The problem with dark matter is that it is a bit too easy to predict where it is. That's why so many people are looking for galaxies without dark matter. We som

The problem with dark matter is that it is a bit too easy to predict where it is. That's why so many people are looking for galaxies without dark matter. We sometimes find them, but I am not sure if there is an instance where we have confirmed that it is not a fluke of observation. The reason why it is a problem is that if you can reliably predict where dark matter is, then you can turn these predictions into equations and get away with dark matter as a form of matter. That's the idea behind modified gravity.