I'm not a physicist, so, please take my opinion like you would take the opinion of somebody chatting in the groceries shop queue, but I find the subject fascinating and I just want to share my crazy theory. At least, I think it would make for good science fiction.
I "think" that dark matter observations are the effect of interference between different Everett branches. The smaller is a volume space, the less possible states it has, so gravity in the center of a galaxy would be less that in the borders. The borders of the galaxy are more entropic because more different states are possible, ergo the stars there experience interference with more Everett universes. Gravity being so weak, it would only show its effects in other branches at huge scales. In this "theory", it seems that dark matter effects would be less visible the further away in space (time) we look. No idea if that's the case.
Again, I have no idea what I'm talking about, so this is just for fun.
This seems sort of like saying a house in California should be more entropic than a house in Rhode Island because California's bigger than Rhode Island. But the laws of physics don't care where we've drawn arbitrary lines on our maps, whether they be geographic or galactic.
But California is more entropic than Rhode Island, because, being bigger, California can be in more states than Rhode Island. In the center of the galaxy a star can be in N positions, in the periphery can be in f(N) positions. The further from the center the more possible positions (maybe the number of positions is related to Newton square law?).
But California ≠ a house in California, which was my point.
How does the universe know it’s supposed to consider the positions on the entire circumference of a galaxy, and not just the “left” edge, or the left edge plus the center, or the right edge plus one quarter of another galaxy’s pinky finger, when deciding how strong gravity should be in the left edge? Only local information should be relevant, otherwise you’re back to assuming the universe respects our arbitrary boundaries.
This is just speculation for fun, but OK, I will bite.
You have a compressed gas, so, low entropy, then it starts expanding. The area where it started expanding has less possible states that the area around, but just because the area around is bigger, nothing to do with the relative position itself.
If the number of states are associated to gravity somehow, then gravity will be bigger the further you go from the center.
Because we are brainstorming in creative mode, I will add a bonus: if the number of possible states increase gravity, maybe, the older the universe gets, the bigger is that influence all around, accelerating its expansion.
I suppose that I will get my Nobel any day now ;-)
On the other hand, the center of a star is much hotter than the periphery, so there are potentially more accessible states in phase space for the particles in the former location (it's "can be in N positions in phase space", which depends on the available physical space and the possible velocities).
Not that this would affect California vs Rhode Island analogies, unless you could demonstrate that things in Rhode Island were a lot hotter...
Have you read Neal Stephenson's "Anathem"? I'm not exactly sure what to say about it in context of your comment for fear of spoilers, but it sounds like you would like it.
I "think" that dark matter observations are the effect of interference between different Everett branches. The smaller is a volume space, the less possible states it has, so gravity in the center of a galaxy would be less that in the borders. The borders of the galaxy are more entropic because more different states are possible, ergo the stars there experience interference with more Everett universes. Gravity being so weak, it would only show its effects in other branches at huge scales. In this "theory", it seems that dark matter effects would be less visible the further away in space (time) we look. No idea if that's the case.
Again, I have no idea what I'm talking about, so this is just for fun.