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2 results

Why Do We Want a Theory of Quantum Gravity?

Why Do We Want a Theory of Quantum Gravity?
  • Karen Crowther
  • Published online:
    28 February 2025
    Print publication:
    27 March 2025
    • Element
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  • The search for a new scientific theory is typically prompted by an encounter with something in the world that cannot be explained by current theories. This is not the case for the search for a theory of quantum gravity, which has been primarily motivated by theoretical and philosophical concerns. This Element introduces some of the motivations for seeking a theory of quantum gravity, with the aim of instigating a more critical perspective on how they are used in defining and constraining the theory sought. These motivations include unification, incompatibilities between general relativity and quantum field theory, consistency, singularity resolution, and results from black hole thermodynamics.

  • 10 - Why Black Hole Information Loss Is Paradoxical

  • from Part III - Issues of Interpretation
  • Edited by Nick Huggett, University of Illinois, Chicago, Keizo Matsubara, Uppsala Universitet, Sweden, Christian Wüthrich, Université de Genève
  • Book:
    Beyond Spacetime
    Published online:
    24 April 2020
    Print publication:
    14 May 2020, pp 209-236

  • Summary

    I distinguish between two versions of the black hole information-loss paradox. The first arises from apparent failure of unitarity on the spacetime of a completely evaporating black hole, which appears to be non-globally hyperbolic; this is the most commonly discussed version of the paradox in the foundational and semipopular literature, and the case for calling it `paradoxical' is less than compelling. But the second arises from a clash between a fully statistical-mechanical interpretation of black hole evaporation and the quantum-field-theoretic description used in derivations of the Hawking effect. This version of the paradox arises long before a black hole completely evaporates, seems to be the version that has played a central role in quantum gravity, and is genuinely paradoxical. After explicating the paradox, I discuss the implications of more recent work on AdS/CFT duality and on the `Firewall paradox', and conclude that the paradox is if anything now sharper. The article is written at a (relatively) introductory level and does not assume advanced knowledge of quantum gravity.