Dark Matter
Bestiary of 20'th Century Magic Physics
The bestiary of 20'th century Einsteinian BS magic physics includes a number of things which are basically artifacts of wanting to believe in a gravity-only cosmology, and which do not exist in real life: black holes, worm holes, dark matter, dark energy, gravitons, gravity waves...
Of those, the easiest to grasp the fictional nature of is dark matter.
In real life, spiral galaxies are held together by electgromagnetic forces. This is particularly easy to see in some cases. Here for instance, we see a case in which two spiral arms are being held almost in straight lines until some point at which the field breaks down and material is seen to dissipate and trail away from the ends of the arms.
But gravity-only astrophysicists don't want to hear anything like that. There being many times too little mass in a spiral galaxy for gravity to have any shot at holding it together, they send out a call to DARK-MATTER MAN!!!!
The claim is that "dark matter(TM)" constitutes 95% of the mass of the universe, They don't try to explain why we're not having to vacuum this stuff up off our carpets six or eight times a day...
What does that mean though? We read that the distance between our own sun and AC is fairly typical for stars in the Milky Way, and also... that if you scale our own system to be a yard or so wide... that our sun would be about the width of a human hair, Earth would be an inch or so from the sun, Pluto a yard out, and AC, the nearest other main-sequence star, would about 4.3 miles out yonder.
That says that asking gravity to hold the Milky Way just together, much less in the form of a spiral galaxy, is basically the same as asking gravity to hold two specks of dust together from 4.3 miles apart!!
NO PROBLEM!! they shout. DARK MATTER MAN will fix it!!
But will he? Ninety five percent is 20 - 1. That says that now, all you need gravity to do is hold two specks of dust together from roughly 1/5 of a mile away.
Guess what?? A fifth of a mile is two of those mile marker signs you see on the highway. Gravity isn't going to hold two specks of dust together from that sort of distance either, or anywhere close to that sort of distance. Probable max possible would be about a yard or two.
Don Scott refers to "Dark Matter" is Fantastic Ad-hoc Inventions Repeatedly Invoked in Efforts to Defend Untenable Scientific Theories, i.e. FAIRIE DUST. Again, Dark Matter is probably the easiest item in the Einsteinian bestiary to understand, but all of it is going away and will no longer be believed in another 20 years.