12.3 其他地方生活的概率

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  其他地方生活的概率

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  So. Life in the Universe? Frank Drake, a pioneer in the search for life with radio telescopes,  first penned an equation in 1961 to estimate the probability that technologically capable and communicating civilizations exist in our galaxy. 
  ::那么,宇宙中的生命?弗兰克·德雷克,一个利用射电望远镜寻找生命的先锋, 1961年第一次用一个方程来估计我们银河系中存在技术能力和交流文明的概率。

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  The Drake equation distills the key parameters that we need to know. Seth Shostak at the SETI institute characterizes this equation as a map, not a destination.  
  ::德雷克方程式蒸馏了我们需要知道的关键参数。Seth Shostak在SETI研究所将这个方程式定性为地图,而不是目的地。

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  $$\begin{align*}N=R_s \cdot f_P \cdot \eta_E \cdot f_L \cdot f_I \cdot f_C \cdot L\end{align*}$$
  ::N=RsfPEfLfIfCL

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  where,
  ::何时,何地,

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  • $\begin{align*}N\end{align*}$   is the number of communicative civilizations that we could detect,
    ::N是我们可以探测到的通信文明的数量,
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  • $\begin{align*}R_S\end{align*}$  is the rate of formation of suitable stars,
    ::RS是合适的恒星的形成速度,
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  • $\begin{align*}f_P\end{align*}$   is the fraction of stars with planets,
    ::FP是有行星的恒星的分数,
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  • $\begin{align*}\eta_E\end{align*}$  is the number of "Earths" per planetary system,
    ::E是每个行星系统“地球”的数量,
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  • $\begin{align*}f_L\end{align*}$   is the fraction of these "Earths" where life develops,
    ::FL是生命发展的“地球”中的一小部分,
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  • $\begin{align*}f_I\end{align*}$   is the fraction of the instances of life where intelligent life develops,
    ::FI是生命中智力生命发展的例子的一小部分,
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  • $\begin{align*}f_C\end{align*}$   is the fraction of intelligent life that develops communicating technology,
    ::FC是发展通讯技术的智能生命的一小部分,
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  • $\begin{align*}L \end{align*}$  is the lifetime of communicating civilizations 
    ::L是交流文明的一生

  

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  The Drake equation is a way of organizing our thoughts about the probability of technological, communicating life elsewhere.
  ::德雷克方程式是组织我们思考 科技可能性的一种方式 将其他地方的生活 传达给别人

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  Let us consider each of these terms. We will provide provisional numbers, but many of them are merely educated guesses (some more educated than others).
  ::让我们想一想其中的每一个条件。我们将提供暂时的数字,但其中有许多只是猜测(比别者更受教育)。

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  Stars
  ::星星星星

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  We can make a rough estimation of the star formation rate of the galaxy by considering what we know about the galaxy today. Currently, the galaxy holds about 100-400 billion stars. We also know the galaxy to be approximately 10 billion years old. From this, we find that on average stars  have been be forming at a rate of 10-40 stars per year.
  ::通过考虑我们目前对星系的了解,我们可以粗略地估计银河系的恒星形成速度。目前,银河系拥有大约1 000—400亿颗恒星。我们也知道银河系有大约100亿年的历史。从这一点来看,我们发现恒星平均每年以10—40颗恒星的速度形成。

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  $$\begin{align*}\frac{100 \: billion \: stars}{10 \: billion \: years} = 10\frac{stars}{year} \end{align*}$$
  ::100亿亿 1000亿 年 = 10亿 年

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                                                          $\begin{align*}\frac{400 \: billion \: stars}{10 \: billion \: years}=40\frac{stars}{year}\end{align*}$
  ::400亿亿 1000亿 年 = 40 年

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  This is a very simplistic estimate. It does not take into account how many of these stars may be suitable for life, such as short-lived O or B type stars, or whether the rate of star formation  has been constant  over the  lifetime of the galaxy. However,  this estimate gives a decent  upper and lower bound.
  ::这是一个非常简单的估计。 它没有考虑到这些恒星中有多少可能适合生命,例如短寿命的O型或B型恒星,也没有考虑到恒星形成速度在银河系寿命期间是否保持不变。 但是,这一估计给出了一个适当的上下圈。

