In The Stranger, what is the significance about the indifference of the world compared to Meursault's life?
"I opened myself to the gentle indifference of the world. Finding it so much like myself" (122).
Mersault is a character who subdues his inner dialogue. He does not delve into his psychology to identify his feelings/motives so much as he denies the impulse to self-analyze and self-assess.
Camus did this because he felt that “psychology is action, not thinking about oneself.” The protagonist, along with a failure to explain everything to the reader, refuses to justify himself to other characters. (eNotes)
In keeping with the philosophical principles of existentialism, Camus presents to us a figure in Mersault who seems to "merely" exist. Questions arise over the course of the novel as to how this state of being impacts a person's life.
We can interpret Mersault's relative isolation in the novel in at least two ways: he is isolated from others by his own indifference or others feel that they cannot relate to Mersault because people generally relate via admission of an internal life.
There is certainly a wide-spread belief in the West that people live two lives, an innner life and an outer life. Psychology is largely based on this notion. By denying his own internal life, Mersault poses a problem for psychological analysis.
We can see this as he refuses to agree that his feelings about his mother's death influenced his impulse to shoot a man. Mersault steadfastly shuts down any such agrument, though others try to foist this psychology onto him.
Perhaps, to return to the main point at hand, Mersault's indifference is simply the natural result of a life led without any interest in psychology.