Introducing Einstein’s General Relativity
In the preceding chapters, we witnessed the new aspects of physics brought about by Einstein’s Relativity. All of this arose because: a) there is a speed limit in nature, \(c\), the maximum speed at which influences can be propagated and b) because all inertial observers are physically equivalent, they must all agree on this speed limit. However, not a word was mentioned about gravity and it is with the inclusion of gravity that Einstein’s Relativity takes on a whole new and exciting complexion. Einstein’s Relativity without gravity is called “Special Relativity” to distinguish it from Relativity with gravity which is called “General Relativity”. In brief, General Relativity is Einstein’s theory of gravity. In what follows, we will delve into General Relativity, showing how it is the curving of spacetime in the general theory that replaces the old Newtonian idea of gravity being just another force.