The discussion explores whether the rest mass of an object can change over time, particularly in scenarios involving mass loss. Participants examine theoretical implications, practical examples, and the relationship between rest mass and energy within the context of relativity.
Participants express multiple competing views regarding the definitions and relationships between rest mass, energy, and the implications of mass loss. The discussion remains unresolved with no consensus on the core questions raised.
Participants reference various theoretical frameworks and terminologies, indicating that definitions may depend on context and interpretation. The discussion includes unresolved mathematical and conceptual nuances regarding the application of the Poincare group and the treatment of mass in relativistic contexts.
stedwards said:
Using older terminology than Peter, you're talking about relativistic mass (a concept that has largely fallen out of favour, by the way), not rest mass.stedwards said:
My $0.02 is that one should consider the dynamical group for the entire system. E.g., in a rocket, matter is ejected in one direction to change the rocket's velocity in the opposite direction. The rocket thus feels acceleration, so one must be cautious about naively applying the Poincare group to the rocket in isolation, and hence should also be cautious about the "invariant mass" Casimir of the Poincare group. Rather, one should probably decompose into com and relative coordinates, and find the full dynamical group applicable to the system with com dofs factored out. Then look at the Casimirs of that group applicable to the relative motion...ChrisVer said:
PeterDonis said:
- The energy of a tree is just as little affected by your change of choice of reference system as the amount of gasoline in a car is affected by your choice of using gallons or liters. Changing the observation (assuming no interaction) can not affect what is observed.stedwards said:
What's your problem, mate? Peter is not the one who made an incorrect statement. You did, in post #6, i.e.,stedwards said:
That's just plain wrong. The word "no" is entirely appropriate in an answer to correct an error.stedwards said:
If by "P" you mean 4-momentum, then,... PeterD said essentially the same thing. But that's different from your incorrect statement that "rest mass is synonymous with energy".
strangerep said:
Uh oh. To answer that properly needs a lot more than a mere "$0.02 worth", but I don't have much spare time at the moment. Sorry.ChrisVer said:
