No, the theory of gravity proposed by Albert Einstein, known as general relativity, does not directly explain why planets are spherical in shape. The shape of planets is primarily determined by a combination of factors, including gravity, mass, and the rotation of the planet.
According to general relativity, gravity is the curvature of spacetime caused by the presence of mass and energy. This theory provides a deeper understanding of how gravity works and how it affects the motion of objects, including planets. However, general relativity does not specifically address the initial formation of planets or their subsequent spherical shape.
The process by which planets form and become spherical is primarily explained by the theory of planetary accretion. According to this theory, planets form from a rotating disk of gas and dust called a protoplanetary disk. Over time, particles within the disk collide and stick together, gradually growing into larger bodies known as planetesimals. Through further accretion and gravitational attraction, these planetesimals continue to grow into planets.
As the mass of a growing planet increases, its gravity becomes stronger, causing the material to collapse into a roughly spherical shape. Gravity acts equally in all directions, pulling material toward the center of mass. This results in a spherical equilibrium, where the force of gravity is balanced by the internal pressure of the planet's material.
In summary, while general relativity provides a framework for understanding gravity, the explanation for why planets are spherical lies primarily in the process of planetary accretion, which is governed by gravitational forces and the physics of matter.