Where are all the aliens? | Stephen Webb

翻译人员: Yan Gao 校对人员:

I saw a UFO once.

我见过一次不明飞行物。

I was eight or nine,

那时我八、九岁，

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

和一个比我大几岁的朋友在街上玩，

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

我们发现一个普通的 银色碟子在上空盘旋。

We watched it for a few seconds,

我们盯着它看了几秒钟，

and then it shot away incredibly quickly.

然后它飞走了，速度极快。

Even as a kid,

虽然我只是个小孩，

I got angry it was ignoring the laws of physics.

但我依然感到气愤， 因为它不符合物理规律。

We ran inside to tell the grown-ups,

我们跑回家告诉大人们，

and they were skeptical --

但他们表示很怀疑——

you'd be skeptical too, right?

谁都会怀疑的，对吧？

I got my own back a few years later:

几年后，我扳回一局：

one of those grown-ups told me,

那些大人中的一个对我说，

"Last night I saw a flying saucer.

“昨晚我看到一个飞碟，

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

我当时刚在酒吧喝了几杯出来。”

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

我当时就打断他说， “我可以解释你看到的是什么。”

(Laughter)

（笑声）

Psychologists have shown we can't trust our brains

心理学家已经证明， 我们不能相信自己的大脑

to tell the truth.

说的都是事实。

It's easy to fool ourselves.

我们很容易被自己欺骗。

I saw something,

我看到了某种东西，

but what's more likely --

但哪种情况可能性更大——

that I saw an alien spacecraft,

我看到的是外星飞船？

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

还是我的大脑误解了眼睛传给它的数据？

Ever since though I've wondered:

从那以后，我一直在想：

Why don't we see flying saucers flitting around?

为什么我们在周围看不到飞碟呢?

At the very least,

至少，

我们为什么看不到 宇宙中的其它生命呢?

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

It's a puzzle,

这是一个谜，

and I've discussed it with dozens of experts

过去的三十年里，我与不同领域的

from different disciplines over the past three decades.

数十位专家讨论过这个问题。

And there's no consensus.

我们并没有达成共识。

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

弗兰克 · 德雷克从1960年 开始寻找外星信号——

到目前为止，什么都没找到。

so far, nothing.

一年又一年，

And with each passing year,

this nonobservation,

什么也观测不到，

没有任何外星活动的证据， 这越来越让人困惑，

this lack of evidence for any alien activity gets more puzzling

because we should see them, shouldn't we?

因为我们应该能看到它们的，不是吗?

The universe is 13.8 billion years old,

宇宙已经存在了大概

give or take.

138亿年了。

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

如果我们用一年来代表宇宙的年龄，

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

那么我们这个物种形成于

12月31日午夜前的12分钟。

31st December.

Western civilization has existed for a few seconds.

西方文明刚出现几秒钟。

Extraterrestrial civilizations could have started in the summer months.

而外星文明可能是夏季开始的。

Imagine a summer civilization

想象一个夏季出现的文明

developing a level of technology more advanced than ours,

开发出比我们更先进的技术，

but tech based on accepted physics though,

但我是说符合公认的 物理理论的技术，

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

而不是虫洞或曲速引擎 ——那种类型的——

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

我只说像TED在这儿庆祝的 那种技术的进步。

That civilization could program self-replicating probes

这个文明也许会编写 可自我复制的探测器，

to visit every planetary system in the galaxy.

去访问银河系中的每一个星系。

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

如果他们在8月的某天午夜， 发射了第一颗探测器，

then before breakfast same day,

那么在当天早餐之前，

they could have colonized the galaxy.

他们可能就已经统治银河系了。

Intergalactic colonization isn't much more difficult,

银河系之外的星际统治也不算太难，

it just takes longer.

只是要多花点时间而已。

A civilization from any one of millions of galaxies

在数百万星系中， 任何一个星系的文明

could have colonized our galaxy.

都有可能统治我们的银河系。

Seems far-fetched?

听起来很牵强?

Maybe it is,

也许是的，

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

但外星人难道就不做一些 可以被探测到的活动吗？

put worldlets around a star to capture free sunlight,

比如在恒星周围造个小世界获取阳光，

collaborate on a Wikipedia Galactica,

合作一个星际维基百科，

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

或者只是对着宇宙大喊： “我们在这里！”

So where is everybody?

