The Big Bang Theory is a show about scientists, and it bolsters its academic credibility by bringing in guest stars from the world (galaxy?) of science to play themselves, as well as casting actors with graduate degrees to play characters on the show.
I'm not qualified to rank these guest stars on smarts, because I failed physics in high school. But as a professional clickbaiter, I am qualified to rank them based on how annoying I find their public persona. So without further ado, here are the 11 smartest people who have appeared on The Big Bang Theory, ranked from most to least annoying.
11. Neil deGrasse Tyson - America's most famous astrophysicist Neil deGrasse Tyson appears in the Season 4 episode "The Apology Insufficiency." Sheldon — and many others IRL — has beef with him because he famously demoted Pluto from planetary status to a mere rock floating in space (technically to "dwarf planet"). Tyson is a real smuggo with a bad habit of "actually"-ing everyone into a stupor, which earns him the low spot on this list.
10. Bill Nye - The Science Guy appeared in the Season 7 episode "The Proton Displacement" as Sheldon's new TV scientist friend in an attempt to make Professor Proton jealous. Bill Nye the Science Guy is fine and likable and uses his platform for good and all that, but he just seems too desperate for attention, you know? Like, we get it, Bill Nye, you're the Science Guy.
9. Ira Flatow - Ira Flatow is public radio's most prominent science host. He's been explaining science to us dingbats as we drive around on Friday afternoons since 1991 on Science Friday. He's appeared on TBBT twice, via voice only in Season 3 and in person in Season 7's "The Discovery Dissipation," when he interviewed Sheldon on his radio show. He scores relatively low here because he paid $145,531 to settle allegations his company misused a federal grant, which doesn't look so good on the resumé.
8. Mike Massimino - Mike Massimino is an astronaut who made two trips into space to work on the Hubble Space Telescope. He appeared on TBBT several times as Howard's outer space sherpa. There's nothing wrong with Mike Massimino, but he's a close associate of Neil deGrasse Tyson's, so he loses points for that.
7. George Smoot - Astrophysicist George Smoot is notable as the only person in history to win both a Nobel Prize and Are You Smarter Than A Fifth Grader? He appeared in Season 2's "The Terminator Decoupling," in which he turned down Sheldon's offer to collaborate with him on a research project.
6. Elon Musk - The visionary founder of SpaceX and Tesla appeared in Season 9's Thanksgiving episode, "The Platonic Permutation," volunteering with the gang at a soup kitchen. He's annoying because he's trying to colonize Mars when he should be using his brainpower to fix problems here on Earth.
5. Steve Wozniak - The co-founder of Apple appeared in the Season 4 episode "The Cruciferous Vegetable Amplification," in which he autographs Sheldon's ancient Apple II computer. Woz is interesting because choices he made in his career have left him with hundreds of millions of dollars rather than billions.
4. Mayim Bialik - Yes, Amy is super-smart in real life, too! Mayim Bialik has a Ph.D. in neuroscience, just like her character. It's good that she has something to fall back on in case this acting thing (and the millions she makes from the incredibly profitable Big Bang) doesn't work out.
3. Buzz Aldrin - Buzz Aldrin was the second person to walk on the moon. Now he's the third person on this list. He once punched a conspiracy theorist who was harassing him with accusations he didn't walk on the moon. It's one of the best videos on the internet. He appeared in the Season 6 episode "The Holographic Excitation" handing out space-themed candies (Milky Ways, Mars Bars, etc.) to trick-or-treaters.
2. Danica McKellar - Danica McKellar didn't act much in the years after playing Winnie Cooper in The Wonder Years as she focused on her studies — she earned a degree in mathematics from UCLA in 1998. She has since authored several books encouraging teenage girls to excel in math. She appeared in Season 3's "The Psychic Vortex" as a potential love interest for Raj.
1. Stephen Hawking - Stephen Hawking sold 10 million copies of his book A Brief History of Time by making cosmology, the most mind-bending subject imaginable, digestible by the masses. You have to be so smart to make stuff that complicated comprehensible to lay people. So shout out to Stephen Hawking. He first appeared in Season 5's "The Hawking Excitation," where he made Sheldon faint with embarrassment by pointing out a crucial arithmetic error in Sheldon's paper, and has since appeared a few more tines, most recently in the 200th episode singing happy birthday to Sheldon.
The Big Bang Theory airs Thursdays at 8/7c on CBS.
(Full disclosure: TVGuide.com is owned by CBS.)