Information Theory The Big Idea Sample Reading Answers & Questions

Information theory the big idea reading answers will not only help you understand the various types of questions that are asked in the test but also ways in which to answer them. 

Information Theory The Big Idea 

A

In 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.

B

It 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.

C

This 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.

D

Noise usually means unwanted sounds which interfere with genuine information. Information theory generalizes 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.

E

Over 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.

F

Shannon also laid the foundations of more efficient ways of storing information, by stripping out superfluous (‘redundant’) bits from data which contributed little real information. As mobile phone text messages like ‘I CN C U’ 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.

Reading Passage has six paragraphs, A-F.

Which paragraph contains the following information?

Write the correct letter, A-F, in boxes 1-6 on your answer sheet.

1. _____an explanation of the factors affecting the transmission of information
Answer: D (This paragraph talks about these factors which impact information transmission including the limits imposed by noise, signal strength, and others).

2. _____an example of how unnecessary information can be omitted
Answer: F (This is mentioned in the Paragraph F including mobile phone text messages and other means).

3. _____a reference to Shannon’s attitude to fame
Answer: B (This is mentioned in this paragraph, including an account of how Shannon initially shunned the acclaim or fame)

4. _____details of a machine capable of interpreting incomplete information
Answer: E    (The paragraph does talk about turbo codes, the Voyager spacecraft and Universal Product Code) 

5. _____a detailed account of an incident involving information theory
Answer: A    (The Voyager I launch is talked about in detail here regarding its connection to information theory)

6. _____a reference to what Shannon initially intended to achieve in his research
Answer: C (The paragraph outlines this as a simple aim, i.e. pinning down the accurate or precise meaning for the information concept)

Questions 7-11

Complete the notes below.

Choose NO MORE THAN THREE WORDS from the passage for each answer.

Write your answers in boxes 7-11 on your answer sheet.

The Voyager 1 Space Probe

• The probe transmitted pictures of both 7_____, then left the 8_____
Answer: Jupiter and Saturn IN EITHER ORDER (You will find this in paragraph A); BOTH REQUIRED FOR ONE MARK   
Answer: Solar System (This is also found in paragraph A) 

The freezing temperatures were found to have a negative effect on parts of the space probe.

• Scientists feared that both the 9_____were about to stop working.
Answer: sensors and circuits IN EITHER ORDER (You will find this in the sequence in paragraph A) ; BOTH REQUIRED FOR ONE MARK   

The only hope was to tell the probe to replace them with 10_____ - but distance made communication with the probe difficult.
Answer: spares (Also present in paragraph A) 

A 11_____was used to transmit the message at the speed of light.
Answer: radio dish (You will find this in paragraph A where it talks about the radio dish that belonged to the Deep Space Network of NASA)

The message was picked up by the probe and the switchover took place.

Questions 12-14

Do the following statements agree with the information given in Reading Passage?

In boxes 12-14 on your answer sheet, write

12. _____The concept of describing something as true or false was the starting point for Shannon in his attempts to send messages over distances.
Answer: TRUE (This is true since his aim was defining otherwise vague ideas about information and also how to transmit the same information from one place to another) 

13. _____The amount of information that can be sent in a given time period is determined with reference to the signal strength and noise level.
Answer: TRUE (This is true, as mentioned in the passage, where it talks about how the rate of information transmission depends on the noise that ventures down communication channels and the strength of the signal)

14. _____Products have now been developed which can convey more information than Shannon had anticipated as possible.
Answer: FALSE (The passage talks about how Shannon laid the foundation for several systems and how turbo codes came close to his expectations) 

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