StarTalk Radio - What Everyone Knows You Know with Steven Pinker

Episode Date: January 23, 2026

What happens when everyone knows what everyone knows? Neil deGrasse Tyson and comic co-host Chuck Nice dive into human psychology and how recursive common knowledge is the invisible glue holding civilization together with cognitive scientist and author, Steven Pinker.NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free.Thanks to our Patrons Zypherior (Fjottrik), Brett Peterson, Sheila Weinhardt, baltimega, Eric Gouse, Mathias Toft, Mike, Alex Boyer, Joey, Nathan, Mark, logan, Tal Rozow, Craig F, Nathir Kassam, Doug Calli, Artem, Jay Sawyer, Owen Aston, Tyler, smbriggs1, Galaxy Master, Stephanie Edwards, Fahad Sadiq, Erasmus, Margaret Kaczorowski, Julia, Marie Rausku, Andrew Talley, Wayne2566, Rob Weber, Eric Cabrera, Galarian Rowlet, Mark S. Meadows, Alexander Burov, Christopher Knight, Dan, William Hughes-Ruddell, Lisa R., Alison Broussard, Alex M. Zepeda, Michael Kroll, Caroline Cockrell, Shakeel Kadri, Cassondra Lowe, Ethan Rudkin, Fabio Scopel, Denisse Bermudez, Jacqui Wakeley, Nick, Shelley, Christina, RT, Jan Souček, Christopher NAVARRETTE, Ken, Dek Shanaghy, Matthew Bosheh, Ms. Netta, Deciphering Yiddish, DxGhostHawk, Olga Cadilla, Rick Prunty, Young Hahn, Yen-Chen Lee, Gail Reed Lobo, Joe Horner, Eps15 Unc, HiTecLoLife, Shazia, PatienceHoney, James Watson, Alex Court, Rylan Accalia, Alex1016, Çağlayan (Chao) Karagözler, Nick Parks, Christopher Causey, William, Dana, Dagim Afework Mekonnen, joseph Rollins, ulus, Brent Knoll, Ron Mueller, Rosa Harris, Casey Hall, Jill Whalen, Honey Moon, Neicy, Justin Laning, Chris Mackenzie, Malik Sankofa, and Jeff Allmendinger for supporting us this week. Subscribe to SiriusXM Podcasts+ to listen to new episodes of StarTalk Radio ad-free and a whole week early.Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus. Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

Finally got Stephen Pinker. I know. Okay, yes, we're going to learn all about how the brain is messed up. We don't need him for that. Coming up. The latest from the mind of Stephen Pinker on StarTalk. Welcome to StarTalk. Your place in the universe where science and pop culture collide.

StarTalk begins right now. This is StarTalk, special. edition. Neil deGrasse Tyson here, you're a personal astrophysicist. And when you hear special edition, that means we have Gary in the house. Hey, Neil. How you doing, Gary? I'm good. Jackie Baby. That's right. How you doing, man? I'm doing great. So today, we're talking about common knowledge. Yes. Common knowledge. Uh-huh. But why is that interesting? If we think about it, we humans have evolved to be social creatures and we rely upon each other for many things. We use language to communicate and coordinate ourselves.

But do we consciously strategize in our social behavior and are we aware of our own signaling when we interact? And to the point, what role does common knowledge play in our everyday lives? I mean, I depend on that all the time as an educator. Fine, but a lot of people won't realize that it is something they're using as a tool. Some people will, as you do. And does it then play a role in the big ticket items like financial crashes or political revolutions. Now, okay, I can drone on. I've said enough. Let's introduce our

guest. We're going to connect common knowledge to revolutions. Let's see. Okay. Okay, we've got the world's expert on that topic. Yes. Sitting right here. Well, thanks, guys. I appreciate that. You know. Camera, pan left. Stephen Pinker. Oh, we met Stephen. Welcome to StarTalk. Thank you. My gosh, we go way back. We do.

Decades, I think, is your first time on StarTalk. Bad oversight on our part, because there's no reason for that. You're too active. Your stuff you work on is too interesting to have gone this long without you being on. So thank you. Better late. And I just have to ask up top, are you still winning the best hair for a scientist contest every year? Oh, I don't know if the luxuriant flowing hair club for scientists is still active.

Oh, that's not so. But I was... That's what it was called? That is a luxuriant flowing hair club for scientists. That means it had no black people in it. I think it did, actually. I mean, there are, I mean, some impressive dreadbox out there. You can dread your way here.

There are some pretty amazing afros out there too. Okay, okay. It's a pretty cool club. This is a project of the respected scientific outlet, the Journal of Irreproducible Results. Oh, good. Okay. We should do a whole episode on them.

one point. And the Ig Nobel Prizes. In Nobel Prizes. To my, I've never won one. That's great. So you are cognitive psychologist. I think that's what they call you.

Do I remember you being a linguist, though, long ago? I'm not a professional linguist, but that was your... I'm kind of a psycholinguist, which is the psychology of language, which is a branch of cognitive psychology. That's how I first met you and knew your work. But for me, language is just one of the amazing things the human mind does. So I'm not... I don't have a PhD in linguistics, but in

talking to psychology. Got it, got it. And I have got you here is the Johnstone family professor of psychology at Harvard University. So are you in the famous building, the psychology building there?

William James Hall. William James Hall. The 15-story white building sticking out like a store, sore thumb in a Cambridge residential neighborhood. I got you down here for a dozen books. Several of them are some of my favorite books. You know, the blank slate,

which had his own bit of controversy, but it's fun to see an intelligent arguments presented into that space. the better angels of our nature? Oh my gosh. It has the two words common knowledge in the title. In the subtitle. So give me the full up title.

