When speaking with researchers and professors at my physics department, I sometime catch this undertone in the conversation when speaking about GR: almost as if some are not entirely convinced about the general theory of relativity.
I was wondering, are there any cosmological observations which general relatively fails to predict?
As a hypothetical example: maybe some star follows an orbit that deviates from the orbit predicted by GR.
I have taken a course on GR, so I have some basic understanding of the subject.