Dimitar Sasselov: How we found hundreds of Earth-like planets

翻译人员: Bo Hu 校对人员: Qian Yue

Well, indeed, I'm very, very lucky.

是的，我非常的幸运

My talk essentially got written

我的演讲实际上是由

by three historic events

三个历史性的事件构成的

that happened within days of each other

这三个事件各自相隔不过几天时间

in the last two months --

都是在过去的两个月内发生的

seemingly unrelated, but as you will see,

看上去它们毫无关联，但是你将看到

actually all having to do with

事实上他们都与

the story I want to tell you today.

我今天要讲的故事有所关联

The first one was actually a funeral --

第一个事件事实上是一个葬礼

to be more precise, a reburial.

更准确的说，是一个二次葬礼

On May 22nd, there was a hero's reburial

5月22日，在波兰的Frombork

in Frombork, Poland

一个伟人得到了重葬

of the 16th-century astronomer

他是16世纪的天文学家

who actually changed the world.

他改变了这个世界

He did that, literally,

是的，他的确改变了世界

by replacing the Earth with the Sun

他让太阳取代了地球的地位

in the center of the Solar System,

让太阳成为太阳系的中心

and then with this simple-looking act,

通过这个看上去简单的改变

he actually launched a scientific

他启动了一个

and technological revolution,

科学技术的革命

which many call the Copernican Revolution.

很多人称之为哥白尼革命

Now that was,

这场革命

ironically, and very befittingly,

帮助我们

the way we found his grave.

找到了他的坟墓

As it was the custom of the time,

按照当时的风俗

Copernicus was actually

哥白尼事实上

simply buried in an unmarked grave,

只是与其他14人一起

together with 14 others

简单的合葬在了位于大教堂的

in that cathedral.

一座没有任何标记的坟墓之中

DNA analysis,

DNA分析

one of the hallmarks

作为一个在这场由他发起的

of the scientific revolution

至今已有400年的科技革命

of the last 400 years that he started,

的关键性标志

was the way we found

帮助我们指出

which set of bones

哪一副骸骨

actually belonged to the person

属于哥白尼

who read all those astronomical books

在哥白尼阅读过的天文学书籍里

which were filled with leftover hair

夹杂了很多脱落的头发

that was Copernicus' hair --

这些头发被证实是哥白尼本人的

obviously not many other people

显然，在他之后也没有人

bothered to read these books later on.

会去碰这些书了。

That match was unambiguous.

这些鉴定结果都是十分明确的

The DNA matched,

DNA的匹配也十分吻合

and we know that this was indeed

所以我们能确定

Nicolaus Copernicus.

这就是尼古拉斯·哥白尼本人

Now, the connection between

当你谈论哥白尼时

biology and DNA

生物学和DNA

and life

以及生命之间

is very tantalizing when you talk about Copernicus

又有什么联系呢？

because, even back then,

因为就算在当时

his followers

他的同伴

very quickly made the logical step

也能很快意识到在逻辑上我们所要面临

to ask: if the Earth is just a planet,

的下一个问题是：如果地球只是太阳的一个行星

then what about planets around other stars?

那么其他恒星的行星呢？

What about the idea of the plurality of the worlds,

也许存在有很多个我们这样的世界

about life on other planets?

也许在其他行星上也存在生命

In fact, I'm borrowing here from one of those

事实上，我也只是借用了

very popular books of the time.

当时非常流行的一本书上的观点

And at the time,

在当时

people actually answered that question

人们对于这些问题的回答

positively: "Yes."

是肯定的

But there was no evidence.

但当时的人们没有证据

And here begins 400 years

这是一个持续了400年的

of frustration, of unfulfilled dreams --

而未得到实现的梦想

the dreams of Galileo, Giordano Bruno,

伽利略，布鲁诺

many others --

以及其他许多追寻这个梦想的人

which never led to the answer

都没有能够得到答案

of those very basic questions

一些最基本的问题

which humanity has asked all the time.

一直困惑着人类

"What is life? What is the origin of life?

什么是生命？生命如何起源？

Are we alone?"

我们是否是唯一的？

And that especially happened in the last 10 years,

在过去的十年间，这些问题显得尤为突出

at the end of the 20th century,

在20世纪末

when the beautiful developments

由于分子生物学的进展

due to molecular biology,

我们对于生命的密码——DNA的理解

understanding the code of life, DNA,

取得了非常令人振奋的进步

all of that seemed to actually

但是所有这些似乎

put us, not closer,

并没有让我们获得

but further apart from answering

以上那些基本问题的答案

those basic questions.