So the title of the book is, when everyone knows that everyone knows dot, dot, dot. And there's a story behind that. The subtitle is common knowledge and the mysteries of money, power, and everyday life. Whoa. And I can explain all of those things. Leave anything out there.

That is, that's a title. That's actually three titles. You see what he done? I mean, I know you're just like. But you've put in mysteries. There you go. And then money and power. I should have put in sex, too.

Yes. She's completely manipulating the buyer. Of course, right. Now I want to hear the story behind this title because that's a lot. Okay. So common knowledge in the technical sense refers to the situation where I know something, you know it, I know that you know it, you know that you know it, you know that I know it, at infinitum. So it's when everyone knows that everyone knows.

And the dot, dot, dot, dot is essential. I had to fight with my editor. He says, oh, it'll screw up the computer listings on Amazon. That's the infinity. Because technically, it does mean... You know, the first I saw that was Ralph Cramden in The Honeymooners. You know that I know that you know. Norton.

Norton. Oh my God, I didn't put that in the book. Norton. Actually, that's Eddie Murphy. No, no, he's imitating the actual honeymoon is right. You know that I know. You know that I know. I can't believe I left that out.

Yeah, that's my first encounter with the infinity. I got to look that. up. Yeah, yeah, yeah. That belongs. And if not the original, then it's definitely Eddie Murphy imitating them. Right.

Just as good. That may be better. Yeah, so to be distinguished from private knowledge where everyone knows something but they may not know that everyone else knows it. And that makes a big difference.

It does. Wow. So it's been explored to think about that. It's been explored by game theorists, the branch of mathematics dealing with the best strategy when other people are dealing

with, have their own strategies. It's a big deal in economics for reasons that we'll get to. It's been studied by philosophers. But it is a psychological phenomenon. It's getting in the heads of other people when they're getting into your heads, or still other people's heads.

And there have never been explored it from a psychological point of view. Now, why is it significant? The reason that it's important is that common knowledge is necessary for coordination. That is, for two people being on the same page, doing things that benefit them both as long as each one can expect the other one to do it

and expect it. Don't we call that civilization? Well, civilization does depend on institutions like government, like money. The reason that's in the subtitle is, the only reason that a piece of paper with Abraham Lincoln on it is valuable is because other people treat it as valuable.

Now, why do they treat it as valuable? Well, because they know that other people will treat it as valuable. That's what makes it a currency. Likewise, for power. There's no way a government can intimidate every last member of its citizenry. Give it time.

I'm working. I recognize the impression. But the government has power. A president is a president, and a governor is a governor, and the chairman of the board of the chairman of the board, because everyone treats them as if they are.

It's a social reality. Our corporations, our religions, our gods, our conventions, even language itself, what makes the word rose refer to a rose, it smells just as sweet by any other name. Rose means rose because everyone knows it means rose, and everyone knows that everyone knows.

So all of our conventions, all of our ways of coordinating, all of our harmony depends on common knowledge. Just to give a concrete example from Thomas Schelling, the political scientist and economist, who was one of the originators of the concept. Imagine that, say, a husband and wife get lost in Manhattan. This is the era before cell phones. How can they meet up?

He can think, well, she likes to go to a bookstore, so I'll meet her there, but then she knows that I like to go to a camera store, so maybe she'll go to the camera store. But then she knows that I know that she'll, that she likes to go to the bookstore. She'll go to the bookstore after all. Meanwhile, each of them can kind of ricochet with this useless empathy and still not end up at the same place at the same time.

Nothing short of common knowledge, not only knowing something, but knowing that the other person knows that you know, gets them together. Now, common knowledge can be generated by language, and that's how I got into it. That is, in this case, a cell phone call. Although it can also just be a convention, something that everyone assumes that just coordinates everyone.

Like, what day of the week do you stay home? Sunday. Why Sunday? Well, because everyone else stays home on Sunday. So that's a good reason for me to do it if everyone else is doing it. So a lot of our society depends on common knowledge. This immediately raises a question. People say, well, you define common knowledge as I know that she knows and I know that she knows and I know that she knows,

but no one can keep track of them. That's why you have plots like the honeymooners or there's an episode in Friends that people always tell me about where, Rayleigh, they don't know that we know that we know, they know that we know. You can't say anything. And he says, I couldn't even if I wanted to.

The point being that your head starts to spin when you have to keep track of more than two or three layers if I know that she knows. So how is this possible? Well, the reason it's possible is that we can get common knowledge at a stroke when there is something that we sense to be public or out there or salient or you can't miss it or it's in your face.

So if I see something at the same time as I see you see it, then that implicitly packs into it as many layers as we would ever need and we don't have to think them all through. But it also means that we're really, really sensitive to something that is public that you can't ignore versus something that may be known privately. And I have chapters in the book on how that shapes our language, why we don't just blurt out what we mean,

but often veil our intentions in euphemism and innuendo to prevent things from being common knowledge. Phenomena like being in the closet or... For any, whatever is the reason... Well, it used to be the gay... That's where my closet is. That means you have a walk-in closet. I didn't know that.

Very good. Ew. Well, my graduate advisor, actually, he insisted he was not gay. He was a homosexual to be... In the day. In the day. That's right. He said that to be gay, you have to be born in the 50s or later. He was born in the 20s. But no one ever acknowledged that he was gay, and he would never acknowledge it.

Someone who described him as a bachelor. Now, each of us... Confirmed the bachelor. Confirmed bachelor. Until he was in his late 50s when he finally, as we say, came out. Now, notice the metaphors in the closet means that it's not public, you can't see it. Coming out means not only can you see him, but you can see everyone else seeing him. But that's a good metaphor for common knowledge. And common knowledge in general governs our relationships as well as our institutions.

