General relativity is a theory introduced by Einstein in 1915 to describe gravity. Until then, the attraction exerted by a body A on a body B had been described as a force, expressed by Newton's law of universal gravitation, while the motion of each body was determined using Newton's laws of motion. These laws provided a fairly accurate description of the experiments conducted at the time, but there was already one astronomical observation that mathematicians and physicists could not account for using the available theory: the orbit of the planet Mercury is not a perfect ellipse, as Newton's laws would predict if the Sun and Mercury were the only two celestial bodies in the universe. More importantly, even taking into account the influence of the other planets in the solar system on Mercury's motion does not fully explain this "anomaly."
The emergence of spacetime
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Physics changed considerably between the 17th century and the early 20th: electromagnetism and special relativity, in particular, transformed the landscape. The principle of "action at a distance" found in Newton's theory of universal gravitation was incompatible with these new theories, which required the introduction of a spacetime unlike that of the brilliant British scientist.
