Could Speed of Light in Intergalactic Space be different?

Here is a thought. Is the speed of light the same in intergalactic space? The measurements of the speed of light seem to always be near stars, either on our end or near the star on the far end. The speed of light is a function of the permittivity and permeability of free space, both of which are derived experimentally and are not calculated from first principles. Could their values turn out to make the speed of light higher in parts of the universe that are not near any matter?

Could the constant speed of light have to do with how it is constant in matter? So the constant speed of light near earth would work for just the same reason speed of light is constant, but at a different speed, in glass and water. Gravity or some other force of nearby matter would be working on a large scale just like it works near atoms on a small scale.

Has anyone actually suggested that as a possibility? If not, why wouldn't that work?

http://en.wikipedia.org/wiki/Free_space

Even in classical physics it was realized [13][14] that the vacuum must have a field-dependent permittivity in the strong fields found near point charges.

http://en.wikipedia.org/wiki/Vacuum_permittivity

Vacuum permittivity (also called permittivity of free space or the electric constant) is the ratio D/E in free space.

8.8541878176… × 10−12 F/m (or C2N-1m-2),
c (or c0) is the speed of light in free space.[1]

http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29

Permeability varies with magnetic field. Values shown above are approximate and valid only at the magnetic fields shown. Moreover, they are given for a zero frequency; in practice, the permeability is generally a function of the frequency. When frequency is considered the permeability can be complex, corresponding to the in phase and out of phase response.




http://en.wikipedia.org/wiki/Intergalactic_space#Intergalactic_space


The density of the Universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to conditions in vast voids that have much lower density than the Universe's average. The temperature is only 2.73 Kelvin[14]. NASA's COBE mission(Cosmic Background Explorer) measured the temperature as 2.725 +/- 0.002 K.