The reason why is so much of the theory is right that knowing how to fix the correct pieces to include the new is the difficult part. As a Theologian/Philosopher Degree holder I love these debates. I think there might be more in the Philosophy side then people care to accept.

> "But if it does turn out that a new theory of gravity is needed, what kind of theory would it be? How could it correctly describe the motion of the bodies in the Solar System, as Einstein's theory is known to do, and still give us the different prediction for the universe that we need?"

https://science.nasa.gov/astrophysics/focus-areas/what-is-da...