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I Redshift and Scale factor

  1. Dec 31, 2017 #1
    We can define the relationship between ##z## and ##a(t_e)## as,

    $$1+z=\frac {a(t_0)=1} {a(t_e)}$$

    When we assume ##z=2##, it means that ##a(t_e)=\frac {1} {3}##

    Is this means that universe was ##\frac {1} {3}## times smaller then now ?

    If its the case then lets suppose ##z=6## which means universe was ##\frac {1} {7}## times smaller, but even in this case it doesnt seem a huge difference between ##z=2## and ##z=6##. But I think there should be a lot of difference.

    I am not sure what am I missing.

    Thanks
     
  2. jcsd
  3. Dec 31, 2017 #2

    Orodruin

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    Why?
     
  4. Dec 31, 2017 #3
    The largest value of z can be 10 and it that case universe was 1 billion years old maybe more young like a 500 million years old. I am not sure but in any case.

    Lets suppose ##z=10##, in that time lets suppose radius of OU is ##r## and now its ##11r##?
    Cause I was espanding like ##10^10## difference cause universe was so young those times.

    For a current scale of the OU is 45 billion light year. 11 times smaller means 4 billion light year. But I was expanding like a million light year or maybe less If I think the time scale which it grow 11 times bigger in 13 billion years ?

    I am not sure how can I explain it.
     
  5. Dec 31, 2017 #4

    Bandersnatch

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    The CMBR is z = 1089. There is no upper limit for z.
     
  6. Dec 31, 2017 #5

    Orodruin

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    Why do you think that z cannot be larger than 10? It is false. The redshift at the last scattering surface is about 1000.
     
  7. Dec 31, 2017 #6
  8. Dec 31, 2017 #7

    Bandersnatch

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  9. Dec 31, 2017 #8

    Orodruin

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    They are studying galaxies. It took some time for galaxies to evolve and you will not find galaxies with a redshift of z = 1000. This does not mean that redshifts larger than 10 does not exist.
     
  10. Dec 31, 2017 #9
    Thanks for your replies. I understand it now
     
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