Where are all the aliens? | Stephen Webb

譯者: Lilian Chiu 審譯者: 易帆 余

I saw a UFO once.

我曾經看過一次幽浮。

I was eight or nine,

我當時約八、九歲，

playing in the street with a friend who was a couple of years older,

和一位朋友在街上玩耍， 他比我大幾歲，

and we saw a featureless silver disc hovering over the houses.

我們看到了一個毫無特色的 銀色碟形物在房子上方盤旋。

We watched it for a few seconds,

我們看了幾秒鐘，

and then it shot away incredibly quickly.

接著，它以非常快的 速度瞬間飛走。

Even as a kid,

即使當時只是孩子，

I got angry it was ignoring the laws of physics.

我很氣它竟然可以不遵守物理定律。

We ran inside to tell the grown-ups,

我們跑進屋內告訴大人，

and they were skeptical --

大人充滿懷疑——

you'd be skeptical too, right?

換成是你們也會懷疑，對吧？

I got my own back a few years later:

幾年後我也找回了我的懷疑：

one of those grown-ups told me,

其中一位大人告訴我：

"Last night I saw a flying saucer.

「昨晚我看到了飛碟。

I was coming out of the pub after a few drinks."

我在酒吧喝了幾杯， 當時正要離開。」

I stopped him there. I said, "I can explain that sighting."

我在那時打斷他。我說： 「我能解釋你的目擊。」

(Laughter)

（笑聲）

Psychologists have shown we can't trust our brains

心理學家已經證明了 我們不能相信我們的大腦

to tell the truth.

會告訴我們真相。

It's easy to fool ourselves.

要愚弄自己是很容易的。

I saw something,

我看到某種東西，

but what's more likely --

但哪種情況比較有可能——

that I saw an alien spacecraft,

是我看到了外星人的太空船？

or that my brain misinterpreted the data my eyes were giving it?

或是我的大腦錯誤詮釋了 我的眼睛給它的資料？

Ever since though I've wondered:

從那之後，我就一直納悶：

Why don't we see flying saucers flitting around?

為什麼我們不會到處看到飛碟？

At the very least,

至少，

why don't we see life out there in the cosmos?

為什麼我們不會看到 在宇宙中有生命？

It's a puzzle,

這是個謎，

and I've discussed it with dozens of experts

在過去三十年，我已經

from different disciplines over the past three decades.

和數十位不同領域的專家討論過。

And there's no consensus.

沒有達成任何共識。

Frank Drake began searching for alien signals back in 1960 --

1960 年，法蘭克德雷克 就開始尋找外星人的線索——

so far, nothing.

目前，一無所獲。

And with each passing year,

隨著每一年過去，

this nonobservation,

都沒人觀察到，

this lack of evidence for any alien activity gets more puzzling

且缺乏外星人活動的證據， 讓這一切更令人迷惑不解，

because we should see them, shouldn't we?

因為我們應該會看見他們，對吧？

The universe is 13.8 billion years old,

宇宙已經 138 億歲了，

give or take.

這是概略數字。

If we represent the age of the universe by one year,

若我們把宇宙的年齡比喻為一年，

then our species came into being about 12 minutes before midnight,

那麼我們這個物種大約是在 午夜前 12 分鐘才出現的，

31st December.

12 月 31 日。

Western civilization has existed for a few seconds.

西方文明才幾秒鐘而已。

Extraterrestrial civilizations could have started in the summer months.

外星文明可能在夏季就已經出現。

Imagine a summer civilization

想像一個夏季文明，

developing a level of technology more advanced than ours,

發展出了比我們更先進的科技水平，

but tech based on accepted physics though,

不過，我是指以已經 被接受的物理為基礎，

I'm not talking wormholes or warp drives -- whatever --

不是指蟲洞或曲速引擎—— 諸如此類——

just an extrapolation of the sort of tech that TED celebrates.

只是 TED 所頌掦的 那種科技的推斷而已。

That civilization could program self-replicating probes

該文明有可能可以設計出 會自我複製的探測飛船，

to visit every planetary system in the galaxy.

