When matter and anti-matter collide, in what form is the resulting energy?

[Jarfi]

I know that when matter is mixed with anti matter they disappear into pure energy. But how can there be energy with no matter? Is it light that forms? do we get a massive blast of light? what else could it be? with no matter you can't have energy(exept for light)... what happens?

 

[JesseM]

Your guess is right, when particles annihilate with antiparticles the result is high-energy photons, which have zero mass so they can be said to be "pure energy". Also note that while electrons and positrons convert entirely to photons, the same is not true for protons and antiprotons, see the second paragraph here.

 

[Jarfi]

Your guess is right, when particles annihilate with antiparticles the result is high-energy photons, which have zero mass so they can be said to be "pure energy". here.

So if electrons and positrons create photons and gamma rays. Could i reverse the process and focus light/gamma rays in one dot and end up with an electron and positron?

 

[JesseM]

So if electrons and positrons create photons and gamma rays.

gamma ray is just a name for the type of photons emitted (a gamma ray is just a photon with a sufficiently high frequency, see the electromagnetic spectrum), they aren't two different types of particles.

Could i reverse the process and focus light/gamma rays in one dot and end up with an electron and positron?

A pair of gamma ray photons can spontaneously create an electron/positron pair (see 'reverse reaction'), I don't know how difficult it is to produce photons with such high energy or the probability they will convert in this way if focused at a sufficiently small region or how difficult it would be to actually focus high-energy photons in this way, maybe someone else can address the practicality of this.

 

[mathman]

Single photon gamma rays with energy above 1.022 Mev may end up as an electron-positron pair. This can only occur in the presence of a nucleus, needed to conserve momentum. This process is one of the principal ways to shield (using lead for example) against high energy gamma rays.