1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Big Crunch/ Big Rip - Eqn of State

  1. May 9, 2007 #1


    User Avatar

    Hello, in the eqn of state [density prop. to a^-3(W+1)] if you subbed in W=-2 you get density prop. to a^3. If you then plot a graph of density vs. scale factor it is a straight-forward graph. Good up until then, but then I got the interpretation wrong. This represents the "big rip". But how? I figured that as scale factor goes to infinity then density goes to infinity, an infinite density implied a "big crunch" to me. On further research, it seems the graph was correct, but I interpreted it wrong. Apparently an infinite energy density is needed for the "big rip", but I don't get why this is. How can an "infinite density" tear the universe apart?
    Thanks for any help.
  2. jcsd
  3. May 11, 2007 #2

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This might be a little late to help.

    A big rip ocurs when the scale factor a goes to infinity at some *finite* time in the future. To show that this happens in this case, integrate the Friedmann equation to find the scale factor as a function of time.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook