# Re: The speed of the speed of light.

John Holmes wrote:
Peter Moylan wrote:
J. J. Lodder wrote:
David Hatunen <hatunen@xxxxxxx> wrote:

On Sun, 13 Nov 2011 12:46:22 +0000, Peter Duncanson (BrE) wrote:

Is a perfect vacuum a perfect vacuum if it has photons in it?
No. Photons are mass.

<runs away and hides behind a rock>
Why? It's perfectly good question.

The perfectly good answer is that a vacuum is perfect
if the index of refraction of it equals one,
to the available accuracy of measurement.

In other words, if the refractive index is the same as the refractive
index of a vacuum. You test this by putting your vacuum next to the
other vacuum, and see what happens to light as it crosses the
boundary.

[A cat jumps out of a box and chases the spot of light.]

LOL.

--
Peter Moylan, Newcastle, NSW, Australia. http://www.pmoylan.org
For an e-mail address, see my web page.
.

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