catloaf , 18 days ago There aren't. Even in "empty" space, there's about one atom per cubic meter, enough for a small amount of annihilation. We haven't detected any regions bordered by gamma ray emissions that would indicate a matter-antimatter boundary. https://en.wikipedia.org/wiki/Baryon_asymmetry#Regions_of_the_universe_where_antimatter_dominates
There aren't. Even in "empty" space, there's about one atom per cubic meter, enough for a small amount of annihilation. We haven't detected any regions bordered by gamma ray emissions that would indicate a matter-antimatter boundary.
https://en.wikipedia.org/wiki/Baryon_asymmetry#Regions_of_the_universe_where_antimatter_dominates