Gravity Theories and Closed Timelike Curves
Summary
Gravity theories form the bedrock of our understanding of spacetime structure, from Einstein’s general relativity to a suite of modified frameworks that seek to reconcile cosmic acceleration or quantum effects. Central to this discourse is the phenomenon of closed timelike curves (CTCs), worldlines that loop back upon themselves and formally permit a return to an earlier event in one’s history. In classical general relativity, exact solutions such as the Gödel universe or certain rotating black-hole spacetimes admit CTCs, raising profound questions about causality and the consistency of physical law. Alternative approaches—among them scalar–tensor theories, Palatini extensions and models built on the inverse Ricci tensor—have been explored both to reproduce observed cosmic dynamics and to assess whether CTCs persist or are forbidden. These investigations probe the deep interplay between geometry, energy conditions and temporal order, with practical implications for quantum gravity proposals and the ultimate viability of time-travel scenarios.
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Gravity Theories and Closed Timelike Curves publication trend
The graph below shows the total number of articles in gravity theories and closed timelike curves across all publications each year (not limited to Nature Index journals).
Technical terms
Closed Timelike Curve (CTC): A path through spacetime that returns to its own past, implying a “time-loop” and potential causality violation.
Ricci Tensor: A geometrical object in general relativity encapsulating how volumes in spacetime diverge or converge under gravity.
Anti-curvature Scalar: A scalar constructed from the inverse of the Ricci tensor, employed in certain modified gravity theories to alter high-curvature behaviour.
Wormhole: A hypothetical tunnel connecting distinct regions of spacetime, potentially acting as a shortcut for matter or information.
Gödel Metric: An exact cosmological solution of Einstein’s equations describing a rotating universe that inherently permits CTCs.
Chronology Protection Conjecture: A hypothesis that fundamental physical laws prevent the formation of CTCs, thereby safeguarding causal consistency.
References
- An axially symmetric spacetime with causality violation in Ricci-inverse gravity. European Physical Journal C (2023).
- Ricci inverse gravity wormholes. Physics Letters B (2024).
- Closed Timelike Curves, Singularities and Causality: A Survey from Gödel to Chronological Protection. Universe (2021).
- Homogeneous Gödel-type solutions in hybrid metric-Palatini gravity. European Physical Journal C (2018).
- Gödel and Gödel-type universes in Brans–Dicke theory. Physics Letters B (2016).
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