Purists might imagine the founding geniuses of the Royal Institution turning in their graves. What does science have to tell us about such a frivolous subject? And how do you define happiness, let alone study it? But happiness has finally burst out of the academic closet. Several weighty volumes on the subject have been published this year. And on the same night as the RI event, the economist Lord Layard and the psychiatrist Dr Raj Persaud were debating the Politics of Happiness at the London School of Economics just a mile away.

Perversely, happiness has a negative image in our culture. Influenced by a sceptical European philosophical outlook, we think of happiness as a trivial pursuit for the Oprah generation, a Shangri-La perpetuated by self-help gurus. Isn't it selfish to try to increase our happiness, while much of the world faces suffering and premature death?

Great writers from Freud — "the intention that man should be happy is not included in the plan of Creation" — to Philip Larkin — "man hands on misery to man" — have painted happiness as an elusive butterfly. But ordinary people believe they are happier than average (an obvious impossibility) and that they'll be even happier in 10 years' time. If true, it would be good news because research shows that happier people are healthier, more successful, harder-working, caring and more socially engaged. Misery makes people self-obsessed and inactive.

These are the conclusions of a burgeoning happiness industry that has published 3,000 papers, set up a Journal of Happiness Studies and created a World Database of Happiness in the last few years.

Can scientists tell us what happiness is?

Economists accept that if people describe themselves as happy, then they are happy. However, psychologists differentiate between levels of happiness. The most immediate type involves a feeling; pleasure or joy. But sometimes happiness is a judgment that life is satisfying, and does not imply an emotional state.

Public surveys measure what makes us happy. Marriage does, pets do, but children don't seem to (despite what we think). Youth and old age are the happiest times. Money does not add much to happiness; in Britain, incomes have trebled since 1950, but happiness has not increased at all. The happiness of lottery winners returns to former levels within a year. People disabled in an accident are likely to become almost as happy again. For happiness levels are probably genetic: identical twins are usually equally bubbly or grumpy.

One thing makes a striking difference. When two American psychologists studied hundreds of students and focused on the top 10% "very happy" people, they found they spent the least time alone and the most time socialising. Psychologists know that increasing the number of social contacts a miserable person has is the best way of cheering them up. When Jean-Paul Sartre wrote "hell is other people", the arch-pessimist of existentialist angst was wrong.

America has pursued the chimera of happiness vigorously, not least through the insatiable consumption of self-help literature such as Climb Your Stairway to Heaven: 9 Tips for Daily Happiness! So it is no surprise that it's an American who is making happiness a subject of scientific study. At first glance, Martin Seligman's bestselling book Authentic Happiness, with its sunshine-yellow title on a sky-blue cover, blends with other manuals on the pop-psychology shelves. But America's latest guru of feeling good is not a stage hypnotist, an evangelical preacher or even a business visionary. Seligman is an eminent professor of psychology with a string of degrees. One of the chief architects of the prevailing model of depression, his work has helped to found modern "cognitive" therapies.

The man who's trying to do for happiness what Newton did for gravity has found it a scarce commodity in life. Seligman describes himself as a "walking nimbus cloud" who spent 50 years "enduring mostly wet weather in my soul". Feeling out of place as a chubby 13-year-old Jewish kid at a wealthy college, he hit on the role of therapist as a route to the hearts of unattainable girls. "What a brilliant stroke! I'll bet no other guy ever listened to them ruminate about their insecurities, nightmares and bleakest fantasies."

As a psychology graduate working in animal- behaviour labs, Seligman discovered "learned helplessness" and became a big name. Dogs who experience electric shocks that they cannot avoid by their actions simply give up trying. They will passively endure later shocks that they could easily escape. Seligman went on to apply this to humans, with "learned helplessness" as a model for depression. People who feel battered by unsolvable problems learn to be helpless; they become passive, slower to learn, anxious and sad. This idea revolutionised behavioural psychology and therapy by suggesting the need to challenge depressed people's beliefs and thought patterns, not just their behaviour.

Now Seligman is famous again, this time for creating the field of positive psychology. In 1997 the professor was seeking a theme for his presidency of the American Psychological Association. The idea came while gardening with his daughter Nikki. She was throwing weeds around and he was shouting. She reminded him that she used to be a whiner but had stopped on her fifth birthday. "And if I can stop whining, you can stop being a grouch."