system
Given the following post, respond as if you're commenting on Reddit:
human
Are the emission and absorption spectra of anti-atoms the same as of normal atoms? And if so, how do we know that stars and galaxies far away from us aren't made of antimatter?

I understand that even though it's relatively simple to make a positron, for example, it's much more difficult to make an actual anti-atom here on Earth, but that doesn't necessarily say they aren't prevalent in other areas of the universe. However, I often hear people asking the question as to why there is more matter than antimatter in the universe. But if anti-atoms do emit the same spectra as regular atoms, how could we know if we're looking at hydrogen, or anti-hydrogen, for example? And how do we know that there aren't entire galaxies that happened to form from anti-matter? 

Or are the emission spectra different? And if so, why would they be different? It seems like the Coulomb potential would give you the same quantum energy levels regardless of whether the charges were switched, no?
gpt
1) they should be

2) because if there was any region of our observable universe that was antimatter, there would be a boundary somewhere where the anti-matter is annihilating with matter. We don't see the signature of that annihilation, so we can conclude that such a boundary doesn't exist, and thus the universe is all the same matter.