Re: [Phys-L] speed c

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2013, Mar 14, , at 13:42, Bill Nettles <bnettles@uu.edu> wrote:

> I was having a discussion with a friend about light, spacetime, max speeds, etc. I mentioned that light passing through matter travels slower than c. He responded, "Then because there isn't any perfect vacuum [SpaceWeather.com today reports 8 protons/cm^3], light never really travels at c." Thinking about this drove me to Feynmann, Vol I, Chap 31 to read about refractive index.
>
> What I gleaned from a quick reading:
>
> 1)      All E&M fields (and changes thereto ) propagate at c ... always.


I'd read about slow light and see F. et aliorum explanation applies.


http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-33-1-46

http://arxiv.org/abs/1104.0158

bc   read this in that former artist's text also.