那么他们到底在哪儿?

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

这是个谜，因为我们确实认为 有这种文明存在，不是吗?

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

毕竟，银河系中可能有 一万亿颗星球——

maybe more.

也许更多。

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

你不需要任何专业知识 来思考这个问题，

多年来，我和很多人 都探讨过这个问题。

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

And I've found they often frame their thinking

我发现他们对这个问题的 思考有个标准，

in terms of the barriers that would need to be cleared

就是如果一个星球要 承载可交流的文明，

if a planet is to host a communicative civilization.

它需要清除一些障碍。

And they usually identify four key barriers.

他们通常会考虑四个关键障碍。

Habitability --

宜居性——

that's the first barrier.

这是第一个障碍。

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

我们需要一颗刚好位于 “适居带”中的陆地行星，

where water flows as a liquid.

上面的水以液态形式流动。

They're out there.

这样的星球是存在的。

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

2016年，天文学家证实， 有一颗行星位于最近的恒星的

of the closest star,

适居带中，

Proxima Centauri --

接近于半人马座——

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

非常近，所以“突破摄星”工程 计划发送一个探测器过去。

We'd become a starfaring species.

我们已经成为 可以穿越星际的物种了。

But not all worlds are habitable.

但不是所有的星球都适合居住。

有些离恒星太近，会被烤焦，

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

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

有些离得太远，会被冻结。

Abiogenesis --

生命起源——

the creation of life from nonlife --

从非生命中孕育出生命——

that's the second barrier.

这是第二个障碍。

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

构成生命的基本要素并非地球独有：

amino acids have been found in comets,

彗星上已经发现了氨基酸，

complex organic molecules in interstellar dust clouds,

在星际尘埃云中的复杂有机分子，

water in exoplanetary systems.

在外层空间发现了水。

The ingredients are there,

那些成分都是存在的，

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

我们只是不知道 它们如何结合起来创造生命，

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

而且可能在一些世界里， 生命还没有诞生。

The development of technological civilization is a third barrier.

第三个障碍是技术文明的发展。

Some say we already share our planet with alien intelligences.

有人说我们已经在和外星人 共享我们的星球。

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

2011年的一项研究表明， 大象可以合作解决问题。

A 2010 study showed

2010年的研究表明，

that an octopus in captivity can recognize different humans.

人工饲养的章鱼可以识别不同的人。

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

2017年的研究表明， 乌鸦可以为未来的事件做规划——

wonderful, clever creatures --

多么奇妙的、聪明的生物——

但是它们想不出“突破摄星”计划，

but they can't contemplate the Breakthrough Starshot project,

and if we vanished today,

如果今天，我们消失了，

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

它们也不会继续“突破摄星”之旅——

why should they?

它们为什么要去呢?

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

进化的最终目标又不是太空旅行。

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

有些世界里的生命 没有发明先进的技术。

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

跨太空通信——这是第四个障碍。

Maybe advanced civilizations choose to explore inner space

也许先进的文明选择探索内部空间，

rather than outer space,

而不是外太空，

or engineer at small distances rather than large.

或者在小范围内而不是大范围上活动。

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

或者，他们只是不想冒险，

with a potentially more advanced and hostile neighbor.

遇到一个潜在的，更先进的敌对的邻居。

There'll be worlds where, for whatever reason,

会有一些世界，无论出于什么原因，

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

那里的文明要么保持沉默， 要么不花太长的时间交流。

As for the height of the barriers,

至于障碍的高度，

your guess is as good as anyone's.

大家的猜测都差不多。

In my experience,

根据我的经验，

when people sit down and do the math,

当人们进行数学计算，

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

通常得到的结论是， 银河系中存在数千个文明。

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

但我们又回到了刚才的谜题： 外星人到底在哪儿?

By definition,

根据定义，

UFOs -- including the one I saw --

不明飞行物—— 包括我看到的那个——

are unidentified.

是身份“不明”的。

We can't simply infer they're spacecraft.

我们不能简单地推断 它们是宇宙飞船。

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

你仍然可以饶有兴趣地 想象着外星人就在这里。

Some say a summer civilization did colonize the galaxy

有人认为，夏季文明确实统治了银河系，

and seeded Earth with life ...

并给地球播下了生命的种子……

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

还有人认为，我们生活在 宇宙的野生保护区——

a zoo.

