A short answer to critics of our article "Eppur si espande"   [arXiv:astro-ph/0612155]
  Recently [arXiv:astro-ph/0612155] we presented a formal mathematical proof that, contrary to a widespread misconception, cosmological expansion cannot be understood as the motion of galaxies in non-expanding space. We showed that the cosmological redshift must be physically interpreted as the expansion of space. Although our proof was generally accepted, a few authors disagreed. We rebut their criticism in this Note. 
Marek A. Abramowicz, Stanislaw Bajtlik, Jean-Pierre Lasota and Audrey   Moudens