Is there a medium in which sound travels faster than light?

  • Thread starter Kyuutoryuu
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  • #26
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In space no one can hear you scream.Having mentioned that a powerfull laser will make a sound when it impacts other objects.So does such a laser make a noise in the not so perfect vacuum of space and is the sound wave produced always behind the impacted object.
 
  • #27
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The Wiki mentions refractive indicies up to 2, but I've never heard of a theoretical upper limit on refractive index. Could it theoretically be arbitrarily large?
I found a Wiki list with index of refraction as high as ~4 (Germanium): http://en.wikipedia.org/wiki/List_of_refractive_indices
I don't think there is a theoretical maximum, just a practical one.
 
  • #28
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Yes, there is a way. Light can be slowed down, even stopped using electromagnetically induced transparency (EIT). I presume that sound could travel through the same crystal medium at some velocity >0. So there you have it now what are you going to do with it? The world wants to know.
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.033601
I think that your presumption is unlikely to be correct. These experiments require very careful isolation from the external environment. I would presume that any vibrations would cause the light to be released immediately and then proceed faster than the vibration. However, in any case the cited article does not provide any data about the speed of sound in the material.
 
  • #29
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Certainly. Harvard physicists have succeeded in bringing down the speed of light to well below that of sound.
http://news.harvard.edu/gazette/1999/02.18/light.html
This is work on Bose Einstein condensates. I already provided a link earlier discussing the speed of sound in them. It is even slower.

Note, a material where the speed of light is slower than the speed if sound would be very bizarre, and I don't think one exists, but such a material wouldn't "break" relativity.
 
  • #30
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This is work on Bose Einstein condensates. I already provided a link earlier discussing the speed of sound in them. It is even slower.

Note, a material where the speed of light is slower than the speed if sound would be very bizarre, and I don't think one exists, but such a material wouldn't "break" relativity.
Yes, isn't one of the dominant energy conditions that the speed of sound be less than the speed of light?
 
  • #31
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Yes, isn't one of the dominant energy conditions that the speed of sound be less than the speed of light?
The speed of sound needs to be less than the invariant speed, c, which is the speed of light in vacuum, not in a material.
 

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