Hi Robert,
Excellent coverage of a complex matter
.
Indeed the problem is simply there is too much gravity for the matter we can observe "visually" and it would seem reasonable given our understanding of gravity to date that we need additional matter to explain the observations.
The amounts of dark matter we need suggests it must make up a great deal of the Universe which is what makes me feel uneasy about using it to explain the observations....however as you say we must stay with the truths we know...
alex
