Investigated
How does quantum gravity affect CTCs?
Short answer
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Quantum gravity may alter CTCs by preventing certain causality-violating geometries, especially in some higher-derivative or nonlocal models. But other analyses find quantum dynamics can remain consistent in specially constructed CTC spacetimes, while emergent-spacetime approaches leave the issue dependent on how spacetime and time arise.
The views on this question
Two lenses on the same evidence. Source weight and the primary source ratio show what each rests on.
Alternative
Source weight 50%A serious dissenting line emphasizes that quantum theory need not automatically destroy CTCs. Specific models and backgrounds can yield consistent propagation or unitary behavior, so claims of universal chronology protection go beyond what current calculations establish.
- In selected time-dependent orbifold backgrounds related to BTZ black holes, quantum propagation can be consistent with unitarity for discrete values of the gravitational coupling, despite perturbative unitarity failure in general.
- Some analyses conclude that quantum corrections may spoil particular CTC-supporting solutions, but this does not prove that every quantum-gravity framework excludes CTCs.
- The literature includes multiple proposed quantum treatments of CTCs, indicating that consistency, paradox resolution, and chronology protection are distinct questions.