Matter & Anti-Matter: Why Do Particles Group in Matter?

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Discussion Overview

The discussion revolves around the fundamental principles that explain the grouping of particles into what is termed "matter" versus "antimatter." Participants explore the implications of matter-antimatter creation, the role of CP symmetry breaking, and the constraints imposed by the Standard Model on particle classification.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions the fundamental principle behind the grouping of particles like up quarks, down quarks, and electrons into "matter," while excluding combinations like up quark, down quark, and positron.
  • Another participant suggests that matter and antimatter are created in equal amounts, leading to a paradox of existence due to annihilation, but posits that CP symmetry breaking in the early universe may account for the observed matter surplus.
  • A later reply reiterates the idea of CP symmetry breaking but seeks clarification on why this process resulted in the specific grouping of particles into matter, questioning whether other combinations could have dominated instead.
  • One participant introduces the concept of fermion generations, explaining that certain combinations of particles must adhere to specific charge conditions to avoid gauge anomalies, which could render the Standard Model inconsistent.

Areas of Agreement / Disagreement

Participants express differing views on the reasons behind the specific grouping of particles into matter versus antimatter, with no consensus reached on the underlying principles or mechanisms.

Contextual Notes

The discussion highlights the complexity of particle classification and the unresolved nature of CP violation effects, as well as the implications of gauge anomalies in the Standard Model.

mathfeel
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Is there any fundamental principle that explains why, for example, (up q, down q, and electron) are in the same group which we "happened" to call "matter", but not say (up q, down q, and positron)?

Because in the latter case, the world would consists of proton, neutron, and position and atoms would not form.
 
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I believe the thought goes like this: Matter and antimatter are created in equal amounts, therefore the world should not exist since the two should annihilate into energy once again. However, some effect in the early universe is thought to change this by breaking the CP (Charge Parity) symmetry. There is however no such effect observed that are strong enough to account for the huge surplus of matter. But if we for the moment accept that something caused this (for example a CP violation effect in the strong force), this would explain why the electron, and the up and down quarks make up our universe.
 
kaksmet said:
I believe the thought goes like this: Matter and antimatter are created in equal amounts, therefore the world should not exist since the two should annihilate into energy once again. However, some effect in the early universe is thought to change this by breaking the CP (Charge Parity) symmetry. There is however no such effect observed that are strong enough to account for the huge surplus of matter. But if we for the moment accept that something caused this (for example a CP violation effect in the strong force), this would explain why the electron, and the up and down quarks make up our universe.

I get that, but why did that CP-breaking process, whatever it might be, put (up, down, electron) into one group, called matter, which become dominated later and (anti-up, anit-down, positron) into another? Couldn't some other combination (up, down, POSITRON) be the dominate group instead?
 
There is one reason why one cannot mix the particles arbitrarily. Grouping fermions into so-called generations one gets (omitting anti-particles)

1st gen.:
- electron
- electron neutrino
- up-quark, down-quark

2nd gen.:
- myon
- myon neutrino
- s-quark, c-quark

3rd gen.:
- tau
- tau neutrino
- t-quark, b-quark

Within each generation certain charges must add up to zero in a non-trivial way (the counting is difficult e.g. due to three colors for the quarks and the weak isospin). w/o this property the standard model would have a gauge anomaly in the chiral electro-weak sector. Afaik gauge-anomalies mean that the quantized theory is mathematical inconsistent.
 

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