So it's not just money and power. The everyday life in the subtitle comes from the fact that our relationships of deference, of intimacy, of friendship, romantic relationships, transactional relationships. They all exist because both parties know they exist. What does it mean to be friends? It's not like you sign a contract. It was an implicit contract in a way. It is implicit.

And it's a complex that depends on common knowledge. Namely, what does it mean for us to be friends? It means that I know that you know that we're friends, and I know that you know that I know that we're friends. That's all there is to it. And so sometimes when we don't want to threaten a relationship, we might avoid common knowledge by hinting, slipping in our intentions as eating around the bush,

euphemism, you kind of catch my drift, you connect the dots. Whereas if you blurt it out, then that changes the nature of the relationship. Hey, this is Kevin the Somalié, and I support StarTalk on Patreon. You're listening to StarTalk with Neil DeGrasse Tyson. So what about those where I'll see the common knowledge, but there is what I'll call an acceptable duplicity. Yeah.

A two-way duplicity. A two-way duplicity. Like, we're both aware of it. Yeah. But at the same time, I don't want to upset the apple cart because what we got here is good. That's exactly what I talk about. I have a chapter called Weasel Words. Weep the words.

That sounds like a fun chapter. But acceptable duplicity, there's all kinds of kind of benign hypocrisy. The politician who resigns to spend more time with his family. The escort services. Would you like to come up for Netflix and chill?

Let's say you were trying to bribe a matriety to jump the queue and be seated immediately. You might kind of holding out a $50 bill in peripheral vision say, Is there anything you can do to shorten my weight? I was wondering if you might have a cancellation. Right. $50.

And not if I give you $50, will you seat me right away? Exactly. Because that would be crass. So what does it mean for it to be crass? What it means is you're disrespecting the relationship you have, where he is the authority and he sees you where and when he pleases. You're treating him like a transactional relationship, which is a very different kind of human relationship.

Interesting. Likewise, what's the difference between? you want to come up for Netflix and chill and you want to come up for sex? Well, with Netflix and chill, there isn't really plausible to naibility. I mean, you know, she's a grown-up. She knows what it means.

But she could have some doubt that you know that she knows that you know what it means. And she could think, well, maybe he thinks I'm naive and I'm just turning down an invitation to a movie. He could think, well, maybe she thinks I'm dense and that I might think she's naive or I might think that she doesn't realize that I'm not naive.

And so they can maintain, go back to their platon relationship, they haven't jumped to the plausible deniability. Right, right, right. Well, it's a plausible deniability of common knowledge. Because when you think about it, it's really not that plausible. Right. Everybody knows. But like you said.

Everyone may not know that everyone knows. Exactly. And what that does is it allows you to save face. So saving face, by the way, another great, going back to the idea, how could, if common knowledge is so important, as I say it is, and it requires, I know that she knows, which makes your head hurt, how

could it work so well? And one of the reasons is that we talk about it, not using the language of philosophy or game theory, but metaphors of something being visible out in the open. That's why we use expressions like in the closet or saving face. Face is the part of you that other people see and that you use to see other people. So saving face or losing face is a great metaphor of common knowledge. Let's really saving the facade of your face in a way, right, saving the face that you had established prior. Face and facade are related.

I guess so. Do you know in the movie Back to the Future, there's a deleted scene, which... How could I know that? Okay, sorry. Where the doc is setting up his connection to the clock in anticipation of the lightning strike. Okay. And the cop comes by and say, oh, Doc, what you do? I'm just doing some weather.

Give me his voice, some weather experiments. Oh, I'm doing some weather experiments. Thank you. And then... And so then, and he said, you got a permit for that? And he says, Of course I do. Okay, so then he comes down and goes up to him.

This is the deleted scene. He walks up to him, opens his wallet, and there's just cash there. Oh, my goodness. That doesn't have his permit. I didn't know. Oh, I was about to see. I didn't see that. Yeah.

So he bribed him, but that's kind of out of character with how he is, he's just a lovable, dottering old scientist. That would have damaged his character. It would have damaged his character. It would have damaged the character. Yeah, that would have damaged the character. That would have been a perfect example. transactional. Well, the thing is that

it's in fact transactional, but it's very dangerous to suggest to a cop that you have a transaction. In fact, it's illegal. So it just makes it visible. Exactly. That's all it is. It's somewhere in here. And so, you know, it's not plausibly

deniable, but it's deniable that the other person knows that you know or knows that you know that he knows that you know. And that's what flips it from deference and respect and authority to transact. And you want to avoid that flip, but you still want to do business. That's why they're reasonable.

Because I'm from Philly, and it was, of course, Philadelphia politicians. But I forget the name of the scandal, but it was very famous because they caught it on tape. And only one politician didn't go for it. But these people, these feds dressed up as like Saudi businessmen. Oh, and they had. Abscam. Abscam. Abscam.

Ab scam. That's exactly right. Abscum. 1980. And they had like piles of money. like in sitting out. That's been done a number of times around the world. As they were discussing what they wanted.

Oh. And then only one of the politicians was just like, yeah, I'm not worried about that. Let's talk about. And everybody else went down. It was the financial seduction. Yes. But they never said this money is yours. They just put a pile of money in front of them.

And they were like, so let's talk about the new rail line. Veiled bribes. Veiled threats. Like I quote an episode from the Sopranos in which a member of the family approaches a high school acquaintance says Hey, great to see you, Danny. I hear you're on the jury for the soprano trial.

It's an important civic responsibility that we should all take part in. You've got a wife and kids. We know you'll do the right thing. That's a veiled bribe. Now, of course, bribes are extortion is illegal. Right, right. I mean, in everyday life, there are occasions

where there are implicit veiled threats that you don't spell out in so many words because that establishes a relationship of dominance. And you may want to avoid that relationship while still getting the message. Because that can really change the dynamic. Change the dynamic. So that's what that chapter is.

That doesn't happen in the black community. It's just like, I will kick your ass. It's resolved in the moment. It's resolved in the moment. What? I will kick your ass. No. Well, there are, I mean,

so that's a case where the relationship of dominance is already established. That's the exact scene in coming to America. Is it? Where they're at the McDowell's home, and the king says, how much for your daughter? Oh, okay? This is America, Jack. And you better stop me before I put my foot up your ass.

Was that John Amos? Yeah, yeah, yeah, yeah. I forget the exact words. In the moment. It was a, because it's a king and just like an rich American. Another great example. So why do cultures differ from each other? Well, if you think of the different kinds of relationships, so the basic kinds of relationships are communal sharing, warmth, intimacy.

That's one model. Not America. Well, another model is... What's mine is mine and yours is mine. Well, there's actually a twist on that. So another relationship is hierarchy, you know, alpha male, pecking order, top dog. And the third one is transactional. Now, where cultures differ is not across the board.

But in what kind of relationships, parent, child, student, teacher, employee, boss, friend, friend, what resource, money, favors, sex, and in what context, home, school, public. If you mix and match those, that gives you kind of all the variation from Anthro 101. And so there's certain resource. So, for example, there are cultures that really openly trade brides or, you know, daughters to become brides. ours doesn't commoditize that explicitly, but we do say buy and sell land, which some cultures don't do, where the land might be communal.

And so if you think of all the resources, all the context, all the pairing... It's quite the matrix of how that can come together. That's kind of the matrix of Anthro 101. Wow. So if we look at common knowledge as a variant of culture and different cultures prize certain common knowledge differently, how often do we get the misinterpretation of our common knowledge?

We often get misinterpretations when they're cross-cultural encounters. Exactly, yeah. And that's part of what culture shock is. You don't know what are they, what is the common knowledge in the new community that you have to deal with. And that can result in war. It could result in war. I mean, it can result in misunderstanding, sometimes comical ones. And it's used in comedy as in coming to America, as in Borat,

where you have the bumpkin from one culture using the assumptions that were native to that guy's culture. completely inappropriate, sometimes leading to embarrassment, sometimes to shock and outrage. Yeah. And then if we look at the communication through body language or unintentional signaling. Yeah. So there's a, I have a chapter called laughing, crying, blushing, staring, glaring, about nonverbal common. Couldn't get a long title then. Laughing, crying, blushing, staring, glaring. Glaring. Okay. Now, we have dozens maybe hundreds of facial expressions, smiling and frowning and grimacing and so on.

But on top of that, we have some really conspicuous forms of nonverbal communication that have puzzled people for millennia, such as laughing. Why do we interrupt our speech with that staccato noise? Yes, Stephen, why? I thought you'd never ask. Because something needs to pay his mortgage.

I mean, come on. I forgot. There's a whole perfection that depends on this, yes. Yes. So what I argue is that for these conspicuous displays, blushing is another one. Why should blood go to your cheeks? Crying, why should fluid drip?

Why do you shed tears? I suggest that they are common knowledge generators. So when you're laughing, you know you're laughing because your breathing is interrupted. Other people know you're laughing because they can hear it. Other people know that you know, you know that other people know, etc. Blushing, you feel the heat of the blood, the inside in your cheeks, knowing that other people can see the...

the change in color from the outside, and they know that you know that you're feeling it, all the more so when they say, you're blushing. I've never had that problem. Yes, it's not a black people. That's why speaking about me. It's a lesser thing.

Okay, so maybe you can find it. So Darwin worried about this, because Darwin was a big proponent of universal emotions. In fact, for him... He had a whole book on it. The expression of the emotions in animals and men. Yes, yes. And in fact, he used it, in fact,

as an argument against, the kind of the scientific racism of his day, which said the different races were independently evolved. Evolved or created, one or the other. Either one. And he said that the similarity in facial expressions, in many other aspects of emotion, showed that we all descended pretty recently

from a common ancestor. Wow. And his data, I mean, he was kind of an invalid, but he corresponded with colonial officers and missionaries and traders, all over the world, and he had them, gave them questionnaires to ask of their interactions with local people, which they then mailed back to him. So just to be in context, this is before photography could capture it.

Right. I'm just at the dawn of photography, what that is. In fact, his book, this book that we're talking about was the first use of scientific photography, although not for cross-cultural studies because the missionaries didn't have cameras out there in the field. But he actually used it to analyze the musculature in facial experiments. including studies where they got a person in an asylum, and they shocked the different muscles

to see what they did to a facial expression. Wow. That was a bit of a digression. Going back to the question, though, of do... Asylums, all they ever use is electricity on you. That's what it seems like. But he asked the question, do dark-skinned people's blush? And is it detectable?

And at least the answer from him, and the answer that I got from Nina Jablonski, who's an expert on skin color, is yes. It may not be... I'm not denying it. I'm just saying it's not an active referent in our comments of people's emotions. But I even cite a Ghanaian physician. Ghana? Ghana.

Yes. I'm very dark-skinned. You said, well, my mother can tell when I'm blushing. It's a change in color. Anyway, the point is that it's a common knowledge generator in that you know that you're experiencing it. You know that other people can see you experience it. They know that you're experiencing it. you're looking at the world through a scrim of fluid.

