Physics
Time travel: a critical review
A critical review of the time-travel program: chronology protection, constructive machines, the quantum stress computations, the relic searches, and the acquisition and engineering ledger.
Jonathan Schemoul
This is a critical review of the time-travel program. It covers the classical and semiclassical chronology-protection literature, the constructive time-machine models, the quantum stress computations on the Ori core, the Xavier train core, the gravitational-wave and Gaia relic searches, and the acquisition and engineering questions.
The review is deliberately qualitative where the companion papers are still in preparation. It states the open problems: the 4D backreaction endpoint, state selection, gauge-complete stability, the 3+1 acquisition theorem, and a survey with a measured efficiency. It does not present the companion numbers as independent results.
Key results
- A single map of the time-travel program: no-go results, constructive models, computed stress, searches, acquisition and engineering.
- The remaining open problems are stated as open, not solved.
- The companion papers are cited as the source of the quantitative claims.
Status and limits
This is a 36-page content-complete review draft with 91 references. It is held for journal submission until the companion papers are posted; on Labs and Zenodo it is a preprint. It has not been submitted or peer reviewed.