It's more like a mathematical outlier that scientists use to reconcile what really seems to make sense with what we see. I think most physicists were skeptical of it. It's really just matter that doesn't emit light. Makes sense on paper. My eyes start to cross when they get into dark energy. I've always been skeptical of it. But I'm an artist, not a scientist. You can tell me something makes the math work. That doesn't mean I understand what the fuck that means
The answer to the first question is yes and no from my fuzzy memory, but Devac and francopoli are both clearer and better informed. And together they give a kick-ass answer. As to skepticisms across communities... Astronomy professors rave about how nutty it is that the only way we can measure it is through our understanding Newtonian mechanics alongside the implications. Physics professors acknowledge it's existance for the same reason, then smile and shrug off preceding questions. The lone math professor who deals with astronomy I talk to flat out calls the above lunatics. I'd love to say that's how each community thinks, but I've got a small sample size. EDIT: Left off the beginning of the last sentence.
Special Relativity, not Newton, but otherwise spot on. History is full of these "I have no idea on the why or how, but here is a bunch of math to describe and make predictions" when it comes to natural phenomena. Hell, speaking of Gravity, what is it? I mean Why is there Gravity? We understand DNA and evolution magnitudes more in depth than we do one of the four universal forces of the universe!Astronomy professors rave about how nutty it is that the only way we can measure it is through our understanding Newtonian mechanics alongside the implications.