Time machines and traversable wormholes in modified theories of gravity

TL;DR

This paper reviews recent developments in wormhole geometries within modified gravity theories, highlighting how higher-order curvature terms can support wormholes without exotic matter and discussing their potential for time travel and related paradoxes.

Contribution

It provides a comprehensive review of wormhole solutions in various modified gravity theories and discusses the conditions under which they can be traversable and support time machines.

Findings

Higher-order curvature terms can sustain wormholes with normal matter satisfying energy conditions.

Modified gravity theories allow for traversable wormholes without exotic matter.

Conversion of wormholes into time machines introduces paradoxes and potential resolutions.

Abstract

We review recent work on wormhole geometries in the context of modified theories of gravity, in particular, in f(R) gravity and with a nonminimal curvature-matter coupling, and in the recently proposed hybrid metric-Palatini theory. In principle, the normal matter threading the throat can be shown to satisfy the energy conditions and it is the higher order curvatures terms that sustain these wormhole geometries. We also briefly review the conversion of wormholes into time-machines, explore several of the time travel paradoxes and possible remedies to these intriguing side-effects in wormhole physics.