My limited understanding is that the only interactions we have with other galaxies is through photons, and that photons have no anti-particle (or are their own anti-particle). I’m also under the impression that the vast majority of galaxies are very far apart from each other and moving further away, so we wouldn’t be able to observe matter galaxies interacting with antimatter galaxies. How do we know that some of the galaxies we can see aren’t made of anti-matter? Would it be important if some of them were?
In: Physics
Were this the case, there would be a border between the ‘matter’ regions and ‘antimatter’ regions. Despite space being pretty empty, it is not nearly empty enough to prevent collisions at this border. The shear amount of energy being released at this border from the collisions would produce a ‘glow’ that should be visible from Earth.
This glow would likely not be visible light, but rather ionizing radiation. We could still detect it.
There is more gas in between galaxies than there is matter in them. If there were a galaxy made of anti matter there would be a boundary where the anti matter gas that makes up that galaxy interacts with matter. This would create an extremely bright and obvious signal. We dont see this.
Space is not completely, entirely empty. At some point between a galaxy made of anti matter and a galaxy made of matter (or even at the scale of galaxy clusters) you are going to have a crossover point.
Even if this crossover point is in deep space, there are going to be some number of anti-particles colliding with some number of particles, which would create possibly detectable bursts of energy on a somewhat regular basis.
there is a very shallow intergalactic medium. if galaxies or the medium are either matter or antimatter, something would still annihilate faintly. We don’t see that signature, so it is very likely to be the same (anti-)matter.
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