Nevertheless, velocities greater than c can be observed. Suppose a lighthouse illuminates a distant shore. The rotating lamp moves quite slowly, but the spot on the opposite shore travels at a far greater velocity. If the shore were far enough away, the spot could even move faster than light. However, this moving spot is not a single "thing". Each point along the coastline receives its own spot of light from the lighthouse, and any information travels from the lighthouse at c, rather than along the path of the moving spot. Such phenomena are described as the "motion of effects", and are not forbidden by relativity.
Comprehension check
Answer the following questions:
1. What is the cosmic speed limit?
2. What does relativity teach us?
3. Can any information be transmitted faster than the speed of light?
Discussion
Comment on the text using the following prompts:
...first of all...,...secondly...,...I’d say...,...I’m convinced that...
Give a brief summary of the text.
UNIT 6
NOISE CONTROLS CHAOS
Vocabbox
noun collocations
§ background hiss
§ unwelcome factor
§ random noise
§ erratic behaviour
§ chaotic system
§ long-standing challenge
§ turbulent flow
§ nonlinear oscillator fluctuation
verb collocations
§ guide the behaviour
§ occur
§ simulate the motion
§ steer the oscillator
§ confirm experimentally
§ establish sequence
§ cause the change
Pre-reading task
1. 1.Do you agree that noise is usually an unwelcome factor?
2. What have you heard about the use of random noise?
Reading
Read the text. Find the main information about the behaviour of systems in different states.
From the background hiss on an old radio to the unwanted signals that limit the performance of an electronic device, noise is usually an unwelcome factor. However, a team of researchers from the UK, Russia and Italy has shown that random noise could be used to guide the erratic behaviour of a chaotic system towards a more stable state. Moreover, these random fluctuations show how the system can be made to behave in a predictable way using the least energy, thereby solving a long-standing challenge in physics.
Many seemingly stable systems can suddenly behave in an unstable and irregular way. This behaviour occurs because the system can exist in two or more possible states, one of which is chaotic. Examples of such systems are diverse and include the turbulent flow of fluids, the behaviour of lasers and even the heart – where chaotic behaviour can be life threatening.
The team led by Dmitri Luchinsky and Peter McClintock of Lancaster University in the UK made the latest discovery by simulating the motion of a periodically driven nonlinear oscillator influenced by noise. Although the fluctuations are completely random, the team found that certain sequences of fluctuations could steer the oscillator towards stable behaviour. In most cases, they had to wait a long time before these “special” sequences occurred. The findings were confirmed experimentally using an electrical circuit as the oscillator.
By recording the shape of the noise just before the change from chaotic to stable motion took place, the team established the optimal fluctuation sequence needed to force the switch to regular behaviour on demand. They also showed that the chaotic system was very sensitive to variations in the shape of this optimal sequence. If the initial conditions or the amplitude of the fluctuations differed even slightly from this pattern, far more energy was required to cause the change.
McClintock and co-workers believe the findings could have important practical applications. An irregular heartbeat, for example, could be controlled by applying tiny voltage pulses. And spacecraft could be kept on course by continuously applying small corrective forces, rather than a single large force, thereby saving fuel.
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