Subsequent his completion of special relativity in the case of reference frames in uniform motion, Einstein then focused his study on accelerated motion. He examined the connection between gravity and acceleration, which led him to suggest the principle of equivalence, which designates gravity and acceleration as being analogous to one another. In a nutshell, Einstein postulated that within an experiment, it would be impossible to tell the difference between being at rest in a uniform gravitational field and being accelerated. He hypothesized this concept by sealing scientists inside boxes under varying circumstances of acceleration and gravity. Initiated from the principle of equivalence, by 1915 Einstein completed his ground breaking new theory, the general theory of relativity, which described gravity in a revolutionary way.
Universe: A Definitive Visual Guide
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