The key point about sound waves is that sound waves must travel through some type of medium. The individual atoms or molecules in the medium vibrate to propagate the sound wave.
If there is no medium, there are no atoms or molecules to vibrate and propagate the sound wave. The medium can be a gas, liquid, solid, or plasma (a hot gas in which electrons have escaped from atoms). There must however be a medium to propagate sound waves.
Sound waves can not pass through a vacuum.
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