Does an electron-positron collision violate the law of conservation of matter?

Answer 1

No, electron-positron collision does not violate the law of the conservation of matter. Momentum and charge are also conserved. Electrons and positrons can collide in what are called scattering events, and they can do this without necessarily undergoing mutual annihilation. Because both these little critters can exist as a wave (particle-wave duality), their behavior can be fairly easily assessed using a "basic tool kit" to analyze electromagnetic wave interaction. But electrons and positrons can annihilate each other rather than scatter. Annihilation doesn't violate the law of conservation of matter, either. And there's a reason for that. The "old" idea of the conservation of matter was that matter could neither be created nor destroyed. But we now know that matter can be converted into energy. That's what happens in annihilation. The article in Wikipedia on the annihilation event touches on electron-positron collision. And there is an article on electromagnetic scattering as well. They aren't that difficult to understand, and the curious person will find links to those posts below.