http://arxiv.org/pdf/1302.6165v1.pdf The quantum vacuum as the origin of the speed of light, M. Urban, F. Couchot, X. Sarazin and A. Djannati-Atai: "When a real photon propagates in vacuum, it interacts with and is temporarily captured by an ephemeral pair. As soon as the pair disappears, it releases the photon to its initial energy and momentum state. The photon continues to propagate with an infinite bare velocity. Then the photon interacts again with another ephemeral pair and so on. The delay on the photon propagation produced by these successive interactions implies a renormalisation of this bare velocity to a finite value."
This is not very reasonable but still it may generate an extremely heretical thought:
If photons coming to Earth from distant astronomical objects constantly bump into vacuum constituents and slow down as a result, this could explain the Hubble redshift without recourse to universe expansion, Big Bang etc.
http://www.astrosurf.com/quasar95/exposes/galaxies.pdf "Paradoxalement, Hubble n'admit jamais cette théorie du Big-Bang et de l'expansion de l'univers. Il défendit la théorie de "la lumière fatiguée" reprise par Pecker, Vigier et Alton Arp. Dans cette théorie, la lumière en parcourant de longues distances perd une partie de son énergie et de sa vitesse, et se décalent vers le rouge."
http://www.springerlink.com/content/w6777w07xn737590/fulltext.pdf Astrophys Space Sci (2009) 323: 205211, Misconceptions about the Hubble recession law, Wilfred H. Sorrell: "Reber (1982) made the interesting point that Edwin Hubble was not a promoter of the expanding universe idea. Some personal communications from Hubble reveal that he thought a model universe based upon the tired-light hypothesis is more simple and less irrational than a model universe based upon an expanding space-time geometry."
http://canadafreepress.com/index.php/article/23682 "In 1929, when spectral analysis revealed a 'red shift' in distant galaxies, astronomer Edwin Hubble speculated that this might be due to acceleration away from Earth and a possible expanding universe. Before he could reflect on other possible explanations, a radio interview stumbled onto the phrase "Big Bang" and a run-away train left the station. Dr Hubble was uncomfortable with both the concept and the catchy nick-name, but he had a 'conflict of interest' on this issue. In a Times magazine interview, on Dec 14, 1936, titled "Science: Shift on Shift", Dr. Hubble made his opposition clear. One reason that he was not more forceful was because he was begging the government for funding of the Mount Palomar telescope."
http://www.time.com/time/magazine/article/0,9171,757145,00.html Monday, Dec. 14, 1936: "Other causes for the redshift were suggested, such as cosmic dust or a change in the nature of light over great stretches of space. Two years ago Dr. Hubble admitted that the expanding universe might be an illusion, but implied that this was a cautious and colorless view. Last week it was apparent that he had shifted his position even further away from a literal interpretation of the redshift, that he now regards the expanding universe as more improbable than a non-expanding one."