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  Planets
  ::行星

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  Thank to discoveries over the past decade, we now have a good estimate for the fraction of stars with planets . This was completely unknown at the time Frank Drake first wrote down his equation.  The discoveries from the   Kepler  mission  provide statistical evidence that  essentially every star has one or more planets. W hen you look up at the night sky, there are actually more unseen exoplanets there than there are stars. We can therefore assign a value of 1 for $\begin{align*}f_P\end{align*}$  and a value of 0.9, or 90%, as a more conservative estimate.
  ::感谢过去10年的发现, 我们现在对有行星的恒星的一小部分有了良好的估计。 这在Frank Drake第一次写下其方程式时是完全未知的。 Kepler 飞行任务的发现提供了统计证据, 表明每个恒星基本上都有一个或多个行星。 当你在夜空上看时, 那里实际上比有恒星的更隐蔽的外行星。 因此我们可以给FP分配一个值, 0.9, 或90%, 作为更保守的估计。

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  The next parameter,  $\begin{align*}\eta_E\end{align*}$ ,  is  the number of Earth-like habitable planets. The Kepler mission stopped just short of determining this value . However, astronomers have extrapolated out from the parameter space where Earth-sized planets were detected and estimate that the number of habitable Earths ranges from 0.5 to 3 per system. Maybe the requirement of an Earth-like planet is too conservative. Would a moon do? Titan, Europa,  and Enceladus all offer possible platforms for life in our solar system that are well outside the habitable zone. 
  ::下一个参数, E, 是类似于地球的可居住行星的数量。 Kepler 飞行任务停止了, 仅仅没有确定这个值。 然而, 天文学家从探测到地球大小行星的参数空间外推了出来, 估计每系统可居住地球的数量介于0.5到3之间。 也许对地球相似的行星的要求太保守了。 月亮会太保守吗? 泰坦、 欧罗巴和土卫二都都为我们太阳系中的生命提供了非常远离可居住区的可能平台。

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     The number of habitable worlds? 
  ::多少个可居住世界?

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  We could  stop   here, at the end of verifiable science, and calculate the number of habitable worlds in the Milky Way galaxy.  We just need to make this estimate dimensionally correct by multiplying by the lifetime of habitable worlds (recall that the first term is the number of stars per year, so we need to multiply by years for this equation to be dimensionally correct).  You know that Earth has had life for about 4 billion years. Whether  homosapiens survives   or not, life is likely to continue as long as our planet has liquid water on its surface. The radius of our Sun is increasing as it ages. Without intervention, the Earth will lose its oceans of water in another billion years. So, we might estimate that  planets like the Earth are habitable (distinct from being "inhabited") for roughly 5 billion years. Multiplying through these factors, we get a range for the number of habitable worlds: 
  ::我们可以在这里停下来,在可核查的科学结束时,计算出银河系中可居住世界的数量。我们只需要通过乘以可居住世界的寿命来使这一估计的维度正确。我们只需要通过乘以可居住世界的寿命来使这一估计的维度正确(回顾第一个学期是每年的恒星数量,因此我们需要乘以年数才能使这个等式的维度正确 ) 。 你知道地球有大约40亿年的生命。无论同族生存与否,只要地球表面有液体水,生命就有可能持续下去。太阳的半径随着时间的老化而不断增长。没有干预,地球将在另外10亿年中失去其水的海洋。因此,我们可以估计像地球这样的行星在大约50亿年中是可居住(与“居住”不同 ) 。通过这些因素的倍增,我们可以得到一个可居住世界的分布范围:

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  $\begin{align*}10 \times 0.9 \times 0.5 \times 5 \times {10}^9 = 22.5 \times {10}^9\end{align*}$  (lower limit of 22.5 billion) 
  ::10x0.9x0.5x5x5x109=22.5x109(下限225亿)

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  $\begin{align*}40 \times 1 \times 3 \times 5 \times {10}^9 = 600 \times {10}^9\end{align*}$  (upper limit of 600 billion) 
  ::40x1x3x3x5x109=600x109(上限为6 000亿美元)

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  If we want to estimate the probability of technological civilizations, then don't multiply by the longevity of habitable worlds (because that's not the number you want to find)... keep going!
  ::如果我们想估计技术文明的概率, 那么不要乘以可居住世界的寿命( 因为这不是你想找到的数字)... 继续!

