Jim Parsons audition for the role of Dr. Sheldon Cooper was so good that creator Chuck Lorre immediately asked Parsons to come in for a second one, because Lorre wanted to be 100% sure Parsons was as brilliant as he seemed. After the 2nd audition went perfectly, Lorre cast Parsons on the spot.
Kaley Cuoco-Sweeting missed filming a few episodes of season four because of a broken leg that was the result of a horseback-riding accident. In her first appearance following the accident, she was filmed standing behind a counter.
On January 3, 2013, it was announced that a team of Brazilian Biologists named a newly discovered type of orchid bee that was eventually named Euglossa bazinga. This was to honor the show and specifically Sheldon's catchphrase "bazinga." Executive producer Steven Molaro responded in a press release: "We are always extremely flattered when the science community embraces our show. Sheldon would be honored to know that Euglossa bazinga was inspired by him. In fact, after Mothra (1961) and griffins, bees are his third-favorite flying creature."
On 14 January 2011, CBS gave the series a rare vote of confidence when it issued a three-year renewal through the 2013-14 season. It then received another three-season renewal on March 12, 2014, meaning the show will run at least ten seasons. This marked the first time in modern television history a scripted television series received back-to-back three-season renewals.
During the third season, the producers became aware of a series called "The Theorists," produced and broadcast in the country of Belarus, that was a virtual copy of The Big Bang Theory (2007). Legal action over copyright infringement would have been futile, since the production company was pretty much owned by the Belarus government. However, a lawsuit turned out not to be necessary, because when word got out that the show was a rip-off, the actors quit and the show was immediately canceled.
Sheldon frequently wears T-shirts with the characters or symbols of Green Lantern, the Flash, or the old TV show The Greatest American Hero (1981). The shirts from the "Green Lantern" comic book series are various colors with a corresponding symbol, with each color representing a different corps of heroes or villains (e.g. Red Lanterns, Orange Lanterns, etc). In the comics, each color also represents an emotion, thus possibly giving the viewer a clue to Sheldon's temperament for the day.
During a first season episode, Raj, Leonard, and Howard are trying to find a fourth person to replace Sheldon on their Physics Bowl team. Raj suggests the actress Mayim Bialik, saying, "You know who's apparently very smart, is the girl who played TV's Blossom. She got a PhD in neuroscience or something." Leonard responds, "Raj, we're not getting TV's Blossom to join our physics bowl team." During Season 3, Bialik started playing the regular role of Dr. Amy Farrah Fowler on the show; Dr. Fowler has a PhD like Dr. Bialik, but in neurobiology rather than neuroscience.
The full names and occupations of the characters are as follows: Dr. Leonard Leakey Hofstader, Ph.D., Experimental Physicist; Dr. Sheldon Lee Cooper, B.S., M.S., M.A., Ph.D., Sc.D., Theoretical physicist; Howard Joel Wolowitz, M.Eng, Aerospace Engineer; Dr. Rajesh Ramayan Koothrappali, Ph.D., Astrophysics; Dr. Bernadette Mary Ann Rostenkowski, Ph.D., Microbiology; and Dr. Amy Farrah Fowler, Ph.D., Neurobiology.
Floors two, three, and four of Sheldon and Leonard's apartment building are the same set just re-dressed for each scene. This can be seen in the fact that the scuff marks on the moulding are identical on each level as they walk up the stairs.
On five episodes or more of season six, Mayim Bialik's right hand was hidden in certain ways and camera shots to conceal the injury and glove with which she covered her hand because of an automobile accident that occurred in August of 2012.
Despite the fact that some viewers take Sheldon's behavior, mannerisms, and social skills as a sign that Sheldon has Asperger's syndrome or otherwise falls on the autism spectrum, the show-runners have persistently denied in many interviews that Sheldon has Asperger's or any other type of autism. It should be noted however, that actor Jim Parsons (Sheldon) has stated that he does think that Sheldon actually does have Asperger's syndrome and portrays him as such.
