236 The Big Bang Theory The Cooper-Hofstadter Polarization 01 09 2008-03-17 Comedy / Romance Jim Parsons - Sheldon Cooper / Johnny Galecki - Leonard Hofstadter / Kaley Cuoco - Penny / Kunal Nayyar - Rajesh Koothrappali / Simon Helberg - Howard Wolowitz / Melissa Rauch - Bernadette Rostenkowski / Mayim Bialik - Amy Farrah Fowler / Laura Spencer - Emily Sweeney / Sara Gilbert - Leslie Winkle / Kevin Sussman - Stuart Bloom / John Ross Bowie - Barry Kripke / Carol Ann Susi - Debbie Wolowitz When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between him and Leonard, and Penny's intervention only exacerbates the situation.