The year is 2540, the triumph of scientific progress is all but complete. Most of humanity lives in a harmonious society where all needs are satisfied.

This is the future imagined by Aldous Huxley in his novel Brave New World.

Huxley's fantasy has a darker side. The universal happiness has been achieved by a tiny elite. Humans are mass-producedAldous Huxley was writing just after the development of production lines, which allowed factories to churn out identical objects very efficiently. His horror at this innovation (and its pioneer, Henry Ford of Ford Motors) was part of the inspiration for Brave New World. and conditioned for the role they play. Nobody is any more intelligent than they need to be. Misery is a thing of the past, but so are art, love and individuality.

Brave New World was published 90 years ago. To mark this anniversary, the philosopher Yuval Noah Harari has written an introduction to a new edition. Harari has a warning: "With each passing year Brave New World is becoming even more relevant."

Huxley wrote his novel in a time of totalitarianismA system of government that forces citizens to follow the will of the state.. But the tools available for manipulating humans have become more sophisticated, Harari argues. From Google to Spotify, algorithmsAny set of rules followed by a computer. In the context of social media, "the algorithm" refers to the intelligent AI that learns the interests of the user and presents them with posts that it thinks will interest them. guide choices about where we go, what we consume and what we think.

"Soon," Harari writes, "some governments and corporations will have enough biological knowledge, enough data and enough computing power to monitor all the people all the time - and to know what each of us is thinking and feeling in every moment. They will know us better than we know ourselves." They will be able to "hack human beings".

To the leaders of the society in Brave New World, this might sound like a wonderful opportunity: society could be arranged so that everybody's desires are satisfied before they become aware of them. They subscribe to a philosophy of utilitarianismA theory of morality invented by English thinker Jeremy Bentham, who also devised a special kind of prison known as a panopticon. or hedonismThe belief that pleasure is the central (or even the only) goal. Utilitarianism is sometimes said to be a form of hedonism.: whatever produces the greatest happiness is morally right.

The idea that increasing happiness should be the main goal is commonplace. Many governments attempt to measure happiness to gauge success. Companies use emotion recognition softwareComputer programmes that analyse images of human faces in order to establish what people are feeling. The effectiveness of this technology is still being debated. to ensure consumers are experiencing pleasure.

Sociologist Will Davies argues that happiness is "the new religion of our age". 

But the protagonist of Huxley's novel, a rebel against the peaceful and orderly society he inhabits, is not convinced that this is such a noble goal. "I don't want comfort," he says. "I want God, I want poetry, I want real danger, I want freedom, I want goodness. I want sin."

Yes: Truth, love, great art and profound insights: these are the things that really matter, and pursuing them is often painful and hard. A life of senseless contentment is hardly a life at all.

No: Ultimately, everything we do is in pursuit of pleasure and contentment. Happiness for all should be our guiding principle in politics and personal life.

Or... There are many varieties of happiness, and perhaps the most precious of them do not come from fulfilling our basic impulses and desires. We should spend less time trying to optimise happiness and more time thinking about what it really means.

Mass-produced - Aldous Huxley was writing just after the development of production lines, which allowed factories to churn out identical objects very efficiently. His horror at this innovation (and its pioneer, Henry Ford of Ford Motors) was part of the inspiration for Brave New World.

Totalitarianism - A system of government that forces citizens to follow the will of the state.

Algorithms - Any set of rules followed by a computer. In the context of social media, "the algorithm" refers to the intelligent AI that learns the interests of the user and presents them with posts that it thinks will interest them.

Utilitarianism - A theory of morality invented by English thinker Jeremy Bentham, who also devised a special kind of prison known as a panopticon.

Hedonism - The belief that pleasure is the central (or even the only) goal. Utilitarianism is sometimes said to be a form of hedonism.

Emotion recognition software - Computer programmes that analyse images of human faces in order to establish what people are feeling. The effectiveness of this technology is still being debated.