Alan Guth and the Inflationary Universe

By the early 1970s there was fairly strong evidence in support of the Big Bang theory. Penzias and Wilson had observed the afterglow of the Big Bang that had been predicted by Alpher and Herman. It seemed to be about 3°K above absolute zero everywhere.  But there were problems with the theory.  For example, it was estimated that the universe was about 15 billion years old.  That means we can see 15 billion light-years in any direction.  If that is the case the observable universe must be at least 30 light years in diameter.  If the universe is only half that age, how could all the different parts of the universe be about the same temperature?  Alan Guth came up with a solution.  He envisioned a period of “inflation,” when a small region of the universe, which was all at the same temperature, suddenly (in some tiny fraction of a second) expanded so much so fast that it became the entire observable universe (and then some).  So all of the parts of the universe were in contact.  Then the universe began the more gradual expansion we see today.