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  Life
  ::生命生命

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  The term $\begin{align*}f_L\end{align*}$  asks us to consider the fraction of Earth-like planets in the habitable zone where life of any kind  (including single-celled microbes) emerges. This term  must be non-zero, because there exists life on Earth but we have yet to find life anywhere else. What we do know is that the Earth formed about 4.56 Gya. We have firm evidence of life from stromatolites at 3.5 Gya, which must have been preceded by less complex organisms. These numbers indicate that life formed relatively quickly on  Earth, even though it is not yet clear to us how. We can infer that perhaps life appears  between 10% and 100% of the time on  habitable planets, but you should make your own guess for this fraction . What is your justification? 
  ::“fL”一词要求我们考虑在可居住区出现任何生命(包括单细胞微生物)的类似地球行星的一小部分。这个术语必须是非零的,因为地球上存在生命,但我们还没有在其他地方找到生命。我们所知道的是,地球大约组成了4.56Gya。我们从3.5Gya的地块中得到了确切的生命证据,在Gya的地块上,必须先有较不复杂的生物。这些数字表明地球上的生命形成较快,尽管我们尚不清楚。我们可以推断,生命也许出现在可居住行星上的时间的10%到100%之间,但你应该自己猜测一下。你有什么理由?

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      The number of planets in the galaxy with  life of any kind?
  ::银河系中有多少行星 与任何种类的生命?

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  We could  stop   here and calculate the probability that life of any kind will arise on Earth.  We add in the new factor for our estimate that life arises. We  could use the previous argument to guess that if life evolves, it may last for about 5  billion years.  Multiplying through these factors we get a range for the number of habitable worlds: 
  ::我们可以在这里停下来,计算地球上出现任何生命的概率。 在对生命产生的估计中加入新的因素。 我们可以使用先前的论点来猜测,如果生命演变,它可能会持续大约50亿年。 通过这些因素的乘法,我们得到了一个可居住世界的分布范围:

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  $\begin{align*}10 \times 0.9 \times 0.5 \times 0.1 \times 5 \times {10}^9 = 2.25 \times {10}^9\end{align*}$  (lower limit: 2.25 billion planets in our galaxy have life of some kind)
  ::10x0.9x0.5x0.0.1x5x109=2.25x109(下限:银河系中22.5亿个行星有某种生命)

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  $\begin{align*}40 \times 1 \times 3 \times 1 \times 5 \times {10}^9 = 600 \times {10}^9\end{align*}$  (upper limit: 600 billion sites  with life in the galaxy) 
  ::40x1x3x3x3x1x5x5x109=600x109(最高限值:有星系生命的6 000亿个地点)

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  If we want to keep going, to estimate the probability of technological civilizations, then don't multiply by the longevity of life on habitable worlds (because that's not the number you want to find) 
  ::如果我们想继续前进, 估计技术文明的概率, 那么不要乘以生命在可居住世界的寿命( 因为这不是你想找到的数字)

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  Intelligent and communicating
  ::智能和通信

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  Intelligence is hard to describe, hard to quantify, and hard to detect. Besides t he example of intelligent life on Earth, we have no other concrete evidence towards a true value for the fraction of life that becomes intelligent. We  could again use what happened on Earth as a general guiding example - a sort of "Copernican" view for biology. Come up with your own estimates and reasoning for $\begin{align*}{f}_{i}\end{align*}$ .
  ::情报很难描述,很难量化,也很难探测。除了地球上智能生命的例子之外,我们没有其他具体的证据可以证明生命中变得智能的一小部分的真正价值。我们可以再次将地球上发生的事情作为一般的指导性例子 — — 一种生物学的“Copernican”观点。提出你自己的估算和推理。