It blurs your vision. At the same time that other people can see the glistening or the trickle. So again, you know that you're crying. Other people know that you know that they know. And eye contact is the ultimate common knowledge generator because you're looking at the part of the person that's looking at the part of you that's looking at the part of them

that's looking at the part of you at infinitum. Here we go again. Although you don't have to think about it at infinitum. But what about this is the eyebrow thing? Like, why should that? mean anything other than what it means. Well, Darwin dealt with that in the book where he noted that some facial expressions are vestiges or remnants of facial postures that animals do when they're about to attack or they're defending themselves. So in the case of the fear expression, he noted

that if you're likely to be a prey animal or someone who's going to be picked on by the alpha, you've got to open your eyes wide to see where threats might be coming from. If on the other hand, you're the predator or you're the alpha. You want to focus. Exactly. And the remnants of that include,

and so the furrowing your brows, which I think narrows the field of vision, that may even narrow, if the folds of skin actually intrude on the pupils might increase depth of field. Yes, it does. Optically. That's why people, if they don't have their glasses on.

They squint. They squint. They squint. They don't even. know that they're increasing their depth of field by doing so. They're not actively thinking it. They just know they see better. Going back to these nonverbal common knowledge generators,

we use them to make something public that formerly was private. Within us. In the common denominator, yes. So in the case of eye contact, now that developed way before we were humans, because among primates, eye contact is a threat signal, the dominant stares at the subordinate who looks away, which is, by the way, also true in humans, the boss looks at play.

People walk with the head down. That was the first thing I was told when I came to New York City as a kid. We were on the subway and they said, whatever you do, do not make our contact. I said, you looking at me? Who are you looking at it? The young person walked past me yesterday evening, and I'm thinking, if you don't look up,

you are going to walk into me. And it was intentional not to make any eye contact. Well, the anthropologist, Irv-Divore, you should tell us class, if two human beings look into each other's eyes anywhere on earth for more than six seconds than either they're going to have sex or one of them's going to kill the other way.

That is so true. There you go. Oh my gosh. What a great saying. That is true. It's true. So why is this so uncomfortable? I mean, even, like, I don't mind

making eye contact, especially with a person's decent looking. I've got to tell you, when somebody's unattractive, I'm, ooh, it's tough. I'm just saying, it is rough to look at somebody who is not attractive and like maintained eye contact. But prolonged eye contact,

and I don't know if it's just me, but I'm just going to put it out there, I'm going to be honest. It gets a little like creepy and uncomfortable. Oh, it absolutely does. Okay, so, and I actually write about this. So what we call eye contact an ordinary conversation is it's a bit of a misnomer.

Your eyes kind of dance all over the face. You spend a lot of time lip reading, but it's the eyeball-to-eyeball stare that's really a pose, which is something different. Now, we're humans, we're not, you know, we're not monkeys, We're not guerrillas. And so eye contact doesn't have one meaning.

I mean, it can be seduction. It can be threat. But more generally, it can be something that formerly was private knowledge is, as of this moment, common knowledge. Which is why we say things like, can you look at me in the eye and say that? That's great. Tell me the truth.

Basically, we're trying to interpret so many different things, and that's why you get uncomfortable. And when you're embarrassed, you look down, you look away, you avoid making eye contact. So what laughter does is it makes what used to be private knowledge, common knowledge, where it's some indignity or infirmity or weakness of some butt of the joke. Now that can be someone that you're trying to bring down. It could be someone you're trying to keep down in aggressive humor.

Although there's also, of course, convivial humor, what we've all been doing, where the signaling is to reinforce the, egalitarianism is the basis of warmth and friendship. Because there's always a danger of dominance creeping in. With any two people, one of them is going to be more better looking, smarter, richer, more powerful. But that's not what you want to do in your friends. When your friends, it's like we are all on the same level. And so by calling attention to some weakness in yourself that you could lord over people,

but you don't want to lord over people, or vice versa, gentle teasing and joshing that the other person accepts. then you're reestablishing the common knowledge that the basis of our relationship is... Self-depreciation. Yes, exactly. So what does one do for, is it, whatever the number is, is it one out of ten or one out of six of us

who's on the spectrum? Where social cues do not play. Exactly. Might that be adaptive? Where now you don't know anything about me because my facial expressions are not responding and therefore I'm not revealing my inner secrets to you. Well, there is the...

That could have survival value. You know, I suspect that's more likely used strategically as in the poker face. That is the poker face where you deliberately hide the tells in a case where you're not in a situation of cooperation, but zero some competition. Right. Then any kind of tell could be used to your disadvantage. So I don't play poker.

Because I'm the worst. It's just, damn! Oh. Just kidding. All right, to go back briefly to the anime scene, what about the elephant in the room? You know the emperor's new clothes scenario? So I actually open a book with the emperor's new clothes

because that's a story about common knowledge. Yes. When the little boy said the emperor was naked, he wasn't telling anything they didn't already know. But he was changing their knowledge, because when he blurted it out in public, now everyone knew that everyone else knew that everyone else knew.

So he converted private knowledge to common knowledge. So first of all, that made a difference. That was the climax of the story. What did it is that change their relationship with the emperor from deference to ridicule and scorn? So a relationship of deference. To the emperor? To the tailor.

Well, but to the emperor too. At least in the... But the tailor fooled him. It's the tailor's fault. It's not the emperor's fault. Which is where I'm going to have him killed right away, as if he was clinging to a boat. Did I have a Disney-ified version of that story?

I mean, the tailor is the one who should be... Yes, but at that moment in public, it was the emperor who suffered the dissent down to the... Embarrassed. Especially in the Danny Kay version of the story where it was met with ridicule and scorn, in the lyrics to the song. Okay.

And deference is a matter of common knowledge. You defer to someone because you know they'll stand their ground. Why do they stand their grown? Because they know that you'll defer to them. Why do you, and how do they know that? Well, because you know that they know that they'll stand their ground at infinitum. And what about the mutuality of respect? I mean, that's the flip side of that.

