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posted 12mo ago by Olin Lathrop‭

Back when what light is and how it propagates was poorly understood, people naturally related it to sound.  Sound propagates thru a <i>medium</i>, like air.  Light was therefore assumed to propagate thru a medium too.  This hypothetical medium was referred to as the <i>ether</i>.
This not only shows that light doesn't propagate thru a medium, but that there is no such thing as an absolute "going fast".  There is no ether sea that you can measure speed relative to.  That's what relativity is all about.