[Andeh]

I was wondering why opposite charges attract and like charges repel, so I considered what would happen if they didn't...

So in pair production, two photons of neutral charge can create an electron (negitive charge) and a positron (possitive charge.) This entire process is conserved, in other words it can be reversed, so that an electron and positron can anhillate and produce two photons. Since the particles are of opposite charge, they attract, then anhillate.

But if opposite charges didnt attract--if they repeled, this wouldn't happen. The eletron and positron would repel instead of attract, and so they couldnt anhillate. This would violate conservation laws, and would be impossibe--the universe simply can't work that way!

[mathematic]

Andeh, on 28 December 2011 - 07:44 PM, said:

I was wondering why opposite charges attract and like charges repel, so I considered what would happen if they didn't...

So in pair production, two photons of neutral charge can create an electron (negitive charge) and a positron (possitive charge.) This entire process is conserved, in other words it can be reversed, so that an electron and positron can anhillate and produce two photons. Since the particles are of opposite charge, they attract, then anhillate.

But if opposite charges didnt attract--if they repeled, this wouldn't happen. The eletron and positron would repel instead of attract, and so they couldnt anhillate. This would violate conservation laws, and would be impossibe--the universe simply can't work that way!

What is your point?

[MigL]

Uncharged particles also have antiparticles, and some are their own antiparticles !?!?

[guenter]

MigL, on 29 December 2011 - 09:14 PM, said:

Uncharged particles also have antiparticles, and some are their own antiparticles !?!?

E.g. photons, neutrinos

Uncharged particles don't annihilate with their antiparticles.

This post has been edited by guenter: 30 December 2011 - 10:25 AM

[swansont]

guenter, on 30 December 2011 - 10:13 AM, said:

E.g. photons, neutrinos

Uncharged particles don't annihilate with their antiparticles.

I'm pretty sure neutrons and antineutrons do. I don't see what would prevent it. There are some uncharged particles that are identical with their antiparticles (e.g. photons) that would not.

[imatfaal]

swansont, on 30 December 2011 - 11:21 AM, said:

I'm pretty sure neutrons and antineutrons do. I don't see what would prevent it. There are some uncharged particles that are identical with their antiparticles (e.g. photons) that would not.

Is that because the neutron / anti-neutron are not elementary and the component quarks/anti-quarks will annihilate because they are different - but the photon and its self-similar antiparticle are fundamental and there are no underlying different structures?

\edited for spelling

This post has been edited by imatfaal: 30 December 2011 - 12:13 PM

[swansont]

imatfaal, on 30 December 2011 - 12:13 PM, said:

Is that because the neutron / anti-neutron are not elementary and the component quarks/anti-quarks will annihilate because they are different - but the photon and its self-similar antiparticle are fundamental and there are no underlying different structures?

\edited for spelling

The standard model does not have any neutral fermions as their own antiparticle (Majorana particles) though there is investigation into neutrinos. I suspect that Fermi statistics has something to do with this, i.e. the underlying reason for the Pauli exclusion principle.

[guenter]

imatfaal, on 30 December 2011 - 12:13 PM, said:

Is that because the neutron / anti-neutron are not elementary and the component quarks/anti-quarks will annihilate because they are different - but the photon and its self-similar antiparticle are fundamental and there are no underlying different structures?

Neutron and antineutron do annihilate, because they consist of charged particles. The criterion is the existence of opposite charges, not the question whether or not the particles are fundamental.

[swansont]

guenter, on 30 December 2011 - 01:56 PM, said:

Neutron and antineutron do annihilate, because they consist of charged particles. The criterion is the existence of opposite charges, not the question whether or not the particles are fundamental.

Electron neutrino-antineutrino annihilations are thought to occur in supernovae. Since they are uncharged and interact only weakly you need a high density to ensure the reaction, otherwise it would be unlikely. But not forbidden, as long as they are not Majorana particles.

[guenter]

swansont, on 30 December 2011 - 03:00 PM, said:

Electron neutrino-antineutrino annihilations are thought to occur in supernovae. Since they are uncharged and interact only weakly you need a high density to ensure the reaction, otherwise it would be unlikely. But not forbidden, as long as they are not Majorana particles.

Oh, interesting. So annihilation isn't restricted to electric charges. But something else must distinguish then neutrinos and antineutrinos to offer the possibility to annihilate, their chirality? And what is the reaction product? I am not at all familiar with neutrino physics.
In case the search for Majorana neutrinos is positiv, would it mean the neutrino is its own antineutrino, like it is true for photons?

[swansont]

guenter, on 30 December 2011 - 04:54 PM, said:

Oh, interesting. So annihilation isn't restricted to electric charges. But something else must distinguish then neutrinos and antineutrinos to offer the possibility to annihilate, their chirality? And what is the reaction product? I am not at all familiar with neutrino physics.
In case the search for Majorana neutrinos is positiv, would it mean the neutrino is its own antineutrino, like it is true for photons?

If it is a Majorana particle, then it is its own antiparticle.

[MigL]

The only particles I know of that are their own antiparticles are both bosons. One is the previously mentioned photon, the other is the Z particle which carries ( along with +/-W particles ) the weak interaction. Being bosons they follow bose-einstein statistics and don't abide by the exclusion principle, they can bunch-up and have overlapping states.

This post has been edited by MigL: 31 December 2011 - 08:38 AM

[guenter]

guenter, on 30 December 2011 - 04:54 PM, said:

So annihilation isn't restricted to electric charges. But something else must distinguish then neutrinos and antineutrinos to offer the possibility to annihilate, their chirality? And what is the reaction product?

As stated here neutrinos and antineutrinos annihilate via virtual Z-Bosons into charged particle-antiparticle pairs (leptons, quarks). Thus finally- at least theoretically - photons could be produced.

[Andeh]

I dont really have a dignified point. I'm not suggesting that this is the cause of the behavior of charge. I'm just interested/astounded that this is the only way that things could work--like the universe is just put together perfectly. It's not like alternative history, where if x event didnt happen, history would be completely different...but that the universe could not exist any other way; it's physically impossible.

mathematic, on 28 December 2011 - 11:51 PM, said:

What is your point?