It may come as news to mainstream media, but spreading the word is now all about networks

How do you decide whether a technological development is significant or not? Here's a simple rule: if the mainstream media — as represented by, say, Daily Mail columnists — are baffled by, or contemptuous of, it then it's probably worth paying attention to.

Twitter is the latest case study of the decision rule in action.

When it launched in July 2006, the non-geek world greeted it with incredulity. I mean to say, what possible use could there be for a service that let you broadcast 140 character updates on what you were doing or thinking at any given time? (The fact that text messaging on mobile phones had spread like wildfire despite being restricted to 160 characters seems to have eluded the mainstream sceptics. But, hey, consistency is a puerile obsession, as Oscar Wilde famously observed).

So at first, Twitter was primarily a geek and early-adopter zone.

Geeks loved it because it enabled them to plug into the thoughtstream of their peers, and to seek quick and informed answers to puzzles or problems. If you wanted to know why your new netbook wasn't picking up the Wi-Fi signal, you had two options: you could Google the problem and maybe find an answer after wading through a few pages of results, or you could put out a tweet and receive an informed answer from a real human being in seconds.

Part of the genius of Twitter was that it wasn't reciprocal. So if I chose to make my tweetstream public, there was no way I could stop you from following me — unlike on Facebook where you can only become my "friend" if I agree to become yours. Twitter's asymmetry thus meant that one could be part of a sociable discourse without incurring the responsibilities — and the email load — that true dialogue imposes.

This had an unintended consequence which eventually triggered mainstream media interest in the service. It turned out that some celebrities — Stephen Fry and Jonathan Ross, for example — were on Twitter and in no time at all they had many thousands of "followers", apparently hanging on their every tweet. Now this was something that even Jan Moir could understand: Twitter must be just another social networking service — an anorexic version of Facebook with no pictures or videos, just 140-character status updates.

One of the most intriguing and useful features in Twitter is the "retweet" facility. If you see something in your tweetstream that you think might interest others, then you can click a button to make it visible to the people who are following you. Retweeting has become so commonplace that its conventions have already been the subject of a serious study by the anthropologist Danah Boyd and her colleagues at Microsoft Research. But it turns out that retweeting is not just interesting in terms of discourse analysis; it's also the key to understanding why Twitter is a radically different form of social networking.

We know this because of a remarkable study conducted by some researchers at the Korea Advanced Institute of Science and Technology and published last week at a major academic conference.

They assembled a cluster of 20 PCs, collected the entire contents of Twitter for the month of July 2009 and then set their algorithms to analysing the resulting mountain of data.

One of the researchers' conjectures concerned the number of "degrees of separation" one would expect between Twitter users. Ever since Stanley Milgram's famous "six degrees of separation" experiments of the 1960s in which he showed that any two people on earth were separated by at most six hops from one acquaintance to the next, studies of social networks – both offline and online – have generally confirmed that figure. Given that only about a fifth of Twitter relationships are reciprocal, the Korean researchers conjectured that the degree of separation among Twitter users would be greater than six. But what their data showed is exactly the opposite: the average path-length in Twitter is just over four.

If you're not into network theory, then the difference between six and four may not seem very significant. But if you're interested in how news spreads around a network then it's dynamite. Next to traditional, few-to-many broadcasting, Twitter is the fastest way to spread news and information. In fact, it's the nearest thing the web has to wildfire. And the key mechanism that enables that is retweeting. The Korean researchers have found that this single facility generally enables any given message to reach a much bigger audience than those who are followers of the original tweet. So the moral for those politicians out there who are thinking about the next election is: forget Facebook, think Twitter.