I'm looking for a list of "natural" frames of reference on the cosmic scale. Something that can be used as "the" frame of reference for everyone in the universe that isn't arbitrary. So let's brainstorm about some potential candidates. The more the better. If need be, start with an idea and people can try to disambiguate it and/or turn it into an objective property. Once we have an objective fully clarified idea, let's try to come up with a suitable name and simple snappy definition. After all that, we can start arguing about which one is "best". As far as I know there are three parameters that determine our frame of reference (at least that are relevant to relativity) Position, Orientation, and Velocity. (or is it Momentum?) We can choose each independently, though it might be more "natural" to choose them all in some related manner. Some food for thought: Average over some relevant or "natural" domain. Landmarks (think center of biggest galaxy or void) Here's an idea that a few of you are probably already thinking: 1) Universal Centroid A: Average position and momentum of every thing that has a position and momentum. OR B: Average position of every thing that has a position and average momentum of every thing that has momentum. (Some things don't have momentum right?) Some other domain? Only background radiation particles? Only neutrinos (for some reason)? Only hadrons? A potential problem I see with these is quantum mechanical funkiness may make that frame indeterminate or something. I'm not sure. Can we get around that? Also, this doesn't say anything about orientation/direction. Maybe an arrow from the center point to the furthest known/knowable thing? Something to do with the beginning or end of the universe? Or maybe the shape? Something to do with background radiation? Something to do with a mathematically special frame of reference? Something to do with the biggest or best civilization?