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  Dark Matter - Tolerance for Deviation

The post listed several questions about dark matter.

This comment followed my earlier comment to the post.

The main problem addressed by dark matter is the current inability to predict motions of individual stars in a spiral galaxy.
The proposed solution is dark matter, where something undetectable is causing deviations from predictions.

I suggest that is the wrong solution to this problem.

Cosmology needs a tolerance for deviation.

Many modern CNC machine tools can repeat to 0.0001 inch or 0.001 mm (1 micron), and 0.001 degree.
It is impossible even with such precision to guarantee a perfect part every time. Temperature growth in components and tool wear can cause slight deviations though with a slight time lag these are managed to maintain accuracy
Each machine must have a defined tolerance for deviation, like 1 micron.

From Wikipedia:
Engineering tolerance is the permissible limit or limits of variation in a physical dimension.

Dimensions, properties, or conditions may have some variation without significantly affecting functioning of systems, machines, structures, etc. A variation beyond the tolerance (for example, a temperature that is too hot or too cold) is said to be noncompliant, rejected, or exceeding the tolerance.

Very expensive machines still require a definition for their performance. A machine's stated tolerance for deviation also affects its purchase price.

Rather than seeking perfection (resulting in dark matter), cosmologists must have an intermediate goal so when it is achieved success can be claimed and subsequent goals are defined to establish milestones for future progress in our understanding.

For example, observations have shown our Sun does not follow an ellipse in the Milky Way. It has a 'disturbed' orbit. We must understand our closest star.
Because the Earth is located within a spiral arm with much of the galaxy obscured it is literally impossible to know with certainty the number of stars here; it ranges between 200 and 400 billion.
M31 has a trillion stars and I believe we do not yet have the technology to determine the exact mass, velocity with vector, and position for every individual star in M31. We certainly do not have that data for distant galaxies.

The only way to develop a model without calculations based on all the individual stars (like can be done with our planets but there are only 8 of them) is to use probabilities. Probabilities cannot be absolutely certain.

Even knowing thiese limitations, cosmologists have a model for a spiral galaxy rotation. Repeated observations are apparently always finding individual stars deviating from prediction.
The cosmologists claim dark matter is the reason for the deviation.
This is bad science for 2 reasons: 1) When a test does not confirm the theory's prediction the theory is wrong and must be fixed.
2) Dark matter does not fix the model.

However the test rules resulting in failure must be reasonable given the scope of the our current knowledge base.
The prediction must have a defined tolerance for deviation.
As deviations reduce with model revisions and subsequent tests then other predictions and tests of the model reveal the overall progress of our understanding.

This will take time given our current status of relying on dark matter as a place holder inhibiting any actual progress.

An initial milestone could be X% stars within Y% of prediction.
We must know what we can do now so we can describe when we improve.
The important first step is get rid of dark matter and alternately check predictions and fix a model to suit observations. Model predictions must approach observations.

This will force learning more about galaxies rather than proposing dark matter - which is considered real. A number of efforts are currently looking for dark matter, including the Large Hadron Collider and a number of telescopes.

This is a radical paradigm shift but cosmology becomes a testable science, with defined milestones and with nothing dark.

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Here is the list of topics in this Cosmology Topic Group .

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