Entanglement Islands Demonstrate No Global Symmetries and Preserve Information Loss in AdS/CFT Correspondence
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The fundamental nature of symmetries and information loss represents a long-standing challenge in theoretical physics, and recent work by Hao Geng from Harvard University, Jesús Huertas from Instituto Balseiro, and Andreas Karch from the University of Texas at Austin, along with Lisa Randall and Dawson Thomas from Harvard University, sheds new light on this connection.
The team investigates how information behaves when gravity in a theoretical spacetime couples with other, non-gravitational systems, a scenario where information might seemingly disappear. Their research demonstrates the existence of global symmetries within a specific framework known as “island setups”, and importantly, reveals these symmetries are intrinsically linked to broken gauge symmetries. This discovery not only provides concrete examples supporting the absence of true global symmetries, but also predicts a detectable “wet hair” effect, a measurable signal of information leakage into the surrounding environment, resolving a previously identified puzzle concerning black hole information. A central conjecture in quantum gravity posits the non-existence of global symmetries. As a fully unitary theory, quantum gravity does not permit information loss, a principle reflected in the AdS/CFT correspondence. This correspondence demonstrates that dynamical processes in Anti-de Sitter space are fully captured by a manifestly unitary Conformal Field Theory, also without information loss. Importantly, global symmetries within the Conformal Field Theory are dual to gauge symmetries in Anti-de Sitter space, consequently implying the absence of global symmetry in Anti-de Sitter space. This work provides concrete evidence supporting the connection between the non-existence of global symmetries and the absence of information loss. AdS/CFT Correspondence and Holographic Gravity This research builds upon extensive prior work in areas such as the AdS/CFT correspondence, quantum gravity, and black hole physics. Key themes include the AdS/CFT correspondence, which posits a duality between gravity in Anti-de Sitter space and a conformal field theory on its boundary, and investigations into quantum gravity and black holes, particularly concerning Hawking radiation and black hole entropy. Holographic entanglement entropy is a crucial tool for understanding spacetime geometry and quantum gravity, closely connected to the island proposal. Recent work focuses on the island proposal, a novel idea attempting to resolve the information paradox by suggesting that entanglement between the black hole interior and emitted radiation creates islands in spacetime. Researchers also explore boundary conformal field theories and investigate how to incorporate matter into the holographic duality using branes.
Entanglement Islands Resolve Black Hole Information Paradox Scientists have demonstrated a crucial connection between the absence of global symmetries and the preservation of information in quantum gravity, resolving a long-standing puzzle concerning black holes and information loss. The work centers on studying gravitational systems coupled with a non-gravitational “bath”, allowing researchers to explore scenarios where information might seemingly disappear. Experiments reveal the emergence of “entanglement islands” at late times, fundamentally altering the holographic picture of black holes and resolving inconsistencies with quantum mechanics.
The team measured the entanglement entropy of the bath subregion, finding that it initially grows with time, consistent with Hawking’s calculations of black hole radiation. However, the growth of entanglement is bounded by the finite Hilbert space of the black hole, defined by the Bekenstein-Hawking entropy formula. The emergence of the entanglement island at late time justifies this expectation and results in a time-dependence consistent with quantum mechanics. This discovery confirms that information is not lost but is instead encoded within the entanglement island, which increasingly overlaps with the black hole interior as time evolves. Measurements demonstrate that the physics within the region encompassing both the radiation and the island is fully captured by the radiation region itself. This holographic interpretation circumvents difficulties arising from the seemingly expanding interior of the black hole. Researchers found that entanglement islands universally exist in these setups, even without a black hole present, because the system can always be divided into a larger and smaller subsystem.
The team’s work establishes a consistency between global symmetries and entanglement islands, resolving a paradox related to the no-hair theorem.
Global Symmetries Preserve Unitarity in Gravity This research provides concrete evidence supporting the long-standing conjecture that the absence of global symmetries is fundamentally linked to the unitarity of quantum gravity. Scientists investigated a system where a gravitational spacetime is coupled to a non-gravitational “bath”, effectively creating a non-unitary gravitational theory, and explored the implications for global symmetries within this setup. By studying “island setups”, which incorporate entanglement islands crucial to recent advances in quantum gravity, the team demonstrated the existence of global symmetries even when the gravitational theory itself is not fully unitary. The key achievement lies in constructing examples, both from bottom-up and top-down perspectives, where global symmetries coexist with a non-unitary gravitational description. These symmetries are intrinsically linked to spontaneously broken gauge symmetries, a crucial detail that resolves a puzzle concerning black hole hair and explains how information can be retained. This work demonstrates a novel way holography can be realised, offering new insights into the relationship between gravity and quantum mechanics. 👉 More information 🗞 Wet Hair: Global Symmetries in Entanglement Islands 🧠 ArXiv: https://arxiv.org/abs/2512.11025 Tags: