In The Big Bang Theory (2007), s4e18, The Prestidigitation Approximation (2011), Sheldon (Jim Parsons) makes reference to when he was a child and got into trouble with Homeland Security after purchasing uranium to use for generating electricity. We see what happened in this episode.
First appearance of Tam, Sheldon's childhood best friend.
This episode was viewed by 12.66 million people and got a rating of 2.2 (adults 18-49).
In this episode, Mary (Zoe Perry) worries that Sheldon (Iain Armitage) is sitting alone in the cafeteria. Older Sheldon (Jim Parsons) explains that he actually liked being alone, pondering the mysteries of the universe.