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  Here is one possible argument: We know that bio-complexity requires energy, which requires efficient  metabolism.  On Earth this  takes the form of aerobic respiration, and the Cambrian explosion marks the time when complex life emerged. This occurred in the last 0.6 billion years  in the lifespan  of Earth.
  ::其中一个可能的论点是:我们知道生物复杂性需要能源,这需要高效的新陈代谢。 在地球上,这表现为有氧呼吸,而坎布里安爆炸标志着复杂生命出现的时刻。 这发生在地球生命期过去60亿年中。

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  $$\begin{align*}\frac{0.6 \: billion \: years}{4.5 \: billion \: years}=0.13\end{align*}$$
  ::0.6亿年 4.5亿年=0.13

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  This makes the argument time-based.  Inherently, right or wrong, we are guessing that life everywhere will evolve and that statistically perhaps  0.13 of the habitable planets that we find with life will have life forms that evolved to become intelligent .
  ::这使得争论以时间为基础。 自然的,对的或错的,我们猜想,世界各地的生命都会演变,从统计学上看,我们与生命一起发现的可居住行星中的0.13个将具有进化成智能的生命形式。

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  However, we have no true understanding of how typical our planet is. We do not have a sense of whether the evolution of complex life is rare or inevitable for all Earth analogs. An upper bound  might be 1, meaning all planets with life will eventually evolve the complexity that leads to intelligence or it might happen on one of a million inhabited worlds.  That's a big range!
  ::然而,我们对于地球的典型程度并不真正了解。我们不知道复杂的生命的进化是罕见的还是所有地球类比的必然的。 上界可能为1,这意味着所有有生命的行星最终都会演变出导致智慧的复杂程度,或者说它可能在百万人居住的世界上发生。这是一个很大的范围!

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  Technology
  ::技术 技术

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  The next term,  $\begin{align*}{f}_{c}\end{align*}$ , tries to capture  another attribute  that is hard to estimate.  On inhabited planets with intelligent life, how often will that life develop technology so that it can communicate across the galaxy?  We are  technological adolescents, and there is the significant problem of light travel time. If we send a message to a civilization that is 10,000 light years away (a small distance in our galaxy, which is 100,000 light years in diameter), then it takes 20,000 years for the round-trip reply. Will we still be here?  Will  anyone still be listening?  The intelligent life on Earth has had this communication technology for only about 100 years. That is a tiny fraction of time for intelligent life on Earth: 100 years out of 200,000 years that homosapiens have existed. 
  ::下一个词, fc, 试图捕捉另一个难以估计的属性。 在有智能生命的有人居住的行星上, 生命能多久开发出技术才能在银河中进行交流? 我们是技术青少年, 并且存在着光旅行时间的重大问题。 如果我们向距离1万光年的文明发出信息( 我们的星系的一条小距离, 直径为10万光年), 那么往返答复需要20,000年的时间。 我们还会在这里吗? 是否有人还在听? 地球上的智能生命只有这一通信技术大约100年。 这是地球上智能生命的一小部分时间: 在20万年中, 共有100年是同质生物存在的时间。

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  The example of Earth points to another possibility. We have taken our first steps out into the solar system.  The Apollo-11 mission  took us to the moon and Elon Musk wants to help us get to Mars.  Even if the emergence of intelligent, technological, communicating civilizations is rare, they may spread to other planets.    
  ::地球的例子说明了另一种可能性。我们已经迈出了进入太阳系的第一步。阿波罗11号飞行任务把我们带到了月球,埃隆·穆斯克希望帮助我们到达火星。即使智能、科技、交流文明的出现很少,它们也可能扩散到其他行星。

