Characterization
Charlie has wild curly hair, is wary of people, and frequently enthralled with objects and patterns. According to Krumholtz, Charlie wants to understand how the world works. His father has said Charlie is easily fascinated, possesses a big heart and is thorough, but he misses certain things completely. Meanwhile, Larry observed that he is "a talented theoretician with an ego problem" and a student once described him as fast-talking and disorganized, to the agreement of Larry. Fleinhardt also accurately noticed that his colleague has a high standard of guilt and is a pragmatist. Charlie is rather fond of providing excessive explanations (e.g., his discussion of Occam's razor) and reducing complex phenomena to intuitively obvious situations through practical analogies that are quite unlike Larry's metaphysical musings and cosmic metaphors. (These analogies are known as "audience visions" or, as friend Megan Reeves calls them, "those cute little analogies.") While contemplating, his antics and mannerisms may even disconcert more conventional thinkers. Wearing his headset, Dr. Eppes has an intense focusing ability as he voraciously writes equations, often covering several chalkboards with a staccato clacking and the aid of a red chalk holder. Nevertheless, if his line of thought is interrupted during a tense moment, as one of restricted foresight, he can become very disgruntled. Further, when deeply concentrating on a particular problem, it seems Charlie is unable to provide insights to other topics for the sake that they are simply needed or wanted—he has to write what is in his head. Like his brother Don, he is characteristically stubborn and obsessive ("one part exuberance, two parts obsession"), especially when it comes to work, but he's rather naïve when it comes to human behavior. The latter often interferes with his FBI work and, thus, is the cause of much distress for him at times.
He is extremely talented in chess, as it requires both his father and brother to play against him and a distraction to defeat him. Charlie also has a vast understanding of theoretical physics, often assisting Larry with his multi-dimensional supergravity theory and papers on gravity waves, and biology, extending to knowledge of ciliate protozoa and the spread of infectious diseases. While brilliant in some areas, he is lacking in others. Dr. Fleinhardt has stated that it is a good thing he went into applied mathematics as opposed to engineering, as machines malfunction in his presence, though he was able to take apart and rebuild his father's cell phone to analyze its GPS transceiver. He is apparently a bad speller (e.g., he misspells "anomaly" and "conceited") and does not know the meaning of "defenestration" (for which Larry chastises him stating that the idealization is to be a Renaissance man and that even math and physics majors had to have a course on English). Thus, his father likes playing Scrabble with him.
Charlie is a rationalist. He is skeptical of UFOs, psychic ability, and gematria—all considered to be pseudosciences. He also does not like illusions. He, however, is also fairly open-minded in terms of faith and religion.
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