I'm not aware of any match between GR theory and observations when it comes to galaxy rotation curves. The wikipedia entry provides a decent description of the issue.
> The discrepancy between the two curves can be accounted for by adding a dark matter halo surrounding the galaxy.
Funny. “This discrepancy can be accounted for by accounting for the discrepancy using the number fudging we developed specifically to account for the discrepancy.”
The top theory is exactly that - most of the mass in a galaxy is in the form of dark matter of some kind that can't fit our current theories of physics. The second top theory is that gravity behaves differently at long distances than at short distances. The third theory that is proposed every so often is general relativity, but those who know it best universally agree that it is too small an effect by several orders of magnitude. Every other theory that I've encountered is generally labeled a crank theory.
The reality is that we don't actually know what's going on with the galaxy curves. But we do know that it involves physics that we do not yet understand. And the leading two theories involve weird fudge factors.
Because it's a conspiratorial mindset that willfully ignores the long list of other evidence for dark matter in favor of mocking physicists who are doing their best to make sense of confusing observations. That's exactly the kind of thing that downvotes are meant for.
Science has a long history of proposals based on various fudge factors. Some of those fudge factors disappear when we get better measurements. Some require learning more about the system. For example Newton's theory of sound was consistently wrong until Laplace figured out how adiabatic heating changed things. Some require learning more about the physics. For example Einstein got rid of the need for a fudge factor for figuring out Mercury's orbit. Some require proposing new physics.
When dark matter is called a fudge factor, that is absolutely technically correct. It *IS* a fudge factor. It is a fudge factor that explains a whole lot of stuff, at the cost of requiring something new whose nature we have no real clue about. This isn't conspiracy theory. This is how science works. It is how science is supposed to work.
It's current status is much like that of the neutrino when it was first proposed. A particle we can't think of a way to detect in any way other than the fact that it is required for conservation laws to work out. As it happens, we did eventually figure out how to detect it. But only through discovering then-unknown physics (chain reactions), and building detectors which required a budget that was unthinkable for physics back when the neutrino was proposed in 1930.
If we're going to get technical, then the source of confusion here is that the term "dark matter" is considered a theory by lay people. Whereas scientists view dark matter as a set of outstanding problems in cosmology.
There are many dark matter theories that address these problems, and we can talk specifics about each one and how it addresses each of the dark matter problems.
On the other hand, squint at pretty much any theory, and you can see a series of related theories. That are each the basic theory, plus another assumption or two about another thing that might be observed. Leading to a cascade of differences that result in distinct theories.
Therefore dark matter can be a theory, and there can also be many theories of dark matter. Just like evolution can be a theory, and there can also be many theories about how exactly evolution progresses. Exactly what we call a "theory" here becomes rather arbitrary.
If you don't see the mocking tone of the comment we're talking about, and you don't see the conspiratorial tone of the anti-dark-matter crowd in general, then yeah, you won't see why they're worthy of downvotes. But then we live in different worlds, so I guess there's not much to discuss.
You are dismissing criticism lightly by accusing others of being conspiracy theorists, mocking you, and so on. These are classic ways of creating cognitive dissonance and shutting off alternate ideas. Which is the exact OPPOSITE of what Feynman tells you to do in https://calteches.library.caltech.edu/51/2/CargoCult.htm.
The truth is this. Dark matter is observationally the best theory that we've got. However it is deeply unsatisfying. It requires fundamentally new physics about fundamentally new stuff with properties that we have absolutely no clue about. It is literally a theory of, "Insert magic cosmic glue here."
Virtually any idea can be inserted. String theory is popular despite having made a single verifiable prediction in decades of trying. So let's say that dark matter is made of strings!
Maybe if the Everett interpretation were more popular we'd theorize that a proper unified theory will have a small gravitational interaction between quantum superpositions. So what looks like dark matter is really the gravitational interaction with the superpositions of the stars in the galaxy that have been evolving since the early universe. Thanks to the fact that multibody gravity systems are chaotic, every tiny variation grows over time until those superpositions just act like a smooth smear, which we can't directly perceive because of quantum decoherence. Is this a reasonable theory? Don't ask me, I just made it up. But I know that it doesn't require any new kind of matter - it just requires a bit of speculation about interpretations of QM and the nature of quantum gravity. And it would look just like dark matter does.
The truth is that we've got a theory, and we know how to fit the data to it. But that theory doesn't integrate well with all of our other theories. Therefore, no matter how well we've made the facts fit, intellectual integrity requires that we remain open to the idea of being wrong. Not so open that we stop pursuing what *WE* think is right. But open enough to recognize that other people's discomfort with the theory is actually somewhat reasonable. No matter how strongly we might think that it is right.
Funny. “This discrepancy can be accounted for by accounting for the discrepancy using the number fudging we developed specifically to account for the discrepancy.”
Discrepancy’s been accounted for, boss!