Is the mass defect still considered with invariant mass?

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Discussion Overview

The discussion revolves around the concept of mass defect in the context of invariant mass, particularly when assembling a sphere of negative charges. Participants explore the implications of energy gain during assembly and the relationship between invariant mass and the mass of individual components, touching on theoretical and conceptual aspects of mass in relativistic physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the invariant mass of a system, such as a sphere of negative charges, is greater than the sum of the invariant masses of its individual components due to energy contributions from the system as a whole.
  • Others argue that the extra mass associated with the system cannot be localized to specific parts and is instead an attribute of the entire system, potentially linked to the electrostatic field produced by the charges.
  • A participant questions whether the overall energy difference in assembling a system could be considered the source of mass defect, suggesting that energy conservation must hold across different frames of reference.
  • Another participant clarifies that while energy is conserved, it is not invariant across frames, which complicates the understanding of mass and energy in different contexts.
  • Some participants express confusion over terminology, particularly the use of terms like invariant mass, rest mass, and relativistic mass, and how these relate to the concept of mass defect.

Areas of Agreement / Disagreement

Participants generally agree that there is a mass defect associated with the assembly of charges, but there is no consensus on how to define or localize this mass defect. Multiple competing views remain regarding the implications of energy contributions and the nature of mass in different reference frames.

Contextual Notes

Limitations in understanding arise from the different interpretations of mass and energy in relativistic contexts, as well as the challenges posed by non-invariance of energy across frames. The discussion reflects varying degrees of familiarity with the concepts and terminology involved.

  • #31
Mister T said:
You could also use solar energy to grow the food needed for a human to lift the book.

Yes, but that is just admitting that in fact the Earth (or the Earth plus the book plus the human) is not a closed system. There is energy flow across its boundary in both directions. What's more, if you are taking this energy flow into account, the system is not stationary either, so the notion of "potential energy" is not even well-defined. Obviously this is no longer "as simple as lifting a book", nor is it any good as an illustration of any point about potential energy or invariant mass.

So either you bring in complications that make the whole subject of this discussion pointless, or you accept a simple model in which the Earth-book system is closed, at least on the time scale required to lift the book (note that this time scale is much shorter than the time scale required to capture solar energy and grow the human's food), and in that model, the externally measured mass does not change when you lift the book.
 

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