Google “google”. Instantly, the query is flashed to an online index several trillion entries long that forwards it to document servers in hundreds of server “farms” across the globe. In less than a hundredth of a second they return nearly 2.5 billion results, among them links to 700 million chat-room postings, maps and satellite imagery of every square foot of the Earth's surface and 3,455 news articles including one headlined “Is Google Turning Into Big Brother?”.

The answer to this question happens to be no. Google is not about to take over the world, but it is reaping the benefits of an extraordinary confluence of its technology and curiosity.

Who knew, ten years ago, that the future of the internet would be guided not by portals claiming to offer all things to all people, but by two young men offering one thing only - “search”?

The word spectacularly underplays its own significance. The insight harnessed by Larry Page and Sergey Brin, Google's founders, was that the exploding volume of information on the internet would be, by itself, of limited use. But if sorted fast and objectively, by relevance and by anyone, its use would be immeasurable. They were latecomers to the search business, but their rivals were using teams of human editors and even index cards. Messrs Page and Brin replaced the human factor with an algorithm that ranks every virtual page by the number of links to it from other pages, and every link by the rank of the page from which it comes.

The result is an exhilarating extension of the human mind. Like humans, it can peddle nonsense. Even at its most useful it does not necessarily deliver fact or the wisdom of the ages - but it offers an uncanny approximation to the wisdom of crowds.

The exact code of the Google algorithm is trademarked and secret. But the principles behind it, like those of powered flight and nuclear fission, seem straightforward and indispensable now that they have been established. They are also the foundation of a $157 billion business empire whose growth is fuelled by spiralling revenue from tightly targeted advertising, and whose users can now use Google for much more than search. It seeks to dominate e-mail, social networking, online video and the web browser industry, and no one has profited by betting against it.

Not bad for ten years' work. What Google can celebrate, above all, is proving that free market capitalism can unleash human curiosity without bending it towards special interests - even its own. Rivals protest that its market dominance is unhealthy, verging on monopolistic. Intellectuals fret that matching imperfect answers to myriad questions on such a vast and ceaseless scale portends nothing less than the reinvention of knowledge. In reality, Google's growth will slow as competitors exploit its weaknesses (see page xy). And while its search engine may change how people acquire knowledge, critical thinking will be as vital as ever to understand it.

Google's danger - to users and itself - is not as an enabler of curiosity, but as a mirror. Questions reveal much about those who ask them, and Google keeps most of this information for at least 18 months. For marketeers, this is intoxicating stuff, but it belongs to private citizens and Google forgets this at its peril. With this caveat, many happy returns.