How would we know if a distant galaxy is made up of anti-matter instead of normal matter?

Question

One of the big questions in physics I've heard about, is why there is more matter than anti-matter.  If Andromeda was almost completely anti-matter with the same percentage of normal matter in it as the milky way has anti-matter, wouldn't that solve the problem? At the time of the big bang, the pairs of virtual particles just got far enough away from each other and clumped up so they didn't annihilate?

Comments

It’s a fascinating question, especially considering that observational data has not yet detected the expected gamma-ray signatures from matter-antimatter boundaries. 

From the viewpoint of Einstein’s General Relativity, gravity is the curvature (geometry) of spacetime. If we extend this geometric principle to the quantum scale, could we consider that matter and anti-matter are not "independent particles traveling through space," but rather different topological twisting patterns (such as right-handed vs. left-handed geometric resonance) of the spacetime fabric itself?

If we model particles as localized topological states of spacetime, the baryon asymmetry might be explained as a structural phase transition where the global topology of the early universe naturally favored one twisting direction.

By the way, Brian, your premise about macroscopic clusters (like Andromeda) morphing or isolating into distinct domains is a highly engaging perspective. What specific line of thought or physical anomaly led you to this intriguing intuition?

I would love to hear more about your underlying reasoning.