Acceleration without force in relativity refers to the concept that an object can accelerate without any external force acting upon it. This is possible due to the curvature of spacetime in Einstein's theory of general relativity.
This is possible because according to general relativity, mass and energy can cause spacetime to curve. When an object moves through this curved spacetime, it experiences acceleration even without any external force acting on it.
One example of acceleration without force in relativity is the orbit of a planet around a star. The planet is constantly accelerating towards the star, but there is no external force causing this acceleration. Instead, it is the curvature of spacetime caused by the mass of the star that causes the planet to accelerate.
In Newton's laws of motion, an object can only accelerate if there is an external force acting upon it. However, in relativity, the curvature of spacetime can cause acceleration without any external force. This is a fundamental difference between the two theories.
This concept has significant implications for our understanding of gravity and the behavior of objects in the universe. It also helps to explain phenomena such as the bending of light around massive objects and the expansion of the universe. Additionally, it has practical applications in fields such as space travel and GPS technology.