What is the importance/symbolism of the sun and the heat in The Stranger?

When evaluating the
significance of the sun in Camus' , we might focus on the connection
between the day of the funeral (when Mersault's mother is buried) and the day that Mersault
commits the murder. 

On each of these days the sun is mentioned as being very
hot, oppressive, and even painful. 

We might conjecture that when Mersault
encounters the extreme heat/sun on the beach he is (consciously or unconsciously) reminded of
his mother's death and burial. The latter sections of the novel offer ample suggestion that
Mersault is affected by his experiences (like his mother's death and his affection for Marie)
even though he denies that these experiences are influencing him.

The
espoused emotional and intellectual neutrality of Mersault's narration of his own psyche is
brought into question by contrasting examples of deeply felt emotion and keenly observed, very
human turmoil.

The second part of the novel deals with Mersault's denial of
an inner life and the ramifications of...