Sometimes there's a matter of deference because you truly respect the person. They understand that you truly respect them, and they respect that, you know? Yeah, there are different flavors of the hierarchical relationship. It could be dominance, which basically means, you know, I could hurt you if I wanted to.

There can be status. I could help you if I wanted to. There can be expertise. You all have a common interest in the decisions being made by someone who knows what they're talking about. Or even sometimes if everyone's going in, you know, the expression hurting cats,

even if no one has a particular reason to be the, the decider, it's best for everyone if there is a decider. And that can give you a hierarchical relationship. But we do use metaphors like saving face out there. And the elephant in the room is obviously something that everyone can see and that you can ignore. It makes sense. So the elephant in the room is the emperor's new clothes because no one is talking about it.

That's right. Even though everyone knows that it's there. Which is why the saying always is, let's acknowledge the elephant in the room. In other words, like, we all see it. Now let's talk about, yeah. Listening to you so far, I get the feeling that there's a kind of a logic to common knowledge and maybe even like a code. And that might then culturally vary.

Yes. So I think the phenomenon of common knowledge and things that generate it like blunt speech, like eye contact is universal. But then what are the relationships that are negotiated with common knowledge or ratified by common knowledge? That is, what can friends share? what can a boss demand of an employee, how is sex treated,

can it be transactional or is it only intimate? All of these mixing and matching of resources, relationship models, and contexts, that's what makes cultures differ from one another. But in each case, there is some kind of common knowledge that holds the relationship in place that sets out what you're allowed to exchange,

what you're allowed to hoard, what you're allowed to demand, and that's what it means to be a competent member of a culture to master that, each one of them being a matter of common knowledge. So, Stephen, I try to know what is common knowledge so that I can access it as an educator. I can tap it into it, I can add to it, because I don't have to train people to know things that represent common knowledge.

Comedians, your joke does not work unless everybody knows what you're talking about. The more universal, the better. And by universal, I mean... You mean earth-wide, I'm an astrophysicist here. Correct yourself. Okay. The more commonly accepted, the better. The more earth-wide.

Right. The more earth-wide, the better. But really, it's about experiential knowledge. Even if you've never been through what I am talking about, if I can put you there, then you will laugh with me. There are many people, many comedians that talk about marriage and people who are a single laugh. because they have observed somebody else in a relationship that they understand what this comedian is talking about. That broadens your access points to the person.

For instance, when Stephen was talking about the lost couple and the woman was going to a bookstore and the man was going to a camera shop, the first thing that popped into my head was, well, listen, if you know what's good for you, you better go to that damn bookstore. Because every husband knows that if I don't show about the bookstore, I'm in trouble.

And that's the first thing that popped into my head. So this is an important point because what humor often does is it establishes common knowledge. That is if you get the joke, then what has just been made public is something that you privately knew along. And so you get that feeling of solidarity with the other person. If you're laughing at the same thing, then what was unstated that makes the joke funny is something that you have in common. That's why humor is such an important bonding agent for in dating, One of the main criteria in accepting a major sense of humor. Sense of humor.

I never thought deeply about that fact. I just thought it would just be more entertaining, but it's more bonding. What it means is that you share a lot of common ground, common knowledge. That is, you can't get the joke unless there is some hidden, unstated premise that makes it work. And that can bond people. It can also be a devastating put-down. an intolerable insult. I give the famous example of the roast

at the national press correspondence dinner during the Obama presidency, where Donald Trump was in the audience, and Obama made a number of jokes at Trump's expense. Ordinarily, people are expected to be a good sport and to accept the barbs, showing that they have commonality, common ground with everyone in the room. But Trump took it personally, he was visibly fuming and scowling at a joke like, well,

it would be good if Donald Trump was president because he could accomplish things like closing Guantanamo, because he has a history of running waterfront real estate into the ground. That's a great joke. Trump didn't think so. No. It's a terrible joke. So the point is that everyone who laughed, first of all, knew that Trump,

despite his boasts of being a business genius, had a string of failures, which made it all the more painful for Trump, for that to be brought out into the open. According to some stories, that's what led him to just... run in the first place. Yeah, for revenge. And they're all now being investigated by my Justice Department. It was a hoax, Obama, and his jokes.

So what happens when the humorist just twists the common knowledge? And I think you've got, you touch this in the book, toilet paper shortage. Oh, yeah. And the origin of that story. So there's some viral fads and phenomena, which can be really significant. So common knowledge is a kind of virulent. property. It can be. Yes, exactly. So in the case of, say, a bank run where a rumor starts that the bank

might be in trouble, now of course, banks don't have enough cash on hand to redeem all their deposits. But if you worry that other people worry, that still other people worry that other people worry that the bank might be insolvent, then everyone rushes to the bank to withdraw their savings, which can actually cause the bank to fail, even if it was sound. And that can bring down an entire economy. That was in part the cause of the Great Depression. And so when Roosevelt said, the only thing we have to fear is fear itself, this was a theorem of common knowledge. It wasn't just a feel-good bromide, but he is accurately diagnosing the situation, which is why financial leaders... That's Roosevelt speaking to flat-earters. The only thing we have to fear is

fear itself. How long have you been waiting for that? Oh, my God. No. That's a good one. his spirit. It's so bad, I'm laughing. It's good. Oh, dear. It's totally good. You got your dad joke out, haven't it? That was a dad joke.

And, of course, the run on the bank. It got me, though, I got to say. The run on the bank in Mary Poppins was caused by a little child. Yes. Where they took his coin, he had some kind of pence or something. Shilling. Yeah, to start an account, but the boy didn't want him to do that. It's like, get me back my money.

