You’re finally on a solo vacation somewhere thousands of miles away from home. To celebrate your much-anticipated getaway, you treat yourself to a meal out. As a solo traveller, you begin talking to your server, who’s born and raised locally, yet you soon find yourself with some surprising things in common. It turns out your server has a connection with a childhood friend of yours who lives on the street you grew up on. Amazed, you think to yourself, “It really is a small world after all.” 

The six degrees of separation theory proposes that everyone in the world—yes, everyone—is connected by a chain of no more than six social ties.1 This idea challenges our intuition about distance and isolation, suggesting that even across cultures, borders, and backgrounds, we're all part of a surprisingly tight-knit global network. This is not only evident when you’re in a distant land on vacation, but it can also be the case between any two individuals across the globe. 

Sounds strange, right? This would imply that you are six degrees or less away from everyone in the world, ranging from former President Barack Obama to a Hmong villager in Vietnam. This isn’t just a coincidental confirmation bias of the world being small when your server happens to know your neighbor—there is a science behind it, with a history of small worlds, social science research, and large-scale studies that we’ll dive into soon. Let’s take a closer look at how the six degrees of separation work when tracing back your connection to this apparent stranger:

While this example of the five intermediaries between you and your server abroad may feel farfetched, we can all recollect a time when we ended up being strangely connected through mutuals, whether in-person or virtually. Today, the six degrees may be decreasing to only three or four with the virtual ties that bring us closer to others online through our professions, communities, and common interests.2 Another common way to visualize degrees of separation is via a social graph, such as: 

Social Networks and the Science of Connection

Modern research in network science has validated aspects of the theory, revealing how hubs, weak ties, and clustering play a role in connecting distant individuals.³ These principles underpin platforms like LinkedIn and Facebook, where mutual connections often span continents. While the original experiment testing the theory of six degrees goes back to the 1960s, recent research by Microsoft shows how billions of digital conversations across tens of millions of people link us by the exact amount of 6.6 degrees of separation.⁴ Let’s zoom in on how some of these principles in the modern technological world relate to how separated we are from each other:³

Whether it’s the spread of ideas, social movements, or misinformation, the idea of six degrees of separation has profound implications for how behavior travels through networks. Understanding these dynamics helps marketers, policymakers, and behavioral scientists anticipate how messages ripple across populations. It's easier now than ever before to trace the six degrees (or fewer!), when decades ago it may have taken several long conversations and arduous phone calls to attempt to make the same connection. Looking into how this is possible and discovering what information influences collective behaviors through increasingly connected networks sheds light on the invisible forces impacting our daily experiences. Social media and other digital spaces have shown the potential for degrees of separation to become even fewer, and we may soon see how advancements in AI, machine learning, or other contemporary technologies manage to bring us even closer together.

Small-World Network: A type of social system where most individuals are only a few steps or connections apart, even in large populations.⁵ For example, your coworker’s cousin might know someone across the globe, illustrating how social distance can be surprisingly small through indirect connections.

Nodes: The individual entities, such as people or organizations, that make up a network. In a social graph, each person is represented as a node, which serves as a building block for the entire system.

Edges: Also known as links, these are the connections or relationships between nodes in a network. Whether strong or weak, each edge represents a social tie that forms the foundation for the “degrees” of separation between individuals.

Small-World Phenomenon: An observation first made by Stanley Milgram in the 1960s that in many networks, most nodes can be reached through a small number of steps.¹ This concept underpins the "six degrees" theory, showing how networks are organized to achieve efficiency with minimal connections.

Degree Centrality: A measure of how many direct connections a node has within a network. The nodes with high degree centrality, like well-connected influencers or central figures, are key in how quickly information spreads throughout the network.

Availability Heuristic: A cognitive bias where people make judgments about the probability of an event based on how easily examples come to mind. For example, after hearing about a plane crash on the news, a person might overestimate the likelihood of being in a plane accident, simply because the event is fresh in their memory.

It wasn’t always so easy to track others down through online connections as we can today, but theories about our interconnectedness predate modern social networks. Prior to research focusing on how closely linked we all are, Hungarian writer Frigyes Karinthy wrote an appropriately named story called “Chains,” in which he proposed the concept that would become known as six degrees of separation. In Karinthy’s narrative, one of the characters challenges others by asking those around him to try to find someone on Earth that he would be unable to connect with through five intermediaries or fewer.⁵ A few decades later, a well-known psychologist decided to test out the “Chains” theory in real life.

