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Do they create energy? Or do they just disappear with zero energy?

If they create energy when disappearing, that means it takes energy to create them, right?

If they disappear into zero energy, could that be a clue about how to create matter from nothing?

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up vote 7 down vote accepted

The do not disappear with zero energy.

Their energy (both that originating from rest mass and any kinetic energy) appears somehow. As photons, a spray of other (lighter) particles, etc.

For instance, when an electron meets a positron (that is, a anti-electron) the most common result is a pair of gamma rays each of 511 keV (in the center of momentum (CoM) frame of the $e$--$e^+$ pair). It has to be at least two because you have to conserve both energy and momentum (and angular momentum, too, but that is a complication we will ignore for the moment), and that also tells us that there have opposite momenta in the CoM frame.

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Interaction like this produce anything that is allowed by conservation laws, which track the sum totals of various values (including quantum numbers). An anti-matter version of a particle has the opposite/negative value of most conserved quantities. So the result of the interaction might be almost any other particle-antiparticle pair, so long as the total energy is available. In particular the result can be a pair of photons: electron-positron collisions produce a pair of gamma rays carrying off the energy from the rest mass of the particles.

You questions about total energy are confused. The total energy before and after a collision will always be the same. Thus some particles have to exist after the collision. For particle plus its anti-particle collisions there will be more than one resulting product because a single product by itself would have some non-zero quantum numbers.

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""electron-positron collisions produce a pair of gamma rays carrying off the energy from the rest mass of the particles."" exept when they produce three gamma quantums. :=) Think of positron-electron as a triplett. – Georg Mar 22 '11 at 12:59
Ortho- and Parapositronium are the names for three or two-gamma decay. (Analogy to Orthohydrogen and Parahydrogen – Georg Mar 22 '11 at 15:45

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