Causality Guides Physics Beyond General Relativity, Exploring Emergent Frameworks Without Gravitational Quantization

The search for a complete theory of gravity, extending beyond Einstein’s General Relativity, continues to drive innovation in theoretical physics, and Gerardo García-Moreno is contributing to this effort by exploring the fundamental role of causality in emergent gravitational theories. This work investigates how gravity might arise not as a fundamental force, but as an emergent phenomenon stemming from more basic underlying principles, drawing inspiration from the field of condensed matter physics. García-Moreno’s research offers a unique roadmap for analysing these emergent frameworks, focusing on the crucial interplay between causal structure and the geometry of spacetime, without committing to any specific model. By concentrating on the implications of background structures and the absence of singularities, this investigation provides valuable insights into the potential pathways for constructing a more complete and consistent theory of gravity.

The research focuses on emergent theories inspired by condensed matter physics, offering a roadmap for analysis rather than committing to a specific model. This study provides a framework for understanding how gravity could emerge from more basic building blocks of the universe.

Reconciling Gravity and Quantum Mechanics

This body of work spans general relativity, quantum mechanics, cosmology, and mathematical functions, revealing a progression of ideas from classical gravity to attempts at reconciliation with quantum principles. Core research in general relativity includes studies of static, axially symmetric fields and timelike curves, alongside detailed analyses of special functions essential for gravitational calculations. Foundational work in quantum mechanics encompasses the quantum postulate, the relative state formulation, and detailed investigations into decoherence and open quantum systems. Studies at the intersection of general relativity and quantum mechanics explore the evolution of quantum states, information loss in spacetime, and the coupling of classical and quantum variables. Investigations into emergent gravity utilize algebraic approaches to classical mechanics and explore post-quantum theories of classical gravity. Advanced mathematical tools, including comprehensive handbooks of mathematical functions and special functions, underpin these theoretical developments.

Causal Protection Emerges in Analog Spacetimes

This work investigates emergent gravity, exploring how gravitational phenomena might arise from more fundamental underlying principles without necessarily requiring a quantized theory of gravity itself. The research focuses on emergent theories inspired by condensed matter physics, offering a roadmap for analysis rather than committing to a specific model. The study is divided into two parts, employing distinct analytical tools to examine fundamental concepts and specific scenarios relevant to emergent gravity frameworks. Initial investigations utilized analog gravity systems, modeling spacetime through the behavior of excitations in other physical systems.

Experiments revealed that these systems tend to avoid configurations exhibiting causal pathologies, such as closed timelike curves, suggesting an underlying fundamental causality at play. The research demonstrates that the analog system becomes unstable before such problematic configurations can fully develop, indicating a self-regulating mechanism preventing the emergence of problematic spacetime geometries. Further analysis of systems with a quantum substrate showed that superpositions of states leading to drastically different emergent geometries are highly unstable, suggesting a dynamic suppression of configurations deviating from well-behaved causality. The team then turned to the construction of black hole models, successfully creating asymptotically flat black holes with locally vacuum toroidal horizons in four dimensions.

These models, built using thin shells and interpolating regions, feature a non-singular exterior region and necessitate violations of standard energy conditions, which the research explicitly characterizes. Furthermore, the study re-examined classical compactness bounds, the Buchdahl and Bondi bounds, for spherically symmetric stellar objects. Analysis demonstrates that relaxing certain assumptions underlying these bounds allows for circumvention of the limits, illustrated through physically simple models mirroring scenarios found in existing literature. These findings suggest that physically realistic scenarios may indeed violate the assumptions of these classical bounds, opening new avenues for understanding the limits of stellar structure.

Emergent Gravity, Singularities, and Energy Conditions

This work investigates emergent theories of gravity, exploring how gravitational phenomena might arise from more fundamental underlying principles rather than being a fundamental force themselves. The research offers a systematic analysis of the conceptual foundations of these theories, particularly focusing on the role of background structures and the implications of assuming the absence of singularities and horizons. By employing simplified models, the team clarifies the physical interpretation of these concepts and highlights their connections to existing literature. The analyses demonstrate that certain limits on theoretical predictions can be surpassed by relaxing specific assumptions, such as those related to energy conditions.

This suggests that modifying these foundational hypotheses can broaden the scope of viable emergent gravity models. The research acknowledges that the conclusions are framed within specific assumptions and that further investigation is needed to fully understand the implications of these findings. Future work could explore the consequences of different energy conditions and investigate the potential for developing more comprehensive emergent theories that incorporate these insights. This systematic approach contributes to a deeper understanding of the conceptual landscape of emergent gravity and provides a foundation for future theoretical developments in the field.