反而让我们更加疑惑

Now, the good news.

但是，在过去的几年中

A lot has happened in the last few years,

我们却得到了不少的好消息

and let's start with the planets.

让我们从行星开始讲

Let's start with the old Copernican question:

从哥白尼的经典问题开始：

Are there earths around other stars?

其他恒星是否有行星绕转

And as we already heard,

我们已经了解了

there is a way in which

通过不断地尝试

we are trying, and now able,

人类已经能够

to answer that question.

解答这些问题

It's a new telescope.

这是一架新的望远镜

Our team, befittingly I think,

我们团队

named it after one of those dreamers

以哥白尼时代

of the Copernican time,

众多探索者之一的名字为它命名

Johannes Kepler,

约翰尼斯 开普勒

and that telescope's sole purpose

这架望远镜的唯一目标

is to go out,

是在更遥远的地方

find the planets that orbit

搜寻环绕其他恒星

other stars in our galaxy,

的行星

and tell us how often do planets like our own Earth

告诉我们，类似地球的行星

happen to be out there.

在整个星系中出现的概率如何

The telescope is actually

这架望远镜事实上

built similarly to

是仿照

the, well-known to you, Hubble Space Telescope,

我们熟知的哈勃空间望远镜建造的

except it does have an additional lens --

但是它增加了一个

a wide-field lens,

广角透镜

as you would call it as a photographer.

你们可以把它称作照相机

And if, in the next couple of months,

如果你在接下来的几个月

you walk out in the early evening

在入夜不久的时候走到室外

and look straight up

向你的头顶上看

and place you palm like this,

然后像这样伸开手掌

you will actually be looking at the field of the sky

你所看到的这一块天空

where this telescope is searching for planets

就是望远镜搜寻行星的地方

day and night, without any interruption,

在接下来的四年内

for the next four years.

它将昼夜不停地工作

The way we do that, actually,

我们进行搜寻

is with a method, which we call the transit method.

的方法叫做掩星法

It's actually mini-eclipses that occur

当行星穿过恒星面前时

when a planet passes in front of its star.

就会发生一次小规模的食现象

Not all of the planets will be fortuitously oriented

当然不是所有的行星都

for us to be able do that,

正好在我们的视线方向

but if you have a million stars,

但是如果有一百万颗恒星

you'll find enough planets.

你就会找到足够多的恒星

And as you see on this animation,

你在这个动画上将看到

what Kepler is going to detect

开普勒望远镜将要探测的

is just the dimming of the light from the star.

只是来自恒星亮度的减弱

We are not going to see the image of the star and the planet as this.

我们看不到像这样恒星与行星的图像

All the stars for Kepler are just points of light.

所有的恒星对于开普勒望远镜来说都只是一个亮点

But we learn a lot from that:

但是我们从中也能获得很多信息

not only that there is a planet there, but we also learn its size.

不仅能判断出是否有行星，还能知道它的大小

How much of the light is being dimmed

恒星的亮度减弱了多少

depends on how big the planet is.

取决于从它面前路过的行星有多大

We learn about its orbit,

我们还能获得它的轨道的信息

the period of its orbit and so on.

例如轨道的周期等等

So, what have we learned?

那么，我们从这些结果中又能得到些什么呢？

Well, let me try to walk you through

让我简单的描述下

what we actually see

我们实际上看到了些什么

and so you understand the news

那么你们就会理解

that I'm here to tell you today.

我今天要告诉你们的东西了

What Kepler does

开普勒望远镜

is discover a lot of candidates,

发现了很多候选对象

which we then follow up and find as planets,

然后我们可以从中确定出

confirm as planets.

真正的行星

It basically tells us

首先我们能够得到

this is the distribution of planets in size.

行星大小的分布

There are small planets, there are bigger planets, there are big planets, okay.

它们大小各异

So we count many, many such planets,

我们对大量的行星计数

and they have different sizes.

它们的大小都不同

We do that in our solar system.

我们对太阳系也进行计数

In fact, even back during the ancients,

事实上，在古代

the Solar System in that sense

太阳系的行星数量

would look on a diagram like this.

可以用这样一个图表示

There will be the smaller planets, and there will be the big planets,

早在在伊壁鸠鲁或者

even back to the time of Epicurus

是哥白尼

and then of course Copernicus

及其追随者的时代

and his followers.

