Definition of "relativity theory" []

• (physics) the theory that space and time are relative concepts rather than absolute concepts (noun)

WordNet. Princeton University. 2010.

• "Building on the concept of the quanta, in 1923, almost a decade after Einstein published his general relativity theory no longer a theory; now it is a law, the French physicist Louis de Broglie introduced an idea that was even more bizarre in its assertions than Einstein’s claim that matter really was a form of energy."