动物园。

Yet others --

也有人说——

我们生活在一个模拟世界里。

that we're living in a simulation.

Programmers just haven't revealed the aliens yet.

只是程序员还没安排外星人出场而已。

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

大多数我的同事认为 外星人是存在的，

we just need to keep looking,

只是我们仍需寻找，

and this makes sense.

这是有道理的。

Space is vast.

宇宙空间是巨大的。

识别一个信号是很难的，

Identifying a signal is hard,

and we haven't been looking that long.

我们寻找的时间也不算很久。

Without doubt, we should spend more on the search.

毫无疑问，我们应该在搜寻上加大投入。

It's about understanding our place in the universe.

这有助于理解 我们在宇宙中的位置。

It's too important a question to ignore.

这个问题太重要了，不容忽视。

But there's an obvious answer:

但有一个显而易见的答案：

we're alone.

我们是孤单的。

It's just us.

宇宙中只有我们存在。

There could be a trillion planets in the galaxy.

银河系中可能有一万亿颗行星。

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

是否可能，我们是唯一有能力 思考这个问题的生物呢?

Well, yes, because in this context,

没错，因为在这种情况下，

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

我们不知道一万亿这个数量大不大。

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

2000年，彼得 · 瓦尔德和唐 · 布朗尼 提出了“稀有地球”的概念。

Remember those four barriers

还记得人们用来

that people use to estimate the number of civilizations?

估算文明数量的四个障碍吗？

Ward and Brownlee said there might be more.

瓦尔德和布朗尼认为， 可能还有更多的障碍存在。

Let's look at one possible barrier.

咱们来看一个可能存在的障碍。

It's a recent suggestion by David Waltham,

这是地球物理学家大卫 · 沃尔瑟姆

a geophysicist.

最近提出的建议。

This is my very simplified version

这是我对大卫的复杂论证

of Dave's much more sophisticated argument.

做了简化处理的版本。

We are able to be here now

我们能够存在于此，

because Earth's previous inhabitants enjoyed

是因为地球的早期居民享受了

four billion years of good weather --

40亿年的好天气——

ups and downs but more or less clement.

时好时坏，但基本上是温和的。

But long-term climate stability is strange,

但是气候的长期稳定是值得探究的，

if only because astronomical influences

因为仅仅是天文影响，

can push a planet towards freezing or frying.

都会让一个星球走向冰冻或炙烤。

有一种迹象表明， 我们的月球起了作用，

There's a hint our moon has helped,

and that's interesting

这很有趣，

because the prevailing theory is

因为普遍流行的理论是，

月球形成的时候，一个火星大小的

that the moon came into being when Theia,

a body the size of Mars,

天体忒伊亚

crashed into a newly formed Earth.

撞上了刚形成的地球。

那次撞击的结果可能产生了 一个截然不同的地月系统。

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

We ended up with a large moon

然而实际上，我们最终 得到的是一个大月球，

and that permitted Earth to have both a stable axial tilt

这使得地球既可以稳定地轴向倾斜，

and a slow rotation rate.

也可以缓慢地旋转。

Both factors influence climate

这两个因素都影响着气候，

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

它们有助于缓和气候变化。

Great for us, right?

对我们来说很棒，对吧？

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

但沃尔瑟姆指出， 如果月球的直径再大几英里，

things would be different.

情况就会不同了。

Earth's spin axis would now wander chaotically.

地球的自转轴将会混乱地漂移。

There'd be episodes of rapid climate change --

气候会快速变化——

这对复杂生命的形成非常不利。

not good for complex life.

The moon is just the right size:

月亮的尺寸正合适：

big but not too big.

不大不小，正好。

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

一颗“刚刚好的”月球环绕着 一颗“刚刚好的”行星——

a barrier perhaps.

也许这也是障碍之一。

You can imagine more barriers.

你可以想象更多的障碍。

For instance,

例如，

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

简单的细胞是数十亿年前形成的……

but perhaps the development of complex life

但也许复杂生命的孕育和发展

needed a series of unlikely events.

需要一系列的不可能事件为前提。

Once life on Earth had access to multicellularity

一旦地球上的生命发展为多细胞生物、

and sophisticated genetic structures,

复杂的遗传结构，

and sex,

和性别，

new opportunities opened up:

新的机会就出现了：

animals became possible.