And then this permeated the holes. Two older ladies overhear the conversations. Over here. and then it stouts. Oh, they're not giving him his money. I want my money. And then there was a run on the bank. That's so funny.

That's great. That's great. So, once again, something that is public can then set off cycles of thinking about what other people are thinking about what other people are thinking. That's the virulence you're talking about. Because it just fires through. And a similar phenomenon might be why there was a toilet paper shortage during the COVID pandemic. It actually wasn't a toilet paper shortage until people thought there was this toilet paper shortage.

Right. They hoarded because they thought other people, were hoarding. When stores started posting maximum three rolls per customer, that didn't so much throttle the demand as it reassured everyone that there was a shortage. Well, that other people

wouldn't be able to strip the shelves bare. So they didn't have to worry about stripping the shelves bare. I only need three rules, but I'm only going to ask for three rules because none of the other people can buy more than three rules either. Right. And so that kind of... It's a level setter. It's a level setter. It's a level setter.

By the way, I still have tulipers. from the pandemic. I hate to win medical. According to one story, it came from a big common knowledge generator in the day, namely Johnny Carson on the Tonight Show. So in the old era of three networks, Johnny Carson was the king of late night. He hosted the Tonight Show for many decades. When you were watching it, you had a good reason to think that the rest of the country was watching it

and knew that the rest of the country was watching it. In the early 70s, after the oil embargo, when there was an oil shortage, he made the general joke one night. You know, we have shortages of everything these days. There's a shortage of gasoline, there's shortage of meat, there's a shortage of coffee. But you hear the latest? I read it in the papers. There's a shortage of toilet paper. Now it turns out

there wasn't a shortage of toilet paper. But as soon as he made the joke, there was a shortage of toilet paper as everyone started to hoard toilet paper. So fulfilling. And according to at least one theory, ever since then, whenever there is a hurricane or a blizzard, people think that toilet paper is the thing you've got to stock up

on because everyone else is going to start hoarding it. There was an episode of Kirby Enthusiasm where someone was revealed to have an entire closet full of toilet paper. Oh, yes, during the pandemic. That's great. The entire closet. But how much ass wiping do you think you need to do? How big is your eye?

By the way, in a hurricane, when your home floods, that toilet paper is not going to be worth anything. Yeah, wet toilet paper. Wet toilet paper really isn't so much fun, I'm saying. Well, in the other direction, you can also get speculative bubbles. You buy crypto because you think other people are buying crypto, at least we'll want to buy crypto tomorrow, so I'll pay more for it tomorrow than you pay today.

They're buying it tomorrow, because I think they'll sell it to someone who wants to buy it the day after tomorrow. The hot potato. Yes, or the greater fool. The greater fool. And that goes back to John Maynard Keynes, who in the 1920s compared speculative investing. So this is investing not because of the return that you expect on the asset. That is the profits that the manufacturer will make selling widgets, or the farmer selling food,

but you think you can unload it the security at a profit on someone else. He said it's like a beauty contest where instead of picking the prettiest face, the object is to pick the face that the most other people pick where they're picking the face with the same goal

that is trying to figure out what everyone else is picking. So it's sometimes called a Keynesian beauty contest. Don't we have that in primaries, the elections? And in elections are Keynesian beauty contest.

that is in a primary election, there may be a field of a dozen candidates, and no one wants to waste their vote in just deciding who's going to come in at seventh place as opposed to eighth place. Which is what rank choice voting is trying to resolve. That's why, yes, that's exactly what is trying to resolve. And so people are hyper aware for any signs

that someone has momentum, that they're in the lead, because they want to vote to determine who comes in first, not who comes in sixth. I don't want to waste a vote. That's what they say. And so during the coverage, any various trivial gaffes and last, or boosts can sometimes shoot a candidate to the top

or sink their candidacy. Like when a few years ago and Howard Dean was running for that. And everyone knew you can't vote for Dean now because his victory scream means that everyone knew that he had a silly victory scream. And that ended his candidacy. Can you imagine? Seriously?

No, I'm, yes. Don't make fun of us. No, no, no, no. You have some weird politics yourself. Oh, no. Highly qualified candidate who was not able to continue his candidacy because he was like, and then we're going to go to New Hampshire, and then we're going to go to Vermont, and then we're going to go to.

And he did that, and everybody was like, oh, dude, you can't be president, not acting like that. And then years later, we're just like, you know, you can grab them by, you can grab them by the whatever. You can just grab them anywhere you want. And they sometimes like, you do it against your thing. And we're like, yeah, that's the guy. That's the guy right there. We got to let that guy. The Trump phenomenon is interesting because what he did is done repeatedly

is that he has flouted norms that everyone thought were inviolable. They were inviolable only because people thought they were inviolable. And they existed as common expectation, common knowledge. And as soon as he flouted them and did not pay the price, they no longer existed as norms, which is why they're, I think, being copied by people like Elon Musk, also a troll, a liar, a braggard, that things that would be unthinkable for a president, for a CEO,

as soon as they're thinkable, they're thinkable. So is this the fracturing of common knowledge that is partly behind the polarity of society right now where people are just refusing and disinterested mainly to find a common ground? Yeah, so common knowledge always is defined relative to a network of sharing of information. It could be two people, in some of the examples we've discussed, it could be the entire country.

