'The Big Bang Theory' Recap: Bob Newhart Funny as Ever

"The Big Bang Theory" might be the highest-rated comedy on TV, but the sitcom -- now in its sixth season -- isn't resting on its geek-chic laurels. Case in point: Bob Newhart! (He even managed to squeeze in a dream reference to his hit '70s/'80s shows.) The 83-year-old comedy legend guest starred in Thursday night's episode, "The Proton Resurgence," as Professor Proton (think Mr. Wizard), and man, did he make science cool for a young Sheldon (Jim Parsons). Maybe a little too cool, because now Sheldon's totally creeping out the former kids' TV show host. The megagenius is not exactly known for his adherence to social norms, after all.

When Sheldon finds out that his childhood idol is available for kids' parties and events, he wastes no time writing a fat check and hiring Professor Proton. But it's not for a kids' party, it's just so that Professor Proton can come over, hang out, put on a private show, and -- if Sheldon gets his greatest wish -- "take 12 pictures with us so we can make a calendar."

[Related: 'Big Bang Theory' Cast on Life Lessons From Bob Newhart]

When Professor Proton arrives, he needs assistance up the steps to the gang's floor (the broken elevator strikes again!), and he doesn't seem particularly thrilled by Sheldon's epic fandom. "Is he dangerous?," Professor Proton -- whose real name is Arthur Jefferies -- asks after Sheldon swoons out loud, "I can get as close to you as I want without my mom saying it's going to ruin my eyes."

The gang leads Jefferies up the steps to their place (Penny's charms help to entice the downtrodden science teacher), but things get awkward again when Sheldon, Penny (Kaley Cuoco), and Leonard (Johnny Galecki) just sit and stare at Professor Proton over a cup of coffee. "Do you do a lot of appearances like this?" Penny asks. Jefferies is at a loss, because he's "not sure what 'this' is."

After the gaping ends, Professor Proton is persuaded to put on an old-school presentation, and he dazzles the trio with his science magic (how did he get that egg in the flask?!), but he still seems discontented. Apparently, life after kids'-show fame isn't all that great. Not only did the science community stop taking him seriously, despite his PhD from Cornell, but his fellow scientist who voiced his sidekick puppet, Geno the Neutrino, slept with his wife. When Sheldon pulls out Geno (it was a bargain at $20 on eBay), Jefferies says, "I'm awake, right? This is happening?" What an awesome shout-out to Newhart's hit series "The Bob Newhart Show" and "Newhart." Who can forget the shocking twist in the "Newhart" finale, when he wakes up only to realize that he was still a part of his previous life on "The Bob Newhart Show" and that the whole series was only a dream?

[Related: 'The '80s: The Decade That Made Us': Not an Exaggeration]

Newhart's spot on "The Big Bang Theory" ends with him at the hospital with Sheldon at his side, singing "Soft Kitty," of course. That haul up the steps must have done a number on poor Jefferies' pacemaker. At least his spirits were boosted before the medics came: Sheldon and Leonard told him what a profound effect he had had on their success: "A generation of young scientists are standing on your shoulders," Sheldon told him. When Jefferies realizes that he can't do his show as Professor Proton the next day, he asks Sheldon to step in. Talk about a nerdy dream come true!

Clearly, Sheldon is a megafan of Professor Proton's, but in real life, Parsons is equally as big a Newhart fan (minus the creepiness) -- who proved that his comedic timing hasn't missed a beat. Parsons told the Hollywood Reporter, "We've had some great people on this set, but he was the first person that I had that feeling of, 'I can't believe you're real.' He's an icon, a person that you have in your mind or in your heart, and they just don't seem real."

Other cast members also chimed in about the iconic guest star via Twitter:

It wasn't just the cast who loved Newhart -- so did the live audience. Galecki told the Hollywood Reporter, "He had a two-minute standing ovation from the live audience. Then the DJ starting playing the theme song from his old show, and he started crying. I was standing next to him, so I started crying. It was very touching."

The feeling was mutual. On his May 1 appearance, Newhart told the women of "The Talk," "It was like déjà vu; the audience was so close. … Chuck Lorre and I were talking about doing a show. I insist on doing a show in front of a live audience. That's the way I grew up. That's how I learned. I can't watch shows that are all laugh track." You definitely made us laugh for real, Bob!

Watch Newhart on "The Talk":

Check out the fan reactions from Twitter; then tell us what you thought in the comments below!

"The Big Bang Theory" airs on Thursdays at 8 p.m. ET on CBS.