How do we see almost at the start that Raskolnikov is divorcing himself from life and from the world of people?

He is intentionally avoiding people, particularly his landlady. In the third paragraph Dostoevsky writes that Raskolnikov is becoming "increasingly absorbed in himself" and that he is " isolating himself" from other people. Raskolnikov's early isolation is important to help set up his later theory of the" superman" and to magnify the fact this his true punishment comes from his own conscience.

Here is a link to an e-text.