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I wonder what anti-matter's shelf life is? Does it decay at the same rate as normal matter?
Theoretically an antimatter particle should have the same decay timescale as its matter particle partner. For example, a positron is the antiparticle of an electron, which as far as we know never decays. In practice, its shelf life depends on the container -- on how well you can confine it and prevent it from annihilating with matter.
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Is the reason the universe is asymmetrical is because it all fused into Dark Matter?
No. The annihilation of matter and antimatter shortly after the Big Bang is responsible for releasing an enormous amount of energy in the form of photons, which made the universe radiation dominated. If instead all the antimatter somehow converted to dark matter, then this source of energy would have been removed -- sequestered in the dark matter. The universe would have evolved very differently. It would have skipped the radiation-dominated phase and gone directly to matter-dominated.We can also be very sure that matter-antimatter annihilation does not produce dark matter, at least at the energies probed in particle accelerator experiments. If dark matter was being created, and if we are unable to detect those dark matter particles directly, then the creation of dark matter would appear as a violation of conservation laws, as the dark matter particles sneak away some of the energy and momentum from the collision.
The reason the universe has an asymmetry between matter and antimatter is thought to instead be a result of small violations of conservation laws in the generation of matter and antimatter (e.g. out of vacuum fields [pair production], or by the decay of other particles), after the Big Bang. If there is a very slight difference in the amount of antimatter vs. matter generated, then a great deal of annihilation will still occur, but leave behind some amount of matter that we observe today. (Or for all we know it was the antimatter that won out and we are antimatter creatures calling matter antimatter -- the physics works out the same).
Maybe some of the annihilation does generate dark matter particles. But the standard model of particle physics makes no predictions for how that would occur, and as of yet there is no consensus model for precisely why this asymmetry should occur. This is one of the significant unsolved problems in physics.