[BipolarBob]

It can be observed. You certainly cannot identify position and direction/momentum at the same time. You can approximate one or the other. The particle can be in several different probable places at the same time. To try to identify its superposition causes it to "collapse". Quantum mechanics is sort of like that kind of woman that drives you nuts if you pay any attention to her. It's best left to the experts.

[Getready]

It is inferred...not observed. One presupposes those cosmic structures hsve been out there so long...some undetectable force MUST be holdimg them together. There is not enuf visible or observable matter to do the trick. No thing we can observe solves the problem. Viola...it must be dark matter by elimination of all other possibilities. Maybe our assumptions are incorrect??