曹聪校友问：Fermi的著名Piano Tuner问题“不见得是个物理学的问题吧，而是个MNC招聘时常见的考题”。

 

不错，都是Fermi惹的祸！很多公司招聘面试都考这个问题。——说明他们想招有创造性思维的人才:p

 

但是既然他们这么想招有创造性思维的人才，为什么自己就没有一点创造性思维呢？——比如一个有名的网络公司就把这个问题改成“世界上有多少调琴师？”——本来是个好问题，倒是这么一改变成坏问题了：还以为非洲人民都和你们这些跨国公司的HR一样，三家一台钢琴呢？！

 

为什么一定是调琴师？其实换成吕喆老师的“北京有多少快递员”、或者马红孺老师的“上海有多少修自行车的”不是也很有意思？

 

说明这些HR们离了“调琴师问题”就不知道怎么分析了。

 

其实“陈水扁问题”也好，“调琴师问题”也好，都是一种方法：数量级物理学课程里叫做“Divided and Conquer”，就是说，先把问题分解开来分析，然后综合出结论。这种方法当然不仅仅是物理学问题，在其它自然科学领域里乃至管理学领域里都用得着。前几天看到一篇博文：“升职称的好处之一是可以做专家了”，讲到做专家可以给被评审单位提一些建设性的意见。这当然是一个方面。但是更重要的是一个项目申请了几千万、甚至上亿的国家科研经费，这些钱到底该不该花？这么多钱，就是买设备，也要几十、上百台。每个专家对里面的细节都明白吗？对每一笔开支都能详细推算吗？那么凭什么把关呢？就是依靠数量级物理学里面说的这些办法。这里面有很多有意思的故事，可惜牵涉评审时的一些意见，而笔者是签了字的：评审内容不能外传。等退休了可以找时间做一点修饰加工，把这些事情写出来——都是数量级物理学的好教材。这是题外的话。

 

有人问，数量级物理学就是这些吗？当然不是。举几个Fermi的杰作：

 

1. 人体发电机：Fermi估算出，人体释放的热能，达到100W，等于一个大灯泡！这是很多类似上面Divided and Conquer分析的基础（比如一个屋子坐满听众的话，两小时以后温度上升多少？——答案是惊人的！你自己想想看）。

 

2. 原子弹当量的估算：第一颗原子弹在内华达州的沙漠引爆成功40秒后，试爆现场附近的科学家感受到冲击波的气浪。费米伸手向空中撒了一把碎纸片，落在他身后2.5米的地方。根据这个“实验数据”费米估算出的爆炸威力相当于一万吨TNT，非常接近仪器测到的两万吨的数值。

 

无独有偶，英国的物理学家G. I. Taylor根据美国公布的爆炸火球的照片，更准确地估算出爆炸当量是1.7万吨TNT！结果发表在英国皇家学会会刊上（Proc. Roy. Soc. A201, 175, 1950），惹得美国情报机构大发雷霆。

 

等等。都是如何从几个基本的数据，推断出大致的物理结果。

 

《数量级物理学》就是讲述这些故事，传授这些方法的。

 

 

附录：Fermi本人的回忆：

 

On the morning of the 16th of July, I was stationed at the Base Camp at Trinity in a position about ten miles from the site of the explosion.

 

The explosion took place at about 5:30 A.M. I had my face protected by a large board in which a piece of dark welding glass had been inserted. My first impression of the explosion was the very intense flash of light, and a sensation of heat on the parts of my body that were exposed. Although I did not look directly towards the object, I had the impression that suddenly the countryside became brighter than in full daylight. I subsequently looked in the direction of the explosion through the dark glass and could see something that looked like a conglomeration of flames that promptly started rising. After a few seconds the rising flames lost their brightness and appeared as a huge pillar of smoke with an expanded head like a gigantic mushroom that rose rapidly beyond the clouds probably to a height of the order of 30,000 feet. After reaching its full height, the smoke stayed stationary for a while before the wind started dispersing it.

About 40 seconds after the explosion the air blast reached me. I tried to estimate its strength by dropping from about six feet small pieces of paper before, during and after the passage of the blast wave. Since at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing. The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the blast that would be produced by ten thousand tons of T.N.T.

 

转载本文请联系原作者获取授权，同时请注明本文来自王晓钢科学网博客。
链接地址：https://blog.sciencenet.cn/blog-39346-633097.html

上一篇：《数量级物理学》的故事（3）：北京有多少调琴师？
下一篇：我们的博士教育