Why don't we chose a random point in the void present between galaxy clusters and define it as the absolute origin?
I know that rest is not absolute and that space expands, but we can easily keep that point at origin and explain the movement of all other bodies in both space and time, if it is acceptable to deal with negative time.
Is it not that useful to define an origin in spacetime coordinates on such a big scale? Or am I missing something?
Addendum : Every answer seems to think I am talking about defining absolute coordinates and then use it for "everything", that is not what I meant. I meant establishing them just as we have made SI units, it does not stop people from using foot, hectare, lightyear, gallons, and other units but it makes it easy to compare with various systems etc.
Similarly I do not intend to say that if we make an absolute standard we would start measuring earthly speeds according to it, I just meant that it may be useful while talking about galaxy clusters or other universal phenomenon. Since we do not have such a system that it is only why I asked why we haven't defined it, I am not at that level in sciences where I would be arguing that motion of ants on earth should be calculated with respect to absolute standards.
This question is just to ask that is such a thing as absolute standards "absolutely" of no use? And if it does find some use why havent we defined it? And should we define it?