Black Hole Remnants and the Information Loss Paradox (1412.8366v3)

Abstract: Forty years after the discovery of Hawking radiation, its exact nature remains elusive. If Hawking radiation does not carry any information out from the ever shrinking black hole, it seems that unitarity is violated once the black hole completely evaporates. On the other hand, attempts to recover information via quantum entanglement lead to the firewall controversy. Amid the confusions, the possibility that black hole evaporation stops with a "remnant" has remained unpopular and is often dismissed due to some "undesired properties" of such an object. Nevertheless, as in any scientific debate, the pros and cons of any proposal must be carefully scrutinized. We fill in the void of the literature by providing a timely review of various types of black hole remnants, and provide some new thoughts regarding the challenges that black hole remnants face in the context of the information loss paradox and its latest incarnation, namely the firewall controversy. The importance of understanding the role of curvature singularity is also emphasized, after all there remains a possibility that the singularity cannot be cured even by quantum gravity. In this context a black hole remnant conveniently serves as a cosmic censor. We conclude that a remnant remains a possible end state of Hawking evaporation, and if it contains large interior geometry, may help to ameliorate the information loss paradox and the firewall controversy. We hope that this will raise some interests in the community to investigate remnants more critically but also more thoroughly.

• The paper proposes that black hole remnants could encapsulate lost information, addressing the conflict between Hawking radiation and quantum unitarity.
• It applies quantum gravity frameworks to analyze how remnants reconcile black hole entropy with their potentially vast internal structures.
• The study calls for further research into remnant stability and their impact on holographic principles and black hole complementarity.

Overview of the Paper: Black Hole Remnants and the Information Loss Paradox

This paper explores the concept of black hole remnants within the framework of quantum gravity, addressing their role in resolving the longstanding information loss paradox and the more recent firewall controversy. Since Stephen Hawking's seminal work introduced the phenomenon of black hole evaporation via Hawking radiation, a fundamental question has persisted: does this radiation carry the information of all the matter that fell into the black hole, thus preserving unitarity, or is such information permanently lost?

Key Concepts and Theoretical Challenges

The information loss paradox arises from the apparent contradiction between two central tenets of quantum mechanics: the preservation of information (unitarity) and the complete thermal nature of Hawking radiation, which, in its simplest form, suggests that it is devoid of any relic remaining from the matter that formed the black hole.

Moreover, the notion of the black hole firewall, introduced to address potential issues with quantum entanglement across the event horizon, poses additional challenges to conventional black hole complementarity—a principle which upholds classical descriptions that anything can cross the horizon smoothly without encountering drama or unusual phenomena.

Black Hole Remnants as a Potential Solution

One proposed resolution discussed extensively in the paper is the possibility that black holes may leave behind remnants: stable or quasi-stable objects that encapsulate all the information of the original matter. These remnants challenge traditional interpretations of the Bekenstein-Hawking entropy, namely, that it reflects purely the surface area of the black hole's event horizon rather than encompassing the details of its interior geometry.

The existence of these remnants, however, raises contentious questions, not least of which are the difficulties of reconciling their presence with standard quantum field theories. If remnants have Planck-scale dimensions but contain significant amounts of information, they might violate principles like the covariant entropy bound or lead to an unwelcome overproduction issue, where remnants could be ubiquitously formed via quantum processes.

Implications and Outlook

Despite the challenges, remnants remain a theoretically viable extension to the landscape of solutions to the information paradox. They highlight areas where our understanding of black holes, entropy, and quantum gravity still intersect the boundaries of current physics. Discussions within the paper suggest that addressing strange states, such as those with irregular internal geometries—"bags of gold" or monsters—might provide insights into how remnant scenarios can fit into a coherent quantum theory of gravity.

The paper encourages a reevaluation of black hole interiors and their implications for gravitational entanglement—all while emphasizing the need for rigorous mathematical formulations that can address how remnants, with potentially large interior volumes and massless states, contribute to or contradict the holographic principle central to AdS/CFT correspondences.

Conclusion

The paper concludes with a call to the scientific community to investigate the potential role of black hole remnants more critically and thoroughly. Given the breadth of theoretical avenues from string theory to loop quantum gravity and non-commutative formulations, the ultimate resolution to the black hole information paradox—and the accompanying firewall problem—may reside in understanding remnants' place within the cosmos and their compatibility with fundamental physical laws. By examining remnants through the lens of quantum gravity and cosmology, researchers might uncover novel insights into the universe's mysteries and the ultimate fate of information therein.