Below are some of the things said about why Einstein's "Theory of Relativity" is valid.

Regarding the 95% of missing matter in the universe, which science currently explains away by saying that you have to have faith in the existence of invisible, undetectable, dark matter and dark energy; there is another explanation, which could be mathematically analyzed using Newton’s equations, which are relatively easy to work with, and some modifications.  However, that would be a huge effort which I would not go to unless I was being paid to do so, as the work I previously did for free was ignored.  The better physicists should be able to figure out to what I am referring, and they are already being paid to understand and explain the universe, so if they have not already done so for their own understanding, they should do the math.