Calculating The Odds of Intelligent Alien Life - Jill Tarter

Transcriber: Ido Dekkers Reviewer: Ariana Bleau Lugo

(Music)

譯者: 峻亨 簡 審譯者: 庭芝 梁

（音樂）

The basic question is, does life exist beyond Earth?

基本的問題是： 地球之外是否有生命存在？

Scientists who are called astrobiologists

被稱為「太空生物學家」的科學家們

are trying to find that out right now.

正在嘗試找出答案

Most astrobiologists are trying to figure out

大多數太空生物學家想要瞭解

if there's microbial life on Mars,

是否有微生物存在於火星上

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

或是在木星的衛星「木衛二」 冰層下的海洋

或是在土星的衛星「土衛六」

or in the liquid hydrocarbon lakes

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

那裡已經被發現的液態烴湖泊中

But one group of astrobiologists works on SETI.

但是，有一群太空生物學家 正在參與 SETI 計畫

SETI is the Search for Extraterrestrial Intelligence,

SETI 的全名是 「尋找外星智慧計畫」

and SETI researchers are trying to detect some evidence

SETI 的研究人員正試圖找出證據

that intelligent creatures elsewhere

來說明外星球的智能生物

have used technology to build a transmitter of some sort.

已經能用科技 建造某種信號發射器

But how likely is it

但是他們有多少機率

that they will manage to find a signal?

能夠偵測到信號？

There are certainly no guarantees when it comes to SETI,

沒有人能夠保證 SETI 會成功

but something called the Drake equation,

但是藉由弗蘭克·德雷克之名所命名的

named after Frank Drake,

德雷克公式

can help us organize our thinking

可以幫助我們整理思緒

about what might be required

並瞭解什麼是成功探測的必要條件

for successful detection.

If you've dealt with equations before,

如果你曾經解過其他方程式

then you probably expect

那麼你可能會期望

that there will be a solution to the equation,

方程式有解

a right answer.

也就是可以求出正確答案

The Drake equation, however, is different,

然而，德雷克公式是截然不同的

because there are so many unknowns.

因為它包含太多未知數

It has no right answer.

它並沒有正確答案

As we learn more about our universe

當我們對於宇宙 以及我們所處的土地

and our place within it,

有更多的學習

some of the unknowns get better known,

我們對於一些未知數 也有更多的瞭解

and we can estimate an answer a bit better.

我們可以估計出更好的答案

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

但是德雷克公式 並不會有明確的答案

until SETI succeeds

除非等到 SETI 計畫成功

or something else proves that

或是其他事物來證明

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

在我們所處的宇宙中

地球人是唯一的智慧生物

In the meantime,

在此同時

it is really useful to consider the unknowns.

研究未知數也具有其意義

The Drake equation attempts to estimate

德雷克公式嘗試估計出

the number of technological civilizations

在銀河系科技文明的數量

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

我們把這個數量稱之為 N

with whom we could make contact,

代表我們有能力 進行接觸的文明數量

and it's usually written as:

公式通常表示為：

N equals R-star

N = R*

multiplied by f-sub-p

乘以 fp

multiplied by n-sub-e

乘以 ne

multiplied by f-sub-l

乘以 fl

multiplied by f-sub-i

乘以 fi

multiplied by f-sub-c

乘以 fc

and lastly, multiplied by capital L.

最後，乘以大寫 L

All those factors multiplied together

將所有因數相乘

help to estimate the number

可幫助我們估計

of technological civilizations

我們也許能立刻偵測到的

that we might be able to detect right now.

科技文明數量

R-star is the rate at which

R* 代表的是

過去幾十億年以來

stars have been born in the Milky Way Galaxy

恆星在銀河系中形成的速率

over the last few billion years,

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

所以它是指每年恆星誕生的數量

Our galaxy is 10 billion years old,

我們所處的銀河系 已經有一百億年以上了

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

但是在它的歷史初期 恆星以不同的速率形成

All of the f-factors are fractions.

所有的 f 因數 都是以分數表示可能性

Each one must be less than or equal to one.

每一個因數都必須小於或等於一

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

fp 是指恆星擁有行星的可能性

N-sub-e

ne 是指

is the average number of habitable planets

在任何一個星系中

適合居住行星的平均數量

in any planetary system.

F-sub-l

Fl 是指

is the fraction of planets on which life actually begins

行星發展出生命的可能性

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

而 fi 是指

生物能夠發展出高等智慧的可能性

that develop intelligence.

F-sub-c is the fraction of intelligent life

fc 是指高等智慧的生物

that develops a civilization

能夠發展出文明

that decides to use some sort of transmitting technology.

並且決定運用某項通訊技術 與外太空聯繫的可能性

And finally, L --

最後

L 是代表壽命的因數

the longevity factor.

On average, how many years

平均來說，就是那些通訊傳輸設備

do those transmitters continue to operate?

