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  Dark Matter Margin of Error - Exchange

this exchange of comments followed my  post on dark matter and a margin for error to the Cosmology facebook group.

The first comment:
The other day I thought of a question thwt I couldn't answer. What sort of variables go into calculating the estimated number of stars born in a certain time period, say a day or a year?

This person tagged my post with Love

The next comment:
David's analysis is badly flawed, the accuracy of the estimates of the total mass don't really make much difference. The rotation curve evidence is based on the shape of the curve versus the luminosity at different radii, not mass estimates.
My response:

My conclusion drawn from a number of sources and a very simple analysis: the complexity of spiral galaxies given an incomplete data set makes it difficult to predict motions of individual stars.
My suggested solution is define a margin of error while improving our model. Instead we are told dark matter is the solution for unexpected motions at the level of individual stars.
If my simple analysis is badly flawed then I must assume you assume we have a complete dataset and our model can achieve perfection to individual stars.
Rather than fixing the model to meet an acceptable amount of small deviations, you prefer to maintain something invisible affects everything else that follows physics.

His response:
 You can see an example of a rotation curve on the Wikipedia page.
This included the Wikipedia image of a rotation curve with observations and deviations.

My response:

That diagram reinforces my point. We have observations using different means to observe the rotation curve.
It is never just like we expect.
I propose we accept we do not have a complete understanding of a spiral galaxy so our expectation is not close enough yet.
The conclusion right now is hidden mass is at fault and no other possible cause could conceivably explain the deviation.
The scientists in this story considered another possibility - the M31 magnetic field, discovered in 1978.
The study's pdf file, with before/after plots, can be found online for:

link to story

someone else tagged this comment by me with a Like.

His response:

DM: We have observations using different means to observe the rotation curve.
Sure, but the end of one method joins up with the next, and even if you ignore the starlight part, the 21cm observations on their own prove the point, the speeds increase with radius while the star density falls.
Your post talked about "margin of error" and you said "This uncertainty is important for dark matter." but the error bars are shown on the chart and the dotted line is a long way outside, that specifically is why I said your analysis was badly flawed. You made the claim without first finding out what the margins were.
And again, you are ignoring the fact that half a dozen other independent techniques give the same answer.
Proposing that we ignore hard evidence just because you don't like the outcome is not science.
my response:

I was proposing we do not ignore this study that found including the M31 magnetic field resulted  in the model matching the rotation curve.
I am proposing proper science is considering studies that question a basic assumption, that dark matter is the only solution.

Since you did not mention that study I linked: I was not ignoring the fact a study did not give the same answer.

I look for an outcome that conforms to all we know. Science is the accumulation of knowledge.

The error bars are irrelevant. The point is dark matter presumes we can predict the curve with certainty so any deviation is beyond physics - undetectable dark matter. Your responses have not questioned that absolute certainty. Instead multiple curves show the same deviation. Those just confirm we cannot model the rotation.

his response:

DM: The error bars are irrelevant
The uncertainty was the primary point of your initial post, now you say they are "irrelevant". The fact is that they are the bounds on the actual measurements and those are what science is based on.
From the paper you link:
"The team notes that this finding is still speculative as the understanding of the magnetic fields at such distances is based solely on modeling. Although the magnetic field has been explored for the inner portions of the galaxy (roughly the inner 15 kiloparsecs), no direct measurement has yet been made in the regions in question."
So now actual measurements, just a model contrived to fit.
However, let's assume it is correct. Without it dark matter would need a slightly higher density at the edges, with the magnetic field addition, the standard model of dark matter fits perfectly and the slight rise in speed at the edges is explained as an addition to the effect of dark matter.
OK, that doesn't through any doubt on dark matter, in fact it reinforces it.

My response:

It throws doubt simply because it had been ignored and including it improved the model. The clear implication is 'what else' is missing in the model?
The magnetic field is interacting with the stars electric fields, not with uncharged atoms.
We are so absolutely certain this model is so accurate; this certainty is the basis for dark matter when the model fails. Models must use abstractions. We cannot solve a 1-trillion body problem with a few equations. Dark matter presumes all our abstractions and probabilities in the model are always correct. The fact one study found something in normal physics not in the model is quite useful implying we missed something before being forced to go beyond physics to something undetectable.

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