What are the methods by which characters in John Osborne's Look Back in Anger "break the fourth wall," and what is the effect of doing so?

In theater, the concept of a "fourth wall" is integral to most playwrights' concepts of story and production. Simply, it refers to an imaginary wall separating the audience from the stage and is intended to emphasize, for the actors, the need to separate themselves from the world beyond that which the playwright, producer, and director have created. The audience is not acknowledged or addressed; the action occurs within its own self-contained universe. To "break the fourth wall," then, is to have the actors acknowledge or interact with, in some manner, the viewers in the audience, thereby acknowledging the artificial nature of that universe.

In John Osborne's play Look Back in Anger, the so-called "fourth wall" is very much in existence. The setting of Look Back in Anger is noticeably claustrophobic—a small apartment (Osborne's set direction specifies "a fairly large attic room, at the top of a large Victorian house") in which reside Jimmy and Alison Porter, the former the play's main "protagonist"—so the very real first three walls are easy to conceptualize and construct. The "fourth wall," however, exists by virtue of the play's focus on the dynamics between the small group of actors and Jimmy's vitriolic tirades against the world in which he finds himself and in his insulting comments toward others. To the extent the "fourth wall" is broken, therefore, it is a deliberate decision on the part of the director of a particular production of Osborne's play. In a 2012 interview, one such theater director, Sam Gold, explained his vision of the separation of actors from audience:

My first instinct was to play the play really close to the audience, to make it intimate. I wanted it to feel like the audience and the actors were in the same room. I didn’t want it to feel like the lights were going down on them and here was the fourth wall and that this was happening in another time and place. This isn’t a play you can look at as a museum piece. I felt like one of the things that was so exciting about the play originally was that it alienated people, it made people uncomfortable and it woke people up to new ways of seeing drama on stage.

This was how one director conceptualized the production. More conservative or "traditional" productions would preserve that invisible barrier between audience and action. There is a certain intimacy inherent in any play that takes place completely within one setting and involves a small number of actors. Osborne's protagonist, Jimmy is venting his anger about the absence of viable causes in which to believe in the post-World War II world, the Nazis having been vanquished in "the last good fight" and the threat of communism a more tenuous proposition among much of the intelligentsia, including the average playwright. The goal of most playwrights is to engage the audience emotionally and/ or intellectually, though, so the "fourth wall" exists only to a limited degree. The actors might not be addressing or acknowledging the audience, but they are seeking the latter's reactions nonetheless. That, then, is the main way Osborne, as a writer, "broke the fourth wall."