Special Relativity posits that:
1.) Evreything in the universe is always “moving” at a constant speed (“C”)
2.) The Universe is made out of a 4 dimensional fabric comprised of 3 spatial dimensions and 1 time dimension
3.) By necessity an object moving through any one dimension goes slower through the others. (Imagine a car going straight east and another going north east. The car going north east will cover less ground in the eastward direction. Same thing with the dimensions of spacetime an object moving through one of the spatial dimensions will by neccessity move slower through the time dimension.)
4.) Being that light has no mass to “hold” it in one of the spatial dimensions it moves at a constant speed of C through the spatial dimensions. An object with mass that is at rest will have all of its movement happen in the time dimension.
General Relativity posits
1.) All of the above
2.) spacetime curves in the vicinity of a massive object.
3.) Left to their own devices an object will travel in a straight line through spacetime.
4.) When spacetime is curved an object will follow the curve.
5.) Gravity is not a “force” but rather it is the result of an object moving along the curvature of spacetime. (The famous ball on a rubber sheet thing)
6.) Gravity is in essence the acceleration (change of direction in the movement) of an object in spacetime due to the curverture of the fabric it is traveling through.
7.) A gravitational field and an acceleration are the same thing