Neil deGrasse Tyson hosts Steven Pinker, cognitive psychologist and John Stone Family Professor of Psychology at Harvard University, along with co-hosts Chuck Nice and Gary O'Reilly for this StarTalk Special Edition. Pinker, author of numerous acclaimed works including The Blank Slate and The Better Angels of Our Nature, discusses his latest book exploring the psychological foundations of social coordination.

The conversation centers on Pinker's new work When Everyone Knows That Everyone Knows, which examines how common knowledge - the infinite recursion of 'I know that you know that I know' - differs fundamentally from shared private knowledge. This psychological phenomenon underlies everything from currency and government power to romantic relationships and financial crashes.

Drawing insights from The Expression of the Emotions in Man and Animals by Darwin, Pinker explains how facial expressions, eye contact, and other nonverbal cues serve as 'common knowledge generators' that make private experiences publicly visible. The discussion spans from evolutionary psychology to contemporary political polarization, revealing how the fracturing of shared assumptions threatens social cohesion.

The Infinite Recursion of Social Knowledge

Common knowledge requires infinite layers of mutual awareness - 'I know that you know that I know that you know' ad infinitum, distinguishing it from situations where everyone privately knows the same thing.

When Everyone Knows That Everyone Knows argues that this psychological phenomenon enables all social coordination, from currency (valuable because everyone knows others value it) to government power (effective because everyone knows others will defer).

The classic example involves a lost couple in Manhattan: 'He can think, well, she likes to go to a bookstore, so I'll meet her there. But then he thinks, oh, but she knows that I like to go to a camera store' - creating endless recursive thinking without resolution.

Biological Signals as Common Knowledge Generators

Laughter, blushing, crying, and eye contact function as 'common knowledge generators' because they make internal states simultaneously visible to self and others, with mutual awareness of this visibility.

Drawing from The Expression of the Emotions in Man and Animals, Darwin studied universal facial expressions as evidence against scientific racism, showing all humans descended from common ancestors through shared emotional displays.

'If two human beings look into each other's eyes anywhere on earth for more than six seconds, then either they're going to have sex or one of them's going to kill the other' - anthropologist Irv Devore's observation about prolonged eye contact.

Blushing occurs across all skin tones and serves as a common knowledge generator: 'You feel the heat of the blood inside your cheeks, knowing that other people can see the change in color from the outside.'

Veiled Communication and Plausible Deniability

Phrases like 'Netflix and chill' or 'Is there anything you can do to shorten my wait?' (while holding a $50 bill) maintain plausible deniability by avoiding explicit common knowledge.

Veiled threats and bribes preserve relationship dynamics: 'We know you'll do the right thing' from The Sopranos establishes dominance without explicitly creating a transactional relationship.

The difference between 'Do you want to come up for Netflix and chill?' and 'Do you want to come up for sex?' lies in maintaining doubt about mutual awareness of intentions, allowing face-saving retreat.

Viral Phenomena and Market Psychology

Johnny Carson's Tonight Show joke about toilet paper shortage in the early 1970s actually created the shortage: 'There wasn't a shortage of toilet paper. But as soon as he made the joke, there was a shortage.'

Bank runs exemplify how common knowledge becomes 'virulent' - spreading rapidly through society with real consequences, even when the underlying concern is unfounded.

Cryptocurrency and speculative investing follow Keynesian beauty contest logic: 'You buy crypto because you think other people are buying crypto, or at least will want to buy crypto tomorrow.'

Roosevelt's 'The only thing we have to fear is fear itself' was 'a theorem of common knowledge' - accurately diagnosing how shared anxiety about others' anxiety perpetuates economic crisis.

Political Polarization and Fractured Common Knowledge

Trump succeeded by flouting norms that 'were inviolable only because people thought they were inviolable' - demonstrating how shared expectations exist only through common knowledge.

Modern polarization stems from 'segregation into two separate pools of common knowledge' caused by cable news, social media, residential segregation, and decline of cross-class organizations.

Howard Dean's candidacy ended after his victory scream because 'everyone knew that he had a silly victory scream' - a moment of common knowledge that destroyed his viability despite his qualifications.

The solution requires norms of 'civil disagreement, epistemic humility' and treating argument as collaborative truth-seeking rather than dominance contests.