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Age of Universe inaccurate?

  1. May 22, 2010 #1
    Age of Universe inaccurate??

    Hi. i have a question that could already been nullified.

    Reading about the CMB it occurred to me that normal light is around 370 - 770 nm in wavelength and a microwave could be upto 30cm long..
    That means light has been expanded a million fold?? (not sure) since the moment light could be emitted.

    Wouldnt that mean we have to take into account the expansion of light's wavelength into the age of CMB?? As it would reach us alot sooner than if light had a higher frequency...Or have we already done that..

    Thanks
     
  2. jcsd
  3. May 22, 2010 #2

    nicksauce

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    Re: Age of Universe inaccurate??

    That doesn't make sense. All light travels at the same speed.
     
  4. May 22, 2010 #3
    Re: Age of Universe inaccurate??

    its like a 1cm string travelling at c to reach a certrain distance but during the course of its journey the string becomes more liken 100km long.
     
  5. May 22, 2010 #4
  6. May 22, 2010 #5

    nicksauce

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    Re: Age of Universe inaccurate??

    A piece of string is something physical with physical extent. A photon is not like this. Loosely speaking, you can think of it as a point particle. Its frequency corresponds to how fast the electric field and magnetic field change direction.
     
  7. May 22, 2010 #6

    DaveC426913

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    Re: Age of Universe inaccurate??

    Sorry, you seem to be suggesting that visible light is somehow transformed into microwaves over time? Why do you think this?

    Are you talking about redshifting?
     
  8. May 23, 2010 #7

    Chronos

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    Re: Age of Universe inaccurate??

    Redshift does lower the energy of a photon - like a baseball caught by a retreating outfielder. Nothing mysterious about that.
     
  9. May 23, 2010 #8
    Re: Age of Universe inaccurate??

    yea..the wavelength of light is stretched...wouldnt that mean we would be able to perceive the light sooner???
     
  10. May 23, 2010 #9

    DaveC426913

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    Re: Age of Universe inaccurate??

    No. It still travels at the same speed. The attentuation does not make the beam reach its destination sooner.

    Intuitively, how could it? Going from visible light to microwaves is a one thousand-fold decrease in energy. The beam is one thousand times more "tired", as it were...
     
    Last edited: May 23, 2010
  11. May 23, 2010 #10

    Fredrik

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    Re: Age of Universe inaccurate??

    If we're talking about light emitted early in the history of an approximately homogeneous and isotropic universe, and I assume we are, then the redshift is caused by the expansion of space when the light is in transit. So the same thing that causes the redshift also forces the light to travel a longer distance than it otherwise would have. I guess you could say that we "perceive the light later", not sooner. Also, when the light gets here 13.7 billion years after it was emitted, the point in space where it was emitted it is about 46.5 billion light-years away. This figure is greater than 13.7 billion light-years because space has expanded.
     
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