Wormhole Time Machines and Multiple Histories (2110.02448v3)

Abstract: In a previous paper, we showed that a class of time travel paradoxes which cannot be resolved using Novikov's self-consistency conjecture can be resolved by assuming the existence of multiple histories or parallel timelines. However, our proof was obtained using a simplistic toy model, which was formulated using contrived laws of physics. In the present paper we define and analyze a new model of time travel paradoxes, which is more compatible with known physics. This model consists of a traversable Morris-Thorne wormhole time machine in 3+1 spacetime dimensions. We define the spacetime topology and geometry of the model, calculate the geodesics of objects passing through the time machine, and prove that this model inevitably leads to paradoxes which cannot be resolved using Novikov's conjecture, but can be resolved using multiple histories. An open-source simulation of our new model using Mathematica is available for download on GitHub. We also provide additional arguments against the Novikov self-consistency conjecture by considering two new paradoxes, the switch paradox and the password paradox, for which assuming self-consistency inevitably leads to counter-intuitive consequences. Our new results provide more substantial support to our claim that if time travel is possible, then multiple histories or parallel timelines must also be possible.

• The paper's main contribution is its model that resolves time travel paradoxes by introducing multiple histories to avoid causal contradictions.
• It employs a realistic Morris-Thorne wormhole framework in 3+1 spacetime dimensions to analyze both consistency and bootstrap paradoxes.
• The study challenges Novikov's self-consistency conjecture and redefines temporal causality by advocating for parallel timelines.

Wormhole Time Machines and the Paradox of Multiple Histories

The paper entitled "Wormhole Time Machines and Multiple Histories," authored by Barak Shoshany and Jared Wogan, focuses on a detailed examination of time travel paradoxes and their resolution through the concept of multiple histories. The authors explore the interplay between time travel, closed causal curves, and Novikov's self-consistency conjecture in the context of general relativity and traversable wormholes, leading to a compelling argument for the necessity of parallel timelines if time travel is indeed feasible.

Overview of the Model

The authors present a model of time travel based on a traversable Morris-Thorne wormhole in 3+1 spacetime dimensions. The construction circumvents some of the limitations seen in previous analyses, like simplistic toy models, by incorporating a more realistic framework grounded in general relativity. The wormhole connects two points in spacetime, potentially enabling travel between different times, thus allowing for the contemplation of time travel paradoxes within physical laws.

Shoshany and Wogan focus on two prominent classes of time travel paradoxes: consistency paradoxes and bootstrap paradoxes. Consistency paradoxes involve scenarios where events lead to contradictions, such as destroying a time machine before the point at which one used it to travel back in time. Bootstrap paradoxes highlight causal loops where events seemingly create themselves, such as receiving information from the future that the receiver uses to recreate the same course of events (e.g., time machine designs passed between timelines).

Resolution of Paradoxes

The paper rigorously argues that while Novikov’s self-consistency conjecture can theoretically resolve certain consistency paradoxes by ensuring that the timeline remains unchanged despite temporal interferences, it falls short in cases leading to bootstrap paradoxes. In these cases, Novikov's approach can imply discomforting philosophical implications like negation of free will or imposition of improbable outcomes to prevent paradoxes.

To address these shortcomings, the authors advocate for resolving paradoxes through the multiple histories model, where each potential paradox-spawning event creates new branches in the timeline. By allowing for alternative histories, one can avert contradictions by positing that events resolved paradoxically or inconsistently simply branch into separate timelines, where the outcomes diverge.

Implications and Future Prospects

The implications of this work are profound, spanning both theoretical and practical dimensions. On a theoretical level, the necessity of multiple histories redefines our understanding of temporal causality and has parallels in quantum mechanics, particularly the Everett interpretation, which allows for an infinite number of branching outcomes.

Practically, if time travel were possible, the need for multiple histories would demand a reevaluation of causality and determinism in physics. Emerging technologies, if ever capable of manipulating spacetime in the vein suggested, would have to account for these multi-timeline realities, with significant repercussions for science and philosophy.

Conclusion

Shoshany and Wogan's paper proposes a comprehensive framework for considering time travel paradoxes and their resolution. By highlighting the insufficiency of Novikov's self-consistency conjecture alone, this research underscores the essentiality of multiple histories in a universe where time travel could hypothetically exist. The authors prompt further investigation into the nature of spacetime continuity and quantum gravity, suggesting a promising path forward for future research in this intriguing area of theoretical physics.