Einstein, Gravity & Relativity
I finally understand why when Einstein had developed special relativity, he wanted to tackle the effects of relativity on gravity. Remember this was a time when the world was still dominated by Newtonian physics. Einstein’s friend Max Planck warned him about attempting to unite gravity with relativity, “You won’t succeed, and even if you do, no one would believe you”.
If the absolute terminal speed of anything in the physical universe is the speed of light, then gravity has also to observe this. What would happen if a massive star were to appear instantaneously next to smaller bodies? Do all the bodies, even those very far away, experience the effect of gravity from that star instantaneously? That is what Newtonian Physics would say.
In the non-Newtonian paradigm we can imagine dropping a bowling ball onto a mattress: the deformation of the mattress will radiate outwards. This would be like the massive star appearing and akin to its effect on space-time. Hence this likely means that there are such things as gravity waves. And that these waves are limited to the speed of light. (Well, we now know that they have been detected with the LIGO instrument.)
PS: The amount of bending of space-time is determined by the amount of mass and energy you throw at it.