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  1. Path: sparky!uunet!dziuxsolim.rutgers.edu!ruhets.rutgers.edu!bweiner
  2. From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
  3. Newsgroups: sci.astro
  4. Subject: Re: Modelling the expanding universe?
  5. Message-ID: <Jan.23.17.25.20.1993.18033@ruhets.rutgers.edu>
  6. Date: 23 Jan 93 22:25:20 GMT
  7. References: <C13sH3.1xL@well.sf.ca.us> <1993Jan19.161523.25667@cs.ucf.edu> <C15vp9.6x5@well.sf.ca.us> <Jan.22.18.22.58.1993.8665@ruhets.rutgers.edu>
  8. Organization: Rutgers Univ., New Brunswick, N.J.
  9. Lines: 25
  10.  
  11. One of my sentences trailed off into nothingness in my previous post,
  12. here's the correction:
  13.  
  14. I wrote:
  15.  
  16. >I was, rather, trying to say that Newtonian gravitational collapse
  17. >and a "contracting universe" were two sides of the same coin.
  18. >Consider two points separated by a small amount in the early universe ..
  19. >                        --------------
  20. >                --------              --------
  21. >  early  *------                              -----_____  galaxy forms
  22. >         *------                              -----
  23. >                --------              --------
  24. >                        --------------
  25. >    time ----->
  26.  
  27. >The lines represent geodesics followed by the particles.  I hope
  28. >this shows 
  29.  
  30. the similarity of the expansion (due to the Hubble flow) to the
  31. contraction, which we usually describe in terms of Newtonian gravity.
  32. One says the spacetime in between is expanding, when they're following
  33. geodesics which take them apart; so in some sense it is appropriate
  34. to say that the intervening spacetime is contracting as they come
  35. together.  However, angular momentum and internal pressure do act
  36. to prevent the solar system/galaxy from contracting to a point.
  37.