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arXiv · 2507.08116

Singularities in loop quantum cosmology

Martin Bojowald·Manuel Diaz·Erick I. Duque
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Abstract

Quantum effects are expected to modify the cosmological dynamics of the early universe while maintaining some (potentially discrete) notion of space-time structure. In one approach, loop quantum cosmology, current models are shown here to either be incompatible with a consistent space-time structure, or to have physical singularities. The latter happens in spite of a non-zero scale factor in the isotropic background dynamics. A new effective Friedmann equation shows that a bounce is obtained at sub-Planckian densities, preceded by a physical singularity at infinite scale factor that resembles a time-reversed big rip. The entire phase is accompanied by rapid changes of the Hubble radius. In addition, a new version of perturbative inhomogeneity in loop quantum cosmology is introduced that maintains a consistent space-time structure and has a non-singular background dynamics.

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Martin Bojowald, Manuel Diaz, Erick I. Duque. 2025-07-10. Singularities in loop quantum cosmology. https://doi.org/10.1103/7g3z-2pgf

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