One rather broad theme/idea that I stumbled upon rather consistently (even in stream-of-consciousness passages that we agree were somewhat baffling), was the idea of chaos and reversal of order.
The line between reality and fantasy is pretty blurred (Pirate having a "strange talent for getting inside the fantasies of others" (12), the giant Adenoid taking over London (14), the dog who talks to Jessica and Mexico (44)... etc.). This fantasy element actually made me think about the film Pan's Labrynth. The movie is set during wartime in pre-facist Spain, and weaves elements of fantasy and violence in order to highlight the absurd, surrealist aspect of war. Everyone seems to be trying to create a pattern within in the chaos, an explanation for the madness and disarray of war. The best example for this, I think, is the continuous work to find connections between Slothrop's sexual climaxes and the bombings (and not even just a regular bombing, but when the explosion happens in reverse). As professor Rozsavolgyi explains to Mr. Pointsman: "When given an unstructured stimulus, some shapelss blob of experience, the subject, will seek to impose structure on it." (81)
There are also various opposites and reversals of truth in the novel. The section about Pavlov referrs to opposites and mental diseases, and the book constantly talks about "paradoxical phases". The first character that comes to mind when I think about paradoxes is the pretty Katje, who, "encolsed in the soignÃ©e surface of dear fabric and dead cells, [...] is corruption and ashes" (94). Captain Bilcero sugges that he will cut her hair short and grow her brother Gottfreid's hair long, reversing the gender stereotypes. The three of them stay together to seek shelter "against what outside none of them can bear- the War, the absolute rule of chance" (96).
I believe that by highlighting chaos, as well as people's intense fear of it, Pynchon asks us to question the social constructions we create in order to preserve some illusion of order and meaning. Because they cling to a "cute" and "Hollywood" idea of romance, Roger and Jessica remain rather innocent and naive. "Roger and Jessica were merged into a joint creature unaware of itself" (38)... "They look so innocent. People immediately want to protect them: censoring themselves away from talk of death" (121).