Really we have four interactions, and of those four the EM and gravity interactions produce the classic EM force and gravitational force at low energies/large distances.
But the weak and strong interactions have no equivalent classical force.
So to talk about the weak and strong force is really a misnomer, though all physicists know what this really means.
Energy is always conserved so if $M$ is the total rest mass of all the particles and $T$ is the total kinetic energy of all the particles then $Mc^2+T$ is constant.
But in scattering KE can be converted to mass and mass can be converted to KE.
So neither $M$ nor $T$ are constant on their own. Only the total energy $Mc^2 + T$ is constant.
I need to work now I'm afraid. I'll be about half an hour.
Momentum is conserved in the scattering, but that doesn't mean the scattering process can simply be interpreted as a force. For example the total rest mass of the particles present can change due to the creation of new particles.
That messes up the simple Newtonian equation $F=ma$ because $m$ is no longer constant.
I think we need to distinguish between the mathematical ideal of defining a coordinate system and the physical reality of a physicist floating in space trying to define a coordinate system.
A completely empty universe is static i.e. unchanging in time. So it makes no difference where we place the origin. Mathematically we can arbitrarily choose a point as the origin and that's a perfectly fine thing to do. The universe is a 4D manifold and we can choose any random 4D poitn and say "that's our origin".
@yuvrajsingh I can post an answer, but writing an answer takes a lot longer than just making a few comments in the chart because the answer has to be clear and well written. So I can't do it right now.
