First prediction from Big Bang model:
Cosmic Background Radiation
• Look out (and back in time) to place  where
H became neutral
• Beyond that the high density ionized H
forms an opaque “wall”
• Originally 3000 K blackbody radiation
• The material that emitted it was moving
away from us at extreme speed
• That v produces extreme redshift (z=1000),
so photons all appear much redder, so T
appears cooler
• With red shift, get 2.7 K Planck blackbody
• Should be same in all directions