Global Trends

How Ideas Spread


Every human advance, and what we call culture, relies on the human capacity to embrace new ideas en masse. But how does that happen? How does an idea become so compelling that it is worth sharing? More important, how is it that ideas come to be adopted? Duncan Watts, a principal researcher at Microsoft Research NYC, has made a career of studying how ideas spread.

How Ideas Spread

Giselle Weiss: Your early research is associated with the wildly popular idea of six degrees of separation, which far predates you. How did that idea spread?

Duncan Watts: I don't know. But the notion that we are all connected through a short chain of acquaintances has been around for a long time. It shows up in a 1929 short story called "Chains" by the Hungarian poet Frigyes Karinthy. And the urbanist Jane Jacobs speculated about it in her famous book, "The Death and Life of Great American Cities."

They didn't call it six degrees of separation, though.

No. That label comes from the title of a Broadway play of the 1990s by John Guare. The actual history is a little involved. But in any event, in 1967 psychologist Stanley Milgram set out to test the idea by having people in Boston deliver letters to people ("targets") in Omaha, Nebraska, through the intermediary of others known only on a first-name basis. He found that the average length of the letter chains that reached the targets was six. He called it the small world problem.

Where did your research come in?

In the 1990s, I was studying synchronization among crickets – who chirps with whom. Then one day on the phone, my dad asked me whether I'd ever heard of the idea that everyone is only six handshakes away from the president of the United States. It occurred to me that both problems involved networks, and that interested me.

What makes the idea so powerful? 

We're attracted to the Enlightenment idea of ourselves as independent individuals who decide what we want to do and go out and do it. But the reality is that we're very much enmeshed in social relations. Everything we do and care about involves other people. These are network concepts.

Recently, you've been working on the structure of viral diffusion, for example, of tweets on Twitter. What's that about ?

We've been mapping the spread of information, particularly online. When you think about how information spreads, it's natural to liken it to the spread of a disease. In fact, people have been doing that for a long time in marketing. And it's been popularized in recent years by people like Malcolm Gladwell, author of "The Tipping Point," who very explicitly draws the analogy between the spread of behaviors or beliefs and diseases.

That sounds reasonable.

At a certain level, it is. But it's tempting to go a step further and apply the same mathematical models that have been developed to understand the spread of a disease to the spread of ideas or products.

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What's wrong with that?

There are all sorts of models of how things spread, and they're often incompatible with each other. Moreover, we have very little data to test any of these models. For example, if you want to trace the spread of an idea, you have to be able to observe that person A has that idea, and then that person tells B, and then person B has the idea, and now person B tells person C. Mapping this out in a population of millions of people with hundreds of thousands and millions of things to observe is a tremendously difficult process.

So how do you approach it?

We've done a lot of work using Twitter data – news, media, images - where we can, to some approximation, observe everything. And we can also track exactly where everything is at a given point. People who study diffusion are generally looking for a critical threshold where ideas go from not spreading to spreading like wildfire.

And what have you found?

Initially, we found that nothing really spreads like that. In a study of millions of observations, 99 percent of everything that happened, every "adoption" of an idea, was within one degree of the source. Which is almost the opposite of spreading. In other words, I tweet something and you re-tweet it. Your followers see your re-tweet, but they don't do anything. It's the re-tweet that we pay attention to. When we described this result to our colleagues, however, they often didn't like it.


People are convinced that certain things "go viral," and that's what interests them. So they would say, "We know some things spread. Look at ‘Gangnam Style' or the use of Hotmail or Facebook. Maybe you didn't see anything spread, but you must only have looked at things that weren't any good." So then we did a second study where we really looked at everything on Twitter – a billion observations – for an entire year. And sure enough, we found that some things do spread quite a lot. But they are very rare, one in a million events. And even they don't look like "social epidemics."

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Why not? Surely "Gangnam Style" is a social epidemic?

Epidemic models assume that ideas become popular by viral word of mouth. But in the media world, information can also spread because some major channel or site picks it up – it gets on the front page of Yahoo! or the "New York Times" or whatever – and a million people or a hundred million people see it. And a bunch of them re-tweet it. That would still be popular, but we wouldn't say it had spread virally. So when something becomes popular, is it a "broadcast" or is it "viral"? Intuitively, you might guess one or the other. But when we looked, we found tremendous diversity: some popular things are pure broadcasts, and some display pure viral spreading. We also found about every conceivable mixture of the two. There's no typical way in which things become popular.

What do your findings tell you?

Unlike diseases, where in general you only have one thing spreading at a time, in ideas, it's always a contest. Everything that's spreading on Twitter is fighting for oxygen with everything else that's spreading on Twitter. It's hard to be exposed to one particular idea because there's just so much other stuff to pay attention to. Occasionally something is able to rise above the noise, and everybody hears about it and pays attention to it. But that is extraordinarily rare and somewhat arbitrary. If you're a social media strategist or a digital advertising agency, basing a marketing or other strategy on triggering a social epidemic is probably not the best use of your resources.

You are also investigating the nature of cooperation between people. How is that related to the spread of ideas?

The spread of information and the spread of cooperation are both examples of social influence, so they're related, at least in principle. But it's also important to understand that different types of influence are likely to spread in different ways. Me persuading you to change your political views is very different from me persuading you to click on a video.

How so?

People do not easily adopt ideas that involve changing their conception of themselves. Not accepting the idea of climate change might be tied up with your political ideology, your suspicion of government and your dislike of elite intellectual types. When is an idea something that you can adopt just because it's obviously right or obviously interesting? And when is it something that is going to be very difficult for you to adopt because it's tied up with all these other things?

What are the stakes?

This is not about cat videos going viral, even if sometimes that's what we study because it's what we have the most data about. Really, it's about changing people's minds, and their behavior; and one way or another, everyone – governments, corporations, marketers, policymakers – is in the business of trying to change people's minds. Understanding how that happens is one of the big questions of social science. It's frustrating that we've been thinking about this for so long and have very little in the way of concrete answers. But maybe this particular period of history is different. That's the hope.

Duncan Watts 

Duncan Watts is a principal researcher at Microsoft Research NYC and an A. D. White Professor-at-Large at Cornell University. From 2000 to 2007, he was at Columbia University, then at Yahoo! Research. He is the author of "Everything is Obvious (Once You Know the Answer): How Common Sense Fails Us" (Crown, 2011).

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