13. Birth, LIfe, and Death of the Universe

• The observable universe originated in a big bang.
  
  
• The expansion of the observable universe was initially controlled by its radiation, and we now see the cooled relic of this radiation as the three-degree cosmic microwave background radiation.
  
  
• The three-degree background radiation has a blackbody spectrum and minute temperature fluctuations from which the first stars and galaxies arose.
  
  
• The look-back time to the big bang is 13.7 billion years.
  
  
• All of the hydrogen and most of the helium in the universe were formed in the first three minutes of the big bang; they recombined as atoms about 400,000 years later.
  
  
• The first stars and galaxies formed about 100 million years after the big bang.
  
  
• The rate of star formation peaked about 2 billion years after the big bang and almost 12 billion years ago.
  
  
• Galaxies were more active in their youth, and most galaxies are thought to contain super-massive black holes at their centers.
  
  
• We do not know for certain what happened before the big bang, since all existing proposals are based on mathematical speculations that do not have observational tests.
  
  
• The expansion of the universe is accelerating, due to the anti-gravity push of a mysterious dark energy. It is an expansion that cannot stop.
  
  

Copyright 2010, Professor Kenneth R. Lang, Tufts University