Particle astrophysicist David Saltzberg was the go-to science guy for The Big Bang Theory. He planned the craziness that appeared on the white boards, he added scientific props to the set, and he added science-y lines to the show's script. Ever wonder what it was they would go on and on about? Here are some basic explanations.
M-Theory, String Theory and Supersymmetry
Michio Kaku Explains String Theory
What is String Theory?
String Theory Explained – What is The True Nature of Reality?
If You Don't Understand Quantum Physics, Try This!
For a more documentary style breakdown; you may enjoy this.