Post #2984357

We know that's not the case because we can see different galaxies with different levels of dark matter. Dark matter doesn't interact with anything else except by gravity, we don't know why, but we can detect that behavior by seeing the way it clumps together. We can also see that galaxies that collide with each other have different levels of dark matter than galaxies that haven't recently done so. The dark matter appears to just pass through each other and continue on while the regular matter hits each other and stays generally together in one group. It's pretty interesting when you work through the details of what we do and don't know.