Ordinary wormholes (2503.12227v1)

Abstract: Euclidean wormholes have played a key role in the recent ``disorder averaged" approaches to quantum gravity and holography, but are typically only considered in somewhat special theories of gravity, such as theories in low dimensions or theories with exotic matter content (such as axions). These exotic theories have advantage that both the matter and gravitational sectors can be treated completely classically. However, once this constraint is relaxed we find that Euclidean wormholes arise generically, with no special constraints on the matter content. The key point is that there is a self-consistent approximation where the metric is treated classically but matter is treated quantum mechanically. The resulting wormholes are {\it ordinary} in the sense that they rely on the usual approximations used in, for example, the construction of star or FRW solutions in general relativity. Indeed, these are the Euclidean continuations of ordinary FRW solutions with big bang/crunch singularities. We describe several examples of these ordinary wormholes and discuss the relation to existing constructions and the holographic interpretation in terms of a dual CFT.

An Overview of "Ordinary Wormholes"

The paper "Ordinary Wormholes" by Alexander Maloney, Viraj Meruliya, and Mark Van Raamsdonk explores the construction and interpretation of Euclidean wormhole spacetimes in the context of quantum gravity and holography. It demonstrates that Euclidean wormholes, commonly associated with exotic theories, can also arise in more conventional settings within gravitational theories when incorporating quantum effects into matter fields. This work provides foundational insights for researchers interested in the semiclassical gravity and holographic duality frameworks.

Key Insights and Methodology

The authors investigate wormhole solutions wherein the metric is treated classically, and the matter is described via quantum mechanics. They present a self-consistent approximation that maintains viability without the exotic matter typically deemed necessary for wormhole stabilization. This method draws parallels with approximations in standard cosmological models such as Friedmann-Robertson-Walker (FRW) solutions.

The paper's approach includes:

• Extending Euclidean Wormhole Concepts: By relaxing traditional constraints on matter content, the research establishes that such wormholes naturally occur under a broader range of conditions. This discovery is instrumental in understanding the geometric and field-theoretic conditions leading to wormhole solutions without relying on specialized or non-standard theoretical structures.
• Analyzing Star-like and FRW Structures: The paper identifies that these wormholes align with familiar cosmological solutions, specifically as Euclidean continuations of FRW spacetimes featuring big bang/crunch singularities, thereby bridging a gap between cosmological and wormhole physics.

Theoretical and Practical Implications

The research contributes to both the theoretical landscape of quantum gravity and practical interpretations of holography:

• Influence on Semiclassical Gravity: It underscores the potential for Euclidean wormholes to emerge as substantial players in quantum gravitational path integrals. These structures may indicate where semiclassical tools deviate from predicting a complete ultraviolet (UV) consistent theory.
• Holographic Insights: The dual perspective in terms of Conformal Field Theories (CFTs) offers a fresh angle on holographic principles, especially given that such wormhole solutions propose interpretations involving dual non-factorizable states in boundary CFTs.
• Handling Quantum Corrections: The work invites further speculation and investigation into how these wormholes might reshape our understanding of non-perturbative features in gravity, specifically offering or requiring consideration of ensembles in holography—a topic ripe for ongoing exploration and debate.

Future Directions in Research

The paper’s results open numerous avenues for future research:

• Generalization to Higher Dimensions: Extending these ideas beyond the three-dimensional constructs considered might yield new insights applicable to higher-dimensional theories where quantum gravity theories such as string theory are formulated.
• Experimental Prospects: Though theoretical at present, the implications could spur conceptual frameworks for netting realistic quantum gravity signatures that influence astrophysical or cosmological observations.
• Non-Perturbative Dynamics: The results could inform new techniques for tackling long-standing puzzles, like the black hole information paradox, by evaluating the role of such wormhole contributions within broader gravitational systems.

In summary, the paper "Ordinary Wormholes" systematically enlarges the understanding of when and how Euclidean wormholes can form, presenting them not as theoretical curiosities but as integral elements of semiclassical gravity and holography. This research provides a noteworthy leap in aligning quantum descriptions with classical intuitions, paving the way to deepen our conceptual buildout of how diverse gravitational phenomena relate to each other in both mathematical and physical terms.