Is Space Really Expanding? A Counterexample
Abstract
In all Friedman models, the cosmological redshift is widely interpreted as a consequence of the generalrelativistic phenomenon of expansion of space. Other commonly believed consequences of this phenomenon are superluminal recession velocities of distant galaxies, and the distance to the particle horizon greater than ct (where t is the age of the Universe), in apparent conflict with special relativity. Here, we study a particular Friedman model: empty universe. This model exhibits both cosmological redshift, superluminal velocities and infinite distance to the horizon. However, we show that the cosmological redshift is there simply a relativistic Doppler shift. Moreover, apparently superluminal velocities and ‘acausal’ distance to the horizon are in fact a direct consequence of specialrelativistic phenomenon of time dilation, as well as of the adopted definition of distance in cosmology. There is no conflict with special relativity, whatsoever. In particular, inertial recession velocities are subluminal. Since in the real Universe, sufficiently distant galaxies recede with relativistic velocities, these specialrelativistic effects must be at least partly responsible for the cosmological redshift and the aforementioned ‘superluminalities’, commonly attributed to the expansion of space. Let us finish with a question resembling a BuddhismZen ‘koan’: in an empty universe, what is expanding?
 Publication:

Old and New Concepts of Physics
 Pub Date:
 March 2007
 DOI:
 10.2478/v1000500700022
 arXiv:
 arXiv:astroph/0601171
 Bibcode:
 2007ONCP....4...15C
 Keywords:

 Astrophysics
 EPrint:
 12 pages, no figures