Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Equilibrium at Universe (possible?)

  1. Jan 30, 2015 #1

    ChrisVer

    User Avatar
    Gold Member

    How can Universe be at equilibrium when the FRW metric has no time-like Killing Vector?


    Request: Please, move this into Cosmology thread... :( Mistakenly I posted it in HEP
     
    Last edited: Jan 30, 2015
  2. jcsd
  3. Jan 30, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    How can you write an ordered post if the universe is at equilibrium?

    Do you mean the large-scale homogeneity instead of equilibrium?
     
  4. Jan 30, 2015 #3

    ChrisVer

    User Avatar
    Gold Member

    http://www.damtp.cam.ac.uk/user/db275/Cosmology/Chapter3.pdf
    page:5 as you scroll down, the subnote with number 7...
    I am trying to pursue a little further and understanding better what they meant in it... In fact I am looking for a better explanation on the slow expansion-argument as well..
     
  5. Jan 30, 2015 #4

    Chalnoth

    User Avatar
    Science Advisor

    It's not an equilibrium in the strict sense of a final state of a system that no longer changes. What it essentially means is that the system is well-described by a thermal energy distribution.
     
  6. Apr 17, 2015 #5

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Sorry to necropost but I'm just running across this thread. The slow expansion argument is that, in the early universe, the time scale for local heat exchange, which is what drives the system to local thermal equilibrium, was much shorter than the time scale of expansion; in other words, on the time scale for achieving local thermal equilibrium, the universe could be approximated as not expanding. Of course over longer time scales, the expansion does affect the thermal properties, because it causes the universe to cool; but as long as the thermalization time scale is much shorter than the expansion time scale, the cooling can be thought of as just a succession of local thermal equilibrium states at gradually decreasing temperature, because local heat exchange happens fast enough to keep adjusting to the expansion.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook