth component was added to the electromagnetic vector potential, representing the Newtonian gravitational potential, and writing the Maxwell equations in five dimensions.