This principle was first enunciated by [[Albert Einstein]] as the starting point for the [[general theory of relativity]]. He formulated gravity as a special kind of fictitious force, arising from the curvature of spacetime. But the idea of fictitious forces was known in classical [[Isaac Newton|Newtonian]] mechanics, and the very similar nature of gravity had been noticed before, for example, by Johann Soldner in 1803. | This principle was first enunciated by [[Albert Einstein]] as the starting point for the [[general theory of relativity]]. He formulated gravity as a special kind of fictitious force, arising from the curvature of spacetime. But the idea of fictitious forces was known in classical [[Isaac Newton|Newtonian]] mechanics, and the very similar nature of gravity had been noticed before, for example, by Johann Soldner in 1803. |