经济学人39:社会科学 关于群体的思考

 　　Science and Technolgy

　　科技
　　Social science
　　社会科学
　　Wisdom about crowds
　　关于群体的思考
　　To model the behaviour of humans en masse, treat them as people, not molecules 1
　　在为人类的全体活动建立模型时，要将他们看作是"人"，而不是"分子"。
　　THE behaviour of crowds is sometimes unpredictable and occasionally deadly, but there is good reason to believe it is governed by simple rules. Presumably, like molecules in a liquid, people in a crowd all behave in more or less the same way. Capture those similarities in a model and it should be possible to predict how a crowd will behave.
　　群体的行动有时候是不可知的，偶然致使的，不过有充分的理由相信，这种行为符合简单的规律。简单说来，这就像液体中的分子，在群体中的人的行动大致是一样的。在一个模型中捕获这些相似性可以对于一个群体的行动进行预测。
　　Existing models of crowd behaviour do just that. They treat moving masses of humanity as though they were fluids. This works, up to a point. But it often fails to predict the changes that happen as a crowd's density 2 increases and its movement becomes chaotic 3. That is why Mehdi Moussaid of Paul Sabatier University, in Toulouse, and his colleagues have made a radical 4 innovation. Instead of treating the individual human beings in a crowd as if they were molecules, they have treated them as if they were human beings. They have, in other words, given them volition 5. Of course, the objective of someone in a moving crowd is usually fairly simple-to get somewhere and then stay there. But it is an objective, nevertheless.
　　现有的大众行动模型就可以做到这一点。这些模型将变化的人类群体当作是液体。在某种程度（或者条件）下，这个模型非常有效。不过当涉及到群体的密度增加，运行变得混乱时，对于预测发生的变化往往不能奏效。这就是保尔?萨巴蒂大学（Paul Sabatier University，在图卢兹）的迈赫迪?穆赛德（Mehdi Moussaid）和他的同事已经进行突破性创新的原因。与以往的理论中将群体看作是分子不同，他们将群体看作是"人"。换句话说，就是考虑到了"人的意志"。当然了，在一个活动的群体中的客观存在的一些人通常比较简单：到哪里，就待在那。即使这样，它还是一个客观存在的事物。
　　As they describe in the Proceedings 6 of the National Academy of Sciences, Dr Moussaid and his team built a computer model in which, initially 7, every virtual person in the crowd followed two rules. The first was that each attempted to chart as straight as possible a path to his destination, such as an exit or the end of a corridor, while avoiding obstacles, including other pedestrians 8. Second, each adjusted his speed, depending on his distance from such obstacles.
　　就像他们在《美国国家科学院学报》中所描述的那样，穆赛德博士和他的团队建立了一个计算机模型，在这个模型里，起先，每个虚拟的在群体中的人都服从两个规律。第一，当避开包括其他行人在内的障碍时，每个人都试图尽量以直线的的路线到达目的地，就像一个出口或一个走廊的尽头。第二，每个人都会调整自己的速度，这个依赖于与障碍物的距离。
　　These two rules were enough to reproduce in the model the sorts of behaviour seen in real crowds, such as the tendency people have to sort themselves spontaneously into separate lanes of traffic moving in opposite directions and the stop-and-go motion that occurs as crowds become more dense 9. When Dr Moussaid really put the pressure on, however, by increasing the density of the virtual crowd, the model did not show the extreme turbulence 10 seen in real crowds-the sudden crushes and chaotic changes in direction.
　　这两个规则在真实的群体中的各种行为上已经得到了足够的验证，例如，在公路上，人们通常会趋向于同时将自己朝相反的方向移动，这种停停走走的行为，让本来发生的拥挤更加拥挤。当穆赛德博士确实增加压力时——通过增加虚拟人群的密度，在真实的人群中，这个模型并没有显示出的骚乱——骤然的碾压和方向变化的混乱。
　　These happen because in extremely dense crowds there is so much shoving and jostling that people's movements are no longer entirely 11 under their own control. In other words, they actually do start behaving like molecules in a fluid, bouncing off one another at random 12. To mimic 13 that behaviour, Dr Moussaid added a third rule, which made members of his crowd more molecule-like when they were at very close quarters-a lack of volition that will be familiar to anyone who has been in a tight jam of humanity.
　　因为在极其密集的人群里，有很多人推搡和拥挤，人们自身的行动并不受自己的控制，因此会发生混乱。换句话说，这个时候，他们就像液体中的分子一样，被任意地反弹。为了模拟这种行为，穆赛德博士又增加了第三条规律，即当群体中的成员之间非常接近的时候，他们就像分子一样，此时群体中的成员是缺乏意志的，对那些处于拥挤人群里的人来说，这种感觉深有体会。
　　With this third rule added, the model accurately 14 reproduced the dynamics 15 of dense crowds as well as those of sparser 16 ones. At first, a crowd flows smoothly 17. Then, as more people are added, it begins to show stop-and-go patterns and sometimes extreme crushing. Finally, it displays the sort of turbulence that can lead to disaster. On one run, for example, the model showed precisely 18 the pattern seen in a video of a catastrophe 19 in Mecca in 2006, when 346 pilgrims there on the haj were crushed to death.
　　有了这第三条规律的补充，无论在动态密集的人群里还是在稀疏的人群里，这种模型都会精确在得到再现。最初，人群流动顺畅。接着，更多的人加入，整个人群开始变成时走时停的模型，有时候还变得极度拥挤。最后，人群变得混乱，并能导致灾难。例如，在2006年麦加的朝觐的灾难上，根据视频的显示内容，这种模型得到了精确的显示，当时有346名朝圣者在混乱中被踩踏至死。
　　The practical upshot of all this, Dr Moussaid hopes, will be improvements in the design of public spaces where crowds are likely to gather, especially in the location of evacuation routes. That is an outcome greatly to be desired. And it was made possible by remembering that people are not molecules.
　　穆赛德博士希望，所以有这种真实的结果会对有助于改善公共场所的设计，尤其是对于疏散通道位置的考虑，在这种场合下，有可能聚集大量的人。这是一个非常值得注意的结果。一定要牢记，人，不是分子。