« on: 08/12/2016 17:35:37 »
Quote from: Wikipedia
particle and antiparticle must have:See: https://en.wikipedia.org/wiki/Antiparticle#Properties
- the same mass m
- the same spin state J
- opposite electric charges q and -q.
Protons and antiprotons are both spin=1/2 particles (fermions).
- Ignoring antiprotons (which are quite rare in our world), your body has lots of protons in Hydrogen atoms.
- Normally, these proton spins are randomly aligned, but it is possible to align them in an external magnetic field (this is what an MRI scanner does).
- It is possible to measure the state of protons as being "spin up" or "spin down", when measured relative to an external magnetic field.
- So "opposite" spins can occur in normal matter, without needing to invoke antimatter
PS: While checking my answer, I discovered that physicists can't fully account for where the spin of a proton comes from. Surprisingly little (maybe none) comes from the spin of the component quarks. This is called the proton spin crisis, and is one of the major unsolved puzzles in physics.
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