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What are the limits of redshift?

  1. Oct 2, 2011 #1
    Does anyone know what the limit is for light from distant objects to be so redshifted that they become undetectable? Could there be a way in detecting objects beyond this barrier? Would any wavelength at all be detectable?
     
  2. jcsd
  3. Oct 3, 2011 #2

    Chalnoth

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    I don't think there is any sort of fundamental limit. There may be practical limits, but no fundamental one.
     
  4. Oct 3, 2011 #3
    After an infinite amount of time the wavelength takes for a full propogation will become infinitely long and would therefore require an infinite amount of time to detect it.

    I think this would be the practical limit - not really a limit but i think you get my meaning.
     
  5. Oct 3, 2011 #4
    Interesting comments, thanks. Is there then a way of detecting extremely redshifted light wavelengths that could indicate the presence of objects beyond the visible universe, and would the means of observation need to be purely determined by and limited to time? Observations in the visible light spectrum might not be possible of highly redshifted objects but what about shorter wavelengths? Wouldn't they still be detectable, like redshifted x-rays and gamma rays? And, if what you say is true about a full propagation ultimately taking an infinite amount of time, does this in turn mean that there are an infinite amount of wavelengths?
     
  6. Oct 3, 2011 #5

    phinds

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    Detecting things beyond the observable U is not possible. In fact, visual (light based) observation is only possible up to "the surface of last scattering" which happened about 400,000 years after the U began. You'd probably find it interesting to read up on it and why it exists. What we SEE from the surface of last scattering is called the Cosmic Microwave Background.
     
  7. Oct 3, 2011 #6

    Chalnoth

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    Nah, because before the surface of last scattering that phinds points out, our universe was opaque. So we can see stuff that was emitted some 13.7 billion light years ago, no earlier.
     
  8. Oct 4, 2011 #7

    phyzguy

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    Just an additional comment. The light from the surface of last scattering, which we call the CMB (Cosmic Microwave Background) is at a redshift of z~1000. So this represents a practical limit for redshift of EM radiation, because beyond this the universe was opaque, as has been said. To see further back we would need to employ some other type of radiation. Use of neutrinos or gravitational waves has been proposed as a way to see further back, but these are very difficult to detect.
     
  9. Oct 4, 2011 #8
    Yes, I've read up on the CMB. One thing that puzzles me about the actual size and topology of the observable universe is that everywhere we look when we use deep field observation we are looking towards the origin of the universe even though we can be looking in diametrically opposite directions. Some estimates I've come across of the size of the universe range from 26 to 50 billion light years across. So if there's an intervening distance of 13.7 x 2 billion lightyears between what we observe as diametrical opposites, will light ever reach across the diameter from one side to the other, or because of the increasing rate of the expansion of space, will light never make it? According to the inflation theory, during the inflation period space exanded faster than light, then slowed and then started to speed up again. So if the rate of expansion increases forever, won't it again surpass c?
     
  10. Oct 4, 2011 #9

    phinds

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    no, the size of the UNIVERSE is not likely to be 50B LY across, that's the size of the OBSERVABLE universe (and actually it's the radius not the diameter) and they are very different things.

    The universe is already expanding faster than light, if you consider, for example, two points on opposite sides of our observable universe and for things far outside our OU, it's going WAY faster since the relative speed of two points due to expansion is a function of how far apart they are ... the farther apart they are the faster they are going relative to each other.
     
  11. Oct 5, 2011 #10

    Chronos

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    The observable universe is just that - the portion we can measure. How big it may, or may not, be NOW is irrelevant.
     
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