In chapter three of A Separate Peace, what is the world that Gene remembers?"A Separate Peace" by John Knowles

In Chapter 3 of "A Separate Peace" there is a World According to Phineas that the narrator, Gene, recalls.  Phineas and he are in summer school at Devon, and Finny loves rules, not the rules of the school, but his own that he creates as he goes along.  Gene writes,

Everyone has a moment in history which belongs particularly to him.  It is the moment when his emotions achieve their most powerful sway over him, and afterward when you say to this person 'the world today' or 'life' or 'reality' he will assume that you mean this moment, even if it is fifty years past.  The world, through his unleashed emotions, imprinted itself upon him, and he carries the stamp of that passing moment forever.

For Gene, this moment was World War II; it "was and is reality" for him.  The color of life for Gene is the same as the color of war:  dull, dark green called "olive drab."  In this special country, Gene writes, he spends his summer at Devon with Finny, who achieves certain feats as an athlete.  Finny, however, creates his own world by designing new sports such as "blitzball,"  named after the Nazis blitzkrieg. a sudden, overwhelming attack by air of a country such as Poland.  Reckless, like his sports, Finny does things just to see if he can do them, such as breaking swimming records.  For Finny to break a school record is, Gene declares, "inebriating in the suppleness of this feat.  It had, in one word, glamour, absolute schoolboy glamour. But, there is also something "too unusual for rivalry" about Phineas's actions, and Gene cannot figure Finny out.

Wildly, Finny breaks the school rules.  They run off from the campus to the ocean where they have dinner at a hot dog stand and drink a beer.  Then they settle in a "good spot in the sand dunes at the lonely end of the beach"  and sleep for the night.  There Finny tells Gene he is his best pal:

It was a courageous thing to say.  Exposing a sincere emotion nakedly like that at the Devon school was the next thing to suicide....Perhaps I was stopped by that level of feeling, deeper than thought, which contains the truth.

Gene feels inferior to Finny, whose ease and charm are spontaneous, whose courage is unlimited.  There is a growing jealousy in Gene, one that becomes destructive to both Finny and Gene himself.