Abstract
Observations1,2 indicate that the expansion of the Universe is accelerating, which is attributed to a ‘dark energy’ component that opposes gravity3,4. There is a purely geometric test of the expansion of the Universe (the Alcock–Paczynski test), which would provide an independent way of investigating the abundance () and equation of state (
) of dark energy5. It is based on an analysis of the geometrical distortions expected from comparing the real-space and redshift-space shape of distant cosmic structures, but it has proved difficult to implement6,7,8,9,10,11,12,13,14,15,16,17,18. Here we report an analysis of the symmetry properties of distant pairs of galaxies from archival data19,20. This allows us to determine that the Universe is flat. By alternately fixing its spatial geometry at
and the dark energy equation-of-state parameter at
, and using the results of baryon acoustic oscillations, we can establish at the 68.3% confidence level that
and
.
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Acknowledgements
C.M. thanks J. Bel, P.-E. Crouzet, M. Davis, L. Guzzo, A. Blanchard, E. Branchini, P. S. Corasaniti, A. Ealet, A. Heavens, O. Le Fèvre, L. Moscardini, T. Schucker, P. Taxil and J. M. Virey for discussions. We thank R. Giovanelli, L. Lellouch and P. J. Morrison for reading versions of the manuscript. This paper has greatly benefited from the comments of M. Strauss. C.M. is grateful for support from the Projets Exploratoires Pluridisciplinaires: Physique Théorique et ses Interfaces of the CNRS and from specific project funding of the Institut Universitaire de France.
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C.M elaborated the testing formalism. C.M. and A.B. worked on the comparison of theoretical predictions with observations.
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The authors declare no competing financial interests.
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The posterior likelihood shown in Fig. 3 is available at http://www.cpt.univ-mrs.fr/~marinoni/Plik.tar.gz.
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Supplementary Information
The file contains Supplementary Text and Data I-VI, additional references, Supplementary Table 1 and Supplementary Figures 1-5 with legends. (PDF 1200 kb)
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Marinoni, C., Buzzi, A. A geometric measure of dark energy with pairs of galaxies. Nature 468, 539–541 (2010). https://doi.org/10.1038/nature09577
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DOI: https://doi.org/10.1038/nature09577
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