Reply to the Comment on: The quantum vacuum as the origin of the speed of light Marcel Urban, François Couchot, Xavier Sarazin and Arache Djannati-Ataï Eur. Phys. J. D, 67 11 (2013) 220 Published online: 01 November 2013 DOI: 10.1140/epjd/e2013-40464-y