Question

why Einstein's general theory of relativity is considered "incomplete"(explain it like I'm 5)​

Answer 1

Answer:

The answer is yes! General relativity works with differentiable manifolds, but it predicts singularities, which are not differentiable. So GR is incomplete even if we does nor take into account quantum effects. Even at classical level one needs a theory of singularities or a sort of modification without singularities.