What is the best demo for demonstrating why we look back in time when we look into deep space?

Question: What is the best demo for demonstrating why we look back in time when we look into deep space?
- Keywords:
  back in time,
  deep space,
  demo,
  demonstrating
Asked by favelaman to Cesar on 18 Jun 2011.
- Cesar Lopez-Monsalvo answered on 18 Jun 2011:
  
  The best demonstration I can think of is a “picture”. It was taken by something called WMAP (Wilkinson Microwave Anisotropy Probe), which is “one of those” satellite missions. What it shows are tiny variations on a very uniform “echo” from the big bang. Those tiny variations are the ones that grew to form stars, and galaxies and everything we see today. It is because the light travels at a finite speed that we know that this image, which is also the farthest away “thing” we can actually see, happened when the universe was just 400000 years old.
  
  See a video here:
  
  http://map.gsfc.nasa.gov/media/030651/030651_640.mov
  
  the universe timeline here:
  
  And a picture of the Cosmic Microwave Background (CMB), the big-bang afterglow here:

Question: What is the best demo for demonstrating why we look back in time when we look into deep space?