Speed of sound in vacuum I am not a scientist but I have a question about speed of sound in vacuum. All I know is that the speed of sound $v$ in a medium is given by formula
$$v= \sqrt{\frac E\rho},$$
where $E$ is elasticity and $\rho$ is density.
And according to a scientist, vacuum is a medium which has elasticity highest comparison to other and it's density is so less it is nearer to zero. Then, from above, the value of velocity of sound in vacuum should be the greatest among all other medium? Am I wrong?
 A: Yes, you're wrong.
Sound waves are small compressions (oscillations) of an elastic medium, travelling through that same elastic medium (as a wave). Air, liquids or solids are typical elastic media through which sound waves can travel.
Vacuum however contains no matter and cannot sustain sound waves at all.
Watch this video on a bell in a vacuum jar.
A: Sound wave is a longitudinal elastic wave which strictly demands the presence of a material medium for its propagation from one place to another. So sound cannot propagate in vacuum (which actually has no mass and thereby no density), leave alone the speed of sound in vacuum.
Moreover, if we consider the definition of elasticity, I think this concept does not really apply to vacuum. Also, for the highest speed of sound, it depends on several external factors like temperature, humidity, material medium of propagation etc. For more information regarding this, you can check the following link.
A: Sound need a medium to travel or to propagate. In Vacuum no medium will present. So, I think velocity of sound in vacuum is zero 000.
