新概念英語第四冊(cè)(含lrc文本)Lesson 43 Are there strangers in space?

[00:01.90]Lesson 43 [00:03.90]Are there strangers in space? [00:07.67]First listen and then answer the following question. [00:11.18] [00:12.90]What does the 'uniquely rational way' for us to communicate with other intelligent beings in space depend on? [00:20.36] [00:22.51]We must conclude from the work of those who have studied the origin of life, [00:27.03]that given a planet only approximately like our own, [00:31.12]life is almost certain to start. [00:34.31]Of all the planets in our solar system, [00:37.44]we ware now pretty certain the Earth is the only one on which life can survive. [00:43.64]Mars is too dry and poor in oxygen, [00:46.91]Venus far too hot, and so is Mercury, [00:51.18]and the outer planets have temperatures near absolute zero and hydrogen-dominated atmospheres. [00:58.65]But other suns, start as the astronomers call them, [01:02.26]are bound to have planets like our own, [01:05.22]and as is the number of stars in the universe is so vast, [01:08.38]this possibility becomes virtual certainty. [01:12.26]There are one hundred thousand million starts in our own Milky Way alone, [01:17.63]and then there are three thousand million other milky ways [01:21.61]or galaxies, in the universe. [01:24.12]so the number of stars that we know exist is now [01:27.49]estimated at about 300 million million million. [01:33.23]Although perhaps only 1 percent of the life that [01:36.00]has started somewhere will develop into highly complex and intelligent patterns, [01:41.45]so vast is the number of planets, [01:43.82]that intelligent life is bound to be a natural part of the universe. [01:50.23]If then we are so certain that other intelligent life exists in the universe, [01:55.92]why have we had no visitors from outer space yet? [01:59.83]First of all, [02:00.99]they may have come to this planet of ours thousands or millions of years ago, [02:05.73]and found our then prevailing primitive state completely uninteresting to their own advanced knowledge. [02:13.13]Professor Ronald Bracewell, [02:15.11]a leading American radio astronomer, [02:17.46]argued in Nature that such a superior civilization, [02:22.23]on a visit to our own solar system, [02:25.02]may have left an automatic messenger behind to await the possible awakening of an advanced civilization. [02:32.82]Such a messenger, [02:34.29]receiving our radio and television signals, [02:36.95]might well re-transmit them back to its home-planet, [02:41.44]although what impression any other civilization would thus get from us is best left unsaid. [02:49.10]But here we come up against the most difficult of all obstacles to contact with people on other planets -- [02:55.97]the astronomical distances which separate us. [03:01.70]As a reasonable guess, they might, on an average, [03:03.76]be 100 light years away. [03:06.73](A light year is the distance which light travels at 186,000 miles per second in one year, namely 6 million million miles.) [03:19.24]Radio waves also travel at the speed of light, [03:22.79]and assuming such an automatic messenger picked up our first broadcasts of the 1920's, [03:28.90]the message to its home planet is barely halfway there. [03:33.53]Similarly, our own present primitive chemical rockets, [03:37.87]though good enough to orbit men, [03:39.89]have no chance of transporting us to the nearest other star, [03:43.82]four light years away, [03:45.80]let alone distances of tens or hundreds of light years. [03:50.66]Fortunately, [03:51.47]there is a 'uniquely rational way' for us to communicate with other intelligent beings, [03:57.76]as Walter Sullivan has put it in his excellent book, [04:01.54]We Are not Alone. [04:03.53]This depends on the precise radio frequency of the 21-cm wavelength, [04:09.98]or 1420 megacycles per second. [04:15.04]It is the natural frequency of emission of the hydrogen atoms in space and was discovered by us in 1951; [04:23.95]it must be known to any kind of radio astronomer in the universe. [04:29.41]Once the existence of this wave-length had been discovered, [04:33.20]it was not long before its use as the uniquely recognizable broadcasting frequency [04:38.95]for interstellar communication was suggested. [04:42.46]Without something of this kind, [04:44.52]searching for intelligences on other planets would be like trying to [04:48.45]meet a friend in London without a pre-arranged rendezvous [04:52.22]and absurdly wandering the streets in the hope of a chance encounter. ANTHONY MICHAELIS Are There Strangers in Space? from The Weekend Telegraph

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