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Redshift is due to the expansion of the universe

  1. Aug 21, 2010 #1
    Okay, from what I understand, the cosmological redshift is due to the expansion of the universe. I'm confused as to how this works. I don't understand why, if the universe is expanding, that the waves don't just have farther to travel. I also don't understand what is waving or why other things don't get 'redshifted'. Why isn't my bed farther from the wall than it was yesterday? Also, how do we know that the redshift isn't due to a heavy object near the 'edge' of the universe? Could someone explain redshifting in further detail?
  2. jcsd
  3. Aug 21, 2010 #2


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    Re: Redshifting

    The waves do have farther to travel. But since the light moves at the same speed regardless of how fast their source is moving (special relativity), its wavelength is different when viewed by someone who's not moving at the same speed as the source.

    It's not just light from distant galaxies that gets shifted. All light that's emitted by a moving (relative your frame of reference) object gets shifted (in your frame of reference).

    Then there's gravitational redshift, which is due to general relativity. In brief gravity curves space-time, so things in a gravitational field get 'stretched'; including light.
  4. Aug 21, 2010 #3
    Re: Redshifting

    None of this has anything to do with quantum physics, by the way, just classical wave theory.

    Gravity holds, say, earth to rotating around the sun; mostly electrostatic forces hold the earth together, and even gravity between your bed and the wall is much stronger than any separation effects. The cosmological expansion or redshift is called that because it's only over vast cosmological distances, not even within a galaxy for example, where the expansion overcomes everyday forces of attraction.

    They do, even sound waves from a passing vehicle or train for example.....

    You can get some physical explanations and diagrams here:
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