What Jim Parsons from The Big Bang Theory thinks about Michael Keaton as Sheldon Cooper

“The Big Bang Theory” was never a critics' darling, and critics were a little baffled when they found that “Young Sheldon” was starting to win them over. But both shows were huge Nielsen ratings hits that attracted plenty of big-name guest stars. The former earned its nerd reputation with appearances by “Star Trek” legends like Leonard Nimoy and LeVar Burton, while it achieved TV immortality by casting sitcom god Bob Newhart as Professor Proton. As for “Young Sheldon,” producers welcomed Newhart to TV as a science host and also brought in big-name talent like Melanie Lynskey, Jason Alexander and Lance Reddick.

No matter what you think of these ultra-mainstream shows, you have to accept that there is no shame in making a cameo in the universe of The Big Bang Theory.

Now that we know that CBS will be delving even deeper into that geek realm with “Georgie & Mandy's First Marriage,” a sequel to “Young Sheldon,” you may be wondering, “Could a spinoff of 'The Big Bang Theory' ever add an A-list actor to the main cast?” Granted, you'd have to be terribly bored and/or obsessed with these shows to ask that question—or, worse, you'd have to be Jimmy Fallon.

Oops, I forgot to finish the sentence properly. Let's try again.

You could be Jimmy Fallon interviewing Jim Parsons on The Tonight Show and noticing that a photo of a young Michael Keaton that was circulating on the Internet for some reason bore a strong resemblance to Iain Armitage, who played a young Sheldon Lee Cooper for seven seasons. And if you were Parsons, you would be compelled to answer the question, because that's how talk shows and interviews generally work.

What would Parsons say in such a situation? The world got an answer to that question when Parsons stopped by The Tonight Show earlier this year.

After noting the similarity between young Sheldon and young Keaton, Parsons answered the question Fallon had: Could “Old Sheldon” starring Michael Keaton be in the works? Parsons quickly responded, “Let me tell you this: I doubt that's going to happen.”

When asked if Parsons believes Keaton could handle the challenging task of playing an aged version of the know-it-all character, the sitcom star was surprisingly complimentary of the legendary Oscar-nominated actor, telling Fallon:

“I would be thrilled if Michael Keaton joined the cast of Sheldon. I would be amazed. I've admired this man my whole life, starting with 'Mr. Mom.' I mean, what a great guy. He's a wonderful actor.”

“Mr. Mom,” eh? I will not tolerate this erasure of “Night Shift,” especially from an actor my age, old enough to have secretly watched the R-rated Ron Howard-directed comedy when it was on pay TV nonstop in 1983. Maybe he wasn't that savvy. Or maybe he just hates Shelley Long.

In any case, it is safe to assume that “Old Sheldon” starring Michael Keaton will never happen, while Jimmy Fallon will continue to justify his existence for the foreseeable future by presenting “The Roots” five nights a week on the network.