In the previous section, we observed and studied the Special theory of Relativity. This theory is very limited because it only deals with Galilean Systems, this means they remain at rest or in constant motion. These kind of systems is rather hard to find in nature and a vehicle can't be this kind of system at all times. A moving vehicle needs to be accelerated, at least once in order to become a "moving" vehicle.
Einstein realized that his theory was very limited when tried apply it to gravitational fields. He realized that special relativity could not apply to gravitational fields or to accelerated systems, so he developed the General Theory of Relativity basing himself in the study of gravitational fields, studies he performed using astronomical observations.
One important thing to have in mind is that special relativity is assumed to be true in general relativity, so all the concepts and deductions from special relativity are used in the general theory.
The mathematical deduction and formulas used in general relativity are highly complicated (only scientists are prepared to understand such math), so we will only focus in the physics part of the theory.
General Relativity bases itself on four postulates, the two from special relativity, the equivalence principle and the general principle of relativity; all of which will be explained in the next few lessons.