Discussion Overview
The discussion revolves around the implications of conservation of mass-energy in the context of time travel, particularly through traversable wormholes as proposed by Kip Thorne. Participants explore theoretical objections related to time travel and the conservation laws in general relativity.
Discussion Character
- Exploratory, Technical explanation, Debate/contested
Main Points Raised
- One participant raises the concern that if a photon were to travel back in time, it could result in a violation of conservation of mass-energy by creating two photons from one.
- Another participant asserts that global conservation of energy does not hold in general relativity without specific conditions on the spacetime.
- A further contribution explains that in flat spacetime, energy conservation is linked to the equations of motion being independent of absolute time, referencing Noether's theorem.
- It is noted that in non-flat spacetime, the lack of time-translation symmetry means energy conservation may not apply.
- A participant expresses satisfaction with the discussion and indicates a shift in focus to other objections regarding closed time-like curves.
Areas of Agreement / Disagreement
Participants generally agree on the limitations of energy conservation in general relativity, but multiple competing views regarding the implications for time travel remain unresolved.
Contextual Notes
The discussion highlights the dependence on the nature of spacetime (flat vs. non-flat) and the assumptions related to energy conservation in general relativity, which remain unresolved.