去探訪銀河系中的每一個星系。

If they launched the first probes just after midnight one August day,

如果他們在八月某一天的午夜之後 發射了第一艘探測飛船，

then before breakfast same day,

那麼在同一天的早餐時間之前，

they could have colonized the galaxy.

他們就已經殖民了整個銀河系。

Intergalactic colonization isn't much more difficult,

跨銀河系的殖民並不會困難太多，

it just takes longer.

只是比較花時間。

A civilization from any one of millions of galaxies

數百萬銀河系中的任何一個文明

could have colonized our galaxy.

都有可能在我們的銀河殖民。

Seems far-fetched?

似乎很牽強？

Maybe it is,

也許是吧，

but wouldn't aliens engage in some recognizable activity --

但外星人不會從事一些 可辨識的活動嗎？——

put worldlets around a star to capture free sunlight,

比如在一顆恆星的周圍建立 小世界來捕捉免費的陽光、

collaborate on a Wikipedia Galactica,

合作撰寫銀河維基百科，

or just shout out to the universe, "We're here"?

或是對著宇宙大叫： 「我們在這裡！」

So where is everybody?

所以，他們在哪裡？

It's a puzzle because we do expect these civilizations to exist, don't we?

這是個謎，因為我們確實預期 會有這類文明存在，對吧？

After all, there could be a trillion planets in the galaxy --

畢竟，銀河系中 可能有一兆個星球——

maybe more.

甚至更多。

You don't need any special knowledge to consider this question,

不需要任何特殊知識， 你也會去思考這個問題，

and I've explored it with lots of people over the years.

這些年來，我已經和許多人 一起探索了這個問題。

And I've found they often frame their thinking

我發現，他們通常 在表述他們的想法時，

in terms of the barriers that would need to be cleared

會用需要被清除的四個障礙

if a planet is to host a communicative civilization.

來思考一個星球是否會有 能夠溝通的文明存在。

And they usually identify four key barriers.

他們通常會去確認四項關鍵障礙。

Habitability --

可居住性——

that's the first barrier.

那是第一個障礙。

We need a terrestrial planet in that just right "Goldilocks zone,"

我們需要有一個剛好屬於 「適居帶」的外星星球，

where water flows as a liquid.

也就是說，水要以液體形式流動。

They're out there.

外面有這種星球存在。

In 2016, astronomers confirmed there's a planet in the habitable zone

2016 年，太空人確認了 在最近的恆星適居帶上

of the closest star,

有一個星球，

Proxima Centauri --

這個恆星是比鄰星——

so close that Breakthrough Starshot project plans to send probes there.

它非常近，近到「突破攝星」 計畫打算要送探測飛船過去。

We'd become a starfaring species.

我們成了在星際旅行的物種。

But not all worlds are habitable.

但並非所有世界都可居住。

Some will be too close to a star and they'll fry,

有些會太靠近恆星，會被烤熟，

some will be too far away and they'll freeze.

有些則太遙遠，會被冰凍。

Abiogenesis --

無生源論——

the creation of life from nonlife --

從無生命到創造生命——

that's the second barrier.

那是第二個障礙。

The basic building blocks of life aren't unique to Earth:

生命的基礎建材並非地球獨有：

amino acids have been found in comets,

已經發現慧星上有氨基酸，

complex organic molecules in interstellar dust clouds,

行星際塵雲中有複雜的有機分子，

water in exoplanetary systems.

行星系統中有水。

The ingredients are there,

原料已經存在，

we just don't know how they combine to create life,

我們只是不知道它們 要如何結合起來創造生命，

and presumably there will be worlds on which life doesn't start.

很有可能，這些世界的 生命跡象尚未開始。

The development of technological civilization is a third barrier.

第三個障礙是科技文明的發展。

Some say we already share our planet with alien intelligences.

有些人說，我們已經在 和外星智慧共享我們的星球。

A 2011 study showed that elephants can cooperate to solve problems.

一篇 2011 年的研究指出， 大象能夠合作來解決問題。

A 2010 study showed

一篇 2010 年的研究指出，

that an octopus in captivity can recognize different humans.

