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IOR of Gold is 0.47.

How is it possible gold density is less than a vacuum? After all, physically, a gold ingot is denser than air, or am I wrong?

Why index is 0.47?

I'm confused.

Jo K
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  • It is for modeling reflectivity in ray-tracing programs but would need a frequency dependence to get the color of gold. –  Apr 12 '20 at 11:48
  • The refractive index can be less than 1 if the phase velocity exceeds $c$, see https://physics.stackexchange.com/questions/353306/can-a-medium-can-have-refractive-index-less-than-the-reference-refractive-index – Clara Diaz Sanchez Apr 12 '20 at 11:56

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The refractive index is a complex valued quantity. For a metal it is not at all proportional to density. This is only the case for a gas or at very short wavelengths. For gold it varies quite a bit in the optical range so the statement that it is 0.47 is oversimplified. Gold is a special case as its color is related to relativistic contraction of its 6s orbital, which make up its conduction band. Find the energy levels of the neutral gold atom here and more about its metallic refractive index here.

my2cts
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