> Couldn't it be the case that there is some local phenomenon happening that we do not understand that still manages to maintain conservation of momentum?
Ever hear of the Luminiferous Aether? From what I can tell, it could explain this phenomenon. Most people consider it an outdated crackpot theory largely because it's at odds with the entirety of quantum theory and the theory of relativity. But, this is the sort of thing that makes you go back to square one and re-consider everything you thought you knew.
L.A. isn't only problematic because it's inconsistent with theory, but also because it's inconsistent with experimental evidence. Michelson & Morley debunked it pretty thoroughly without having to invoke quantum or relativity IMHO.
Ever hear of the Luminiferous Aether? From what I can tell, it could explain this phenomenon. Most people consider it an outdated crackpot theory largely because it's at odds with the entirety of quantum theory and the theory of relativity. But, this is the sort of thing that makes you go back to square one and re-consider everything you thought you knew.