CBS has released two sneak preview clips from tonight's episode of The Big Bang Theory, which is titled "The Proton Displacement." The first clip is a montage of various scenes from the episode, teasing the return of Bob Newhart as Professor Proton, as well as a surprise appearance from Bill Nye. In the second clip, Leonard, Amy, & Sheldon spot Professor Proton while shopping at a pharmacy. Sheldon introduces his girlfriend Amy to Professor Proton, and Professor Proton is shocked to find out Sheldon has a girlfriend. However, things become more clear to Professor Proton, when Amy points out that they are wearing the same orthopedic shoes. In "The Proton Displacement" episode, Sheldon feels slighted when Professor Proton seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, Bill Nye. Meanwhile, Raj gets jealous when Howard crashes "girls' night." "The Proton Displacement" episode of The Big Bang Theory airs on Thursday, November 7, 2013 from 8:00 PM to 8:31 PM ET/PT on CBS.