[Diogo_Afonso_Leitao (OP)]

Hello! I would like to know if an antiparticle has not only opposite charge, but also opposite spin to regular particles.
Thank you! =)

[evan_au]

particle and antiparticle must have:
- the same mass m
- the same spin state J
- opposite electric charges q and -q.

See: https://en.wikipedia.org/wiki/Antiparticle#Properties

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.

[jeffreyH]

I would imagine that as the wiki article suggests at the end that gluons may make up the missing spin. An experiment in a lab traveling at a significant proportion of the speed of light should obtain the same results. Since time dilation applies then spin must be a function of choice of coordinates.