23 questions linked to/from How would we tell antimatter galaxies apart?
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### If matter and antimatter repel, how do we know other galaxies aren't made of antimatter? [duplicate]

Wikipedia's article on antimatter says this: There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to a more even mixture of ...
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### Could Alpha Centauri be made of anti-matter? [duplicate]

How can we tell if a star is made of matter or anti-matter? For example, is there any difference spectroscopically? Or could we tell from cosmic rays? If half of the stars were made of matter and ...
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### Andromeda is made of antimatter. Am I wrong? Why? [duplicate]

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 ...
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### How can we differentiate between matter and antimatter? [duplicate]

For instance if there was a galaxy, assume it to be made up of antimatter (isolated from other "normal" galaxies), how would we, or rather, would we be able to distinguish if it was made up of matter ...
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### Antimatter in the universe [duplicate]

Is it possible that some parts of the universe contain antimatter whose atoms have nuclei made of antiprotons and antineutrons, sorrounded by antiprotons? If yes what can be the ways to detect this ...
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### How can we assert $\mathrm{ matter } / \mathrm{ antimatter } \gg 1$ further than $locally$? [duplicate]

I read many hypothesis to explain the asymmetry between the quantity of matter and antimatter in the universe, most notably through an asymmetry in initial baryogenesis. This assymetry would explain ...
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### Are there entire anti-matter galaxies? [duplicate]

Would we be able to tell if an entire neighboring galaxy was made up of anti-matter? What would we see in its signals? It seems like the anti-matter could be stable if it was completely surrounded by ...
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### Observationally distinguishing a galaxy of antimatter from a galaxy of matter [duplicate]

I was just wondering how, observationally, we would distinguish a distant galaxy of "normal" matter from one of antimatter. Maybe there is a simple answer but I don't see it. Once I started thinking ...
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### How would one detect antihydrogen in the universe?

Since the spectra of hydrogen and antihydrogen are the same, how do astronomers know which one they're detecting? Is, perhaps, the Lamb shift in antihydrogen different?
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### Are there models/simulations of antigravitational antimatter-galaxies?

In the comments to another question's answer, I started wondering: Assuming antimatter possessed negative gravitational mass§ (which is not proven impossible to date, though deemed unlikely), ...
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### What happens when Antimatter interacts with a photon?

So... I was just pondering the energy and particles in the universe. It makes sense that matter is attracted to it's self by a gravitational force - it clumps and forms some kind of gravity ...
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### Could the missing antimatter lie outside the observable universe?

While I was reading a similar question asking if other galaxy could be made of antimatter, to which the answer was: if they were, we should detect the radiation from matter interacting with antimatter ...
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### how do we know that the base of entire universe is the proton (hydrogen) and not the antiproton?

It may be that the base of a part of the world is anti-proton, We've always been on the planet Earth and the Milky Way. how do we know that the base of entire universe is proton (hydrogen atom)?