Are there strangers in space?
宇宙中有外星人嗎?
We must conclude from the work of those who have studied the origin of life, that given a planet only approximately like our own, life is almost certain to start. Of all the planets in our own solar system, we ware now pretty certain the Earth is the only one on which life can survive. Mars is too dry and poor in oxygen, Venus far too hot, and so is Mercury, and the outer planets have temperatures near absolute zero and hydrogen-dominated atmospheres. But other suns, stars as the astronomers call them, are bound to have planets like our own, and as is the number of stars in the universe is so vast, this possibility becomes virtual certainty. There are 100,000 million stars in our own Milky Way alone, and then there are 3,000 million other Milky Ways, or galaxies, in the universe. So the number of stars that we know exist is now estimated at about 300 million million million.
Although perhaps only 1% of the life that has started somewhere will develop into highly complex and intelligent patterns, so vast is the number of planets, that intelligent life is bound to be a natural part of the universe.
If then we are so certain that other intelligent life exists in the universe, why have we had no visitors from outer space yet? First of all, they may have come to this planet of ours thousands or millions of years ago, and found our then prevailing primitive state completely uninteresting to their own advanced knowledge. Professor Ronald Bracewell, a leading American radio astronomer, argued in Nature that such a superior civilization, on a visit to our own solar system, may have left an automatic messenger behind to await the possible awakening of an advanced civilization. Such a messenger, receiving our radio and television signals, might well re-transmit them back to its home-planet, although what impression any other civilization would thus get from us is best left unsaid.
But here we come up against the most difficult of all obstacles to contact with people on other planets -- the astronomical distances which separate us. As a reasonable guess, they might, on an average, be 100 light years away. (A light year is the distance which light travels at 186,000 miles per second in one year, namely 6 million million miles.) Radio waves also travel at the speed of light, and assuming such an automatic messenger picked up our first broadcasts of the 1920's, the message to its home planet is barely halfway there. Similarly, our own present primitive chemical rockets, though good enough to orbit men, have no chance of transporting us to the nearest other star, four light years away, let alone distances of tens or hundreds of light years.
Fortunately, there is a 'uniquely rational way' for us to communicate with other intelligent beings, as Walter Sullivan has put it in his excellent book, We Are not Alone. This depends on the precise radio frequency of the 21-cm wavelength, or 1420 megacycles per second. It is the natural frequency of emission of the hydrogen atoms in space and was discovered by us in 1951; it must be known to any kind of radio astronomer in the universe.
Once the existence of this wave-length had been discovered, it was not long before its use as the uniquely recognizable broadcasting frequency for interstellar communication was suggested. Without something of this kind, searching for intelligences on other planets would be like trying to meet a friend in London without a pre-arranged rendezvous and absurdly wandering the streets in the hope of a chance encounter.
ANTHONY MICHAELIS Are There Strangers in Space? from The Weekend Telegraph
New words and expressions 生詞與短語
Mercury
n. 水星
hydrogen
n. 氫氣
prevailing
adj. 普遍的
radio astronomer
射電天方學(xué)家
uniquely
adv. 唯一地
rational
adj. 合理的
radio frequency
無線電頻率
cm
n. 厘米
megacycle
n. 兆周
emission
n. 散發(fā)
intersteller
adj.星際的
rendezvous
n. 約會地點(diǎn)
本文參考譯文
根據(jù)研究生命起源的人們所作的工作，我們必然會得出這樣的結(jié)論：如果設(shè)想有一顆行星和我們地球的情況基本相似，那幾乎肯定會產(chǎn)生生命。我們目前可以肯定的是，在我們太陽系的所有行星中，地球是生命能存在的唯一行星�；鹦翘稍镉秩毖�，金星太熱，水星也一樣。除此之外，太陽系的其他行星的溫度都接近絕對零度，并圍繞著以氫氣為主的大氣層。但是，其他的太陽，既天文學(xué)家所說的恒星，肯定會有像我們地球一樣的行星。因?yàn)橛钪嬷泻阈堑臄?shù)目極其龐大，所以存在著產(chǎn)生生命星球的這種可能性是肯定無疑的。僅我們的銀河系就有1000億顆星，況且在宇宙中還有30億個天河，即銀河系。因此，我們所知道的現(xiàn)有恒星數(shù)目估計(jì)約有30億X1000億顆。
雖然在已經(jīng)產(chǎn)生生命的某個地方，可能只有1%會發(fā)展成高度復(fù)雜有智力的生命形態(tài)，但是行星的數(shù)目是那么龐大，有智力的生命必然是宇宙的自然組成部分。
既然我們?nèi)绱藞?jiān)信宇宙中存在著其他有智力的生命，那么我們?yōu)槭裁催�未見到外層空間來訪的客人呢?首先，他們可能在幾千年前或幾百年前已來過我們地球，并且發(fā)現(xiàn)我們地球那時普遍存在著的原始狀態(tài)同他們的先進(jìn)的知識相比是索然無味的。美國一位重要的射電天文學(xué)家羅納德.布雷斯韋爾教授在《自然》雜志上提出了這樣的觀點(diǎn)：假如有如此高級文明生命訪問了我們的太陽系，很可能會在離開太陽系時留下自動化信號裝置，等待先進(jìn)文明的覺醒。這種自動化信息裝置，在接收到我們的無線電和電視信號后，完全有可能把這些信號發(fā)回到原來的行星。至于其他文明行星對我們地球會有什么印象，還是不說為好。
然而，在和外星人聯(lián)系中我們遇到的最大困難是分隔我們的天文距離。據(jù)合理推算，外星人離我們平均距離也有100光年之遠(yuǎn)(1光年是光以每秒186，000 英里的速度在一年內(nèi)走的距離即6萬億英里)。無線電波也是以光速傳播的。假定外星人的這種自動化信息裝置接收了我們二十世紀(jì)二十年代的第一次廣播信號，那么這個信號在發(fā)回到原來的行星途中剛剛走了一半路程。同樣，我們目前使用的原始化學(xué)火箭，雖然把人送入軌道，但尚不能把我們送到離我們最近、相距4光年的其他星球上去，更不用說幾十光年或幾百光年遠(yuǎn)的地方了。
幸運(yùn)的是，有一種我們可以和其他智力生命通迅聯(lián)系的“唯一合理的方法”，正如活爾特.沙利方在其杰作《我們并不孤獨(dú)》中闡述的。這種通迅聯(lián)系要靠21厘米波段，即每秒1420兆周的精確無線電頻率。這個頻率是空間氫原子釋放的自然頻率，是在1951年被人類發(fā)現(xiàn)的。這個頻率是宇宙中任何射電天文學(xué)家都應(yīng)該熟悉的。
一旦這種波長的實(shí)際存在被發(fā)現(xiàn)，提出把它作為星際間唯一可辨認(rèn)的廣播頻率就為期不遠(yuǎn)了。沒有這手段，要想尋覓其他星球上的智力生命，就如同去倫敦見一位朋友，事先未約定地點(diǎn)，而荒唐地在街上游逛，以期待碰巧遇上一樣。
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