How to discuss religion with believers?

[polymath257]

This is just Nonsense on Parade:

Wikipedia -- Bullet Cluster

That's conjecture and uses circular logic.  It doesn't demonstrate dark matter.  It assumes dark matter and uses bullet clusters to try and support that conclusion instead of using bullet clusters to prove dark matter.

If I put out a mousetrap (system), it doesn't prove there is a mouse (object) in the house.  The idea of a mouse doesn't prove the system.  The system proves the mouse by identifying it.  As such we can conclude the mousetrap as an effective system.

Wrong. It compares a modified theory of gravity to the one with standard gravity and dark matter. The modified theory of gravity was initially proposed as an alternative to using dark matter to explain the rotation curves of galaxies and the dynamics of galactic clusters. But, when applied to the Bullet Cluster, it was found that the gravitational lensing and the distribution of 'ordinary' mass simply didn't correlate. Even under modified gravity, *some* sort of dark matter is required to explain the observations.

So, yes, indeed, these observations *do* demonstrate dark matter. Together with some of the observations of the CMBR, we can have very specific, testable statements concerning the properties of dark matter.

The only issue at present is what subatomic particles are present in dark matter, not the existence of dark matter itself.