And there has been a segregation into two separate pools of common knowledge. Everyone blames social media, and it probably has something to do with it. But I think it's also cable news, Fox News, prior to social media, had that effect. You weren't watching Walter Cronkite at the same time as everyone else was watching Walter Cronkite or Johnny Carson. And residential segregation. when you had educated people walking to cities, leaving behind the less educated, when you had a decline in organizations that brought people together across the socioeconomic divides, like the army in the era of the draft, like churches, like service organizations,

like the Lions Club, like bowling clubs. You stop rubbing shoulders with people from different social classes. Each one then hung out with people like them, and then the common knowledge that they shared started to grow disjointed. Wow. So it feeds divisiveness. Because, I mean, it's the same issue,

as you said, multiculturally, right? Except now it's within the same culture, but now people are dividing with the same motive. Different cultures within the same country. Within the same country. Yeah. That makes me feel like it's exacerbated by what I'll call the vituperative disposition

of leadership right now. I don't know what that word means. I'm sorry. What does that word mean? Vituportive. It means like... It's very SAT. Is it?

It means like mean and nasty, like a diaper. So when we're siloed into these different camps like this, it becomes very easy then to point fingers and say, that's your enemy, that's your enemy, that's your enemy. And then it's okay to be mean and nasty towards those people. and it seems like that's exactly where we are. Nazi Germany took that all the way through. I wasn't even thinking along those lines, but absolutely, yes, that's how it went down. But norms of civility, things you just don't say.

You might disagree with someone, you might even not think highly of them, but you don't insult them to their face. I mean, you do on the playground, but there was a norm in politics, in corporations, in the media, that you pretend that you like them even if you don't. And those are some of the norms that are shattered. You don't lie blatantly.

Now, everyone lies somewhat. just, I'll always probably tell two lies a day. But you don't blatantly lie, you don't show a contempt for the truth, you at least try to pretend that you're honest. Can I give an example? So I befriended a, I have a sort of Republican confidant who's in Congress for like 25 years. You can tell them that it's me, Neil. He was in through Reagan and beyond.

And then I was talking to Al Gore. and I was saying I was friends with this guy, but I had to work it because we come from different places. And you know what he said? He didn't say anything bad. He just said, yeah, he's an acquired taste. That was pretty politic. That is a very politic.

Right? He didn't insult. He just said, you know, you got to work it. And then as any acquired taste would be. So that's an example. You don't hear that today. Yeah. Or when Winston Churchill was asked,

maybe the reason you lost the election to Clement Attlee is that people thought that Atley was more modest. He said, well, Mr. Atley has much to be modest about it. He did have a good term of phrase, John. Let me ask you, before we have to wrap this up. Yeah, we got to start rapping. What plays out if society remains unchecked where the common knowledge is distorted

or the common knowledge is dictated by the loudest voice, no matter what that voice is saying? Yeah, by nefarious forces. Yeah. Influencing. Yeah, well, we're seeing some of it. We're seeing the polarization, particularly the negative polarization,

that is not just disagreeing by thinking that the other side is stupid or evil. I don't have an algorithm for reversing that, but the kind of norms that we should spread would be ones of civil disagreement, epistemic humility, charity, things that go against human nature, where we tend to think of argument

as a competition, as a war. I attacked his arguments, he defended them, but then I demolished them. We use the metaphors of war in talking about argument. And in one of the chapters, I talk about a different model for argument, coming out of a mathematical theorem, claiming that we rational agents should not agree to disagree.

That's how I feel, by the way. Well, there's actually some, it's a proof by the Israeli mathematician Robert Alman that depends on common knowledge. We don't have time to go through it. now, but it does set a kind of an alternative paradigm for argument that instead of two people beating each other up and the one left standing wins, that's not how you discover the truth. Or even bargaining and negotiating and you come to some compromise.

You think about why should the truth just happen to lie halfway in between two opinionated guys? But rather, it's kind of a random walk where when two people exchange information, they might go all over the until they converge on a common conclusion. That's precisely how I feel. I mean, otherwise you just... Well, you would as a scientist. That is kind of like your whole field. If we disagree, it's because there's insufficient data

to create the agreement. Exactly. Let's go have a beer. And invent the experiment that will resolve this... There you have it, yeah. So that would be the kind of norm. It goes against human nature. I think the progress of science shows

it's the best way to do things. And even, of course, scientists are not immune to pissing contests, dominant dominance contests. And that's, you know, at least we acknowledge it's a bad thing. For that norm to spread in journalism, in politics, in the court system would be, would be a good thing. It would be transformative. Yes.

More truth, less vituperation. Once again, science saves the day. Science! And he said vitruperation. He doubled down on you. There it is. I see what he did there. Yeah, I think we got to call it.

quits there. Oh, my God. That's a great conversation, man. Let me see if I could take us out with a quick cosmic perspective with your permission. If you're feeling it, do it, but then, yeah. Yeah. I spend my life studying the universe, which is a huge, complex place. All the laws of physics I learn in physics class are applied in some place, in some way, at some time, in the unfolding universe. Also, the laws of chemistry and a search for life in the universe.

there's the biology that we bring with us, all of this. And every time I reflect on that, I think to myself, this is not the hardest thing we can think about out there. You know what the hardest thing is? The human mind. What's going on inside there? And we've got psychologists, neuroscientists.

It's a whole field trying to figure ourselves out. And, you know, I'm glad I'd do something as easy as astrophysics. relative to what they've got to worry about. And I just hope that the study of the human mind by the human mind is not the most complex thing we ever have to tackle in this universe. But if it is, get ready for that ride because the human mind is not logical,

it's not rational, only occasionally. it was not only the source of everything we value and call civilization, it may actually be the end of it as well if we're not careful. And that's a cosmic perspective. Stephen, thanks for joining us. Thank you so much. It's been a great pleasure. It's great.

Stephen Pinker's latest book. Give me the title again. When everyone knows that everyone knows, dot, dot, dot. You got it. There you go. Chuck. Always a pleasure. All right, Gary.

Pleasure, my friend. This has been StarTalk, special edition. Neil deGrasse Tyson, you're a personal astrophysicist. As always, keep looking up.