Wow it looks like Summer Glau isn't going to be the only stunt casting they're doing on The Big Bang Theory. On the same episode that Glau is guest starring (March 9th), Nobel Prize-winning Dr. George Smoot will be guest starring as himself!
According to the Los Angels Times, Leonard, Sheldon, Wolowitz and Raj take a train ride to San Francisco to attend a symposium in which Dr. Smoot is the keynote speaker. Dr. Smoot, is famous for much of his work, but the most relevant for The Big Bang Theory is his work helping establish the big bang theory of the universe.
Now, while the rest of the boys are drooling over the chance to talk to Glau, it's Sheldon dream to meet Dr. Smoot instead. Sheldon's plan is to present the paper he's been working on to Smoot.