Calculating The Odds of Intelligent Alien Life - Jill Tarter

计算智能外星生命的可能性 - 吉尔·塔尔特

Transcriber: Ido Dekkers Reviewer: Ariana Bleau Lugo

(Music)

翻译人员: Geoff Chen 校对人员: Zhiting Chen

（音乐）

The basic question is, does life exist beyond Earth?

我们的基本问题是， 地球之外还存在生命吗？

Scientists who are called astrobiologists

那些被叫作天体生物学家的科学家们

are trying to find that out right now.

正在尝试研究这个问题。

Most astrobiologists are trying to figure out

许多天体生物学家正在试图确定

if there's microbial life on Mars,

在火星上，

or in the ocean under the frozen surface of Jupiter's moon Europa,

或者在木星的海洋冰面之下，

or in the liquid hydrocarbon lakes

又或者是在液态烃湖中， 是否存在微生物，

that we've found on Saturn's moon Titan.

（我们已在土星的卫星“提坦”上发现液态烃湖）。

But one group of astrobiologists works on SETI.

但一个天体生物学家小组 正致力于 SETI 研究。

SETI is the Search for Extraterrestrial Intelligence,

SETI 是指对外星智能探索，

and SETI researchers are trying to detect some evidence

SETI 研究者正尝试发掘一些证据

that intelligent creatures elsewhere

来说明除了智能生物之外的其他生物

have used technology to build a transmitter of some sort.

已经使用科技建造了某种发射器。

But how likely is it

但是他们想法设法发现信号的

that they will manage to find a signal?

可能性有多大？

There are certainly no guarantees when it comes to SETI,

没有 SETI 能勘测到信号的绝对保证，

but something called the Drake equation,

不过有个东西叫德雷克方程，

named after Frank Drake,

由法兰克•德雷克命名，

can help us organize our thinking

可以帮我们整理思路：

about what might be required

成功的探测

for successful detection.

究竟需要什么。

If you've dealt with equations before,

如果你之前已经处理过方程

then you probably expect

那么你可能会期待

that there will be a solution to the equation,

这个方程会有一种解法

a right answer.

可得出正确答案。

The Drake equation, however, is different,

然而，德雷克方程是截然不同的。

because there are so many unknowns.

因为有许多未知数。

It has no right answer.

它没有正确答案。

As we learn more about our universe

随着我们对宇宙

and our place within it,

以及我们所处在的土地了解越来越多

some of the unknowns get better known,

一些未知数将会得到更好的理解，

and we can estimate an answer a bit better.

我们可以预估一个更好的答案。

But there won't be a definite answer to the Drake equation

但是德雷克方程将不会有明确的答案

until SETI succeeds

直到 SETI 成功

or something else proves that

或者其他事情能够证明

Earthlings are the only intelligent species in our portion of the cosmos.

地球人是宇宙中唯一的智能物种。

In the meantime,

同时,

it is really useful to consider the unknowns.

考虑未知数极为有用。

The Drake equation attempts to estimate

德雷克方程试图预测

the number of technological civilizations

科技文明社会的数量

in the Milky Way Galaxy -- we call that N --

在银河系中——我们叫它N——

with whom we could make contact,

我们将能和谁联系,

and it's usually written as:

这常常被写作：

N equals R-star

N 等于 R 星

multiplied by f-sub-p

乘以 f-sub-p

multiplied by n-sub-e

乘以 n-sub-e

multiplied by f-sub-l

乘以 f-sub-l

multiplied by f-sub-i

乘以f-sub-i

multiplied by f-sub-c

乘以 f-sub-c

and lastly, multiplied by capital L.

最后，乘以大写 L.

All those factors multiplied together

所有这些因素乘在一起

help to estimate the number

可以帮助预测

of technological civilizations

科技文明的数量

that we might be able to detect right now.

这也许是我们目前能够做的。

R-star is the rate at which

R 星是一种比率，

stars have been born in the Milky Way Galaxy

星星已经在银河系诞生了

over the last few billion years,

几十亿年，

so it's a number that is stars per year.

所以这是指星星每年诞生的数量。

Our galaxy is 10 billion years old,

我们的银河系已有几百亿岁，

and early in its history stars formed at a different rate.

在它的历史早期 星星就已经形成了不同的比率。

All of the f-factors are fractions.

所有的 f 因素都是其中一部分。

Each one must be less than or equal to one.

每个因素都必须小于或等于另一个，

F-sub-p is the fraction of stars that have planets.

f-sub-p 是指具有行星的星星。

N-sub-e

n-sub-e

is the average number of habitable planets

是指在任何一个行星系统中的

in any planetary system.

可居住行星的平均数量。

F-sub-l

f-sub-l

is the fraction of planets on which life actually begins

是指开始有生命的行星。

and f-sub-i is the fraction of all those life forms

而 f-sub-i 是指那些所有

that develop intelligence.

能够发展智力的生命。

F-sub-c is the fraction of intelligent life

f-sub-c 是指

that develops a civilization

能够发展文明的智能生命，

that decides to use some sort of transmitting technology.

