Can the apparent expansion of the universe be attributed to an increasing vacuum refractive index ? X. Sarazin, F. Couchot, A. Djannati-Ataï and M. Urban Eur. Phys. J. C, 78 6 (2018) 444 Published online: 02 June 2018 DOI: 10.1140/epjc/s10052-018-5932-8