# Matter-antimatter symmetry and particle charge

• Hypatio
In summary: The asymmetry had to be present from the beginning, and understanding why it exists is the problem. In summary, the conversation discusses the matter-antimatter symmetry problem and why there is an unequal amount of matter and antimatter in the universe. It also touches on the conservation of baryon and lepton numbers in the Standard Model and how this relates to the matter-antimatter asymmetry. The issue of semantics is raised, but ultimately the focus is on understanding the origin of the matter-antimatter asymmetry in the early universe.
Hypatio
If matter composed of quarks of positive charge, and anti-quarks have negative charge, why do we call electrons particles of matter rather than anti-matter?

Is it possible that the matter-antimatter symmetry problem exists because we are actually calling something that is a particle of anti-matter, a particle of matter?

Also, am I correct to assume that annihilation between particles of matter and anti-matter may not occur if they are different types of particles of each. For instance, an electron and positron will annihilate but an electron will not annihilate with another types of anti-matter.

I am probably confused, but I hope someone can critique my thought process.

Hypatio said:
If matter composed of quarks of positive charge, and anti-quarks have negative charge, why do we call electrons particles of matter rather than anti-matter?

Well, there is more to being antimatter than simply having a certain charge. But you do raise an interesting question to which I don't really know the answer: why in the early universe were electrons produced in approximately the same ratio as protons, such that the overall charge of the universe is approximately zero, as it more or less appears to be?

I suppose it must be the case that if we assume net zero charge to begin with, then we must end up with either an excess of protons and electrons, or an excess of anti-protons and positrons, but I don't know that we have to make this assumption, except that experimentally it seems to fit the bill and that it is a minimal sort of assumption. Plus I suppose there are nice ideas about the universe being some sort of inflated vacuum fluctuation, and the vacuum has net zero charge.

Hypatio said:
Is it possible that the matter-antimatter symmetry problem exists because we are actually calling something that is a particle of anti-matter, a particle of matter?

Well, no, because you would still have a set of particles which behaved (almost) exactly the same as the ones we see around us, yet not know why the universe should have chosen one set over the other.

Hypatio said:
Also, am I correct to assume that annihilation between particles of matter and anti-matter may not occur if they are different types of particles of each. For instance, an electron and positron will annihilate but an electron will not annihilate with another types of anti-matter.

Yes that is the case. Particles only annihilate with their own antiparticles. They come in pairs, unless they are their own antiparticles (like photons).

Well, if particles only annihilate with their own antiparticles, then if you call a particle like a positron the particle and an electron an anti-particle, then this changes the matter-antimatter symmetry.

The question might be why we have unequal amounts of matter and anti-matter of certain types of particles, while the net energy of anti-particles is the same as particles.

Also, it seems the picture is complicated by the fact that you can get anti-particles from particles, such as in proton decay into a neutron, positron, and a neutrino.

How do we really know then that this is a problem for early synthesis of particles, and not of later mechanisms rearranging things?

Hypatio said:
Well, if particles only annihilate with their own antiparticles, then if you call a particle like a positron the particle and an electron an anti-particle, then this changes the matter-antimatter symmetry.

The question might be why we have unequal amounts of matter and anti-matter of certain types of particles, while the net energy of anti-particles is the same as particles.

I am not quite sure what you are asking here, sorry. Semantics are not important. Perhaps we should try and speak in terms of baryon and lepton numbers. Those are the quantities that we are really talking about, and we want to know why they are not both zero (in the whole universe). In the Standard Model, both baryon number and lepton number are conserved (except for some weird thing about sphalerons that I don't understand, and which have never been observed, although they may have been important in the early universe). So if you move forward past the early universe, the number of baryons minus antibaryons and leptons minus antileptons in the universe is fixed. The numbers that they are fixed to are such that we have loads of protons/neutrons/electrons flying around instead of their antiparticles, and understanding why both these numbers are not zero, and what happened in the early universe to cause this, is the matter/antimatter asymmetry problem.

Hypatio said:
Also, it seems the picture is complicated by the fact that you can get anti-particles from particles, such as in proton decay into a neutron, positron, and a neutrino.

In this picture both baryon number and lepton number are conserved as the positron and neutrino have opposite lepton number. So nothing weird there. You made some matter and antimatter at the same time, so no asymmetry.

Hypatio said:
How do we really know then that this is a problem for early synthesis of particles, and not of later mechanisms rearranging things?

Well, because the Standard Model conserves baryon and lepton number (except for this non-perturbative sphaleron business and perhaps some other exotic things I don't know about), so there are no later mechanisms for rearranging things.

## 1. What is matter-antimatter symmetry?

Matter-antimatter symmetry is a fundamental principle in physics that states that for every type of matter particle, there exists an antimatter particle with the same mass but opposite charge and other properties. This symmetry is important in understanding the behavior of particles and the origin of the universe.

## 2. What is an antimatter particle?

An antimatter particle is a fundamental particle that has the same mass as its corresponding matter particle but has opposite charge and other properties. For example, an antiproton has the same mass as a proton but has a negative charge, and a positron has the same mass as an electron but has a positive charge.

## 3. Why is matter-antimatter symmetry important?

Matter-antimatter symmetry is important because it helps us understand the behavior of particles and their interactions. It also plays a crucial role in the study of the origin of the universe, as it is believed that equal amounts of matter and antimatter were created during the Big Bang. The mystery of why there is more matter than antimatter in the universe is still being studied by scientists.

## 4. How does particle charge relate to matter-antimatter symmetry?

Particle charge is a fundamental property of matter and antimatter particles. In matter-antimatter symmetry, particles and their corresponding antiparticles have equal but opposite charges. This allows for the creation and annihilation of particles and antiparticles, resulting in the conservation of charge in interactions.

## 5. Can matter and antimatter particles coexist?

No, matter and antimatter particles cannot coexist for an extended period of time. When a matter particle and its corresponding antiparticle come into contact, they annihilate each other, releasing a massive amount of energy. This is why in our universe, we only see matter particles and not antimatter particles, as they have mostly annihilated each other during the early stages of the universe.

• High Energy, Nuclear, Particle Physics
Replies
9
Views
2K
• High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
• High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
• High Energy, Nuclear, Particle Physics
Replies
21
Views
3K
• High Energy, Nuclear, Particle Physics
Replies
3
Views
1K
• High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
• Quantum Physics
Replies
8
Views
735
• High Energy, Nuclear, Particle Physics
Replies
21
Views
2K
• High Energy, Nuclear, Particle Physics
Replies
9
Views
902
• High Energy, Nuclear, Particle Physics
Replies
2
Views
12K