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  Lifetime
  ::使用寿命

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  The chance of discovering life inherently depends on how long life survives  on a planet. On Earth, life has persisted for at least 3.5 billion years. At most, life on Earth will exist until the Sun evolves and the Earth loses its oceans  (about  5 billion years). From  the geological history, we know that life is fairly resilient. Our answer for the lifetime of microbes would be very different from our guess for the lifetime of technological civilizations. 
  ::发现生命的机会从本质上看,取决于地球上生命的存续时间。在地球上,生命已经持续了至少35亿年。最多,地球上的生命将存在,直到太阳进化和地球失去海洋(大约50亿年 ) 。 从地质史上看,我们知道生命具有相当的弹性。我们对微生物生命的答案与我们对技术文明寿命的猜测大相径庭。

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  There is a good expectation that we have the engineering skills to mitigate certain natural disasters, such as asteroid impacts. At the same time, the development of technology  can negatively impact the lifetime of a civilization .  I ndustrialization has led to rapid climate change and nuclear weaponization that could threaten our existence on timescales of  a few generations. 
  ::人们很期待我们具备减轻某些自然灾害(如小行星撞击)的工程技能,与此同时,技术发展可能对文明的一生产生负面影响,工业化导致迅速的气候变化和核武器武器化,可能威胁我们几代人的时间生存。

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  Finale
  ::终极

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  Finally, the finale. We can collect our musings from above to calculate a value for N, the number of communicating civilizations that we could detect. We should note that when we multiply these numbers together, we do not really get a low and high estimate for technological life. Because we put in the extreme limits of our guesses, we get extreme limits for the range of possibilities.  It is better to treat each of these as distribution functions and combine them in a statistically rigorous manner. 
  ::最后,最后一段。 我们可以从上面收集我们的微量元素, 来计算N的值, 即我们能够检测到的通信文明的数量。 我们应该注意到,当我们一起乘以这些数字时, 我们并没有真正得到对技术生命的低和高估计。 因为我们在猜测的极端限度里, 我们得到了对各种可能性的极端限制。 最好把每一个都当作分配功能, 并以严格统计的方式将它们结合起来。

  Term	播放段落 Lower  Estimate ::下 下 估计数	Upper  Estimate
  $\begin{align*}R_S\end{align*}$	10 stars/yr	40 stars/yr	rate of star formation
  $\begin{align*}f_P\end{align*}$	0.9	1	fraction of stars with planets
  $\begin{align*}\eta_E\end{align*}$	1	3	number of "Earths" per planetary system
  $\begin{align*}f_L\end{align*}$	0.1	1	fraction of "Earths" where life develops
  $\begin{align*}f_I\end{align*}$	0.001	1	fraction of instance of life where intelligent life develops
  $\begin{align*}f_C\end{align*}$	10^-6	0.5	fraction of intelligent life that develops communicating technology
  $\begin{align*}L\end{align*}$	200 years	10,000 yrs	lifetime of communicating civilizations
  		300 billion	conservative estimates for the possible number of communicating civilizations that we could detect

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  Some  of the terms for which we have observations are quite certain. We know  the rate of star formation and  the fraction of stars with planets , and we have solid estimates for the number of habitable planets per planetary system. In contrast, the last four terms are extremely  uncertain. But all we need to firm this up is one other example of a world  where life exists.  
  ::我们观测到的一些术语相当肯定。 我们知道恒星的形成速度和有行星的恒星的分数,我们对每个行星系统的可居住行星的数量有可靠的估计。相反,最后四个术语是极其不确定的。但我们只需要将它固定下来,就是一个存在生命的世界的另一个例子。

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  So where are they? The Fermi Paradox 
  ::他们在哪里?

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  Particle physicist Enrico Fermi is credited with posing this question. If the universe is teeming with life, why haven't we observed it yet? There are many resolutions to this question. Watch the 6-minute animated TedEd video below to hear  some resolutions to this question.   
  ::粒子物理学家Enrico Fermi提出了这个问题。 如果宇宙充满生命,为什么我们还没有看到它呢? 这个问题有很多决议。 观看下面6分钟的TedEd动画视频,听取关于这个问题的一些决议。