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Thread: Red shift

  1. #1 Red shift 
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    In whatever direction we observe the universe we are looking into the past. That means, assuming an expanding universe, that we are looking at a smaller universe, despite the evidence of our senses. If we look far enough, in any direction, we will be looking at a singularity or whatever existed at the origin of the universe. Although we appear to be seeing far distant objects as if in the inside of a vast sphere, these objects are in fact relatively close together in a much more compact volume. Any thought of some objects being separated by a distance, greater than could have been accomplished within the apparent lifetime of the universe without exceeding the speed of light, is spurious. Can anyone tell me the effect on the wavelength of light pass​ing through expanding space? Is it red shifted??


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    Any thought of some objects being separated by a distance, greater than could have been accomplished within the apparent lifetime of the universe without exceeding the speed of light, is spurious.

    You see to be confused. Objects are moving away from each other faster than the speed of light due to the expansion of the universe. Actual motion cannot exceed the speed of light.


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    Quote Originally Posted by BobJeffs View Post
    In whatever direction we observe the universe we are looking into the past. That means, assuming an expanding universe, that we are looking at a smaller universe, despite the evidence of our senses. If we look far enough, in any direction, we will be looking at a singularity or whatever existed at the origin of the universe.


    Actually, no. If we run the clock backwards from the present, we find the universe to be opaque before we get to the bang, so we cannot see earlier than that, regardless of the resolving power of future technology [a possible loophole, being explored theoretically, involves probing that early epoch using other than photons]. Google for the term "surface of last scattering".

    Although we appear to be seeing far distant objects as if in the inside of a vast sphere, these objects are in fact relatively close together in a much more compact volume. Any thought of some objects being separated by a distance, greater than could have been accomplished within the apparent lifetime of the universe without exceeding the speed of light, is spurious.
    That's what one might believe from a common misreading of relativity, such as one might get from having read only poorly-written popularisations of science, rather than studying relativity in some detail. If you do undertake that additional study, you find that there is no prohibition against space expanding superluminally, carrying with it matter contained within. So distant objects can indeed have a recession velocity far in excess of c, without contradicting any known laws of physics, so nothing is "spurious" at all about this observation. Google for the term "metric expansion of space".

    "Can anyone tell me the effect on the wavelength of light pass​ing through expanding space? Is it red shifted??


    And yes if space is stretching, so are the wavelengths of light. The metric expansion of space gives us the famous observed redshift.
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    Why then is the observed red shift interpreted and indicating solely recessional velocity?
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  6. #5  
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    How then does the light reach us?
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  7. #6  
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    How then does light pass from one body to another ie. our own planet.
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  8. #7  
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    Quote Originally Posted by BobJeffs View Post
    Why then is the observed red shift interpreted and indicating solely recessional velocity?
    I don't understand the "then" in your question. It seems a non-sequitur to what I wrote.
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    Quote Originally Posted by BobJeffs View Post
    How then does the light reach us?
    Another non-sequitur. It is almost as if you are ignoring what I wrote, and then simply listing a series of barely related questions.

    You would benefit greatly from studying Ned Wright's cosmology faq and tutorial pages (google for it; he's a UCLA prof., he was a PI on WMAP and COBE, among other accomplishments).

    As to your latest question, not all light reaches us. Some will be forever out of reach, so your question presumes an erroneous premise. Other light can reach us, and will eventually. Still other light is reaching us now.
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  10. #9  
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    Thank you for the input. My responses on 23 July were supposed to relate to specific items but due to my inexperience of this website I am at a loss to know how to link them.
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  11. #10  
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    And yes if space is stretching, so are the wavelengths of light. The metric expansion of space gives us the famous observed redshift.

    Why then is the observed red shift interpreted as indicating solely recessional velocity? Ignore this I'm just practising!!
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  12. #11  
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    Red shift indicates recessional velocity. This can come from two sources, expansion of the universe or actual motion. For most galaxies it is the expansion.
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    I've always been bothered by the observed red shift too. I'm not smart enough to understand the physics, but it seems unlikely to me that the observed red shift should be the same in all directions. Which it apparently is.

    I wonder if time is somehow involved.

    Einstein introduced the idea that time is not a constant, that time can slow down under extreme gravity (near a black hole) -- or presumably at the singularity of a Big Bang? Is it not possible (he asked na´vely) that time is speeding up as the universe expands, so when we look backwards in time to distant galaxies, they're red shifted to a slower timeframe?
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