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Information theory lies at the heart of everything - from DVD players and the genetic code ofDNA to the physics of the universe at its most fundamental It has been central to the development of the science of communication, which enables data to be sent electronically and has therefore had a major impact on our lives

信息理论是所有现代科技理论——从DVD播放器到DNA遗传密码，再到最基础的宇宙物理学说——的核心内容。它在通讯科学的发展过程中占有重要的地位，它使得信息数据能够实现电子传送，从而对我们的日常生活产生了极大的影响。

AIn April 2002 an event took place which demonstrated one of the many applications of information theory. The space probe, Voyager I，launched in 1977，had sent back spectacular images of Jupiter and Saturn and then soared out of the Solar System on a one-way mission to the stars. After 25 years of exposure to the freezing temperatures of deep space, the probe was beginning to show its age. Sensors and circuits were on the brink of failing and NASA experts realised that they had to do something or lose contact with their probe forever. The solution was to get a message to Voyager I to instruct it to use spares to change the failing parts. With the probe 12 billion kilometres from Earth, this was not an easy task. By means of a radio dish belonging to NASA’s Deep Space Network, the message was sent out into the depths of space. Even travelling at the speed of light, it took over 11 hours to reach its target, far beyond the orbit of Pluto. Yet, incredibly, the little probe managed to hear the faint call from its home planet, and successfully made the switchover.

A 2002年四月的一个事件呈现了应用信息理论的一种途径。1977年发射的旅行者1号空间探测器曾经传送回火星和土星的壮观图像，之后又开始了飞向太阳系之外恒星的单向旅程。在经历了25年的太空低温环境后，探测器开始呈现出老化的迹象。探测器的感应器和电路都处于失灵的边缘，美国国家航空和航天管理局（NASA）的专家此时意识到如果他们不采取相应措施的话，他们将会永久的失去和探测器的联系。这个问题的解决方案就是向旅行者1号发送指导其用备用件替换失灵件的信息。由于探测器距离地球1200亿千米，所以这并不是个简单的任务。然而通过美国国家航天和航空管理局太空网的射电抛物面天线，这条信息被传送到了太空的深处。即使是以光速航行，要到达既定目标也需要花费11个小时，但这离冥王星的轨道还相距甚远。尽管如此，让人难以置信的是，这小小的探测器居然成功接收到了来自自己星球的微弱呼唤，并且成功完成了替换工作。

BIt was the longest-distance repair job in history, and a triumph for the NASA engineers. But it also highlighted the astonishing power of the techniques developed by American communications engineer Claude Shannon, who had died just a year earlier. Born in 1916 in Petoskey, Michigan, Shannon showed an early talent for maths and for building gadgets, and made breakthroughs in the foundations of computer technology when still a student. While at Bell Laboratories, Shannon developed information theory, but shunned the resulting acclaim. In the 1940s, he single-handedly created an entire science of communication which has since inveigled its way into a host of applications, from DVDs to satellite communications to bar codes - any area, in short, where data has to be conveyed rapidly yet accurately.

B 这应该是历史上最远距离的修复工作，也是美国国家航空和航天管理局众多工程师的重大胜利。这B 次事件也突出展现了美国通讯工程师克劳德香农（ClaudeShannon）所研发技术的惊人能力，但是克劳德香农（ClaudeShannon）此时已经离世1年了。香农（Shannon）生于1916年的密歇根州佩托斯基（Petoskey,Michigan），他从小就展现出卓越的数学才能和制作器材的才能，并且当他还是个学生的时候，他就在基础计算机技术领域取得了重大的突破。香农（Shannon）在贝尔实验室期间发现了信息理论，但却避开了应有的赞誉。在二十世纪四十年代，他自己一个人创建了整个通讯科学，从此通讯科学被应用于众多不同的方面，从DVD播放器到卫星通讯到条形码——简而言之，任何需要快速且准确的传输信息数据的领域。

CThis all seems light years away from the down-to-earth uses Shannon originally had for his work, which began when he was a 22-year-old graduate engineering student at the prestigious Massachusetts Institute of Technology in 1939. He set out with an apparently simple aim: to pin down the precise meaning of the concept of ‘information’. The most basic form of information, Shannon argued, is whether something is true or false - which can be captured in the binary unit, or 'bit', of the form 1 or 0. Having identified this fundamental unit, Shannon set about defining otherwise vague ideas about information and how to transmit it from place to place. In the process he discovered something surprising: it is always possible to guarantee information will get through random interference - ‘noise’ - intact.

