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Planck evidence for a closed Universe and a possible crisis for cosmology

Nature Astronomy volume 4, pages 196–203 (2020)Cite this article

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Abstract

The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in cosmic microwave background power spectra compared with that predicted in the standard Λ cold dark matter model, where Λ is the cosmological constant. A closed Universe can provide a physical explanation for this effect, with the Planck cosmic microwave background spectra now preferring a positive curvature at more than the 99% confidence level. Here, we further investigate the evidence for a closed Universe from Planck, showing that positive curvature naturally explains the anomalous lensing amplitude, and demonstrating that it also removes a well-known tension in the Planck dataset concerning the values of cosmological parameters derived at different angular scales. We show that since the Planck power spectra prefer a closed Universe, discordances higher than generally estimated arise for most of the local cosmological observables, including baryon acoustic oscillations. The assumption of a flat Universe could therefore mask a cosmological crisis where disparate observed properties of the Universe appear to be mutually inconsistent. Future measurements are needed to clarify whether the observed discordances are due to undetected systematics, or to new physics or simply are a statistical fluctuation.

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Fig. 1: Preference for a closed Universe, ΩK < 0, from Planck.
Fig. 2: Degeneracy between curvature and lensing.
Fig. 3: Curvature and shift in parameters.
Fig. 4: Tension with BAO.
Fig. 5: Tension with CMB lensing.
Fig. 6: Tension with cosmic shear measurements.
Fig. 7: Tension with combined data.
Fig. 8: Tensions in combined data.

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Data availability

The data that support the plots within this paper and other findings of this study are available at http://pla.esac.esa.int/pla/#cosmology or from the corresponding author upon reasonable request.

Code availability

All of the codes used to produce the presented results are publicly available. See Methods for more details.

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Acknowledgements

E.D.V. acknowledges support from the European Research Council in the form of a Consolidator Grant with number 681431. A.M. thanks the University of Manchester and the Jodrell Bank Centre for Astrophysics for hospitality. A.M. is supported by TAsP, iniziativa specifica INFN. We thank M. Melchiorri for discussions.

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Authors and Affiliations

  1. Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, UK

    Eleonora Di Valentino

  2. Physics Department and INFN, Università di Roma ‘La Sapienza’, Rome, Italy

    Alessandro Melchiorri

  3. Institut d’Astrophysique de Paris (UMR7095: CNRS & UPMC, Sorbonne Universities), Paris, France

    Joseph Silk

  4. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA

    Joseph Silk

  5. BIPAC, Department of Physics, University of Oxford, Oxford, UK

    Joseph Silk

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Contributions

E.D.V. performed all MCMC analyses, simulations and the Planck parameters analysis at different scales, produced all the figures, wrote the paper and helped with additional ideas. A.M. proposed the main idea, performed the tension analyses and wrote the paper. J.S. wrote the paper and helped with additional ideas.

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Correspondence to Alessandro Melchiorri.

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Di Valentino, E., Melchiorri, A. & Silk, J. Planck evidence for a closed Universe and a possible crisis for cosmology. Nat Astron 4, 196–203 (2020). https://doi.org/10.1038/s41550-019-0906-9

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