Re: does it matter
It's different than aether, because while we have no idea what it is we can detect it. So, yes, we can measure it: we can look at galactic rotation curves and infer from them how much dark matter must be there. This is essentially the same trick we did to discover Neptune and Pluto: look at some stuff we can see, infer things about the gravitational field from their motion and infer there must be some other thing we can't see. Of course, in the case of Neptune & Pluto we did see them when we looked hard enough. The trouble with aether was that it turned out that there was no way to detect it even in principle, and some smart guy decided that things which you could not detect, even in principle, were not there. He did this trick several times with different things: it's a good trick.
Biting the hand that feeds IT
