[Retric]

Calculating the percentage of the universe’s observable mass is dark matter adds 200+ billion parameters because the mass fraction of each galaxy varies.

So there’s no simple way to calculate it from say looking at the Milky Way alone and extrapolating from the baryonic mass of the rest of the universe. Trying to approximate things from a representative sample is its own problem.

[andrewflnr]

You're still confusing a physics model with a map of the universe. That said, it's sure a heck of a coincidence that the number they get from adding up estimated dark matter in galaxies lines up with the number they get from other cosmological measurements, isn't it? Almost like galaxy rotation curves aren't the only evidence for dark matter and haven't been for a long time. https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...

[Retric]

Gravitational lensing, velocity dispersions, etc circles back to the total mass of galaxies. So it shows up on many of the ways we calculate the total mass fraction not just rotation anomalies.

[andrewflnr]

Many of the ways? I guess that's it then, there's no reason to look at the whole picture, and especially no point in reading all the way to https://en.wikipedia.org/wiki/Dark_matter#Cosmic_microwave_b...

[Retric]

Your being redundant, Many in this instance obviously implied not every.

[andrewflnr]

Then, in what way is it relevant to my claims here? Namely,

1. Dark matter does not meaningfully introduce billions more parameters into cosmological models than they already have, and

2. Individual galaxies' dark matter fractions are not essential to (not proving, but) strongly suggesting dark matter exists.

[Retric]

Something being consistent with a model is different than something being sufficient evidence on its own to support a model.

If the observed dark matter fractions of all known galaxies were 0% but the CMB was unchanged we wouldn’t assume dark matter exists. Thus your #2 is false. There’s infinite models consistent with any observation so finding something after a model was created for other reasons is useful as validation, but the chain of logic is still dependent on the prior observations not the model.

In a meaningfully different cosmos different observations would have happened and different models would exist. Trying to pick out specific experiments as sufficient on their own glosses over that particular limitation.