What is general relativity primarily about?

General relativity is primarily a theory proposed by Albert Einstein that describes how mass and energy influence the geometry of spacetime. This concept of curvature is central to understanding gravitational phenomena. Unlike previous theories of gravity, which treated it as a force acting at a distance, general relativity demonstrates that mass causes spacetime to curve around it. As a consequence, objects move along paths determined by this curvature, which we observe as the effect of gravity.

For instance, when a planet moves in its orbit, it is not just following a straight path in space; instead, it is moving along a curved path due to the way spacetime is affected by the mass of the sun. This has profound implications for astrophysics and cosmology, as it helps explain not only planetary motion but also phenomena such as the bending of light around massive objects and the behavior of objects in strong gravitational fields.

In summary, the essence of general relativity lies in the relationship between mass-energy and the curvature of spacetime, making option C the correct response to the question.