Final answer:
Einstein's general theory of relativity expands on Newton's gravitational theory by explaining phenomena such as the orbit of Mercury and light deflection due to gravity, proposing that gravity is the warping of spacetime.
Step-by-step explanation:
While both Newton's universal law of gravitation and Einstein's theories of general relativity can calculate the acceleration due to gravity between two massive objects, Einstein's general theory of relativity goes further by explaining additional phenomena. For instance, Einstein's theory can account for the precession of the orbit of the planet Mercury which Newton's theory could not fully explain. Moreover, Einstein proposed that gravity is a result of the warping of spacetime caused by mass, which includes the idea that gravitational fields change the path of light. This concept was illustrated by Einstein's thought experiments, such as the effect of gravity on light in an accelerating elevator, showing that gravity affects even massless particles like photons.
In essence, Einstein's theory provides a more comprehensive explanation for gravitational interactions, especially in strong gravitational fields such as those near black holes. It also includes the equivalence principle, which equates the effects of acceleration with those of gravity. Notably, general relativity has led to the prediction and observation of phenomena such as gravitational lensing, where light from distant stars is bent around massive objects like galaxies.