Science For All American -- Chap. 8 -- Communication and Information Processing

Science For All American -- Chap. 8 -- Communication and Information Processing

[8-1 .. 23]および[8-24 .. 34]に続いて、[Science For All Americans翻訳プロジェクト --Chapter 8: THE DESIGNED WORLD ... 8-35〜8-48]



AGRICULTURE ............................ 農業
COMMUNICATION ............ コミュニケーション

HEALTH TECHNOLOGY .................. 医療技術


People communicate frequently, if not always well. Hundreds of different languages have evolved to fit the needs of the people who use them. Because languages vary widely in sound, structure, and vocabulary and because language is so culturally bound, it is not always easy to translate from one to another with precision. Written communications -- from personal letters to books and junk mail -- crisscross continents and reach the farthest outposts. Telephones, radio, television, satellites, sound and optical recordings, and other forms of electronic communication have increased the options and added to the flow of information.


Communication involves a means of representing information, a means of transmitting and receiving it, and some assurance of fidelity between what is sent and what is received. Representation requires coding information in some transmission medium. In human history, the natural media have been mechanical contact (touch), chemicals (smell), sound waves (speech and hearing), and visible light (vision). But reliability and permanence require a medium for recording information. The reliable medium that developed first was the marking of solid materials—wood, clay, stone, and eventually paper. Today, we also mark, microscopically, plastic disks and magnetic tape. These modified materials can endure for many years, and can be moved great distances with their encoded information intact.


With the invention of devices to generate and control electric current, information could be encoded as changes in current and could be conveyed over long distances by wire almost instantaneously. With the discovery of radio waves, the same information could be encoded as changes in wave pattern and distributed in all directions through the atmosphere without the need of connecting wires. Particularly important was the invention of electronic amplifiers, in which a weak electrical signal controls the flow of a much stronger electric current, impressing it with the same pattern of information. Recently, the efficient control of light waves in lasers has made possible the encoding and transmitting of information as pulses in light intensity over optical fibers.


Information can be coded in analog or digital form. For example, originally both wired and wireless electric communication were only in the digital form of off-and-on bursts, requiring an artificial code to represent letters and numbers. A great advantage came with the invention of electronics -- devices to transform sound and light signals into electrical signals, and vice versa. Electronics made it possible to transmit analog signals that represent subtle variations in sound or light and to transcribe those signals as continuous variations in some medium. The ability to transcribe information microscopically and to transmit information at very high rates now makes possible the reduction of distortion and noise in processing analog signals by returning to the reliability of off-and-on digital signals. Analog signals of all sorts can now be sampled and represented as numbers, stored or transmitted in that form, and conveniently processed by computers, and perhaps returned to analog form for sound or graphic display.


The basic technical challenge of communication is to keep the signal large compared to the noise, which always tends to increase when information is recorded, transformed, or transmitted. The ratio of signal to noise can be improved by boosting the signal or by reducing the noise. Signals can be kept strong by amplification or by preventing energy loss (as by focusing them in a narrow beam of waves). Noise can be limited by isolating the signal from external noise sources (as by shielding microphone cables) or by reducing internal sources of noise (as by cooling an amplifier). A very different way to minimize errors from noise in communication is by means of repetition or some other form of redundancy that allows comparison and detection of errors. Some redundancy is always desirable in communication, because otherwise a single error may completely change the meaning of a message.


Communication sometimes requires security. Mail can be intercepted and copied, telephone wires can be tapped, over-the-air communications can be monitored. Privacy can be protected by preventing access to signals (for example, by using locks and passwords) or by preventing interpretation of them (such as by using secret codes). The creation of secret codes that are extremely difficult to figure out is an interesting application of number theory in mathematics. As the techniques of providing security improve, however, so do techniques for penetrating it.



Technology has long played an important role in collecting, storing, and retrieving information, as well as in transporting it. The invention of writing, tables of data, diagrams, mathematical formulas, and filing systems have all increased the amount of information we can handle and the speed with which we can process it. Large amounts of information are essential for the operation of modern societies; indeed, the generation, processing, and transfer of information is becoming the most common occupation of workers in industrialized countries.


