Imagine: you’re sipping coffee in Boston, and someone in Omaha (Nebraska, 1,200 miles away) receives your letter. Not from a friend or relative — from a random person who only knows the name and address of a Boston-area stockbroker. And the letter arrives. Through six hands. This isn’t fiction or a modern social network. It’s Stanley Milgram’s 1967 experiment that gave birth to the “six degrees of separation” theory.

What They Actually Did

Milgram sent letters (160 in his Omaha study) to residents of Omaha, Nebraska, and Wichita, Kansas. Each contained the name, address, and a brief description of a target person (a stockbroker) in Massachusetts. Participants couldn’t mail it directly: they had to pass it to a personal acquaintance they thought was closer to the target. That person then did the same. Out of the 160 letters starting in Omaha, 44 reached the destination. The average path length (the number of intermediaries) was about 5.5. This figure was rounded up to six. That’s how the powerful idea emerged: any two people on the planet are connected by a chain of, on average, six acquaintances.

Why This Is Psychology, Not Just Statistics

The human brain hates randomness. We instinctively seek connections and patterns because it gives us a sense of control and predictability. Milgram’s theory works in the real world thanks to social hubs — people with hundreds or even thousands of contacts. Your acquaintances might know dozens of people, but if one of them is a “hub” (perhaps a salesperson, a community organizer, or a bartender), the path to a distant target shortens dramatically. This isn’t magic — it’s the strength of weak ties, a famous sociological concept introduced by Mark Granovetter in 1973. A "weak tie" is someone you might only greet once a year, but because they operate in a different social circle or field, they are an invaluable bridge to people and information you wouldn't otherwise be able to access.

Evidence from Today

The "small world" phenomenon has only accelerated with digital networks. Here's how the principle holds up:

• Facebook (2016): Researchers analyzed 1.59 billion active users on the platform. They found that the average distance between any two users was 3.57 “friends.” This means, on average, you are separated from any other user by 4.57 degrees (3.57 intermediaries). The world got "tighter" thanks to the internet, but the core principle remains the same.
• LinkedIn: The entire professional network is built on this principle. It explicitly shows you how you are connected to others through 2nd-degree (a friend of a friend) and 3rd-degree (a friend of a friend of a friend) contacts, demonstrating how small the professional world truly is.
• The Mathematical Model: In a purely random graph with $N$ nodes, the average distance between nodes is approximately $log(N)$. For 8 billion people, $log_2(8 \times 10^9)$ is about 33. This seems high. However, human social networks are not random; they are scale-free networks, which have "hubs." When mathematical models factor in these highly-connected hubs, the average path length drops dramatically to the 5–6 range, explaining exactly why Milgram's theory holds true.

What This Means for You

This theory has practical implications for your daily life:

1. Anxiety about the “big world” decreases. The world is far more connected than it feels. If you need help, advice, or a job, there’s a very real statistical chance that someone in your immediate or secondary circle knows the exact person you need to talk to.
2. Networking works differently. This theory shows networking isn't just about the number of business cards you collect. It’s about the quality and diversity of your weak ties. Those acquaintances in different industries are often your most valuable bridges to new opportunities.
3. Social responsibility increases. Your actions, both positive and negative, can ripple outward and reach a stranger much faster than you think. We are not isolated atoms; we are deeply and mathematically interconnected.

Fun Psychology Fact

Milgram is, paradoxically, more famous for a much darker experiment: his 1961 study on obedience to authority, where participants were ordered by a scientist to deliver (what they believed were) painful electrical shocks to a stranger. But his “small world” experiment shows the other, more hopeful side of human connection: we’re not just obedient atoms. We are all nodes in a giant, intricate web, and every move we make creates ripples.

Observations Without Studies

Even without complex studies, you see this principle daily. Recall how fast gossip spreads in an office or how a niche meme suddenly blows up in your group chats. It follows the same principle: a few well-connected “hubs” see it, share it, and suddenly the whole class, office, or city knows. The world didn’t shrink physically. It shrank socially. And it’s not just about Facebook — it’s about how our minds are wired: we always look for the shortest, most efficient path to another person.

Key References

• Milgram, S. (1967). The Small World Problem. Psychology Today, 1(1), 60–67. (The original, accessible article publishing the experiment that established the ~6 degrees finding.)
• Granovetter, M. S. (1973). The Strength of Weak Ties. American Journal of Sociology, 78(6), 1360–1380. (The foundational sociological theory explaining *why* the small world phenomenon works, emphasizing the role of acquaintances.)
• Facebook Research (2016). Three and a half degrees of separation. (The internal analysis of 1.59 billion users that found an average separation of 3.57 people, updating their 2011 findings.)