@pln2bz: Who wrote this, I wonder? "The very origin of dark matter originated because galaxies were observed to be rotating far too fast on the outer edges -- almost as if the galaxy was a fixed plate."Surely it can't have been an engineer, can it? I mean, the rotation curve of a fixed plate is a straight line .. with a non-zero slope (i.e. it is not flat). Yet spiral galaxies have flat rotation curves (beyond a certain radius - "on the outer edges"), and it is this flat part which is so hard to explain using only the observed mass (stars, the interstellar medium). No engineer would make such a silly mistake, would they?