When prisoners are released from prison, they often say that they have paid their debt to society. This is absurd, of course: crime is not a matter of double-entry bookkeeping. You cannot pay a debt by having caused even greater expense, nor can you pay in advance for a bank robbery by offering to serve a prison sentence before you commit it. Perhaps, metaphorically speaking, the slate is wiped clean once a prisoner is released from prison, but the debt is not paid off.

It would be just as absurd for me to say, on my imminent retirement after 14 years of my hospital and prison work, that I have paid my debt to society. I had the choice to do something more pleasing if I had wished, and I was paid, if not munificently, at least adequately. I chose the disagreeable neighborhood in which I practiced because, medically speaking, the poor are more interesting, at least to me, than the rich: their pathology is more florid, their need for attention greater. Their dilemmas, if cruder, seem to me more compelling, nearer to the fundamentals of human existence. No doubt I also felt my services would be more valuable there: in other words, that I had some kind of duty to perform. Perhaps for that reason, like the prisoner on his release, I feel I have paid my debt to society. Certainly, the work has taken a toll on me, and it is time to do something else. Someone else can do battle with the metastasizing social pathology of Great Britain, while I lead a life aesthetically more pleasing to me.

My work has caused me to become perhaps unhealthily preoccupied with the problem of evil. Why do people commit evil? What conditions allow it to flourish? How is it best prevented and, when necessary, suppressed? Each time I listen to a patient recounting the cruelty to which he or she has been subjected, or has committed (and I have listened to several such patients every day for 14 years), these questions revolve endlessly in my mind.

When the federal government assesses the long-term financial problems of Social Security, it assumes that increases in life expectancy will be slow and measured. But many population experts say they believe that Americans' life expectancy will increase rapidly in the 21st century, making the program's financial problems even worse.

President Bush and Congress are preparing for a debate over the future of Social Security, whose solvency depends not only on factors including productivity, inflation and birth rates but also on how long beneficiaries will be living.

Life expectancy at birth increased by 30 years in the last century, and many independent demographers, citing the promise of biomedical research and the experience of some other industrialized countries, predict significant increases in this century. The Social Security Administration foresees a much slower rise.

"Life expectancy will make a very big difference in the fiscal viability of Social Security, but the agency's projections of longevity appear too conservative," said Prof. Samuel H. Preston of the University of Pennsylvania, one of the nation's leading demographers.

Dr. Preston said the agency assumed that "past advances in life expectancy are unrepeatable, even though the medical research establishment is routinely producing important breakthroughs that reduce the incidence or fatality of a variety of diseases."

The tech guru sees a "new economic system" in the unconscious cooperation embodied by Google links and Amazon lists.

Howard Rheingold is on the hunt again. With his last book, Smart Mobs: The Next Social Revolution, in 2001, the longtime observer of technology trends made a persuasive case that pervasive mobile communications, combined with always-on Internet connections, will produce new kinds of ad-hoc social groups. Now, he's starting to take the leap beyond smart mobs, trying to weave some threads out of such seemingly disparate developments as Web logs, open-source software development, and Google.

At the same time, Rheingold is worried that established companies could quash such nascent innovations as file-sharing -- and potentially put the U.S. at risk of falling behind the rest of the world. He recently spoke with Robert D. Hof, BusinessWeek's Silicon Valley bureau chief. Here are excerpts from their conversation:

Q: Where do you see the social revolution you've been talking about going next?

A: It's too early to say. The question is: What does it point toward? Some kind of collective action...in which the individuals aren't consciously cooperating. A market is a great example as a mechanism for determining price based on demand. People aren't saying, "I'm contributing to the market," they say they're just selling something. But it adds up.

Contemporary world population patterns are shaped by the "demographic transition" concept introduced to the field by the great demographer Frank Notestein several generations ago. That schema offers a stylized description of the great shifts in modern population patterns. Death and birth rates start out high, but more or less in equilibrium. Then, advances in knowledge and improvements in income result in broad declines in mortality, precipitating rapid population increase. Finally, socioeconomic development brings about sustained fertility reductions via voluntary, deliberate changes in childbearing patterns, at which point births and deaths once more come into balance.

While Notestein's schematic may still describe the human condition in broad stroke, today we can observe some important and surprising exceptions to these generalizations. Four of these unanticipated trends are (1) the rapid spread of sub-replacement fertility, (2) the emergence of unnatural gender imbalances among the very young, (3) sustained increases in death rates, and (4) American "demographic exceptionalism."

Two scientists from Poland claim to have found a solution to the problem of voting in the newly enlarged European Union. The current voting system, which is based on guidelines set by the Treaty of Nice, and the new system proposed in the draft EU Constitution both lead to inequalities between the different member states. The new system, proposed by Karol Życzkowski and Wojciech Slomczyński of Jagiellonian University in Kraków, is based on a square-root formula and would ensure that all European citizens had equal voting powers.

A new paper questions the notion of a worsening digital divide between rich and poor

That there are more telephones, computers and internet connections in rich countries than there are in poor ones is obvious. There are also more cars, televisions and air-conditioners. But the difference in the availability of information and communication technologies (ICTs) is the focus of particular concern among policymakers, academics and non-governmental organisations. Such technology, it is generally agreed, boosts productivity, though how quickly and by how much is the subject of much debate. The far wider availability of ICTs in rich countries, goes the argument, will therefore enable the rich to get richer, while the poor are left behind. In short, not only is there a worrying “digital divide” between rich and poor, the divide is widening—with ominous consequences.

These beliefs are widely held. But a new paper by two economists at the World Bank, Carsten Fink and Charles Kenny, questions the logic of this argument and highlights the woolly thinking that pervades the digital-divide discussion. The authors conclude that the divide's size and importance have been overstated, and that current trends suggest that it is actually shrinking, not growing—which means policies designed to “bridge the digital divide” may need rethinking.