This paper explores the implications of closed timelike curves (CTCs) for the existence of life. It argues against the common assumption that CTCs would prevent life, instead proposing that stable and complex life could exist within them. The authors demonstrate, using a simple model based on Conway's Game of Life, how self-consistent, non-trivial evolution can occur on a spacetime containing CTCs. They suggest that the apparent paradoxes associated with time travel, such as the grandfather paradox, are avoided not by preventing changes to the past, but by the universe's dynamics naturally converging to self-consistent states. This implies that observers on a CTC would not perceive anything unusual, and their experience of causality would remain intact, despite the closed timelike nature of their spacetime.
The paper "Life on a Closed Timelike Curve" by Toffoli and Margolus explores the hypothetical implications of biological life existing within a region of spacetime containing a closed timelike curve (CTC). CTCs, permitted by Einstein's general relativity, theoretically allow for time travel by creating loops in the fabric of spacetime. The authors specifically focus on how such a scenario would affect evolutionary processes and the development of complex organisms.
They construct a simplified model of an ecosystem existing on a CTC using cellular automata, a computational model where cells on a grid evolve according to predetermined rules. This allows them to simulate the effects of time travel within a controlled environment. The CTC is incorporated into the model by introducing a region where the future state of the cells is directly influenced by their past states, effectively creating a causal loop. This loop mimics the effect of information being transmitted through time along the CTC.
The authors then investigate how organisms represented by specific patterns within the cellular automata would evolve under these unusual conditions. They observe that traditional Darwinian evolution, driven by random mutations and natural selection, faces significant challenges in the presence of CTCs. The fixed nature of the temporal loop constrains the possible evolutionary trajectories, potentially preventing the emergence of novel traits. Moreover, the constant feedback loop introduced by the CTC can lead to stable but suboptimal configurations, hindering the optimization process usually associated with natural selection.
Instead of relying solely on random mutations, the authors propose a new mechanism they term "evolution by self-consistency." In this framework, organisms adapt not just to their immediate environment but also to their own future states, accessible through the CTC. This leads to a sort of "pre-adaptation," where organisms develop traits that are advantageous not only in the present but also in the future, creating a self-consistent loop across time.
The paper demonstrates that life on a CTC can indeed evolve towards complex and stable configurations, but through a fundamentally different process than Darwinian evolution. This "evolution by self-consistency" emphasizes the importance of global optimization and temporal coherence, rather than local adaptation driven by random mutations. The results suggest that the presence of CTCs would drastically reshape the landscape of biological evolution, leading to life forms with unique adaptations tailored to the peculiarities of closed-timelike-curve environments. While purely theoretical, the research provides valuable insights into the potential intersection of biology and exotic spacetime geometries, prompting further exploration of the profound implications of time travel for the fundamental laws of nature and the development of life itself.
Summary of Comments ( 36 )
https://news.ycombinator.com/item?id=42677158
HN commenters discuss the implications and paradoxes of closed timelike curves (CTCs), referencing Deutsch's approach to resolving the grandfather paradox through quantum mechanics and many-worlds interpretations. Some express skepticism about the practicality of CTCs due to the immense energy requirements, while others debate the philosophical implications of free will and determinism in a universe with time travel. The connection between CTCs and computational complexity is also raised, with the possibility that CTCs could enable the efficient solution of NP-complete problems. Several commenters question the validity of the paper's approach, particularly its reliance on density matrices and the interpretation of results. A few more technically inclined comments delve into the specifics of the physics involved, mentioning the Cauchy problem and the nature of time itself. Finally, some commenters simply find the idea of time travel fascinating, regardless of the theoretical complexities.
The Hacker News post titled "Life on a Closed Timelike Curve," linking to a scientific paper exploring theoretical life in a closed timelike curve (CTC) spacetime, has generated several comments. Many commenters engage with the core concepts of the paper, grappling with the implications of CTCs and their potential paradoxes.
A significant portion of the discussion revolves around the Novikov self-consistency principle, which the paper relies upon. This principle, suggesting that events within a CTC must be consistent with themselves, sparked debate about its validity and implications. Some commenters express skepticism about the principle, questioning whether it truly resolves paradoxes or merely sidesteps them. Others explore the philosophical ramifications of self-consistency, pondering the nature of free will and determinism in a universe with CTCs.
Several comments delve into the specifics of the paper's model, discussing aspects like the use of game theory and the nature of the simulated organisms. Some users raise questions about the model's assumptions and limitations, while others offer alternative interpretations or suggest potential extensions of the research.
The idea of "predestination paradoxes" receives considerable attention, with commenters presenting thought experiments and hypothetical scenarios to illustrate the complexities of causality in a CTC. The famous "grandfather paradox" is mentioned, along with variations and counterarguments.
Some commenters also connect the theoretical discussion to broader topics in physics and computer science. Connections are made to quantum mechanics, information theory, and the concept of computation. A few users even draw parallels to science fiction, mentioning stories and films that explore similar themes.
While there's general agreement on the fascinating nature of CTCs and the thought-provoking questions they raise, there isn't a consensus on the plausibility or implications of the paper's findings. The comments reflect a mix of curiosity, skepticism, and intellectual engagement, showcasing the diverse perspectives of the Hacker News community. The discussion doesn't reach definitive conclusions but serves as a platform for exploring the complex and often paradoxical nature of time travel and its potential impact on life.