The Joke

Leonard told  Raj, Penny and Howard his opening Joke for his talk on Sheldon's and his paper on Paradoxical Moment-of-Inertia Changes Due to Putative Super-Solids in  The Cooper-Hofstadter Polarization.

The Joke

A farmer has some chickens who don't lay any eggs. The farmer calls a physicist to help. The  physicist  does some calculation and says "I have a solution but it only works for spherical chickens in a vacuum!".

When Sheldon crashed the conference, he said that it was a good joke

 Explaination

In a vacuum, air pressure on a sphere. This would make the chicken lay eggs.