SETI 的历史 - 7

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<资料来源:The Planetary Society>


第7章:德雷克方程的诞生

The Green Bank meeting was also remarkable because it featured the first use of the famous formula that came to be known as the "Drake Equation". When Drake came up with this formula, he had no notion that it would become a staple of SETI theorists for decades to come. In fact, he thought of it as an organizational tool - a way to order the different issues to be discussed at the Green Bank conference, and bring them to bear on the central question of intelligent life in the universe.


Green Bank 会议还由于第一次使用了那个著名的“德雷克方程”而闻名。当 Drake 提出这个方程的时候,他完全没有想到这个方程会在之后的几十年被 SETI 的研究人员大量使用。实际上,他当时只是把它作为一个组织工具 - 用来对 Green Bank 会议上将要讨论的一些话题进行排列,通过这个方程来承载关于宇宙中的智能生命的中心问题。


The grand question of the number of communicating civilizations in our galaxy could, in Drake's view, be reduced to seven smaller issues:

The rate of star formation in our galaxy at the time our Solar System was formed (R*);
The fraction of stars that have planets around them (fp);
The number of planets per star that are capable of sustaining life (ne);
The fraction of planets in ne where life evolves (fl);
The fraction of fl where intelligent life evolves (fi);
The fraction of fi that communicate (fc);
The lifetime of a communicating civilization (L);

Denoting the number of communicating civilization in our galaxy by N, and multiplying the different elements, we get the famous Drake Equation:


在 Drake 看来,关于在我们银河系中可能与我们接触的文明数量的问题,可以归结为如下几个要素:

银河内恒星形成的速率(R*);
恒星有行星的可能性(fp);
其中具备生命诞生条件的行星的平均数量(ne);
行星发展出生命的可能性(fl);
生命进化成有智慧的生命体的概率(fi);
拥有与其他星球进行通信的技术的概率(fc);
该技术文明能够存在的时间(L);

用 N 来表示我们的银河系内容可能与我们接触的文明数量,将上述各个要素相乘,我们就得到了著名的德雷克方程:

N= R* fp ne fl fi fc L


恒星的诞生
由哈勃太空望远镜拍摄的照片,内容是在 M33 星系中 NGC 604 星云内恒星的形成。而恒星的形成,目前仍然是德雷克方程中唯一得到实证的要素。
图片提供:Space Telescope Science Institute, Hui Yang (U. IL), and NASA

The equation served its purpose well at the Green Bank conference. It provided a framework that enabled the different researchers, who had very different backgrounds and specialties, draw upon their specialized knowledge, and at the same time contribute to the general question of the meeting.


德雷克方程在 Green Bank 会议上很好地发挥了它的作用。这个方程提供了一个很好的框架,使得所有的与会人员,尽管他们的背景和专业各不相同,却仍能利用他们各自的专业知识,来促进会议中心议题的讨论。


Soon, however, to Drake's surprise, it became much more than that. The short mathematical formula proved irresistible to SETI promoters: it reduced a huge and almost unmanageable speculative question to a neat series of seemingly specific questions. While the larger question seemed too large and speculative, its seven components appeared to lend themselves to scientific inquiry. No less important, posed as a formula, the question seemed mathematical and quantitative. What better way of gaining scientific respectability than formulating a mathematical equation?


但是很快,出乎 Drake 的意料,他的方程式还发挥了更大的作用。这个简短的数学方程式对 SETI 发起人的吸引力非常大:它把一个很大的、不太明确的问题化解成了一系列简单而明确的问题。虽然原始的那个问题看上去仍然很大且不明确,但它的几个组成部分却能够经得住科学上的推敲。同样重要的,以方程式的形式,原来的问题就变成了一个数学上的、定量的问题。如果要得到科学界的认真对待,还有什么方式能比提出一个数学方程式更好?


The Green Bank meeting weighed in on each of the elements in the equation, and came up with generally optimistic estimates. The rate of star formation (R*) was the only element in the equation about which some reliable information existed, and the conference settled on a conservative estimate of about one star per year. Otto Struve was the resident expert on extrasolar planets (fp), and he suggested that planets orbiting distant stars were, in fact, very common. Su-Shu Huang gave an optimistic assessment about the likelihood of planets having life supporting environments (ne), and Calvin and Sagan suggested that on suitable planets life would ultimately emerge (fl). Lilly gave an optimistic assessment on the likelihood of intelligence emerging on a life-bearing planet (fi), based on his work on dolphins. If at least two intelligent species emerged on Earth, doesn't that suggest that intelligence is common? Lilly's views, however, were highly controversial, and often dismissed by mainstream biologists. Even the sympathetic audience at Green Bank was quick to note that dolphins were not a technological species, and would be unlikely to send radio beams into space.

Green Bank 会议上权衡了方程式中的每一个因子,得到了还算乐观的估算结果。恒星形成的速率(R*)是方程式里面唯一有可靠依据的因子,会议上对这个做了比较保守的估计,也就是平均每年形成一颗新恒星。


The final two elements in the equation were in the field of social science: how likely are intelligent beings to communicate with other civilizations (fc), and how long do civilizations last (L)? Significantly, there were no social scientists at Green Bank. But while lamenting their absence, Morrison also pointed out that even specialists were unlikely to have the answers for such grand questions. In their absence, he suggested that based on Earthly experience civilizations were likely to develop advanced technology, and that curiosity and the urge to communicate appear to be universal. Furthermore, he suggested, if civilizations are able to overcome the dangers of nuclear self-destruction, they can probably sustain themselves for very long periods of time.


In summarizing their discussions, the conference members concluded that the number of communicating planets could range from fewer than 1000 to more than a billion. Most of them thought the higher number a more likely estimate. On this basis they called for a vigorous radio search for extraterrestrial intelligence, using a 300-foot dish, very large computers, and patience to search for at least 30 years.


第6章:Green Bank 的海豚会议 ← | → 第8章:The New Searches,新的搜索

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