The highlight of any episode of The Big Bang Theory is, unquestionably, the interactions between Sheldon Cooper, B.S., M.S., M.A., Ph.D., Sc.D., and Penny, community college dropout. Despite the gaping disparity in their academic achievements, or maybe because of it rather, the Caltech physicist and the Cheesecake Factory waitress have developed a somewhat unlikely friendship. It's a friendship that works though because of the mutual respect and caring the two genuinely feel for each other.
Penny may not be Sheldon's intellectual equal, as he is often quick to remind her, but she is undoubtedly his superior in terms of street smarts and social awareness. She often exhibits a quick wit in issuing a craftily-barbed retort whenever his overinflated ego requires a little puncturing. Her "Who's Radiohead?" effectively silences him into an eye-twitching stupor when the theoretical physicist begins pontificating about how he has "a working knowledge of the entire universe and everything it contains." (The Work Song Nanocluster) It's moments like these that provide the grist for their droll alliance and also re-establish the two on equal footing. Interestingly Penny is the only one within their immediate circle who possesses such a fine-tuned sensibility, the others preferring to meekly surrender or "knuckle under" before Sheldon's sometimes tyrannical disposition.
If their complementary personalities kindle a respect between the two, the moments of unguarded vulnerability that require the other to step up to the plate are what further solidify their friendship. In The Electric Can Opener Fluctuation, a deeply wounded Sheldon is comforted by Penny, who puts the emotional welfare of her friend above the lusty advances of her "furry little boy toy." The fact that Sheldon only winds up sobbing harder into his pillow is irrelevant - the sincerity of her concern for him is what truly matters here. Sheldon, in turn, has extended himself for Penny, in his inimitable way of course, by lending her money when she needs it, by teaching her "a little physics" when she feels insecure, and by introducing her to the world of online gaming when she's depressed.
The most remarkable instance of Sheldon caring for Penny occurs in The Adhesive Duck Deficiency when he must emerge from his comfort zone and power past so many of his neuroses and fears, which he does with not that much prodding from Penny. It could be argued that Sheldon does what he does for Penny, here and elsewhere, merely to maintain a sort of homeostasis, but, even if that's true, the fact that Homo Novus has admitted Penny, and the attendant chaos of her life, into his highly organized and codified sphere of existence speaks volumes. It's equally likely however that beneath that robot exterior is a sensitive and caring soul that is intensely loyal and that he considers Penny to be one of his dear friends.
by Check E. Light