What is the logical setup that determines the epoch of the CMB?

  1. I'm not sure how it is derived.

    Do we follow this order?
    1. Temperature at last scattering/recombination/decoupling (3000 K)
    2. Measuring the temperature of the CMB (~3K)
    3. 3000K/~3K = 1100
    4. z=1100
    5. t(z)

    Or this order?
    1. Assume Big Bang and Inflation
    2. Determine Volume and Pressure
    3. Determine required temperature
    4. Temperature at last scattering/recombination/decoupling (3000 K)
    5. Measuring the temperature of the CMB (~3K)
    6. 3000K/~3K = 1100
    7. z=1000
    5. t(z)
     
  2. jcsd
  3. marcus

    marcus 25,070
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    Hey marinas, you are solving for a time (or a z) when a certain medium becomes transparent. It is not perfectly straightforward, I think it is more like solving several SIMULTANEOUS equations.

    If the medium is less dense, then it does not have to be so cooled down. If it is more cooled down then it can be less rarified. there are various different trade-off conditions that can cause it to become transparent.

    I read about this in a book one time, it was slightly complicated to do it right. It was not a straightforward 1. 2. 3. logic.
    You had to doodle around until you got some combination of density and temperature that was sufficiently transparent for the photons to run free (at least for long enough so that before they got scattered again it could cool down some more and get more transparent.... and so on)
    It is a "mean free path" kind of calculation.
    on a clear day you can fly forever:smile:

    Maybe one of us here will explain to you with equations. maybe it is simpler than I remember. It took about one page IIRC
     
    Last edited: Mar 29, 2006
  4. Chronos

    Chronos 10,210
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    You pretty much have it right kmarinas. There is a fairly linear relationship between z and the current CMB temperature - albeit the mathematical details are daunting. If you apply fluid mechanics [as many theorists have done], you derive a decent approximation of the CMB temperature over time, and it flattens out [becomes increasingly linear] over time.
     
  5. hellfire

    hellfire 1,047
    Science Advisor

    From the measurement of the current CMB temperature you can get the redshift of the last scattering surface if the temperature at recombination is known. This is correct. It is missing, however, that to determine the temperature at recombination you have to measure or estimate the baryon to photon ratio before.
     
  6. Chronos

    Chronos 10,210
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    try starting with [1/(1+z)]^3/2
     
  7. Chronos,
    I am very interested in the subject of 'fluid mechanics' in regards to cosmological problems. I have more than a sneaky hunch the visible universe is acting as if it were an 'ideal liquid' pulse/jet that has transited from a laminar to a turbulent condition due to lose of momentum.

    Could you hook me up sitewise with some of the theorists you spoke of?
    aguy2
     
    Last edited: Apr 2, 2006
  8. Chronos

    Chronos 10,210
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    Sure, here is a good place to start:
    http://www-acs.ucsd.edu/~ir118/MAE87F03/MAE87F03.html. But, given your question, I'm not certain that is a satisfactory answer. I perceive you have a hidden agenda. I understand your argument regarding turbulence, I do not understand how you perceive there is any loss of momentum.
     
    Last edited: Apr 3, 2006
  9. Thank you for the site. Maybe I should have asked about "cosmological, fluid dynamics theorists", other than me. I have an agenda, but I am certainly not trying to keep it hidden.

    I am putting forward a model that sees the all-matter, observable, visible universe as a "polar pulse/jet" from a still existent BB event/body. The "pulse" has lost momentum and as a consequence has transited from its former laminar flow to its present turbulent one.

    Do you see what I getting at?
    aguy2
     
  10. Chronos

    Chronos 10,210
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    Gold Member

    Yes. But it appears to require us to be very fortunately aligned with the flow. Would we not otherwise see huge anisotropies in the CMB?
     
  11. Sorry about the late response. I have found a site that although it was not ment as a cosmological model of a possible pulse/jet condition, if you place our streaming galactic cluster a little left of center, you might see a developing structure that has a eerie resemblance to a possible dipole/octipole situation. see the animation of figure 3 at: http://www.physics.nmt.edu/~dynamo/PJRX/Results.html

    I also made a public semi-pseudo-science prediction in Oct. 2003, concerning possible WMAP3 data at: http://physics.about.com/b/a/2003_10_15.htm?terms=bb+electronics

    While you at it, you might want to check out www.self-creation.net although this is more philosophy than science.

    Sorry again for the late response.
    aguy2
     
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