How can you prove why space is black?

Question: How can you prove why space is black?
- Keywords:
  colour,
  light,
  space
Asked by 241yttc47 to Anna, Hayley, Iain, Rebecca on 23 Jun 2015.
- Iain Bethune answered on 23 Jun 2015:
  
  Space appears to be black because although there are stars and galaxies scattered all around most are so far away that the light from them has not yet reached us. However, when the universe was small and dense, just after the big bang radiation was emitted from the ‘plasma’ state before the first stars had formed. This radiation is of such a long wavelength that it is not visible to our eyes, but it is visible in all directions to a sensitive detector like the WMAP probe. This radiation is called the cosmic microwave background (CMB), and you can find pictures of it on the web.

Question: How can you prove why space is black?