Neil deGrasse Tyson states that "dark matter exerts gravity according to the same rules that ordinary matters follows" How do we know this? If we have no idea what dark matter is, how can we say how it behaves? How do we know that a single "molecule" of the stuff doesn't weigh as much as the sun? Or vise versa? Also, if it makes up 85% of the matter in the universe, shouldn't it be called "ordinary?"