This week’s turbulence in the markets was not just a reminder of the ever -growing importance of China’s economy; it was also testimony to how computers dominate the workings of the west’s stock exchanges.

8月最后一周的市场动荡，不仅提醒人们，中国经济的重要性在不断提升；也证明了，计算机是如何主导西方股票交易所的运行的。

Never mind that the Dow Jones index plunged by 1,000 points in just a few minutes on Monday morning (before later rallying). What was more startling was that the share price of stalwart American companies such as

别在意这个周一的上午，道琼斯指数(Dow Jones index)在几分钟内暴跌了1000点（后来有所回升）。更令人吃惊的是，苹果(Apple)、Home Base和通用电气(GE)等强大美国公司的股价在几分钟之内的波动更剧烈。同时，有些交易所交易基金(ETF)的价值下跌了逾30%。这类基金行情平淡的观点可以休矣。

Apple, Home Base

尽管监管者或许需要几周时间才能明白暴跌的原因，但市场动荡的原因之一，在于自动化计算机程序改变了市场的运行方式。类似程序——比如高频交易策略——的使用推广得如此之快，美国证交会(SEC)目前估计，程序化交易已占到美国全部股票交易额的一半以上，在其他资产市场也占到很高比例。

or General Electric

目前，海量订单正在以闪电速度被执行。但是，还有另一个经常被忽略的影响：编程让这些计算机把市场中的无数个部分都联接起来，纳入了交易策略。所以，当计算机程序无法在市场的某个部分买入或卖出资产时，就将冲入另一部分寻找流动性。

gyrated even more dramatically in minutes. Meanwhile, the value of some exchange traded funds tumbled more than 30 per cent. So much for the idea that such funds are boring.

由于它们的算法常常是类似的（或是由受过相同培训的计算机科学家创建的），这一模式经常会产生“羊群”效应。如果市场的某个部分发生断路，那么影响可能会快速向整个系统蔓延，超过了人脑所能处理的速度。这是一个容易发生计算机踩踏的世界。

While it may take weeks before regulators understand why the plunges occurred, one reason for the swing is that automated computer programs have changed how markets function. The use of similar programs — such as high-frequency trading strategies — has expanded so rapidly that these are now estimated by the Securities and Exchange Commission to represent more than half of all US stock trades, and a big chunk of other asset markets.

有些金融家坚称，这并不要紧。金融史充分证明，人类也常常发生恐慌性抛售（在1929年崩盘之后的3年内，美国股市的总市值蒸发了近90%）。有关21世纪计算机踩踏的好消息是，尽管踩踏很惨烈，但持续时间通常很短。到周二，周一发生的价格剧烈波动已基本平息；近来债券市场上类似的疯狂波动，也消失得相当地快。

Orders are being executed at lightning speeds in huge volumes. But there is another, often overlooked implication: these machines are being programmed to link numerous market segments together into trading strategies. So when computer programs cannot buy or sell assets in one segment of the market, they will rush into another, hunting for liquidity.

但坏消息是，当的确发生这类计算机踩踏时，小户和散户遭受的损失通常最大。我们还不十分清楚，那一周谁亏损最大，谁受益最多。但世界最大高频交易机构Virtu的掌舵人道格拉斯•斯福(Douglas Cifu)披露称，周一是他的公司有史以来获利最多的日子之一；其他高频交易商业也有类似说法。相反，周一许多尝试通过经纪商以暴跌价格抛售ETF基金的投资者几乎一定是散户。

Since their algorithms are often similar (or created by computer scientists with the same training) this pattern tends to create a “herding” effect. If a circuit breaks in one market segment, it can ripple across the system faster than the human mind can process. This is a world prone to computer stampedes.

说来难怪，颇受小投资者欢迎的CNBC电视主持人吉姆•克拉默(Jim Cramer)，周一在“讨伐机器”(Rage Against the Machine)的标题下主持了节目。也难怪迈克尔•刘易斯(Michael Lewis)那本有关高频交易者的批判性书籍成了去年的畅销书。对许多西方投资者而言，那一周的行情表明，现代市场上存在巨大的不公平。

Some financiers insist this does not matter. Financial history amply shows that panic selling often occurs with humans too (the US stock market lost almost 90 per cent of its value in the three years after the 1929 crash). The good news about 21st-century computer stampedes is that while they are violent, they tend to be shortlived. By Tuesday the price gyrations seen on Monday had largely died down; similar recent wild bursts of volatility in bond markets also vanished fairly rapidly.

目前并没有简单的解决办法。在过去，银行充当做市商，使交易得以顺畅执行。但是，由于监管挤压，银行已在一定程度上放弃了这一角色。似乎谁也没准备把计算机交易程序踢出市场，因为在正常时期，它们似乎提供了银行不再提供的流动性。如果没有高频交易商，各种规模的投资者很可能都将付出更多交易成本。

But the bad news is that when these computer stampedes do occur, small players and retail investors tend to suffer most. We do not yet know precisely who lost and gained most this week. But Douglas Cifu, head of Virtu, the world’s largest high-frequency trader, has revealed that Monday was one of the most lucrative days his firm has ever seen; other high-frequency traders have echoed this. Conversely, many of the investors who were trying to sell exchange traded funds at tumbling prices via their brokers on Monday were almost certainly retail players.

作为回应，目前政策制定者正努力让算法交易更透明、更稳健。在2010年的一场“闪电崩盘”后，纽交所(NYSE)引入了新的“断路器”——可在市场波动太大时暂停交易。尽管该机制有时能让市场平静下来，但那个周一它或许加剧了恐慌情绪：ETF价格波动如此剧烈的原因之一，在于其标的股票已没有了交易价格。

Little wonder that Jim Cramer, the CNBC television host who is popular with small investors, presented his show on Monday under the tag “Rage Against the Machine”; nor that Michael Lewis’s critical book about high-frequency traders was a best seller last year. For many western investors, this week’s events showed there is a yawning inequality in modern markets.

结果是，政策制定者和投资者陷入了困境。谁也不想取缔机器人——就在那一周贝莱德(BlackRock)宣布，其将购买一个所谓的“机器人顾问”，以满足消费者对于自动化投资组合管理不断扩大的需求。但是，谁也不甚明白机器人正对市场产生何种影响，就更谈不上信任它们了。绝对清楚的是，那一周发生的剧烈波动如今已成为由机器人主导的现代市场的一个核心特点。人类投资者，请保持警惕。

There are no easy solutions. In the past, banks smoothed trading flows by acting as market makers. But they have partly withdrawn from that role due to a regulatory squeeze. And nobody seems ready to kick computing trading programs out of the market, since in normal times they appear to provide the liquidity that banks no longer offer. Without high-frequency traders it would probably be more costly for investors of all sizes to trade.