In the first ever edition of Psychology Today, Stanley Milgram published an article titled “The Small-World Problem.”¹  Here, Milgram vouched for what Karinthy had originally proposed through his story: we’re all connected with distant strangers by about six other people. Going beyond the story itself, Milgram ran two studies in 1967 to see if the world is truly smaller than we think by randomly picking Americans in Kansas and Nebraska to deliver a package to a “target” stranger in Boston. The 300 senders only knew the recipient’s name, job, and approximate location, and were instructed to send the package to a friend, family member, or acquaintance (someone they knew by their first name) who had the highest chances of personally knowing the target. The recipient was given the same instructions, continuing the chain until the package reached its target destination. Though there were only a small number of successful postal exchanges, Milgram found that there were typically only five to seven intermediaries in each chain—suggesting an average of about six. Though Milgram’s studies only included participants in the continental United States, he suggested further studies would find similar results across the world.

While the theory of six degrees of separation began as a thought experiment about shrinking distances in a connected world, Milgram showed that it seemed to have some merit in reality, accurately encapsulating how closely connected everyone is. Despite the empirical dismissal from small sample sizes and lost mail, the concept’s entrance into popular culture and ensuing research would follow. The six degrees went from a social theory to a mathematical proof when the probability of two strangers having a shared acquaintance was tested. It took until the 1990s, when two mathematicians made a computer model to mimic Milgram’s findings, when they discovered that most people have long-range connections, not just local ones.⁶ The researchers, Duncan Watts and Steven Strogatz, formalized the concept of small-world networks, showing how even large, random systems can maintain surprisingly short paths between nodes. 

In the 2000s and 2010s, the rise of platforms like Facebook and LinkedIn offered an unprecedented opportunity to test the six degrees theory at scale. What once seemed like an abstract idea became a measurable phenomenon, with studies showing the average separation between users shrinking to just three or four degrees.² This digital compression of social distance challenges our assumptions about how networks form and evolve—revealing that connection isn’t just more accessible than ever before, but also more dynamic and behaviorally rich than traditional models once suggested.

Frigyes Karinthy

A Hungarian author who introduced the core idea of six degrees of separation in his 1929 short story "Chains," proposing that modernity had shrunk social distance and anyone could be connected through a handful of acquaintances.

Stanley Milgram

An American social psychologist who famously tested the six degrees theory with his “small-world experiment” in the 1960s, empirically supporting the notion that people are linked by short chains of social ties. Milgram’s studies brought the theory to mainstream attention.

Duncan J. Watts

A network scientist who, along with Steven Strogatz, developed the concept of “small-world networks” in the late 1990s, offering a mathematical framework for how large networks can maintain short average path lengths.

Steven Strogatz

An applied mathematician who collaborated with Watts to model the small-world phenomenon, bridging psychology, sociology, and complex systems science. Strogatz helped take six degrees from a theory to having mathematical backing. 

Six degrees of separation goes beyond discovering unlikely connections between yourself and not-so-distant strangers. We can see how it has influenced the development of social media, what goes viral, and the complexity of human networks.

Blueprints for Social Networking Platforms

The theory laid the groundwork for social media platforms like Facebook, LinkedIn, and Twitter, where friend-of-a-friend algorithms mimic the small-world phenomenon. These tools are built on the idea that people are more connected than they think, and enable everything from job recommendations to the proliferation of viral content. An intuitive way to think about this is the trust that we place in an online stranger when we see they have a high number of mutual friends or followers. It is this type of experience that shows us how close we can be in degrees of separation.

Social media founders understand that shrinking degrees of separation are no accident. A Microsoft study analyzing 30 billion messages from 240 million users found an average of 6.6 degrees.³ More recent data shows social media cuts this number down even further: Facebook averaged 4.7 degrees across 721 million users, while X (formerly Twitter) users were just 3.4 degrees apart.³ With platforms like Instagram and TikTok, it’s worth exploring just how much closer we've become—and what that means for how we connect online and the “closeness” of these virtual bonds.

Influence on Local and Global Scales

By understanding how quickly information spreads across short social chains, marketers, activists, and behavioral scientists can better predict how trends, behaviors, or misinformation go viral. The theory helped shift the focus of outreach from mass messaging to strategic targeting through influential nodes or “weak ties.” For example, a marketing campaign may send a message about a product to an influencer who can easily advertise it to millions. We have all seen cases of this with viral videos, where all it takes is one message to start the next global movement.