被囚禁的章魚能夠認出不同的人類。

2017 studies show that ravens can plan for future events --

2017 年的研究則指出， 渡鴉會規劃未來事件——

wonderful, clever creatures --

很美好、聰明的生物——

but they can't contemplate the Breakthrough Starshot project,

但牠們無法去思考 「突破攝星」計畫，

and if we vanished today,

如果今天我們都消失了，

they wouldn't go on to implement Breakthrough Starshot --

牠們也不會去執行 「突破攝星」計劃——

why should they?

為什麼牠們要去執行？

Evolution doesn't have space travel as an end goal.

演化的最終目標並不是太空旅行。

There will be worlds where life doesn't give rise to advanced technology.

有一些世界中的生命 不會去發展先進科技。

Communication across space -- that's a fourth barrier.

跨越太空的溝通—— 那是第四個障礙。

Maybe advanced civilizations choose to explore inner space

也許先進文明會選擇探索內太空，

rather than outer space,

而不是外太空，

or engineer at small distances rather than large.

或做短距離的工程建設， 而非長距離的。

Or maybe they just don't want to risk an encounter

或許，他們只是單純 不想冒險，以免遇到

with a potentially more advanced and hostile neighbor.

可能更先進且有敵意的鄰居。

There'll be worlds where, for whatever reason,

在某些世界，不論是什麼理由，

civilizations either stay silent or don't spend long trying to communicate.

文明可能會保持沉默，或不會 花費心力去試圖與遠方溝通。

As for the height of the barriers,

至於障礙有多高，

your guess is as good as anyone's.

大家都只能猜測。

In my experience,

依我的經驗，

when people sit down and do the math,

當大家坐下來算數學時，

they typically conclude there are thousands of civilizations in the galaxy.

他們的結論通常是， 在銀河系中有數千個文明存在。

But then we're back to the puzzle: Where is everybody?

但，我們又回到 原本的謎：他們在哪裡？

By definition,

就定義來說，

UFOs -- including the one I saw --

幽浮（不明飛行物）—— 包括我看見的那一個——

are unidentified.

是「不明」的。

We can't simply infer they're spacecraft.

我們不能很簡單地說 它們是太空船。

You can still have some fun playing with the idea aliens are here.

你仍然可以為了好玩 而想像有外星人來到這裡。

Some say a summer civilization did colonize the galaxy

有人說，夏季文明 的確已經殖民了銀河系，

and seeded Earth with life ...

且在地球播下生命的種子……

others, that we're living in a cosmic wilderness preserve --

其他人說，我們是住在 宇宙的荒野保護區——

a zoo.

一個動物園。

Yet others --

還有其他人——

that we're living in a simulation.

說我們住在模擬世界中。

Programmers just haven't revealed the aliens yet.

只是程式設計師尚未 讓外星人現身而已。

Most of my colleagues though argue that E.T. is out there,

不過，我大部分的同事 主張有 E.T. 存在，

we just need to keep looking,

只是我們得要繼續尋找，

and this makes sense.

這是合理的。

Space is vast.

太空很大。

Identifying a signal is hard,

找到一個訊號是很困難的，

and we haven't been looking that long.

且我們才開始找沒有很久。

Without doubt, we should spend more on the search.

無疑的，我們應該 投入更多心力去搜尋。

It's about understanding our place in the universe.

重點在於了解我們 在宇宙中的定位。

It's too important a question to ignore.

這個問題太重要了，不能無視它。

But there's an obvious answer:

但，有一個很明顯的答案：

we're alone.

我們是孤單的。

It's just us.

只有我們。

There could be a trillion planets in the galaxy.

在銀河系可能有一兆個星球。

Is it plausible we're the only creatures capable of contemplating this question?

若說我們是唯一會思忖 這個問題的生物，聽起來合理嗎？

Well, yes, because in this context,

是的，因為在這個情況中，

we don't know whether a trillion is a big number.

我們不知道一兆是否 算是很大的數目。

In 2000, Peter Ward and Don Brownlee proposed the Rare Earth idea.

2000 年時，彼得沃德和唐布朗利 提出了「地球殊異」的想法。

Remember those four barriers

還記得人們用來

that people use to estimate the number of civilizations?

