On Jul 5, 4:50*pm, "Sal" wrote:
I infer that a perfect vacuum wouldn't propagate EM waves.

Wrong - a perfect vacuum teems with the quantum soup and therefore
does propagate EM waves. What will not propagate EM waves is the
absence of the quantum soup, i.e. absolute nothingness which surrounds
the known universe..
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73, Cecil, w5dxp.com