能夠持續運作多少年？

Astronomers are now almost able

天文學家現在 幾乎已經能告訴我們

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

前三項的乘積是多少

We're now finding exoplanets almost everywhere.

我們目前正在 四處尋找系外行星

The fractions dealing with life and intelligence

德雷克公式中關於孕育生命

and technological civilizations

發展高等智慧 與技術文明的分數

are ones that many, many experts ponder,

目前有許許多多的專家 正在仔細探究

but nobody knows for sure.

但是沒有人知道確切的數字

So far,

直到目前為止

we only know of one place in the universe

我們知道宇宙之中

where life exists,

唯一有生物存在的地方

and that's right here on Earth.

毫無疑問的，就是地球

In the next couple of decades,

在接下來的幾十年之中

as we explore Mars and Europa and Titan,

隨著我們對火星 木衛二和土衛六的探索

the discovery of any kind of life there

只要我們能在那些地方 發現任何物種的生命

will mean that life will be abundant

就代表著銀河系之中

有著豐富多樣的生命存在

in the Milky Way.

Because if life originated twice

因為如果在這個太陽系之中

within this one Solar System,

出現了兩種不同的生命起源

it means it was easy,

那麼這就表示 生命起源很容易發生

and given similar conditions elsewhere,

因此可以假設 如果別的地方也有相似條件

life will happen.

就會產生生命

So the number two is a very important number here.

因此，「二」這個數字 在這裡非常重要

Scientists, including SETI researchers,

科學家，包括 SETI 計畫的研究人員

often tend to make very crude estimates

經常試著作粗略的估計 希望能取得進展

and acknowledge that there are very large

但是也必須承認

uncertainties in these estimates, in order to make progress.

這些估計仍然有很大的不確定性

We think we know

我們認為已知的

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

R* 和 ne 這兩個變數

are closer to 10 than, say, to one,

都是比較接近 10 而不是 1

and all the f-factors are less than one.

而所有的 f 因數都小於 1

Some of them may be much less than one.

其中某些因數還可能遠小於 1

But of all these unknowns,

但在所有的未知數之中

the biggest unknown is L,

最大的變數是 L

so perhaps the most useful version of the Drake equation

所以在德雷克公式中 可能最有用的版本

is simply to say that

簡單來說是

N is approximately equal to L.

N 大約等於 L

The information in this equation is very clear.

這個等式表達出 一個很清楚的訊息

Unless L is large,

除非 L 很大

N will be small.

否則 N 就會很小

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

但是你也可以把它倒過來看

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

如果 SETI 計畫在不久之後 成功偵測到了信號

after examining only a small portion

而我們又已經能夠證明

在銀河系中 只有少數行星具有生命

of the stars in the Milky Way,

then we learn that

於是我們就可以得知

L, on average, must be large.

平均來說， L 是很大的

Otherwise, we couldn't have succeeded so easily.

否則，我們不會那麼容易 偵測到外星智慧

A physicist named Philip Morrison

有一位物理學家菲力普·莫里森

summarizes by saying

提出一句總結：

that SETI is the archaeology of the future.

SETI 計畫是針對未來的考古學

By this, he meant that

這句話他想表達的是：

because the speed of light is finite,

因為光的傳播速度是有限的

any signals detected from distant technologies

任何我們所偵測到 來自遠方科技的信號

will be telling us about their past

當信號到達地球時

by the time they reach us.

所能告訴我們的一切 都已經成為過去

But because L must be large

但由於 L 必須是很大的數字

for a successful detection,

對外星智慧的偵測才能成功

we also learn about our future,

所以可以了解到我們的未來

particularly that we can have a long future.

尤其是我們可能 還有很長的未來要走

We've developed technologies that can send signals into space

我們已經開發出 能夠將信號送入太空

and humans to the moon,

以及將人類送上月球的科技

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

但我們也開發了破壞環境的科技

that can wage war

以及利用武器和生物恐怖主義

with weapons and biological terrorism.

發動戰爭的科技

In the future,

will our technology help stabilize our planet

在未來

我們的科技是否能協助穩定

我們的星球與全體民眾

and our population,

leading to a very long lifetime for us?

讓人類可以長久存在？

Or will we destroy our world and its inhabitants

或者是，我們將會在 短暫出現於宇宙的舞台之後

after only a brief appearance on the cosmic stage?

便毀掉我們的世界和居民呢？

I encourage you to consider

我鼓勵大家思考

the unknowns in this equation.

德雷克公式中的未知數

Why don't you make your own estimates

你們何不自己預測這些未知數

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

然後看看如何解決 N？

Compare that with the estimates made by Frank Drake,

將你的預測結果和法蘭克·德雷克

Carl Sagan, other scientists

卡爾·薩根或是其他科學家

or your neighbors.

甚至和你的鄰居作比較

Remember, there's no right answer.

記得，並沒有標準答案

Not yet.

至少目前還沒有