One other way to reflect on the impact of six degrees of separation is acknowledging how a few strategic connections may have landed you a meaningful personal or professional outcome, like a new social group or job opportunity. After all, how many times have you heard of someone meeting their significant other through “mutual friends,” or someone landing a job through a recent connection they made? These types of ripple effects can happen seemingly out of the blue, while six degrees of separation reminds us how we aren’t all that far away from a significant connection to a stranger. 

Advancements in Network Science and Complexity Theory

Six degrees of separation inspired a wave of research into how social networks form, evolve, and self-organize. Building on the idea of strategic connections, we may consider instances when we desire certain degrees of separation to work in our favor. In this sense, it is not about simply having the most connections possible—rather, it’s important to have the right connections. More recent research has attempted to unpack how human behavior itself may explain the origins of this phenomenon in a physical and relational sense, when considering the pros and cons of various social ties.

A paper investigated how this may be the case: the social networks we all have, which we spend effort creating and maintaining in both face-to-face and online settings, are constantly evolving.⁷ We all play a game of attempting to make the connections that are most beneficial to us while we also cut those ties that come at a cost or are harmful to us, with the end goal of a settled social centrality.⁷ Here, each individual has a defined position in the social network that fulfills their desire for influence while being necessarily limited by their capacity for new relationships—a pattern that comes back to six degrees, whether it's intentional or not.

A theory with such a massive claim about a precise number of how closely connected we are is not without its limits and skepticism. From oversimplifying how complex humans are, to issues with Milgram’s original experiment, and broader non-small-world networks, there are problems to parse out with six degrees of separation.

Oversimplification of Social Complexity and Weak Links

While the theory captures a compelling idea, real-world relationships are far more nuanced than a simple number of connections. Not all bonds are equal: we all know that connecting with someone on LinkedIn isn’t the same as having a trusted relationship. Applied research by Watts, Dodds, and Newman (2002) emphasizes that weak ties in sparse networks don’t always guarantee reliable paths for information or influence.⁸ In practice, barriers like social capital, geographic distance, or language can limit how "close" we truly are, even when a mathematical path exists between us. 

Take looking for a new job as an example. While you may technically be three degrees away from the CEO of your dream company, getting a referral still depends on trust, reciprocity, and context. These factors are not captured in degree-counting, assuming you’re even able to get a reply from someone, however many degrees apart from you. Granovetter’s (1973) classic work on the "strength of weak ties" showed that weak links help connect nodes through a few steps, but this doesn't hold for every type of network.⁹ In fragmented, rural, or marginalized communities in specialized knowledge domains, connections can be sparse and distant, challenging the universality of the concept. 

Behavioral science often overestimates global connectedness due to the availability heuristic: we notice what’s close and visible to ourselves while falsely assuming everyone has access to tightly clustered, well-connected networks. Not all social systems are wired for rapid diffusion, where we tend to misjudge the influence and reach of networks we don’t genuinely understand. 

Consider a Hmong villager in a remote Northern Vietnamese community. Their social world may be dense locally but disconnected globally. While they may be exposed to the occasional foreigner, the lack of consistent internet access, institutional ties, or shared language, even with others in Vietnam, may mean that their network doesn’t map onto the six degrees model. Structural isolation, not social preference, may shape their reach more in comparison to Western contexts. Behavioral interventions relying on the assumption of proximity or virality miss the mark when they ignore the uneven terrain of real-world networks that are nuanced by culture, geography, or other factors.

Degrees of Separation and Access: Behavioral Insights from M-Pesa

When we talk about “six degrees of separation,” we often imagine a densely connected world where information and resources can pass from one person to another in merely a few steps. Yet, we must be inclusive of parts of the world where infrastructure, trust, or access is uneven, where that promise of “connectedness” doesn’t always hold. A real-world example of this dynamic played out in Kenya with the launch of M-Pesa, a mobile money service that allowed people to send and receive money using basic mobile phones.¹⁰ Though M-Pesa was intentionally designed to remove traditional banking barriers, its early adoption data revealed something more complex was going on.

Studies by Jack and Suri (2011, 2014) found that while M-Pesa was widely adopted in urban areas, rural and marginalized communities lagged behind. ^{11, 12} The people who arguably needed this technology most—those without access to banks or formal financial systems—were often the last to join the network. Infrastructure gaps, digital literacy, and social trust all played a role. Rather than instantly connecting everyone, M-Pesa revealed where the fractures in the social and economic network lay.

