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假使你正驾车行驶在公路上,在你行进的方向上有三条车道,遇到的过路收费区设有六个收费岗亭。三个收费亭位于行车车道正前方,另三个则在路右方。你该选择哪条车道呢?情况通常是,不论你选哪条,等候时间都差不多长。通常有很多人试图寻求最短的队列,其结果足以使所有队列的长度大致相等。如果一支队列比其他队列短许多,汽车就会快速驶入该队列,直到使各队列等长为止。通常有很多的驾车者寻求最迅速的队列,其数量也足以使一般等候时间均等。 [2] The term profit in economics has a very precise meaning. Economists, however, often loosely refer to "good deals" or profitable ventures with no risk as profit opportunities. Using the term loosely, a profit opportunity exists at the toll booths if one line is shorter than the others. The general view of economics is that profit opportunities are rare. At any one time there are many people searching for such opportunities, and as a consequence few exist. At toll booths it is seldom the case that one line is substantially shorter than the others. 术语"利润"在经济学里具有很确切的含义。然而,经济学家常常宽松地把"好交易"或有利可图又无风险的投机活动称为"获利机会"。要是不怎么精确地使用该术语的话,则假如一队列比其他队列短,那么,在那些收费岗亭之中就存在获利机会。经济学的常规观点是:获利机会是少有的。在任一时刻,都有许多人在寻求这种机会,结果导致获利机会几乎不存在。在众多收费岗亭中,很少有一队列确实比其他队列短的情况。 [3] Another example of a possible profit opportunity is the following. At major banks in big cities, you can buy foreign currencies. The prices of these currencies are determined in world money markets. Let's concentrate on the U.S. dollar, the German mark, and the French franc. Prices are posted for marks in terms of dollars, francs in terms of marks, and dollars in terms of francs, among other possible combinations. With dollars we can buy marks; with these marks we can buy francs; and with these francs we can buy back dollars. Can we make money on this transaction? In other words, can the prices be such that we end up with more dollars at the end than we started with? If this is possible, we say that there are profit opportunities in the market. There are in fact almost never any profit opportunities of this kind in foreign currency markets. There are always individuals looking for such opportunities, and if any opportunity does arise it is quickly eliminated. 下面还有一个可能获利机会的例子。在大城市较大的银行里,你可以购买外币。这些货币的价格是在世界货币市场中决定的。让我们集中讨论美元、德国马克和法国法郎。美元对马克、马克对法郎、法郎对美元以及其他各种可能的组合的牌价被公布出来。我们可以用美元购买马克,用这些马克购买法郎,用这些法郎又可以买回美元。我们能不能在这笔交易中赚到钱?换句话说,那些价格转换能不能使我们的美元在结束时比开始多?倘若这是可能的,我们就说市场上存在获利机会。事实上,在外汇市场上几乎从来不存在这种获利机会。总是有人在寻找这样的机会,就算机会真的出现了,它也会很快消失掉。 [4] If, for example, the mark-franc price is too low with respect to the other prices, there is an immediate rush to buy marks and sell francs, not by ordinary citizens at bank windows, but by a few large currency traders in Tokyo, London, or Zurich who watch prices every minute. Such a rush drives up the mark-franc price to the no-profit-opportunity point. Markets like this, where any profit opportunities are eliminated almost instantaneously, are said to be efficient markets, 举个例子来说,假如马克对法郎的价格比起其他价格低得太多了,就会立即出现一阵争购马克、抛出法郎的热潮,进行买卖的不是银行服务窗口前的普通市民,而是在东京、伦敦或苏黎世时时刻刻关注着价格的少数大的通货交易商。这股热潮促使马克对法郎的价格达到无利可图的地步。像这种任何获利机会都几乎被即刻消除掉的市场被称为有效市场。 [5] The common language way of expressing the efficient markets hypothesis is "there's no such thing as a free lunch". How should one react when a stockbroker calls up with a hot tip on the stock market? With skepticism. There are thousands of individuals each day looking for hot tips in the market, and if a particular tip about a stock is valid there will be an immediate rush to buy the stock, which will quickly drive its price up. By the time the tip gets to your broker and then to you, the profit opportunity that arose from the tip (assuming that there was one) is likely to have been eliminated. Similar arguments can be made for bond markets and commodity markets. There are many "experts" in these markets, who take quick advantage or any news that affects prices. 表达有效市场假设的通俗说法是:"没有免费午餐那种事儿。"一个人在接到一位股票经纪人打来的电话,告诉他一条关于股市行情的有利可图的内部消息时,该有什么反应?半信半疑。每天,有成千上万的人在市场上搜寻可获利的内部消息,要是一条有关某股票的消息是确凿的,就会立即出现抢购该股票的热潮,而该股票的价格几乎迅速攀升。到消息传到你的经纪人再接着传到你耳中时,获利机会已经消失了。类似论点可 适用于债券和商品市场。在这些市场上有许多"专家",他们会迅捷地利用任何可影响价格的消息。 
当然,经济学家的获利机会处处都非常有限的观点可能会被运用得太过份。有个故事,说的是两个人一起走路,一个是位经济学家,另一个不是。那个不是经济学家的看见人行道上有张20美元的纸币,便说道:"人行道上有张20美元的纸币。"那个经济学家答道:"那不可能。要是有的话,早有人拾起来了。" [7] There are clearly times when profit opportunities exist. Someone has to be first to get the news, and some people have quicker insights than others. Nevertheless, news does get disseminated quickly, and there are thousands of people with quick insights. The general view that profit opportunities are rare is close to the mark. 有些时候,获利机会的确存在。必定有人第一个得到消息,且有些人的洞察力比别人敏锐。不过,消息无疑会传播得很快,而洞察力敏锐的人有成千上万。获利机会罕见这个常规观点并不离谱。
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