The Luminous Fish Effect
No wonder Sheldon's not a happy chappy. He's not only had his wild time travel theories pooh-poohed by Leonard, but now he's got to meet CalTech's new department head, Dr. Eric Gablehauser, who, much to Sheldon's chagrin, has conducted no original research in 25 years. When it comes to being introduced to his new boss, Sheldon can't hide his resentment for the man and is promptly sacked, which was probably something to do with calling him, "a glorified science teacher whose last successful experiment was lighting his own farts". Quite.
On his first ever day off work Sheldon ropes in Penny to help him with an experiment involving four dozen eggs. By the time Leonard arrives back in the apartment Sheldon's already moved onto another brave new venture - giving fish "nightlights". After weeks of various scientific ponderings and not much leaving of the flat, Leonard gets concerned for his roommate’s well-being and calls Sheldon's mother, Mary.
Sheldon's mother does what all mothers across the land feel obliged to do - tell his friends embarrassing stories from her son's past. So, after regaling Leonard, Raj, Howard and Penny about Sheldon's aim to build a sonic death ray, Mary persuades her "Shelly" to apologise to his old boss and get his job back.
Literally holding Sheldon's hand, Mary accompanies her son to see Dr. Gablehauser. The doc is taken aback by Mary Cooper's beauty, and this was good enough reason for Sheldon to be immediately reinstated into his old job. All's well that ends well.