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Does the Universe Expanding Make a Sound?

  1. Mar 16, 2013 #1
    Due to the doppler effect, when the source of the sound is moving away from the observer, the sound waves are spread out. Light waves also hace this effect and when a star or galaxy is moving away from us, we see the light wth a slight reddish tint. So my quesion is, does the expansion of the universe make sound waves that we can observe?
     
  2. jcsd
  3. Mar 16, 2013 #2
    Do you know what a "SOUND" wave is and what is required to make/hear one?

    I hope you do realize that one of the most proven things in physics is that in space there is no atmosphere no "air" as we would say.
    Sound is nothing more than just a vibration of a medium like air that is made of matter at a certain frequency.Now you can have this vibration going on in air in water in metals and rocks and all kinds of "mediums".
    In space you just don't have this medium so there can be no sound wave, because one has no place where to be.
    We do have light from all parts of space , but light is a Em field and travels by it's force carrier photon which is massless and doesn't need a special medium for it to travel through.The same goes for gravity but not sound.
     
    Last edited: Mar 16, 2013
  4. Mar 16, 2013 #3
    Thanks. And yea I know what a sound wave is.
     
  5. Mar 16, 2013 #4

    Drakkith

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    Staff: Mentor

    Expansion is just that. Expansion. Things move further apart over time. Nothing gets closer to anything else, and no sound or light is emitted because of this expansion.
     
  6. Mar 16, 2013 #5
    What you might be thinking of is sound as perturbation waves in the pressure field. If you adopt a more general definition of pressure, which may include the analogous pressure field in the cosmological fluid model of the universe, then you can define sound waves within the universe as acoustic oscillations of the universe's density at recombination...

    This is pretty standard early universe cosmology analysis, and one of the more famous graphs comes from it:

    cmb-cmbpowerspectrum.png

    They are not sound waves, but they are something vaguely analogous.
     
  7. Mar 16, 2013 #6
    But then why do we see galaxies that are belived to be moving away from us with a slight redish tint?
     
  8. Mar 16, 2013 #7

    phinds

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    Huh? Of course they are redshifted. They are moving away from us. Would you expect something different?

    EDIT: google "cosmological red shift" and "doppler red shift"
     
  9. Mar 16, 2013 #8

    Drakkith

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    Staff: Mentor

    The light is not emitted because of expansion. It is emitted by normal means, such as hot objects like stars, or ionized gas recombining with electrons. The expansion merely causes the light waves to be stretched out and redshifted as a result.
     
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