In recent questions:
What’s the status of dark matter/energy in the setting?
Munson sez: ‘There ain’t no such thing. Somebody just needs to correct their math, is all.’
The honest answer is “I haven’t established that yet”…
…but here’s some bullshit I just made up that should not be considered official canon:
If the in-‘verse theory of information physics (and its non-local hidden variable implications) is true, then the universe has a lot of metadata to keep track of. (Traditionally described as kept “Elsewhere”.) The more interesting interactions happen in any given location, the more metadata is generated.
Let us now handwave some sort of information-energy equivalence, or at least that information has its own effect on the space-time metric. (In honor of the original author who came up with this one, we can call it Pratchett’s L-Space Hypothesis.)
Conclusion: dark matter is actually all the universe’s metadata distorting space-time from its secret lair. It tends to halo around galaxies because that’s where all the interesting stuff happens.
(Let the weeping of the physicists now commence.)
((For those who don’t mind a particularly silly universe – and this one is definitely not canon – we could also postulate that dark energy, which has the opposite – universe-expanding – effect, is produced by ignorance; or, I suppose, technically, computational operations which could have happened but didn’t produce it as a byproduct. So study hard, folks, and keep thinking — or the universe will explode!))