动物就会诞生。

But maybe it's the fate of many planets

但是，可能许多行星的命运是

for life to settle at the level of simple cells.

只有简单细胞级别的生命存在。

Purely for the purposes of illustration,

纯粹为了说明的目的，

let me suggest four more barriers to add to the four

让我再加四个障碍，

基于人们所说的阻碍了 文明交流渠道的四个障碍。

that people said blocked the path to communicative civilization.

Again, purely for the purposes of illustration,

强调一下，纯粹为了解释清楚，

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

我假设跨越每一个障碍的 几率是千分之一。

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

当然，可能会有不同的方法 来克服这些障碍，

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

有些机会可能不止千分之一。

Equally, there might be more barriers

同样，也可能有另一些障碍，

and some chances might be one in a million.

它们的机会只有百万分之一。

Let's just see what happens in this picture.

那么，就按这假设来看看会发生什么。

If the galaxy contains a trillion planets,

如果银河系里有一万亿颗行星，

how many will host a civilization capable of contemplating like us

那么有多少个行星上存在 像我们这样的文明，

能计划出“突破摄星”项目的文明？

projects such as Breakthrough Starshot?

Habitability --

适居性——

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

合适的行星围绕着合适的恒星——

the trillion becomes a billion.

一万亿里面有十亿个。

Stability --

稳定性——

a climate that stays benign for eons --

永远保持良性的气候——

the billion becomes a million.

十亿里面有一百万个。

Life must start --

必须孕育生命——

the million becomes a thousand.

百万里面有一千个。

Complex life forms must arise --

拥有复杂的生命形式——

the thousand becomes one.

一千里面只有一个。

Sophisticated tool use must develop --

必须开发出精密的工具——

that's one planet in a thousand galaxies.

上千个星系中只有一颗行星能做到。

To understand the universe,

为了了解宇宙，

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

必须发展科技和数学——

that's one planet in a million galaxies.

百万个星系中只有一颗行星能做到。

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

要接触其他恒星， 必须有社会性的生物，

capable of discussing abstract concepts with each other

能够用复杂的语法

using complex grammar --

相互讨论抽象概念——

one planet in a billion galaxies.

十亿个星系中只有一颗行星能做到。

And they have to avoid disaster --

而且它们必须避开灾难——

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

不只是人祸，还有天灾。

That planet around Proxima Centauri,

围绕比邻星的那颗行星，

last year it got blasted by a flare.

去年被一个耀斑烤焦了。

One planet in a trillion galaxies,

所以，一万亿星系中 只有一颗行星能做到，

just as in the visible universe.

可见的宇宙就是如此。

I think we're alone.

我想我们是孤单的。

Those colleagues of mine who agree we're alone

我的同事们，那些同意 人类是孤单存在着的同事们，

often see a barrier ahead --

常会看到摆在我们面前的障碍——

bioterror,

生物恐怖主义、

全球变暖、战争。

global warming, war.

A universe that's silent

宇宙是沉默的，

because technology itself forms the barrier

因为科学技术本身会形成障碍，

to the development of a truly advanced civilization.

让真正先进的文明无法发展。

Depressing, right?

听起来令人沮丧，是吧？

I'm arguing the exact opposite.

而我的观点恰恰相反。

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

我是看《星际迷航》和《禁星》长大的，

and I saw a UFO once,

并且我亲眼见过一次不明飞行物，

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

所以，这种宇宙独有的概念 肯定让我有些伤感。

But for me,

但对我来说，

the silence of the universe is shouting,

宇宙的沉默是在呼喊，

"We're the creatures who got lucky."

“我们是幸运的生物。”

All barriers are behind us.

我们跨越了所有障碍。

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

我们是唯一扫清所有障碍的物种——

the only species capable of determining its own destiny.

唯一能够决定自己命运的物种。

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

如果我们意识到这个星球的特殊性，

how important it is to look after our home

意识到：照顾好我们的家园

and to find others,

和找到其他生命的重要性；

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

意识到：我们十分幸运地 了解了宇宙的存在，

humanity might survive for a while.

那么人类可能会存活得更长。

所有那些不可思议的事情，

And all those amazing things

we dreamed aliens might have done in the past,

我们幻想外星人曾经做过的事，

that could be our future.

也许就是我们的未来。

Thank you very much.

非常感谢。

(Applause)

（掌声）