估計文明數目的那四個障礙嗎？

Ward and Brownlee said there might be more.

沃德和布朗利說，可能還有更多。

Let's look at one possible barrier.

咱們來看看一個可能的障礙。

It's a recent suggestion by David Waltham,

這是地球物理學家大衛沃爾瑟姆

a geophysicist.

在近期提出來的。

This is my very simplified version

這是我的極簡化版，

of Dave's much more sophisticated argument.

大衛的原版是更精密許多的主張。

We are able to be here now

我們現在能夠在這裡，

because Earth's previous inhabitants enjoyed

是因為地球先前的居民享受了

four billion years of good weather --

40 億年的好天氣——

ups and downs but more or less clement.

雖然起起落落， 但總的來說仍然是溫和的。

But long-term climate stability is strange,

但長期的穩定氣候是很奇特的，

if only because astronomical influences

因為天文氣候的影響是有可能

can push a planet towards freezing or frying.

將一個星球推向結冰或烤熟狀況的。

There's a hint our moon has helped,

我們的月球似乎是有幫上忙，

and that's interesting

那很有趣，

because the prevailing theory is

因為普遍流行的理論是

that the moon came into being when Theia,

月球會出現是因為忒伊亞，

a body the size of Mars,

和火星一樣大的天體，

crashed into a newly formed Earth.

撞上了剛形成的地球。

The outcome of that crash could have been a quite different Earth-Moon system.

撞擊的結果本來有可能 是個很不同的地球—月球系統。

We ended up with a large moon

我們最後得到的是一個大月球，

and that permitted Earth to have both a stable axial tilt

那讓地球有一個穩定的 軸向傾斜角度，

and a slow rotation rate.

和緩慢的轉速。

Both factors influence climate

這兩個因子影響了氣候，

and the suggestion is that they've helped moderate climate change.

意味著它們協助調節了氣候改變。

Great for us, right?

對我們很好，對吧？

But Waltham showed that if the moon were just a few miles bigger,

但沃爾瑟姆指出， 如果月球再大個幾英哩，

things would be different.

一切就會不同。

Earth's spin axis would now wander chaotically.

地球的轉軸現在就會 混亂地偏離正軌。

There'd be episodes of rapid climate change --

就會發生快速氣候變遷的情形——

not good for complex life.

對複雜的生命來說不是好事。

The moon is just the right size:

月球的大小剛剛好：

big but not too big.

夠大但不會太大。

A "Goldilocks" moon around a "Goldilocks" planet --

在一個「適居」的星球周圍 有個「適居」的月球——

a barrier perhaps.

也許也是個障礙。

You can imagine more barriers.

你們可以想像出更多障礙。

For instance,

比如，

simple cells came into being billions of years ago ...

數十億年前， 簡單細胞就出現了……

but perhaps the development of complex life

但也許要發展出複雜的生命，

needed a series of unlikely events.

還需要一連串 不太可能發生的事件。

Once life on Earth had access to multicellularity

一旦地球上的生命能夠有多細胞

and sophisticated genetic structures,

以及精密的基因結構，

and sex,

還有性，

new opportunities opened up:

就會有新的機會產生：

animals became possible.

可能會出現動物。

But maybe it's the fate of many planets

但，也許，許多星球的命運就是

for life to settle at the level of simple cells.

只會有簡單細胞等級的生命存在。

Purely for the purposes of illustration,

純粹只是為了說明清楚，

let me suggest four more barriers to add to the four

讓我再提出四個 可能的障礙，來補充

that people said blocked the path to communicative civilization.

前面已提到大家認為會阻擋 與外星文明溝通的四個障礙。

Again, purely for the purposes of illustration,

我再說一遍，純粹只是為了 補充說明清楚，

suppose there's a one-in-a-thousand chance of making it across each of the barriers.

假設跨越每一個障礙的 機會是千分之一。

Of course there might be different ways of navigating the barriers,

當然，可能會有不同的 方式來通過障礙，

and some chances will be better than one in a thousand.

有些機會可能會高於千分之一。

Equally, there might be more barriers

同樣的，可能會有更多障礙

and some chances might be one in a million.

