[andrewflnr]

So, not a physicist, but the claims in the PDF about how GR has "never predicted a single galaxy rotation curve" are overblown, right? Aren't there a handful of galaxies where the rotation curve lines up pretty close with the predictions from the visible mass? Any new physics has to explain those, too.

Anyway, I think I can see why QI is so appealing. The paper contains a very short and sweet explanation.

[ilove_banh_mi]

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.

https://en.wikipedia.org/wiki/Galaxy_rotation_curve

[basil-rash]

> 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.”

Discrepancy’s been accounted for, boss!

[btilly]

I don't know why this got downvoted.

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.

[andrewflnr]

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.

[btilly]

I see zero evidence for any of that.

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.

[kelseyfrog]

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.

[andrewflnr]

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.

[andrewflnr]

For instance: https://en.wikipedia.org/wiki/NGC_1277 Citation trail leads to https://www.aanda.org/articles/aa/full_html/2023/07/aa46291-... I vaguely recall there being a few more such instances, but can't find them with a casual googling. The paper is from 2023. Perhaps the Galaxy Rotation Curve wiki article is out of date.

[pdonis]

> The paper contains a very short and sweet explanation.

As the saying goes, all complex questions have simple, easy to understand wrong answers. This is an example. See my response to georgeburdell upthread.

As for galaxy rotation curves, yes, the paper's claim is overblown.

[andrewflnr]

Haha, yes, I remain skeptical at best of QI. I know just enough physics that I probably should have thought of the issue you mentioned up there, too. Still, the idea remains pretty enough that it's tempting to try to salvage it, like even if it's not technically Unruh radiation, maybe there's a reference frame or other perspective where the math works anyway... But that only makes sense if the real life numbers work out, and I'm not going to take this guy's word for it.

[pdonis]

> even if it's not technically Unruh radiation, maybe there's a reference frame or other perspective where the math works anyway

There can't be, by Lorentz invariance. If a free-falling observer sees zero radiation in one frame, they must see zero radiation in any frame.