But WHY do antimatter and matter annihilate on contact?

[biffus22]

Everyone knows that matter and antimatter annihilate upon contact. But exactly WHY this should happen is not at all obvious, at least to me. So what exactly happens when two such particles encounter one another that leads them to disappear in a large release of photons? And for that matter, just how many photons ARE released in, say, the contact of an electron and a positron? And what determines their energy and frequency?

 

[DennisN]

Hi biffus22,

And for that matter, just how many photons ARE released in, say, the contact of an electron and a positron? And what determines their energy and frequency?

If I tell you that the basic rules are that both the total energy and total momentum must be conserved, that is, the total energy (intrinsic mass energy + kinetic energy) of the electron and positron must equal the energy of the resulting photon(s) AND the total momentum of the electron and positron must equal the momentum of the resulting photon(s), what do you think? Do you know of any suitable equations?

If you do not, here's a...

Spoiler

http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.html#c1
(see entire page)

Edit:

Everyone knows that matter and antimatter annihilate upon contact. But exactly WHY this should happen is not at all obvious, at least to me.

It's not obvious to me either. I guess the Universe likes it that way. And why do antimatter exist at all? I have no idea. "Why" questions are easy questions to ask, but very tricky questions to answer.

Edit 2:

And what determines their energy and frequency?

See also...

Spoiler

http://hyperphysics.phy-astr.gsu.edu/hbase/mod2.html#c3