The hint made by the journal NATURE leads to an extremely dangerous (for both relativity and cosmology) conclusion: since the vacuum is filled with some material, the speed of light coming to us from distant astronomical objects may not be constant, and this explains the cosmological redshift:
http://www.sciscoop.com/2008-10-30-41323-484.html "Shine a light through a piece of glass, a swimming pool or any other medium and it slows down ever so slightly, it's why a plunged part way into the surface of a pool appears to be bent. So, what about the space in between those distant astronomical objects and our earthly telescopes? COULDN'T IT BE THAT THE SUPPOSED VACUUM OF SPACE IS ACTING AS AN INTERSTELLAR MEDIUM TO LOWER THE SPEED OF LIGHT like some cosmic swimming pool?"
http://bourabai.narod.ru/shtyrkov/evolution.htm "At present it is ascertained that vacuum is not an "empty space" - rather, it is a certain material continuum with quite definite although still unknown properties. This has been confirmed by observation of vacuum effects such as "zero-oscillations", vacuum polarization, particle generation by electromagnetic interactions. Therefore it is reasonable to suggest that physical vacuum could have internal friction due to its own small but real viscosity, which in the end produces redshift. (...) ...the differential equation for the speed of light dc/dt=-Ho*c(t)"