C 自香农（Shannon）最初所做的有实际性用处的工作好像已经过去很久了，那时他还是个22岁的工程系研究生，自1939年起在著名的麻省理工学院开始了研究工作。他为自己设定了一个相当简单的目标：明确“信息”这个概念的准确含义。香农（Shannon）认为信息的最基本形式是其对错性——这个形式可以用0或1的形式以二进制的单位来表达，或者称为“位”。在确定了这个基本单位后，香农（Shannon）开始了为其他模糊的信息概念下定义和探索如何将信息从一个地点传送到另一个地点的工作。在这个过程中，他发现了一个令人惊奇的现象：保证信息在传输中通过随机干扰——“噪音”——后的完整性是有可能的。

DNoise usually means unwanted sounds which interfere with genuine information. Information theory generalises this idea via theorems that capture the effects of noise with mathematical precision. In particular, Shannon showed that noise sets a limit on the rate at which information can pass along communication channels while remaining error-free. This rate depends on the relative strengths of the signal and noise travelling down the communication channel, and on its capacity (its ‘bandwidth’〕. The resulting limit, given in units of bits per second, is the absolute maximum rate of error-free communication given signal strength and noise level. The trick, Shannon showed, is to find ways of packaging up - *coding’ - information to cope with the ravages of noise, while staying within the information-carrying capacity -‘bandwidth’ - of the communication system being used.

D 噪音通常指的是不希望有的声音，它会对真正的信息造成干扰。信息理论通过用数学精确性来捕捉噪音影响的定理对这个观点进行了一般化。具体的说就是，香农（Shannon）指出噪音在比率上有一个极限，在这个比率之内时，信息就可以保持毫无错误的通过通讯渠道传输。这个比率取决于信号的相对强度、通过通讯渠道的噪音水平和通讯渠道的容量（即“带宽”）。最终的极限是以每秒钟的单位量来表现的，它是在不考虑信号强度和噪音水平的情况下保证无错误通讯的一个绝对化的最大值。香农（Shannon）还说明这里的微妙之处就是要找到打包——“编码”——信息来应对噪音所造成的损害的方法，在此同时又要保证所采用的通讯系统的信息传输容量——“带宽”。

EOver the years scientists have devised many such coding methods, and they have proved crucial in many technological feats. The Voyager spacecraft transmitted data using codes which added one extra bit for every single bit of information; the result was an error rate of just one bit in 10,000 - and stunningly clear pictures of the planets. Other codes have become part of everyday life - such as the Universal Product Code, or bar code, which uses a simple error-detecting system that ensures supermarket check-out lasers can read the price even on, say, a crumpled bag of crisps. As recently as 1993, engineers made a major breakthrough by discovering so-called turbo codes - which come very close to Shannon’s ultimate limit for the maximum rate that data can be transmitted reliably, and now play a key role in the mobile videophone revolution.

E 多年来，科学家们设计出了众多类似的编码方法，而且已经证实了它们在许多科技成就中都占有重要的地位。旅行者太空飞船发送信息数据时采用了在信息的每一位上都多加一位的编码，结果是一个10000里仅有一位的错误比率和相当清晰的星球图片。其他的众多编码也已经成为了日常生活中的一部分——例如通用产品码（theUniversalProductCode）或者条形码，它利用一个简单的错误发现系统来确保超市收银处的激光扫描器能够读出商品的价格，即使是从被压皱的薯片包装袋上读取价格也没有问题。近至1993年，工程师们取得了一个重大的突破，他们发现了所谓的turbo码（Turbocodes），这个编码非常近似于香农（Shannon）所定义的最大比率的最优极限值，这个最大比率可以保证数据传输的可靠性。现在这个编码在移动视频电话的革命中发挥着重要的作用。

FShannon also laid the foundations of more efficient ways of storing information, by stripping out superfluous Credundant，）bits from data which contributed little real information. As mobile phone text messages like 4l CN C IT show, it is often possible to leave out a lot of data without losing much meaning. As with error correction, however, there’s a limit beyond which messages become too ambiguous. Shannon showed how to calculate this limit, opening the way to the design of compression methods that cram maximum information into the minimum space.

F 香农（Shannon）还为更加有效地储存信息奠定了基础，提出从数据中省略掉多余的（即过剩的）位的方法，这些多余的位对于真正的信息贡献甚少。正如对于类似“ICNCU”的手机信息，在不丢失过多含义的情况下省略一些数据是很有可能实现的。然而由于错误改正的存在，这种省略需要有一个限制额度，如果超出了这个额度，信息就会变得含义不清。香农（Shannon）介绍了计算这个限制额度的方法，从而打开了通往压缩数据方法的大门，通过压缩的方法可以将最大的信息量存放于最小的空间内。