The nature of anti-particles and anti-matter (a dilettante asks)

[Any name will do]

TL;DR Summary

I am not a pupil, and I have basically highschool physics education. I am confused by the naming conventions. What constitutes the quality that creates the difference between matter and anti-matter? Particle and anti-particle?

Do particles and anti-particles have gravitational force between them? If they are made of matter, both of them, what is the reason one particle is regular, and the other is a counter-particle? Or anti-particle? I am confused by the naming. Anti- means against, opposite, counter-. A matter has mass, and mass has no anti-mass. So what IS the difference that warrants the name anti- in physics? I've heard of anti-matter, and I look at that the same befuddled way. A matter must exists. Matter can't exist with mathematically negative mass to counter-balance the mass of matter. There is no negative existence; the naming does not take that into consideration. Can you enlighten me, please?

 

[PeroK]

TL;DR Summary: I am not a pupil, and I have basically highschool physics education. I am confused by the naming conventions. What constitutes the quality that creates the difference between matter and anti-matter? Particle and anti-particle?

Do particles and anti-particles have gravitational force between them? If they are made of matter, both of them, what is the reason one particle is regular, and the other is a counter-particle? Or anti-particle? I am confused by the naming. Anti- means against, opposite, counter-. A matter has mass, and mass has no anti-mass. So what IS the difference that warrants the name anti- in physics? I've heard of anti-matter, and I look at that the same befuddled way. A matter must exists. Matter can't exist with mathematically negative mass to counter-balance the mass of matter. There is no negative existence; the naming does not take that into consideration. Can you enlighten me, please?

You should be able to find a summary of the standard model of particle physics online. In the standard model, particles come in pairs. We have the electron, of course, and we must have an anti-electron (aka the positron), which has the same mass as the electron but a positive charge. Even though the positron is called "anti-matter", you could just as easily call the positron matter and the electron antimatter. The important point is that the electron and positron have a tendency to annihilate each other. For some unknown reason the universe originally had more electrons than positrons and all the positrons got annihilated, leaving only the extra electrons.

Note that you should never read too much into a name. Instead of anti-matter, it could have had another name like complementary matter (or something like that). There's no sense in which anti-matter has a negative existence. It exists in precisely the same way that matter exists.

 

[PeroK]

Do particles and anti-particles have gravitational force between them?

Yes, but the gravitational interaction is immeasuarbly small compared to the electromagnetic interaction. This is one reason it's so difficult to unify gravitation with the quantum mechanics that described the other fundamental interactions.

 

[Any name will do]

Thansk, PeroK and VanHees71. A little bit of understanding can go a long way. Is an anti-matter atom made of positive electrons, negative protons and then what is the anti- of neutrons? they got no charge. They got no pair-particles. Therefore they can't get annihilated.

 

[Any name will do]

Thansk, PeroK and VanHees71. A little bit of understanding can go a long way. Is an anti-matter atom made of positive electrons, negative protons and then what is the anti- of neutrons? they got no charge. They got no pair-particles. Therefore they can't get annihilated.

I got an answer to this in the thread

How can gravitons have anti particles?​

Thanks, I sort of have an understanding now. But one more question: (in another thread)

 

[PeterDonis]

I got an answer to this in the thread

How can gravitons have anti particles?​

Which thread is that? Can you provide a link?

 

[PeroK]

Thansk, PeroK and VanHees71. A little bit of understanding can go a long way. Is an anti-matter atom made of positive electrons, negative protons and then what is the anti- of neutrons? they got no charge. They got no pair-particles. Therefore they can't get annihilated.

Protons and neutrons are made of quarks, so the anti-proton and anti-neutron are composed of the relevant anti-quarks:

https://en.wikipedia.org/wiki/Antiproton

https://en.wikipedia.org/wiki/Antineutron

The photon, however, is its own anti-particle.

There is also anti-hydrogen:

https://en.wikipedia.org/wiki/Antihydrogen

As you can see, Wikipedia is a reasonable source for all these things.

 

[PeterDonis]

what is the anti- of neutrons?

Antineutrons.

they got no charge. They got no pair-particles. Therefore they can't get annihilated.

Incorrect. Neutrons are made of one up quark and two down quarks. Antineutrons are made of one up antiquark and two down antiquarks. The quarks have charge even though the neutron and antineutron do not (because the charges of the quarks making them up cancel).

 

[vanhees71]

Thansk, PeroK and VanHees71. A little bit of understanding can go a long way. Is an anti-matter atom made of positive electrons, negative protons and then what is the anti- of neutrons? they got no charge. They got no pair-particles. Therefore they can't get annihilated.

Yes, and anti atom is made of positrons (anti-particle of the electron), anti-protons, and anti-neutrons. Although anti-neutrons are electrically neutral, they are not their own anti-particles, because they carry another charge-like quantum number, which is baryon number. A neutron has baryon number +1 and an anti-neutron has baryon number -1.