它们能决定运用某种类型的传输技术。

And finally, L --

最后，L 是指

the longevity factor.

寿命因素。

On average, how many years

平均来说，那些传输器

do those transmitters continue to operate?

能够持续运作多少年？

Astronomers are now almost able

天文学家现在几乎能够

to tell us what the product of the first three terms is.

告诉我们前三种术语分别是什么。

We're now finding exoplanets almost everywhere.

我们正在尽可能四处探索外星行星。

The fractions dealing with life and intelligence

有无数的专家正在研究

and technological civilizations

那些孕育生命、智能

are ones that many, many experts ponder,

与技术文明的行星，

but nobody knows for sure.

但是没有人能完全了解。

So far,

到目前为止，

we only know of one place in the universe

我们仅知道宇宙中有一个地方

where life exists,

有生命存在，

and that's right here on Earth.

那个地方，毫无疑问，就是地球。

In the next couple of decades,

在接下來的几十年，

as we explore Mars and Europa and Titan,

随着我们对火星、木星以及提坦的探索，

the discovery of any kind of life there

任何物种的发现

will mean that life will be abundant

都意味着银河系

in the Milky Way.

将会有丰富多样的生命。

Because if life originated twice

因为如果生命在这个太阳系内

within this one Solar System,

起源了两次，

it means it was easy,

那么这意味着生命起源很容易，

and given similar conditions elsewhere,

并假设别的地方也有相似条件，

life will happen.

生命就会产生。

So the number two is a very important number here.

所以二这个数字在这里尤其重要。

Scientists, including SETI researchers,

科学家，包括 SETI 研究者，

often tend to make very crude estimates

经常想要做一些大致预测，

and acknowledge that there are very large

并承认在这些预测中会有巨大的未知数，

uncertainties in these estimates, in order to make progress.

以获取进展。

We think we know

我们认为我们了解

that R-star and n-sub-e are both numbers that

R 星和 n-sub-e 都是

are closer to 10 than, say, to one,

比 10 更接近 1 的参数，

and all the f-factors are less than one.

并且这些 f 因素都小于 1，

Some of them may be much less than one.

其中一些可能要远远小于 1。

But of all these unknowns,

但在这些未知数中，

the biggest unknown is L,

最大的未知数是 L，

so perhaps the most useful version of the Drake equation

所以可能德雷克方程最有用的版本

is simply to say that

可以简单地说是

N is approximately equal to L.

N 近似于 L。

The information in this equation is very clear.

这方程式的信息十分清晰。

Unless L is large,

除非L是较大的参数，

N will be small.

N就是较小的参数。

But, you know, you can also turn that around.

但是你也可以把推论倒过来。

If SETI succeeds in detecting a signal in the near future,

如果 SETI 在不远的将来探测信号成功，

after examining only a small portion

验证到银河系的行星中

of the stars in the Milky Way,

只有一个小样本，

then we learn that

那么我们可以得出，

L, on average, must be large.

L 通常一定是较大的参数。

Otherwise, we couldn't have succeeded so easily.

不然，我们不可能如此容易成功。

A physicist named Philip Morrison

一个叫菲利普•莫里森的物理学家

summarizes by saying

总结说

that SETI is the archaeology of the future.

SEIT 是对未来的考古学。

By this, he meant that

通过这个观点他想表达

because the speed of light is finite,

因为光速是有限的，

any signals detected from distant technologies

任何从远传技术探测到的信号

will be telling us about their past

将会在传输到我们这儿时，

by the time they reach us.

告诉我们它们的过去。

But because L must be large

但是因为对于一个成功的探测而言，

for a successful detection,

L 一定是较大的参数，

we also learn about our future,

所以我们还会了解到我们的未来，

particularly that we can have a long future.

尤其是我们可能会拥有 一个很长远的未来。

We've developed technologies that can send signals into space

我们已经发展出 能发送信号到太空的科技，

and humans to the moon,

并且能将人类送上月球，

but we've also developed technologies that can destroy the environment,

但是我们也发展出了能够破坏环境的科技，

that can wage war

利用武器以及生物恐怖主义

with weapons and biological terrorism.

发动战争。

In the future,

在未来，

will our technology help stabilize our planet

我们的科技能帮助我们稳定星球

and our population,

以及人口，

leading to a very long lifetime for us?

从而使我们更长寿吗？

Or will we destroy our world and its inhabitants

又或者，我们将会宇宙舞台短暂的出现后

after only a brief appearance on the cosmic stage?

毁掉我们的世界及其居民？

I encourage you to consider

我鼓励你们去思考

the unknowns in this equation.

这个方程式里的未知数。

Why don't you make your own estimates

为什么你们不为这些未知数 做一些自己的预测，

for these unknowns, and see what you come up with for N?

然后看看你将如何解决 N?

Compare that with the estimates made by Frank Drake,

将这些预测与弗兰克·德雷克、

Carl Sagan, other scientists

卡尔·萨根、其他科学家，

or your neighbors.

或者你邻居的预测比较。

Remember, there's no right answer.

记住，没有标准答案。

Not yet.

至少目前还没有。