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A comment on Triplet of 'Ghostly' Galaxies Hints at What Dark Matter Is – and Isn't. Parent comment

Re:Triplet of 'Ghostly' Galaxies Hints at What Dark Matter I... by martinpw on Tuesday October 20, 2026 @04:15PM (#50172034)
The problem with any theory of modified gravity is that there is just no physical justification for it. It's only motivation seems to be to explain away dark matter by adding and tweaking free parameters until you fit the data, which you can always do given enough variables.

van Neumann's quote comes to mind - "With four parameters I can fit an elephant, and with five I can make him wiggle his trunk."

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Re:Triplet of 'Ghostly' Galaxies Hints at What Dark Matter I... by Sniffnoy on Tuesday October 20, 2026 @05:34PM (#50173009)
Hm, MOND is full of new parameters (an entire interpolation function!), but do other modified gravity theories really have so many? I guess actually I don't know the answer to that, maybe they do. Do you know how many others have?
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Re:Triplet of 'Ghostly' Galaxies Hints at What Dark Matter I... by KingMob on Wednesday October 21, 2026 @02:22AM (#50176760)
> explain away dark matter

This kind of presumes dark matter has been definitively proven already, though.

From the outside, CDM may be a better theory than MOND, but it doesn't seem settled to me. I haven't heard anyone describe it as a "Law" yet.

Couldn't someone equally characterize the creation of dark matter as "adding and tweaking mass until you fit the data"?

[ Parent | on HN ]
Re:Triplet of 'Ghostly' Galaxies Hints at What Dark Matter I... by Sniffnoy on Thursday October 22, 2026 @02:08AM (#50191755)
Man, you're doing the thing I just complained about, where you implicitly frame MOND and CDM as the only two alternatives! :P
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Re:Triplet of 'Ghostly' Galaxies Hints at What Dark Matter I... by KingMob on Friday October 23, 2026 @02:57AM (#50205340)
Fair, I'm not a physicist. I don't really know the more obscure variants of dark matter and modified gravity theories.

But what about you? Are you not doing https://xkcd.com/2501 ? Is your expectation reasonable on HN?

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