Last week marked an anniversary worth celebrating. On February 4, nine years ago, Mark Zuckerberg launched Facebook from a Harvard dormitory room along with other classmates. What started as a way for Harvard graduates to stay in touch has become the web?s dominant social ecosystem and the ultimate networking tool in a world going increasingly digital. By the time he moved to Silicon Valley and set up office, Zuckerberg was already a billionaire, aged 23. The site has over one billion users worldwide, who spend an average of 70 minutes on the site each day. It is available in 70 languages and is one of the most valued companies on the planet. More than 70% of the service?s members live overseas. In India, it is the leading social network, both in terms of users (18 million) and page views (4.25 billion).

Facebook?s promise has largely been fulfilled?to change how we communicate by digitally mapping and linking peripatetic people across space and time. What that entailed?allowing users to publicly share very personal elements of their lives?has not been without controversy, but as modern inventions go, Facebook has truly changed the world for millions, putting them in touch with long-lost friends and classmates and even united families separated by circumstance. The New York Times tracked down Karen Haber, an Israeli from Tel Aviv, who used Facebook to search for relatives who had fled from Germany during the Holocaust and settled in various countries around the globe. She tracked down over a dozen in places as far apart as New York, Zurich and Hong Kong. She used Facebook to reunite a family separated by tragedy and war. No other available tool, digital or otherwise, puts that kind of connective power into the hands of ordinary people. All it needs is a computer and an Internet connection.

Everyone has their Facebook story. I have managed to re-establish contact with half-forgotten schoolmates, friends who one knew as a teenager, who are now scattered across the globe, college pals, who one had lost touch with, former work colleagues, relatives and friends in other cities and countries, as well as fellow professionals and those with similar interests. We share everything from photos to recipes, ideas and updates on life and careers so seamlessly that it?s easy to forget what a game-changer Facebook really is.

These days, it?s become a tool for activists and like-minded people to motivate others to get involved in protests in various cities against perceived injustices or incidents, like the Delhi gang rape, and meet in a maidan or the street with thousands of others. A majority of whom got connected on Facebook. The ?like? button has also become a call to arms.

There is, of course, the downside; the privacy issue, the time that children spend on the site as opposed to their homework, its potential for employers to spy on employees?the list is fairly long. Yet, for all that, it is an amazing tool, one of the most democratic ever invented. In an interview with Oprah Winfrey, Zuckerberg related the story of Claus Drachmann, a schoolteacher in northern Denmark, who became a Facebook friend of Denmark?s then prime minister, Anders Fogh Rasmussen. Scandinavians are among the most equal societies on earth, which is why the country?s PM can accept a schoolteacher he has never met, as a Facebook friend. Once they connected, Drachmann invited Rasmussen to speak to his class of special-needs children and the prime minister obliged. This would not have happened if the teacher had sent a written invitation to the PM?s office. Zuckerberg told this story to illustrate Facebook?s power to cut through arbitrary social barriers. He called it ?a generational shift in technology?, and there is no question that it is.

Yet, there is another generational shift it has triggered and one that is not so inviting. I know of many parents who are on Facebook and so are their teenaged children. The youngsters find it tough to share what they did on Saturday night?including incriminating photos?when it is also the site where their parents are swapping holiday ideas with their friends. That generational connection also illustrates another remarkable change Zuckerberg?s creation has brought about: to unite disparate groups on a single Internet service, which actually contradicts 50 years of research by sociologists into what is known as ?homophily?, the tendency of individuals to associate only with like-minded people of similar age and ethnicity. I, like many other users in India, have Facebook friends from over ten countries, none of whom are of Indian origin. Facebook India, however, has four million followers across the globe, representing every religion, caste, class and ethnicity, all united in their love for cricket, samosas, politics, religion and anything that can lead to a debate or an argument. Amartya Sen just needs to log on to the site to know the Argumentative Indian is alive and well, and living in Facebook.

The writer is Group Editor, Special Projects & Features, ?The Indian Express?