In the observable universe there is an antimatter-matter asymmetry. Are there any theories that propose that this is just a local asymmetry one fluctuation in a universe with an overall symmetry?
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2$\begingroup$ Yes there are en.wikipedia.org/wiki/Baryon_asymmetry $\endgroup$– Jbag1212Commented Apr 27, 2022 at 23:33
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$\begingroup$ I give some details on the detection of cosmic antimatter here: physics.stackexchange.com/a/590085/123208 $\endgroup$– PM 2RingCommented Apr 28, 2022 at 8:58
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2 Answers
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I touched on this in an answer I wrote in the Astronomy SE. The brief answer is there's no theoretical reason why it can't be local, but it's observationally excluded:
At some level the idea that there are antimatter galaxies out here is appealing. First it can solve the baryon asymmetry problem at a stroke. It's also the case that an antimatter star would shine. From long distance, it would also be practically indistinguishable from a "normal" star.
However, there are strong reasons to believe that there are no antimatter galaxies. That's because antimatter annihilates with normal matter, which leaves experimental signatures. If any part of the Earth were made of antimatter, it would immediately vanish in a flash, so we can be sure that the Earth is mostly matter. Similarly, if the Sun were made of antimatter, we would be quickly annihilated (thanks to the antimatter solar wind radiating from the anti-Sun), so we can be sure the Sun is also mostly matter. Similar arguments allow us to conclude that the Milky Way is almost entirely matter, the Local Group is almost entirely matter, etc, all the way up to the largest structures in the sky.
If antimatter galaxies exist, they are probably outside our observable universe, at which point some will argue it's no longer science.
This dealt with antimatter galaxies, which is not exactly what you're asking about, but it's effectively the same: if the matter-antimatter asymmetry is local, then there must be regions of the universe where antimatter dominates, and in those regions there must be antimatter galaxies.
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$\begingroup$ This is helpful, thanks. I suppsose the scenario I'm proposing is one where the universe has age enough to the point where there is no longer any annihilation taking place. What I'm imagining is a lot of annihilation transpiring in the very early stages of the universe (perhaps even contributing to the CMBR!). This would leave vast portions of the universe void of both matter and anti matter, and some regions with either only matter remaining or anti matter remaining (due to slight variation in density). $\endgroup$ Commented Apr 28, 2022 at 21:52
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$\begingroup$ Do yo think such a scenario would be experimentally detectable? $\endgroup$ Commented Apr 28, 2022 at 21:53
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1$\begingroup$ @AdrienAmour age is not the deciding factor here. The deciding factor is the density. If there is antimatter and matter in close proximity, then it will annihilate and emit detectable signatures. At present even the density of intergalactic space is high enough to emit detectable signatures, see the link in the answer. $\endgroup$– AllureCommented Apr 28, 2022 at 23:29
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The Alpha Magnetic Spectrometer experiment, installed on the International Space Station, is designed to study antimatter before they have a chance to interact with the Earth's atmosphere or deflect in Magnetosphere.
If antimatter-dominated places of space existed, then the gamma rays produced in annihilation would be sufficient for instruments to detect. Antimatter is produced in nature, everywhere where high energy particle collissions occur.