Information is most useful when it is organized and represented by orderly collections of symbols. People use tables, indexes, alphabetical lists, and hierarchical networks to organize large amounts of data. The best way to store information depends on what is to be done with it. Information stored with one purpose in mind may be very troublesome to retrieve for other purposes (for example, the alphabetical listing of telephone numbers is ideal if one knows a person's name, but not if one knows only the address). Multipurpose data bases enable the information to be located in several different ways (for example, books listed by author or title or subject). A typical feature of such information systems is attaching to each data entry a prescribed set of key words that a computer can search for matching items.


Mechanical devices to perform mathematical or logical operations have been around for centuries, but it was the invention of the electronic computer that revolutionized information processing. One aspect of mathematical logic is that any information whatsoever -- including numbers, letters, and logical propositions -- can be coded as a string of yes-or-no bits (for example, as dots and dashes, 1's and 0's, or on/off switches). Electronic computers are essentially very large arrays of on/off switches connected in ways that allow them to perform logical operations. New materials and techniques have made possible the extreme miniaturization and reliability of no-moving-parts switches, which enable very large numbers of connected switches to be fitted into a small space. Very small size also means very short connections, which in turn mean very brief travel time for signals; therefore, miniaturized electronic circuits can act very quickly. The very short times required for processing steps to occur, together with the very large number of connections that can be made, mean that computers can carry out extremely complicated or repetitive instructions millions of times more quickly than people can.


The activity of computers is controlled partly by how they are wired, partly by sets of coded instructions. In general-purpose computers, instructions for processing information are not wired in but are stored temporarily (like other information). This arrangement permits great flexibility in what computers can do. People give instructions to computers through previously programmed software or by means of original programs written in a programming language. Programming languages enable a programmer to compose instructions with something like English or algebra, or geometrical manipulation of diagrams. Those instructions are then translated by another program into machine language for the computer. Often, the program calls for other inputs in the form of data entered by keyboard, from an information-storage device, or from an automatic sensing device. The output of a computer may be symbolic (words, numbers) or graphic (charts, diagrams), or it may be the automatic control of some other machine (an alarm signal, an action of a robot) or a request to a human operator for more instructions.


An important role of computers is in modeling or simulating systems -- for example, the economy or the weather, a grid of traffic lights, a strategic game, or chemical interactions. In effect, the computer computes the logical consequences of a set of complicated instructions that represent how the system works. A computer program is written that specifies those instructions and is then run, beginning with data that describe an initial state of the system. The program also displays subsequent states of the system, which can be compared to how the systems actually behave to see how good our knowledge of the rules is and to help correct them. If we are sure we know all the rules well, we can use the consequence-deducing power of computers to aid us in the design of systems.


An important potential role for computer programs is to assist humans in problem solving and decision making. Computers already play a role in helping people think by running programs that amass, analyze, summarize, and display data. Pattern-searching programs help to extract meaning from large pools of data. An important area of research in computer science is the design of programs -- based on the principles of artificial intelligence -- that are intended to mimic human thought and possibly even improve on it. Most of human thought is not yet well understood, however. As is true for simulations of other complex systems such as the economy or the weather, comparison of the performance of programs with the phenomena they represent is a technique for learning more about how the system works.


In mechanical systems that are well understood, computers can provide control that is as good as, or more precise and rapid than, deliberate human control. Thus, the operation of automobile engines, the flight control of aircraft and spacecraft, and the aiming and firing of weapons can be computerized to take account of more information and to respond much more rapidly than a human operator could. Yet, there are also risks that the instructions or the information entered may contain errors, the computer may have malfunctions in its hardware or software, and even that perfectly reliable computers, programs, and information may still give faulty results if some relevant factors are not included in the programs or if any values of included factors fall outside of their expected range. Even if the whole system is technically flawless, though, a very complex high-speed system may create problems because its speed of response may exceed human ability to monitor or judge the output.


The complexity of control in today's world requires vast computer management of information. And as the amount of information increases, there is increasing need to keep track of, control, and interpret the information -- which involves still more information, and so on through more layers of information. This flood of information requires invention of ways to store it in less space, to categorize it more usefully, to retrieve it more quickly, to transmit it at a higher rate, to sort it and search it more efficiently, and to minimize errors -- that is, to check for them and to correct them when they are found. As for communication, information storage also involves issues of privacy and security. Computer-managed information systems require means for ensuring that information cannot be changed or lost accidentally and that it will be unintelligible if unauthorized access does occur.

posted by Kumicit at 2008/03/07 01:11 | Comment(0) | TrackBack(0) | Public Documents | このブログの読者になる | 更新情報をチェックする



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