The most important part is the conversion of a vector quantity into a scalar. Energy packets, photons, always have a prescribed velocity or direction. When mass is created, this direction is lost. It shows us a fundamental anisotropy of our universe. Total momentum is conserved..but since 0 momentum is degenerate and has no direction, we get the mixing of isotropic emissions, that should in theory, cancel out any biases that may have once existed.
Our universe cares about conservation globally - but as scattering shows, at the quantum scale, our universe could care less about you switching a left and a right for an up and a down.
We are talking about a net momentum of zero. It can be in all kinds of different forms without violating conservation. Exchanging a left and right moving particle for up and down ones, changes the system but retains global conservation
Our universe cares about conservation globally - but as scattering shows, at the quantum scale, our universe could care less about you switching a left and a right for an up and a down.