Not so long ago, noone knew about the weak force, and even the most brilliant minds would never think electricity and magnetism are two sides of the same coin. Now we have a theory that unites all three under the same umbrella.
In many interpretations of GR it is believed that mass deforms spacetime, but is also influenced by the spacetime it moves through. In the absence of mass, spacetime expands. Carrying along any mass with it. When mass is present this default expansion is overpowered by its influence which causes a contraction. Hence black holes.
Gravity is still colored by classical definitions so most assume its power is unidirectional. However there is a quantitative factor for expansion in the very same Einstein equation which defines GR.
We need to stop thinking of gravity as a force acting on objects, and rather something that acts on spacetime. Many people advocate this but stop at the rubber sheet analogy, which is completely devoid of the idea that the sheet actually moves as well.
