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xkcd #3238: Soniferous Aether
(imgs.xkcd.com)
Title text:
Imagine you could ride alongside a sound wave. It would probably be pretty cool, right? We're putting in a departmental budget request to buy a really fast plane so we can check it out.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3238/
From my understanding, a fair amount of the "delay" is caused by the absorption and remission of photons, which takes time. The photon you measure at one end is often not the same photon that was sent. I could be wrong though, if anyone wants to let me know.