Productivity-the amount of output delivered per hour of work in the economy-is often viewed as the engine of progress in modern capitalist economies. Output is everything. Time is money. The quest for increased productivity occupies reams of academic literature and haunts the waking hours of C.E.O.s and finance ministers.

For at the end of the day, prosperity goes beyond material pleasures.

Today we find ourselves faced with the imminent end of the era of cheap oil, the prospect (beyond the recent bubble) of steadily rising commodity prices, the degradation of forests, lakes and soils, conflicts over land use, water quality, fishing rights and the momentous challenge of stabilising concentrations of carbon in the global atmosphere.

Questioning growth is deemed to be the act of lunatics, idealists and revolutionaries. But question it we must.

If pornographers are among the early adopters of the new technology, then it has definite commercial possibilities.

Prosperity consists in our ability to flourish as human beings - within the ecological limits of a finite planet. The challenge for our society is to create the conditions under which this is possible. It is the most urgent task of our times.