About noon on Christmas Day in London, I became the victim of a crime. Somebody smashed in the rear window of our family car; nothing serious, fortunately.
Nonetheless, it led me to the inevitable questions: Who did it and why? Was this an impersonal act driven purely by cold calculation? Or did the perpetrator harbour malice or resentment?
I'll probably never know. But on the causes of crime more generally, we do know a few things. First, seemingly trivial factors _ the location of street lights, road layouts, housing designs and so on _ often have a decisive influence on whether crime hits one place rather than another. Second, and more important, a sure recipe for more frequent crime is rising socioeconomic inequality.
This ought to be especially worrying in the US and UK, where, over the past two decades, inequality has increased tremendously.
Some influential economists, notably Nobel laureate Gary Becker, have sought to explain crime as a simple consequence of rational economic self-interest. At any moment, in this view, people weigh up the potential risks and rewards of their possible actions and decide to commit a crime whenever that turns out to be the best option. Moral considerations of right and wrong, trust and cooperation, have nothing to do with it.
Tidy as the theory may be, it contradicts the facts. If crime follows purely economic calculation, then an area's crime rate should correlate closely with its economic conditions. That's just not the case.
In an important study a few years ago, for example, economists Edward Glaeser, Bruce Sacerdote and Jose Scheinkman found that economic factors explain less than 30% of the variation in crime rates among cities or among different parts of one city.
A more persuasive theory, initiated by criminologist Marcus Felson, focuses more on the simple physical factors that influence where and when crime might happen. In Mr Felson's "routine activity" theory, crime has a chance to take place anytime a potential offender comes into contact with a potential target in conditions conducive to crime _ for example, in the absence of a third party who might intervene or witness the event.
Police forces in the US, UK. and elsewhere have used the theory extensively in deploying their limited resources, paying closer attention to simple details such as patterns of street lighting and flows of people. Data shows, for example, that a house on a main street is more likely to be burgled than a house accessible only by driving down two further side streets.
The reason appears to be that burglars spend most of their time on routine, non-criminal activities, and when they commit crimes, they do so in places they are most familiar with.
But this theory, which sees crime as a kind of chemical reaction between potential offenders and targets, ignores the question of how a person becomes a potential offender in the first place. This is equally important.
Criminologists have long failed in efforts to identify early on those particular youngsters who will later become serial offenders. It seems that most criminals are made, not born, created through social influences and a progressive sequence of experiences and external influences.
A culture of crime in a community can make it more likely for young people to become criminals. The behaviour can spread mechanically, more or less like an infection or chemical reaction.
Equally decisive in determining crime rates are the more invisible barriers to crime set up by social norms and social cohesion. Indeed, one of the most robust statistical patterns known is that crime rates tend to go up with rising economic inequality, which itself tends to go along with erosion of social trust.
In a brilliant 2009 book titled The Spirit Level, researchers Richard Wilkinson and Kate Pickett reviewed hundreds of earlier studies and presented overwhelming evidence that economic inequality correlates directly with levels of crime and many other measures of social dysfunction. Nations with lower inequality have higher life expectancies, fewer homicides, lower infant mortality, higher levels of trust, and less obesity and addiction.
The children of poor parents in the US or UK have a significantly lower chance of becoming wealthy than do similar children in countries such as Sweden, Denmark or Japan, where people are more equal. As Mr Wilkinson quipped, "An American who wants to pursue the American dream should move to Denmark."
Mr Wilkinson and Ms Pickett also explored the mechanisms by which economic inequality may drive social problems. One of the foremost is how low evaluations of social status can trigger long-term stress. In a 2004 study, for example, psychologists measured the levels of the stress hormone cortisol in volunteers facing various kinds of threats.
They found much higher levels associated with "social evaluative" threats _ the negative judgements of others. As societies become more unequal, such judgements tend to become implicit in social interactions, as the poor and underprivileged are excluded from a wide range of activities.
Heightened cortisol levels over long periods are associated with a variety of health risks, including high blood pressure, weakening of the immune system, memory loss and impaired learning. These could contribute to even greater stress and social withdrawal.
Inequality, of course, is a natural phenomenon that no one would sensibly hope to eradicate completely. Basic models of financial flows and patterns of wealth aggregation indicate that the possession of most wealth by a small fraction of the population is a virtual certainty in any more or less free market. It's what you get if you have an economy of free exchange coupled with multiplicative returns on investment.
Still, even if we accept inequality as a given, that doesn't necessarily mean we should accept it in the extreme. It's probably no accident that the US, ranked among the most unequal nations, also has the largest fraction of its population in prison _ five times as large as that of any other industrialised nation (excluding Russia).
The socially destructive consequences of inequality will become increasingly obvious unless we reduce it _ through the tax system (as the US did through much of the 20th century, before the last few decades), or through measures aimed at making pre-tax incomes more equal.
I don't know which approach is better, just as I'll never know who smashed my car window and why. I do see that if we opt for the status quo, everyone's chances of becoming a victim will be that much greater.
Mark Buchanan, a theoretical physicist and the author of "The Social Atom: Why the Rich Get Richer, Cheaters Get Caught and Your Neighbor Usually Looks Like You," is a Bloomberg View columnist.