Can quantum gravity forbid time travel?
- Filed under
- Tech
- Type
- Background entry
- Sources
- 8
AI-generated illustration
Does quantum gravity hide time inside a deeper timeless substrate, making closed timelike curves a relic of emergent spacetime rather than a physical possibility?
Summary
The cautious mainstream position is that quantum effects may prevent physically constructing or reaching time machines, but existing results are model-dependent. Semiclassical calculations suggest divergences or large stress-energy near chronology horizons, while some higher-derivative theories exclude particular Gödel solutions with closed timelike curves. These findings motivate chronology protection, not a universal theorem.
- Vacuum fluctuations were investigated as a possible source of instability at the boundary where closed timelike curves form, though the calculation used restricted quantum fields and approximations.
- A 2023 analysis finds that, in a broad class of higher-derivative gravitational theories, Gödel-type metrics with closed timelike curves are not exact solutions under stated assumptions.
- One analysis argues that quantum effects make time machines inaccessible to observers and prevent traversable wormholes from becoming time machines without quantum-gravity effects.
Source mix
3 of 8 institutional
- 3 Journals & institutions
- 3 Early research (not yet peer-reviewed)
- 1 Forum, video, personal
- 1 Other / unclassified
Deeper Insight
Physics' ban on time machines assumes we know what time is. Quantum gravity says we might not.
The usual argument says nature protects the past: get close to building a time machine and quantum effects blow it apart. But that argument leans on a classical picture of spacetime. If space and time emerge from something deeper, a loop in time might not be forbidden so much as redefined. The no-go theorems are less general than they sound.
- What it could changeA theory where time is emergent could turn time travel from a paradox into a question about what before means.
- How it touches todayResearchers in quantum gravity are still rebuilding the idea of time from the ground up.
- Our futureThe past may be less locked than we think, just harder to reach.
- Because many quantum-gravity approaches regard relativistic spacetime as emergent, their implications for closed timelike curves cannot be read off straightforwardly from classical general relativity.
- Arguments that logical or physical contradictions rule out time travel may rely on time concepts that are themselves problematic in quantum gravity.
- A philosophical-physics analysis stresses that proposed no-go theorems depend on how a time machine is defined and have not achieved sufficient generality.
Sources · 8
- 3 Journals & institutions
- 3 Early research (not yet peer-reviewed)
- 1 Forum, video, personal
- 1 Other / unclassified
What do these mean?
- Journals & institutions. Published in a peer-reviewed journal, or from a university, government body, court or other institution.
- Early research (not yet peer-reviewed). A research paper posted publicly before independent experts have reviewed it (a preprint). Real researchers, but not yet checked.
- Forum, video, personal. Forums, social posts, video, blogs and personal accounts.
- Other / unclassified. A site we have not classified yet. This says nothing good or bad about it.
Featured · Primary source · arxiv.org
Time travelling in emergent spacetime
Early research · not yet reviewed
Time travelling in emergent spacetime arXiv is now an independent nonprofit! Learn more × # Time travelling in emergent spacetime Christian Wüthrich ††thanks: I am grateful to the editors for their kind invitation and to Hajnal Andréka, Stefano Furlan, Niels Linnemann, István Németi and an anonymous
Read sourceAnalysis · philarchive.org
Do the laws of physics forbid the operation of time machines?
Early research · not yet reviewed
Synthese (2009) 169:91–124 DOI 10.1007/s11229-008-9338-2 Do the laws of physics forbid the operation of time machines? John Earman · Christopher Smeenk ·Christian Wüthrich Received: 28 July 2006 / Accepted: 1 April 2008 / Published online: 7 May 2008 © Springer Science+Business Media B.V. 2008 Abstr
Read sourceAnalysis · physics.stackexchange.com
Do any quantum gravity theories deal with closed timelike curves?
Forum or personal account
# Do any quantum gravity theories deal with closed timelike curves? Tags: general-relativity, quantum-gravity, closed-timelike-curve - Score: 28 - Views: 2423 - Answers: 3 - Answered: yes - Asked by: Slereah (17195 rep) - Asked: 2016-01-20 - Edited: 2016-03-03 - Site: physics ## Question As far as I
Read source