cjcampbell wrote:
> dweeb wrote:
>
>>cjcampbell wrote:
>>
>>>Okay, seriously, I know that the speed of light changes slightly
>>
>>OK, seriously, are we going to hear you start jabbering about the sea
>>of ether next?
>>...
>
>
> You were not aware, Dweeb, that what we call C, the speed of light, is
> the speed of light in a vacuum? The speed of light slows as it passes
> through any transparent medium; the denser and colder the medium the
> more it slows. This was discovered by Jean Foucault in 1850 and is
> considered one of the basics of physics. The amount that light slows is
> called the refractive index and this index is always greater than one.
> It is why refraction occurs.
Now this may really blow some minds considering the discussion
in this thread, but the index of refraction is NOT always
greater than one.
Look at Figure 4a at:
Spectroscopy of Rocks and Minerals, and
Principles of Spectroscopy
http://speclab.cr.usgs.gov/PAPERS.refl-mrs/refl4.html
where you will see the index of refraction of quartz
goes well below one, and in fact approaches zero at
a wavelength of 8.5 microns! (0.53 micron is green light,
0.7 deep red, 0.4 deep blue).
So, does the speed of 8.5 micron light in quartz go faster
than c, the speed of light in a vacuum? Yes and no!
The group velocity does not. That is the actual photon
packet. But the phase velocity does (the phase of the
electromagnetic radiation within the packet).
Roger
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