且當中某些的機會 只有百萬分之一。

Let's just see what happens in this picture.

咱們來看看，在這狀況下 會發生什麼事。

If the galaxy contains a trillion planets,

如果銀河系有一兆個星球，

how many will host a civilization capable of contemplating like us

有多少個星球上會有文明存在， 且像我們一樣能夠去思忖

projects such as Breakthrough Starshot?

像「突破攝星」這樣的計畫？

Habitability --

可居住性——

right sort of planet around the right sort of star --

在對的恆星周圍有對的星球——

the trillion becomes a billion.

一兆剩下了十億。

Stability --

穩定性——

a climate that stays benign for eons --

氣候要長久都能很宜人——

the billion becomes a million.

十億剩下了一百萬。

Life must start --

生命必須要能開始——

the million becomes a thousand.

一百萬剩下了一千。

Complex life forms must arise --

必須要有複雜的生命形式出現——

the thousand becomes one.

一千剩下了一個。

Sophisticated tool use must develop --

必須要能夠去使用精密的工具——

that's one planet in a thousand galaxies.

一千個銀河中只有 一個星球能符合。

To understand the universe,

要了解宇宙，

they'll have to develop the techniques of science and mathematics --

他們就得要發展出 科學和數學的技術——

that's one planet in a million galaxies.

一百萬個銀河中只有 一個星球能符合。

To reach the stars, they'll have to be social creatures,

要去接觸其他恆星， 他們必須要是社交型的生物，

capable of discussing abstract concepts with each other

有能力和彼此討論抽象的概念，

using complex grammar --

使用複雜的文法——

one planet in a billion galaxies.

十億個銀河中只有 一個星球能符合。

And they have to avoid disaster --

他們還得要避開災難——

not just self-inflicted but from the skies, too.

不只是自己造成的災難， 還有來自天空的災難。

That planet around Proxima Centauri,

繞著比鄰星的那個星球，

last year it got blasted by a flare.

在去年被太陽耀斑給轟擊了。

One planet in a trillion galaxies,

一兆個銀河中只有 一個星球能符合。

just as in the visible universe.

這是在可見宇宙中的假設。

I think we're alone.

我想我們是孤單的。

Those colleagues of mine who agree we're alone

我那些認同我們是孤單的同事

often see a barrier ahead --

通常能夠先看到障礙——

bioterror,

生物災難、

global warming, war.

全球暖化、戰爭。

A universe that's silent

一個沉默的宇宙，

because technology itself forms the barrier

因為科技本身就會形成障礙，

to the development of a truly advanced civilization.

讓一個真正先進的文明很難發展。

Depressing, right?

讓人沮喪，是吧？

I'm arguing the exact opposite.

我的主張正好相反。

I grew up watching "Star Trek" and "Forbidden Planet,"

我是看《星艦迷航記》 與《禁忌星球》長大的，

and I saw a UFO once,

且我見過一次幽浮，

so this idea of cosmic loneliness I certainly find slightly wistful.

所以我肯定對這個宇宙孤獨的 想法感到有點愁悶。

But for me,

但，對我來說，

the silence of the universe is shouting,

宇宙的沉默正在吶喊：

"We're the creatures who got lucky."

「我們是走運的生物。」

All barriers are behind us.

我們越過了所有的障礙。

We're the only species that's cleared them --

我們是唯一清除了 所有障礙的物種——

the only species capable of determining its own destiny.

唯一能夠決定自身命運的物種。

And if we learn to appreciate how special our planet is,

如果我們學會帶著感激 欣賞我們的星球有多特別、

how important it is to look after our home

照顧我們的家園並尋找其他的

and to find others,

是多麼重要的事、

how incredibly fortunate we all are simply to be aware of the universe,

單單知道宇宙的存在 我們就有多麼幸運，

humanity might survive for a while.

那麼人類也許還能生存一陣子。

And all those amazing things

所有那些不可思議的事，

we dreamed aliens might have done in the past,

我們幻想外星人 在過去可能做過的事，

that could be our future.

都可能成為我們的未來。

Thank you very much.

非常謝謝各位。

(Applause)

（掌聲）