Each of the male characters has a signature clothing article that is worn in virtually every episode: Sheldon: t-shirts worn over long-sleeve shirts; Leonard: hoodies worn over a T-shirt and under a jacket; Raj: sweater-vest worn over a shirt and usually under some type of outerwear; Howard: dickie worn under some type of outerwear. Howard usually has a pin on the left side of his dickie of the head of a space alien, and he wears large belt buckles.
The opening cast shot always features the series' regulars enjoying dinner together. The opening cast credits cast shot in seasons two through four, for instance, depict Howard, Raj, Leonard, Penny, and Sheldon, on what appears to be pizza night. However, Leonard is seen holding a plate with a white meat and some type of vegetable, such as asparagus spears. This is apparently a reference to his lactose intolerance, which would make him adverse to pizza. Amy and Bernadette were added to the shot starting in season six, even though both had been regulars on the show since season four.
Howard's mother's voice is heard throughout the show, but her face has never been actually seen on-screen. (She did appear very briefly on-screen in the season 5 finale, as the camera pans up from the roof top, but her face was still never shown.)
The theme song uses the line "Autotrophs began to drool." This is a science joke. The word "autotroph" means "self-nourishing" and refers to life-forms (plants and algae) that create their own food internally and don't need to eat.
Penny was an add-on from a different sitcom concept. She had been originally envisioned as Katie, a more cynical, hard-drinking, streetwise girl who worked at a makeup salon. In the original unaired pilot, she was played by Amanda Walsh.
According to numerous entertainment reports, CBS has reported a large jump in the series' ratings for Season 6 and have attributed the increased audience to the exposure of the show in re-runs on TBS which airs the series three nights a week in prime time blocks of up to three hours.
All the figurines and posters in Howard's room (and later on in his house with Ber date) are female super heroes or science fiction characters. The one non-female figurine, Jabba the Hutt, has Princess Leia (in her slave girl costume) sitting on top. Later on in the series, they accumulate a figurine of Berndette after the episode where he and Raj got a 3D printer.
Leonard's last name, Hofstadter, refers to two well-known scientists: Robert Hofstadter, the 1961 Nobel Laureate in Physics, and his son Douglas Hofstadter, who researches consciousness and cognition, and whose best-selling book about philosophy, mathematics, puzzles, art, and music, "Gödel, Escher, Bach: an Eternal Golden Braid," was published in 1979 and won him the 1980 Pulitzer Prize for general nonfiction.
In the early episodes of Season One, Sheldon has two character traits that were not established right away. First, Sheldon understood the nature of romantic/sexual relationships. In the first few episodes, he chides Leonard for his hopes of getting into a relationship with Penny, often telling Leonard that he has no chance of having sex with her. Also, Sheldon understood the nature of sarcasm as he occasionally used it himself in the early episodes. Later, his character evolved into a purely intellectual person and an emotional "man-child" who does not fully understand sex, love, or sarcasm. Second, in the early episodes, Sheldon did not use his 3 times knock. (I.E.: Knock-knock-knock "Penny", etc.) that has become one of the character's now well known idiosyncrasies that did not begin until midway through Season One.
In early episodes of Season One, Sheldon mentions having an older brother in addition to his twin sister, Missy. In one instance he mentions being bullied by this older brother. However, while Missy has been seen on the show, the brother was never mentioned again, even when his mother visits. She only mentions Missy. He was mentioned in season 3 episode 4 as well.
While a guest on the National Public Radio program "Talk of the Nation," Mayim Bialik confirmed that the university that the characters attend and/or teach at is based on the California Institute of Technology (Caltech) in Pasedena. Additionally, in one episode, the character of Leonard stated that he worked at Caltech.
As avid comic-book fans, the guys frequently talk about comic book characters or are wearing t-shirts or other paraphernalia of comics. They frequently mention DC Comics characters such as Superman, Batman, Green Lantern, the Flash, and Wonder Woman. Both DC Comics and the series are owned and produced by subsidiaries of Time Warner.
