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I heard that anti-particles annihilate when in contact with normal-particles but the odd thing is that in fusion reaction normal-particles often "fuse" into each other but the weak force often prevents it from happening so my question is how can anti-particles annihilate with each other for anti-particles from what I know (not much!) are affected by gravity as they fall downwards like like expected and their electrically behave same in sense that they attract with opposites and repel with other particles with same charge.

Now logic follows weak-force must also act as expected however clearly it annihilates so what force dictates that, I personally do not think it is the electrical forces as they are far from as strong as the weak force so what dictates this annihilation?

Is there a force? Is there a quantum effect? or what is it?

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    $\begingroup$ I am pretty sure that the electron and positron are strongly attracted electrically. Can you explain where you think the repulsive term comes from? $\endgroup$ – Floris Apr 4 '15 at 22:05
  • $\begingroup$ The electromagnetic force is still stronger than the weak force (see also here) by a few orders of magnitude. $\endgroup$ – HDE 226868 Apr 4 '15 at 23:16
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If your question is how can antiparticles get close enough to annihilate, they are always oppositely charged (electron/positron, proton/antiproton, etc.) or both neutral (neutrino/antineutrino, neutron/antineutron, etc.) so there is at least no repulsion and maybe electrostatic attraction. This is in contrast to normal matter fusing, where all the nuclei are positively charged and repel one another.

The force involved in annihilation is normally either the color force (in the case of quarks/antiquarks) or the electromagnetic force (in the cases of electrons/positrons).

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  • $\begingroup$ "...so there is at least no repulsion..." Well, no electromagnetic repulsion. There are other forces however, and though I am no expert, it occurs to me that the repulsive component of the strong force might come into play with hadrons (such as Proton-AntiProton interactions). $\endgroup$ – RBarryYoung Apr 5 '15 at 1:10
  • $\begingroup$ @RBarryYoung the EM attraction is much stronger than weak force $\endgroup$ – Jimmy360 Apr 5 '15 at 2:13
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    $\begingroup$ @RBarryYoung antiparticles have opposite charges of all types (except mass/energy) so forces carried by spin-1 bosons will be attractive. $\endgroup$ – Hugh Allen Apr 5 '15 at 2:56
  • $\begingroup$ There is no repulsive component of the strong force. You might be thinking of the nuclear force "The nuclear force is only felt among hadrons. At small separations between nucleons (less than ~ 0.7 fm between their centers, depending upon spin alignment) the force becomes repulsive, which keeps the nucleons at a certain average separation, even if they are of different types. This repulsion is to be understood in terms of the Pauli exclusion force for identical nucleons (such as two neutrons or two protons), and also a Pauli exclusion between quarks of the same type within nucleons, $\endgroup$ – anna v Apr 5 '15 at 3:44
  • $\begingroup$ when the nucleons are different (a proton and a neutron, for example). " google.gr/… Antiparticles have the exact opposite in quantum numbers and are not identical to particles. $\endgroup$ – anna v Apr 5 '15 at 3:47
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Whatsoever properties of matter or antimatter are related to "charge" at particle level.........are responsible for annihilation phenomena .Now an interesting question could be that if so then how is it possible that two particles neutron and its anti-particle can annihilate each other...? The reason for this is the , fact of composite nature of neutron and anti neutron.

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