Talk:Refractive index

Poincaré symmetries

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From the article:

"If in a given region the values of refractive indices n or ng were found to differ from unity (whether homogeneously, or isotropically, or not), then this region was distinct from vacuum in the above sense for lacking Poincaré symmetry."

First, being that "refractive index" is such a common phenomenon it should be addressed in layman's words. If mentioning the Poincaré symmetry would be interesting I think it would be better if there would be a separate section about that near the end of the article.

Second, I don't fully understand why the entire Poincaré group is considered. What do the "boosts" from this symmetry group have to do with an isotropic material? Moreover, does it make sense to talk about "to differ from unity (whether homogeneously, or isotropically, or not)"? what's the difference between a homogeneously different than unity refractive index and an isotropically different than unity one?

Recent edits by Maggyero

Hi Maggyero. You have done some improvements to the article, but also many changes that made it worse. Please make changes only when there is a reason to, often things are the way they are for a reason. I will revert a number of your recent edits, and give the explanations here:

• The reason we write speed of light instead of phase velocity in the lead is that most readers do not know what phase velocity is and we cannot explain that in the lead. Both are correct, and the more exact definition is given directly after the lead where there is space to explain phase velocity.
• About the change from LaTeX to HTML the Wikipedia Manual of Style reads: "One should not change formatting boldly from LaTeX to HTML, nor from non-LaTeX to LaTeX without a clear improvement. Proposed changes should generally be discussed on the talk page of the article before implementation."
• The speed of light c should be in italics
• The phase subscript to indicate phase velocity has a purpose and follows the reference.
• This article is not intended only for a scientific audience, so not everyone will now that unity is the same as 1.
• X-ray and x-ray are both accepted, so please keep with the original style of the article or discuss it here.
• having a figure above the "main article" tag may look strange in the wikicode but it places the figure better in the article.
• S and p-polarized light is usually written with lower case s and p, see Polarization_(waves)#s_and_p_designations.
• In the Refractive index#Relative permittivity and permeability you introduced new notation that differs from what is used previously in the article. I still kept this since it was an overall improvement of this section, but will come back to it later.

I haven't done the changes yet and haven't had time to go through all your edits but will come back to this soon. Ulflund (talk) 17:28, 12 March 2015 (UTC)

Microscopic explanation: source?

Microscopic explanation: source? — Preceding unsigned comment added by 77.199.97.101 (talk) 08:20, 27 June 2015 (UTC)

Neglecting permeability when relating to permittivity

The reason, and particularly the limitations, of the frequent approximation mu=1 used when relating n=sqrt(epsilon mu)=sqrt(epsilon), need be explained. The version until now has been citing Urzhumov et al., "Electric and magnetic properties of sub-wavelength plasmonic crystals", Journal of Optics A, 7, S23(2005) -- however, that paper only talks about the unusual properties of metamaterials, but does not explain why (nor, as far as I can see, even explicitly state that) the "usual" materials have mu=1. I am removing this reference as irrelevant and placing the "citation needed" instead. 73.189.243.193 (talk) 10:20, 23 November 2015 (UTC)