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I Entropy of the last scattering surface and today's universe?

  1. Dec 12, 2017 #1
    Hi,
    I am quite confused about followed question,
    I think scientist think the last scattering surface was dense plasma at the temperature of 3000K. If the today's universe much cooler and less dense then "the last scattering surface" how can anyone says entropy increased by time? Isn't universe now have more order than a plasma phase?

    Note: I am sorry If I couldn't make good sentences to explain my problem, it is almost 2 am and I just woken up and this question just bugs me a lot. I'll really appreciate if someone explains it.
     
  2. jcsd
  3. Dec 12, 2017 #2

    Orodruin

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    The universe is much bigger now than it was at the time of last scattering.
     
  4. Dec 12, 2017 #3

    kimbyd

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    In what way do you think the universe now has more "order"?

    If you are talking about gravitationally-bound systems such as planets and stars, then those systems have higher entropy than the diffuse gas clouds they collapsed from. While the precise details of how much entropy complicated systems have is unknown, we do know that the end point of matter contained within a black hole is the maximum-entropy configuration that amount of matter can have.

    If you just mean the cooling of the plasma into a gas, that process is largely adiabatic (as in, entropy didn't change much).
     
  5. Dec 12, 2017 #4

    Orodruin

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    This is actually not true. However, the point is that the evolution from a gas cloud to a gravitationally bound system is not an isolated one.

    John Baez’s discussion on this is well worth a read.
     
  6. Dec 13, 2017 #5
    Well I got one more question now, but it was fun to read.

    I am still thinking about other answers and I'd like to hear if there is any other thoughts on this subject.
     
  7. Dec 13, 2017 #6

    kimbyd

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    That's fair. It does make sense that you'd have to not only consider the configuration of the matter, but also of the outgoing radiation, which represents a large loss of heat for the system. That does bring things into clearer focus. Certainly the entropy of the observable universe is not decreased by this process regardless.
     
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