Not just for theoretical physics,
but for ASTROPHYSICS.
The Big Bang Theory Season 8, Episode 6
I have a doctorate in ASTROPHYSICS
and I'm every bit as awesome
The Big Bang Theory Season 10, Episode 11
I have a PhD in ASTROPHYSICS.
The Big Bang Theory Season 10, Episode 18
This is Dr. Rajesh Koothrappali
from the Astrophysics Department.
The Big Bang Theory Season 6, Episode 20