From: vitalmis@bigpond.net.au   
      
   Nate Smith wrote:   
      
   > Roger wrote:   
   >   
   >> I was hoping someone could help me with the following   
   >> question. I am trying to understand something of the size   
   >> of the universe, and I came across a quote that said   
   >> "the universe is expanding in all directions, and that   
   >> the 'Cosmic Microwave Background' (the remaining heat   
   >> from the Big Bang, is found at a distance of 15 billion   
   >> light years from us in all directions."   
   >>   
   >> Tow questions result from this:   
   >> - does this not suggest the universe is ball-shaped, and   
   >> - that the earth is pretty much at the centre of the   
   >> universe, near where the Big Bang occurred?   
   >>   
   >> Any input you can give me (in laymen's terms, please)   
   >> would be welcome!   
   >>   
   >> Rogier   
   >   
   >   
   >   imagine the surface of an inflating balloon.   
   >   there are a number of dots inked on it.  these   
   >   dots are attached and not part of the expanding   
   >   rubber surface, so they do not grow in size as   
   >   the balloon inflates.  one of these dots is where   
   >   we are.  from our vantage point it looks like all   
   >   the dots are receding from us.  the dots further   
   >   away are receding faster because there is more   
   >   expanding balloon between us and them.   
   >   
   >   in the rubber space between the dots there is a   
   >   residual glow from the big bang, your cosmic   
   >   background.  the bang corresponds to when the   
   >   balloon was empty.  the cosmic background reveals   
   >   when the balloon was empty.   
   >   
   >   notice that our dot is not at the center of the   
   >   balloon's surface, nor is any other dot.  infact,   
   >   also notice, although i did not specify it, that   
   >   the balloon is not necessarily spherical.  it might   
   >   be close to exact to satisfy certain cosmological   
   >   theories.  now consider that the balloon's surface   
   >   is a two-dimensional surface.   
   >   
   >   in the real universe, the corresponding surface   
   >   manifests itself, as far as we can be practical about   
   >   it, as a 3-dimensional surface in a higher order   
   >   setting.  we are as hampered in comprehending the   
   >   actual picture as 2-d creatures on the balloon would   
   >   be trying to imagine the center of the balloon or   
   >   being "inside" or "outside" of the balloon.   
      
   The balloon analogy is good for the geometry but bad for the   
   physics. It implies that there is something pushing the   
   bits apart, which is not the case. The Big Bang was   
   actually an explosion and, in any explosion, all the bits   
   are rushing apart with a speed that is proportional to how   
   far apart they are. However, this implies that there is an   
   edge to the expanding matter, and that's not the case   
   either, the expanding matter occupies the entire universe.   
      
   For this particular problem recall that when you look at   
   something you see it, not as it is, but as it was when the   
   light you see left it some time ago. That's about one   
   nanosecond per foot. When you look out into space you see   
   objects as they were further and further into the past the   
   further away they are. If you look past all the more recent   
   objects you see the universe as it was at the time when the   
   entire universe was a glowing plasma; well, strictly   
   speaking you see it as it was at the time it stopped being   
   a glowing plasma and became transparent. It's the light   
   from that plasma, seriously redshifted, that is the   
   microwave background. And it's constant (more or less) all   
   round us because whatever direction we look, if there's   
   nothing in the way, we see that far back in time.   
      
   The `more or less' arises partly because we are whirling   
   around our galaxy which produces a slight asymmetry in the   
   direction we are moving and partly because the entire   
   universe didn't become transparent all at the same instant,   
   bits came first and bits came later, which produces tiny   
   ripples in the cosmic background. By looking at these   
   ripples we can deduce things about the universe before it   
   became transparent.   
      
   Keith Harwood.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)