Wolowitz says that Spock had a date every seven years. He is referring to Pon Farr, the Vulcan mating cycle that occurs every seven years. Vulcans must mate in the time of Pon Farr, otherwise they will die. So Spock has a mandatory date every seven years.
Sheldon verbally reveals his and Leonard's Pasadena apartment 4A's location as being 2311 Los Robles in "The Desperation Emanation." In the 100th episode, Sheldon also reveals that their apartment building is across the street from the Colorado Avenue Chevron gas station, making their building a corner location, on the corner of Los Robles and Colorado. There are two incidences of this intersection in southern California, both located in Los Angeles County, the first one is E. Colorado Boulevard & N. Los Robles Avenue, Pasadena, CA 91101, and the second one is Colorado Boulevard & Los Robles Street, Los Angeles, CA 90041. However, 2311 Los Robles is not an address by either one of those intersections. Leonard does reveal, however, that they live in Pasadena while declaring himself the Darth Vader of Pasadena.
Leonard's middle name is Leakey. Leakey is the name of a renowned family in the fields of archaeology, anthropology, and paleontology. Louis Leakey (1903-1972) was a British archaeologist and naturalist whose critical work helped to establish human evolutionary development in Africa. He also created or co-created several organizations for future research and for protecting wildlife in Africa. He also helped to establish a tradition of palaeoanthropological inquiry, and was able to motivate the next generation to continue, especially within his own family. Mary Leakey (1913-1996), Louis's wife, was a British archaeologist and anthropologist, who discovered many firsts. For much of her career she worked together with her husband, Louis Leakey, in Olduvai Gorge, uncovering relics of ancient hominines. She also developed a system of classification the relics they found. After the death of Louis, she became a leading palaeoanthropologist, helping to further establish the Leakey name and tradition with the training of her son, Richard.
Simon Helberg's father is also an actor. In 1982, Sandy Helberg guest-starred on M*A*S*H (1972) in the episode M*A*S*H: The Moon Is Not Blue (1982). in which he plays Corporal Bannister, who is plagued with panic attacks whenever he is around women. Hawkeye and B.J. give him pills for confidence without telling him they are placebos. The pills work and he becomes a ladies' man. This is very much how Raj tends to be with alcohol on The Big Bang Theory (2007).
Bernadette did not originally have such a high pitched voice. When she first appeared, she had a rather normal pitch voice and as her character began to take shape, she adopted the quirky high pitched voice which Melissa Rauch says she based off her mother's voice "without the Jersey".
While Wil Wheaton was appearing on the show, he took a photo of the set's coffee table and posted it on his much-followed blog. Among the materials on the coffee table were copies of "Mental Floss" magazine; "The Sandman Vol. 6: Fables and Reflections" by Neil Gaiman; a package of Pepperidge Farm Sausalito milk chocolate macadamia nut chunk cookies; a package of Red Vines licorice; and a package of Tim's brand original-flavor lightly salted potato chips.
In the episode 'The Justice League Recombination', Sheldon states they have no choice but to switch to their Muppet Babies (1984) costumes. Writer of the Big Bang Theory (2007), Chuck Lorre, wrote an episode of the Muppet Babies (1984).
While having lunch at the University canteen or other eating scenes, characters don't actually eat most of the times. Howard only pretends to eat the food by moving his mouth like he is chewing it, Sheldon and Leonard just play with their food with fork.Amy and Penny are sometimes shown eating food actually. They only talk most of the time.
The trivia items below may give away important plot points.
In the 100th episode where Leonard asks Penny out again, Penny is wearing the same shirt she wore in the pilot. This was probably to represent Leonard falling in love again with the same girl he did 100 episodes before.
Of all the main characters, Leonard has had more relationships over the course of the show (Penny, Priya, Leslie and Stephanie), Penny is second (Leonard, Stuart, Zack), then Raj (Lucy and Emily) and Howard (Leslie and Bernadette). Sheldon (Amy), Amy (Sheldon) and Bernadette (Howard) have only been with one person each.