[isthatafact]

> "That's a per-galaxy parameter."

No, variation in galaxy properties is an output, not an input, of the model.

You could decide to quantify and catalog different galaxies with one or more parameters that describe their properties. You could then compare whether that catalog is statistically consistent with the output of the model (and must take into account all uncertainties in the model and the observations).

By analogy, you can measure that different people have different heights, but it does not mean that the specific height of each individual person is a unique input parameter in any fundamental model of biology.

[AnimalMuppet]

Let me change your analogy. You take each person, and measure their height. You also "measure" how tall they "should be". You then show that the differences between their actual height and the height they should have had fits a model. That's nice, but for each person, you still assigned a value for the difference between how tall they are and how tall they should have been.

That's what I mean by "it's a per-galaxy parameter". For each galaxy, to explain the behavior of that galaxy, you're saying "it must have X amount of dark matter".

[isthatafact]

There is no DNA for galaxies, so how could you know what the properties of a particular galaxy "should be"?

The focus on "per-galaxy parameters" is like expecting to be able to predict how tall Tom Cruise should be after reading a textbook on the theory of evolution.

[throwawaymaths]

Ok so you are admitting that just as evolution is a poor model for human height, DM is a poor model for galaxy rotation curves.

[isthatafact]

Maybe my metaphor was too sloppy to illustrate the point, but I do not follow your logic here at all.