Particle anhilation - what happens to entropy ?

Factual Questions
1

I believe energy is conserved during a matter antimatter particle collision. But what about entropy ? Does entropy goes up and by how much ?

2

If it’s a spontaneously-occurring reaction, then yes, entropy goes up. Particle-antiparticle annihilation tends to involve extremely large increases in entropy. In fact, one rule-of-thumb measure of the net entropy of the Universe is the ratio of the number of massless particles (such as gamma rays) to massive ones (such as electrons and positrons).

3

Thanks Cronos. Is the entropy change the same say when an electron and a positron anhilate to produce 2 gamma rays and a nucleus undergoes decay to produce 2 gamma rays ?

Thanks

4

For what it’s worth, the opposite process also occurs: two photons can produce an electron and positron, for example. Energy is conserved in pair annihilation or production (or any other similar sort of decay process); entropy is not.

5

Entropy is not conserved in the sense that it does not remain constant, but that’s no surprise: Entropy changes in almost all physical processes. But like all physical processes, it never decreases, and almost always increases.