I don't expect an answer since it has been a couple years now since this video was put up. My question is that 4-momentum is by definition dR/dtau where tau is the proper time of the object in question, however, here there are four different objects, object 1, 2 (before collision) and 3 and 4 (after collision), and you said "rest frame" ... but the "rest frame" of which of the 4 objects? Each of the 4 objects have (potentially) different times since they could be moving at different relative velocities. I'll be grateful if you could answer my question.
I don't expect an answer since it has been a couple years now since this video was put up. My question is that 4-momentum is by definition dR/dtau where tau is the proper time of the object in question, however, here there are four different objects, object 1, 2 (before collision) and 3 and 4 (after collision), and you said "rest frame" ... but the "rest frame" of which of the 4 objects? Each of the 4 objects have (potentially) different times since they could be moving at different relative velocities. I'll be grateful if you could answer my question.
There are for taus, one for each object. Each object has a rest frame in which its proper time can be measured
Since the t component is kinetic energy, wouldn’t that mean in cases where kinetic energy isn’t conserved, momentum isn’t conserved?