questions about matter/antimatter collisions

economancer

These may seem like silly questions, but seeing as I'm not a physics major (I teach myself about what interests me in any subject really), I could use some clarification on the issue.

Does an anti-particle annihilate only when it meets its "regular matter" particle counterpart, or will the destruction occur when any antimatter particle meets any matter particle? Further, what is the cause of/mechanism for this annihilation?

Drakkith

Every particle is indistinguishable from other particles of the same type. One electron is exactly the same as another electron in the same states. As such, an antimatter particle will annihilate with anything that is it's anti-particle. Positrons will annihilate with any electron. Many times an particle doesn't even have a corresponding antiparticle when it is created.

sambristol

Economancer

well, lets start with the easier part your question. A true elementary particle will 'annihilate' with its antiparticle in the sense particle plus antiparticle goes to pure em radiation (ie gamma rays) BUT with two important caveats

Firstly most particles are not elementary so for instance a proton is more complex since it is made of 3 quarks so it can do a whole lot more than just produce pure em radiation.

Secondly give a particle (or antiparticle) enough energy and it can interact in any way that satisfies all the conservation laws (charge, spin etc etc)

Now for the second part of the question – Why do elementary antiparticles and particles annihilate?

This can be answered at all levels of complexity but my favourite is a quote from the late great Richard Feynman “anything which can happen will happen”.

So they annihilate because they can ! (ie they satisfy all the conservation laws)

A more sophisticated argument would talk about the probability of the annihilation in terms of the 'volume' the phase space for the products of the event but without a whole truck load of quantum field theory thats as far as we can go.

Hope this helps

Regards

Sam

economancer

So its more complicated than simply antimatter *will* annihilate with matter. I'm reading a book (Antimatter by Frank Close) and either I missed it, haven't gotten there yet, or it just doesn't go into that kind of detail. Thanks, i'm sure I'll be back with more questions eventually.