Everyone points to the Bullet Cluster as the best proof of Dark Matter. But I have a few questions about the rationale. There are aspects of the proof I don't understand. 1) What is the mechanism which makes the interstellar gas visible at such a distance in this particular case? Is all intergalactic gas visible in the same way and at the same brightness levels? 2) How do we know that all or most of the intergalactic gas collided? How do we know that it wasn't the case that most of the gas stayed with the galaxies and only some collided which was subsequently made much brighter because of the heating due to the collision? So in effect, how do we know that the part that forms the bullet wasn't merely just a visible small fraction of the intergalactic gas that collided while the bulk of the gas passed through the other cluster with the visible galaxies themselves? 3) What would have caused the gas to slow down so much as it passed through the other gas? At the densities of intergalactic gas, it seems odd that much of it would have actually collided at the atomic level. What am I missing? Thanks in advance.