It was a light research day today! But I did get in a conversation with Ana Bonaca (Harvard) about dark matter and information. She has written a nice paper on what information cold stellar streams bring about the gravitational force field or potential in static models of the Galaxy. We have a bit of work on what information perturbed streams (perturbed by a compact dark-matter substructure) bring. We have ideas about how to think about information in the time-dependent case. And on a separate thread, Bonaca has been thinking about what information the stellar kinematics and chemistry bring.
In some sense, the dark matter is the ultimate latent-variable model: The observations interact with the dark matter very weakly (and I'm using “weak” in the non-physics sense), but ultimately everything is driven by the dark matter. A big part of contemporary astrophysics can be seen in this way: We are trying to infer as many properties of this latent-variable field as we can. Because of this structure, I very much like thinking about it all in an information-theoretic way.