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| Soniferous Aether |
 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. |
Explanation
This comic makes a joke on the speed of light and the speed of sound, and the way in which speed and light travel.
Beginning in the late 1690s, scientists posited a luminiferous aether to explain properties of light (especially its ability to travel in a vacuum) which should not be possible for a wave. The 1887 Michelson–Morley experiment disproved its existence, and nowadays this property is explained by wave–particle duality, which says that light can act as both a particle and a wave.
In this comic, Cueball & Ponytail are also suggesting a luminous aether for the speed of sound instead. However, this 'aether' is actually air, pointeed out in the text below. Reinventing things on first principles has been discussed before multiple times on xkcd.
The title text references Albert Einstein's thought experiment where he imagined riding alongside a light particle/wave (which was referenced in 2959: Beam of Light), but with a sound wave instead. Travelling at the speed of sound can be accomplished with a fast airplane. Usually these would be military aircraft, though the Tu-144, Concorde, and (briefly) a DC-8 were commercial aircraft that did achieve supersonic flight.
Transcript
- [Ponytail is addressing an unseen audience in front of her while she holds her hand out towards them. She is standing on a podium with Cueball behind her. Cueball holds an arm out behind him indicating a screen behind him showing a graph with three sinus waves with different wavelengths. The top has two cycles, the middle four cycles and the bottom one cycle.]
- Ponytail: We all know the speed of light is constant for all observers.
- Ponytail: But our experiments show that the speed of sound changes based on the observer's motion.
- Ponytail: Thus, we posit the existence of the Soniferous Aether, a medium that fills the space between us and carries sound waves.
- [Caption below the panel:]
- Sometimes physicists forget that air exists and rediscover it from first principles.
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