Like how can there be an anti-particle for a neutron, if it has no charge? And can there be an “anti-person” that’s made purely of antiparticles (positrons and antiprotons)?
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A neutron is a composite particle made up of an up quark and two down quarks. So an anti-neutron would be made of an anti up quark and two anti down quarks. All particles theoretically have anti particles though, at least in the case of a photon, it is its own anti particle.
Theoretically, anti matter physics and chemistry would operate the same as our own.
>Like how can there be an anti-particle for a neutron, if it has no charge?
So neutrons and protons are actually made up of *quarks* and those are what have charge. There’s 6 types of quarks but the only two that matter right now are the “up” and “down” quark.
An up quark has a charge of +2/3 and a down is -1/3.
A normal proton is 2 ups and 1 down. For a total charge of 1 (2/3+2/3-1/3)
A normal neutron is 1 up and 2 down. For a total charge of 0 (2/3-1/3-1/3)
But there’s also *anti-quarks.* Which have the opposite charge of their pair.
So an antineutron is made up of 1 anti up (-2/3 charge) and 2 anti-downs (+1/3 charge). Which indeed does give it a charge of zero again.
But like… -0 is still a thing. It just happens to also equal positive zero. Which is a weird quirk of the number zero.
>And can there be an “anti-person” that’s made purely of antiparticles (positrons and antiprotons)?
We don’t know for certain. We have observed such a small amount of anti matter that we don’t know a lot about it’s properties. Infact, we don’t even know if gravity affects anti-matter the same way. We assume it does, but we aren’t certain.
With that out of the way to answer the question in the title.
No, not *everything* has an anti-particle but everything that makes up “normal” matter does. Wikipedia has an article that’s a [list of particles](https://en.wikipedia.org/wiki/List_of_particles) (if it says “self” for anti-particle that means it don’t got one). The most “famous” particle that doesn’t have an anti-particle would be the photon.
There is nothing special about electric charge. In antiparticles all charge-like quantities are reversed. A particle is its own antiparticle if all these quantities are zero, otherwise it has a distinct antiparticle.
Neutrons have a baryon number of 1, so there has to be an antineutron with a baryon number of -1. You don’t need to know about quarks for that.
Yes, but some things are their own antiparticle. Namely, photons, Z bosons, and possibly neutrinos.
Neutrons can have antiparticles because they are made of quarks (up, down, down) so an antineutron is made of anti-up, and two anti-downs.
The only ways to determine a neutron from an anti-neutron would be to either annihilate it with regular matter or watch it beta decay.
A neutron will beta decay into a proton and W- boson (which will become an electron and antineutrino)
An anti-neutron will beta decay into an anti-proton and W+ boson (which will become a positron and neutrino)
And yes, you can have a person made entirely of antiparticles. As far as we can tell, antiparticles behave exactly the same as normal matter if you just put it in a mirror and reversed the flow of time. This is called CPT symmetry (charge, parity, and time). The time step is only necessary for certain particles that oscillate between different states in a particular order. The antiparticle does the same oscillation in the reverse order. On a macroscopic scale, reversing time is completely unnoticeable.
Charge is not the only quantity which is inverted between a particle and its antiparticle. Three other notable quantities are Weak Isospin (which governs interactions with W Bosons) plus Baryon and Lepton number (both of which are conserved under the Standard Model, but may be changed under certain circumstances in certain other theories). The Neutron has Isospin -1/2, Baryon number 1 and Lepton number 0. The *anti*neutron has Isospin 1/2 and Baryon number -1.
The question of whether or not there’s antiparticles for everything is heavily dependent on semantics. The Gluon is a particle for which all “invertible” quantities are zero. From one perspective, there is no “anti-gluon” that exists distinct from the gluon. From another, the gluon is its own anti-particle.
The boring answer is “we don’t know, but probably”.
To be clear, there’s no way for an anti-person to come into existence, there just isn’t enough antimatter around to make a whole anti-person, and because there’s matter everywhere, the anti-person would immediately disintegrate, along with the same amount of matter, as soon as they touch.
But, if somehow you were able to build a device that could keep a big chunk of antimatter from coming into contact with matter, and you were also somehow able to arrange that chunk of antimatter into an anti-person, then the current understanding is that that anti-person would be identical to a regular person made of matter, except that they’re made of antimatter.
We’re still not 100% sure though. The main thing that has physicists confused is why there’s so much matter and so little antimatter, where does this imbalance come from? So far, all of the antimatter we’ve observed behaves the same as regular matter, but maybe there are differences we haven’t figured out yet, and maybe those differences would make it impossible for an anti-person to exist, like perhaps some of the chemical reactions that are vital for life would be a little different, and the anti-person wouldn’t survive.
So the answer is that we don’t know, but probably…
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