Particle Annihilation

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How do we know/observe a particle annihilating a anti-particle?

Is it impossible to theorize that in the early universe atoms of hydrogen were as abundant as anti-hydrogen atoms yet did not annihilate each other? Instead anti-Hydrogen repelled and pushed Hydrogen together to form clumps? In this instance Protons flow towards groups and anti-protons would surround and push groups together helping them stabilize into large clumps of gas.
 

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  • #2
e.bar.goum
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In practice, pair annihilation (one particle annihilating with its antiparticle) is observed by looking at the particles that result from the annihilation.

For example, the most common type of annhilation that happens all the time is electron-positron annihilation that occurs whenever a nucleus decays via β+ decay. In that case, you will see two 511 keV photons emitted 180 degrees apart. That is, you have e+ + e- -> γ + γ. You must have two (or more) photons due to energy/momentum conservation, and the energy of 511 keV comes from the rest mass of the electron/positron - E = mc2.

Something like baryon-anti-baryon annihilation far more complicated, as they are composite particles, and there are many available exit channels.

As to antimatter galaxies: That's possible, although your suggested mechanism for action wouldn't work. You can get antimatter "clumps" during inflation. However, such a galaxy would be very difficult to distinguish from one made of matter, so it's an idea that is reasonably difficult to test. One way to do it is to look for annihilations during supercluster mergers, as done by CHANDRA. (Another good reason to have gamma telescopes!) However, no such signatures have been observed, to my knowledge.
 
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phinds
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Your concept of matter/antimatter repelling each other is exactly backwards. They have opposite charges so would ATTRACT each other.

Since antimatter has identical properties to matter other than charge, there is no possibility that dark matter could be antimatter. As just one example, antimatter would clump, exactly like matter, but dark matter does not clump.
 
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Yes I realized that, But is it possible that the antimatter with a negative charge in its nucleus could drop its positron and then repel against the negative charged electron clouds of Protons?

Or for instance if a you take a proton with 2 elections and antiproton with one positron, would the one electron annihilate the positron leaving the antiproton as a Negative charged atom repulsive to electron clouds?
 
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phinds
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Yes I realized that, But is it possible that the antimatter with a negative charge in its nucleus could drop its positron and then repel against the negative charged electron clouds of Protons?

Or for instance if a you take a proton with 2 elections and antiproton with one positron, would the one electron annihilate the positron leaving the antiproton as a Negative charged atom repulsive to electron clouds?

Irrelevant. I say again: Since antimatter has identical properties to matter other than charge, there is no possibility that dark matter could be antimatter. As just one example, antimatter would clump, exactly like matter, but dark matter does not clump.
 

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