From a behavioral perspective, this highlights how availability bias and the illusion of universality can distort design decisions. We often assume our own networks—tech-savvy, mobile, and well-resourced—are representative of everyone’s, but in reality, social proof and trust-building operate differently across communities. People in remote regions might rely more on kinship ties and word-of-mouth, meaning adoption is slower and more fragile when change is introduced by distant institutions rather than local champions.

This case reminds us that not all social systems are small worlds. Behavioral interventions based on assumptions of universal connectivity may miss the very communities they aim to empower. Before designing for diffusion, we need to ask: who is still five or six steps away—and why? Identifying those structural gaps is as important as designing the solution itself. After all, inclusion isn’t just about reach—it’s about recognizing the different paths people take to get there.

Six Degrees of Wikipedia

Unexpected closeness doesn’t just emerge in social networks—there are fun digital ways we can play around with the six degrees of separation to explore the interconnectedness of information. The internet may feel infinite, but sometimes it takes just six clicks to get from Turkey to Tintin. That’s the premise behind “Six Degrees of Wikipedia,” a game where players try to connect two seemingly unrelated articles, using only internal Wikipedia links, faster than other players.¹³ What begins as a competitive race through hyperlinks quickly becomes something more revealing: a window into how human knowledge is structured, and how surprisingly close the most distant ideas can be.

“Six Degrees of Wikipedia” is a game where players attempt to get from one random Wikipedia article to another, similar to how we might experience the six degrees of separation “a-ha” moments when far-away connections surprise us. At first glance, this game is simply a fun challenge, though in reality it reveals something profound about the topology of human knowledge: the most obscure topics, from ancient Mongolian pottery to fungal pathogens, can usually be connected by fewer than six clicks. This mimics the famed “small-world” phenomenon that underpins the six degrees theory—our social worlds are deceptively small themselves, yet so is the seemingly vast knowledge we’ve gathered across human existence.

As we play what is also called “the Wiki Game” or “Wikispeedia,” the game reveals if our web of knowledge is denser or sparser than we imagine. We soon notice how mainstream, Western-centric topics are richly interlinked. It is easy to bounce from the Beatles to the Cold War to the Theory of Relativity. As we look into niche subjects, especially those outside dominant cultures or academic disciplines, they often form isolated branches. Their links back to the “core” of Wikipedia require more abstract or nuanced routes, highlighting bias in how we document and structure knowledge. 

From a behavioral science lens, “Six Degrees of Wikipedia” reminds us how mere exposure, familiarity, and salience shape both our cognitive shortcuts and our systems of information architecture. While the goal is to find the shortest path, our ability to connect topics is determined by our subjective points of view about how they relate. The same prompt could elicit pathways of varying lengths with diverse nodes, depending on the player's unique associations, resulting in distinct and possibly meandering routes that reflect our individual patterns of thinking. Availability bias makes commonly cited or linked topics feel more “central” or “important”—not because they actually are, but because they’re more visible. The way Wikipedia is written and edited by volunteers (often without proper, reliable sources or citations) reflects how certain demographics and interests reinforce these patterns, in turn shaping how people discover and learn about countless topics online.

While “Six Degrees of Wikipedia” might suggest a world where all knowledge is closer than we think, it also hints at important things we too easily neglect: perspectives, histories, and connections that haven’t been widely documented or linked, regardless of how many degrees away from them we are. Before assuming a network is complete, we should ask: whose knowledge is easy to reach—and whose still requires six steps of searching? In a world increasingly shaped by algorithms and information flows, making those invisible links visible may be one of the most important steps to maintain genuine human connections, only a few degrees away from ourselves. 

“500+ Connections”: Inundation, Addiction, and Delusion in Social and Professional Networking

Speaking of connections, how many do you have on LinkedIn? In this piece, TDL columnist Caleb Cohen dives into the ubiquitous reality of networking, with some caveats as to how many connections our brains can really handle, as quantified by Dunbar’s number and the social brain hypothesis. 

The “Social Dilemma” Dilemma

Social media is inescapable, and despite its promise of connection by narrowing degrees of separation, it is no longer a secret that there are risks and potential for harm that come with its design and user experience. In this piece, TDL columnist Preeti Kotamarthi looks into the addictive qualities of social media, the ethics around such features, and how behavioral science can help.

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