Andromeda is made of antimatter. Am I wrong? Why?
Of course I do not know that Andromeda is made of antimatter.
_but____ I do not know that Andromeda is made of matter.
Does anybody know what is the correct sentence? Why?
I used Andromeda as a substitute for any non-local galaxy.
Lets put some geometry (due to the first two comments):
Antimatter galaxies (AMGs) have in general AMGs in the neighborough. MGs only MGs.
For instance suppose the hurricanes in the northern hemisphere rotate X way and in the southern rotate anti-X way, and they dont meet ;).
That is to say, it is not mandatory that AMGs colide at all with MGs.
I suspect that we have no way to decide if the light we receive is originated in an anti-atom or from an atom.