人们就已经知道行星有大有小

Up until recently, that was the Solar System --

到现在为止，我们的太阳系

four Earth-like planets with small radius,

有四个半径较小的类地行星

smaller than about two times the size of the Earth --

它们都小于两倍地球的大小

and that was of course Mercury,

这就包括水星

Venus, Mars,

金星，火星

and of course the Earth,

这个显然是地球

and then the two big, giant planets.

然后是两个巨行星

Then the Copernican Revolution

之后哥白尼革命

brought in telescopes,

给我们带来了望远镜

and of course three more planets were discovered.

另外的三颗行星也就这样被发现了

Now the total planet number

现在太阳系中的

in our solar system was nine.

行星数目是九颗

The small planets dominated,

较小的行星占多数

and there was a certain harmony to that,

哥白尼很高兴的发现

which actually Copernicus was very happy to note,

行星数量之间的关系是如此和谐

and Kepler was one of the big proponents of.

开普勒望远镜也同样支持这一观点

So now we have Pluto to join the numbers of small planets.

现在我们把冥王星归为较小行星的那一类

But up until, literally, 15 years ago,

但是严格来说，15年前

that was all we knew about planets.

关于行星，我们知道的还只有这些而已

And that's what the frustration was.

我们对此也很失望

The Copernican dream was unfulfilled.

哥白尼的梦想还没有得到实现

Finally, 15 years ago,

最终，在15年前

the technology came to the point

科技的发展终于

where we could discover a planet around another star,

能够让我们看到绕转其他恒星的行星了

and we actually did pretty well.

我们也充分的利用了各项技术来达到这个目标

In the next 15 years,

这15年里

almost 500 planets

我们通过各种方法发现了将近500颗

were discovered orbiting other stars, with different methods.

绕转其他恒星的行星

Unfortunately, as you can see,

但是，你会看到

there was a very different picture.

这与我们的太阳系有很大的差别

There was of course an explanation for it:

对此也是有解释的

We only see the big planets,

我们只能看见较大的行星

so that's why most of those planets

所以大多数被发现的行星

are really in the category of "like Jupiter."

都是“类似木星”的

But you see, we haven't gone very far.

但是，我们几乎没有取得太多的进展

We were still back where Copernicus was.

我们又回到了哥白尼当时的情况

We didn't have any evidence

我们没有找到关于

whether planets like the Earth are out there.

像地球这样的行星存在的任何证据

And we do care about planets like the Earth

而我们关心的正是这个问题

because by now we understood

因为我们知道

that life as a chemical system

生命这样精密的化学反应系统

really needs a smaller planet

只能存在于较小的行星上

with water and with rocks

需要有水，有岩石

and with a lot of complex chemistry

需要很多复杂的化学过程

to originate, to emerge, to survive.

生命才得以起源，成形，以及生存下去

And we didn't have the evidence for that.

但是我没有关于生命的任何证据

So today, I'm here to actually give you a first glimpse

所以今天我将会给你展示

of what the new telescope, Kepler,

开普勒望远镜

has been able to tell us in the last few weeks,

在几周之前所取得的最新成果

and, lo and behold,

请看，

we are back to the harmony

我们又得到了类似太阳系的平衡

and to fulfilling the dreams of Copernicus.

这几乎实现了哥白尼的梦想

You can see here,

你们可以看到

the small planets dominate the picture.

小的行星占了大多数

The planets which are marked "like Earth,"

“类地”的这一类行星

[are] definitely more than

比其他任何我们所看到的行星

any other planets that we see.

都要多

And now for the first time, we can say that.

这也是我们首次获得这样的发现

There is a lot more work we need to do with this.

当然，还有很多的工作等着我们完成

Most of these are candidates.

大多数这些行星都还只是候选者

In the next few years we will confirm them.

在接下来的几年内，我们需要确认它们

But the statistical result

但是统计的结果

is loud and clear.

是非常明确的

And the statistical result is that

统计的结果表明

planets like our own Earth

类似我们地球的行星

are out there.

确实存在着

Our own Milky Way Galaxy is rich in this kind of planets.

我们的银河系有非常多这样的行星

So the question is: what do we do next?

那么现在的问题是：我们接下来该做什么？

Well, first of all, we can study them

当然，我们首先需要研究它们

now that we know where they are.

现在我们已经了解了它们的位置

And we can find those that we would call habitable,

然后我们就能找到那些所谓的“可居住”的行星

meaning that they have similar conditions

这就意味着，这些星球的环境

to the conditions

与我们在地球上所处的环境

that we experience here on Earth

是类似的

and where a lot of complex chemistry can happen.

在这种环境下，能够发生一系列复杂的化学反应

So, we can even put a number

我们甚至可以给出

to how many of those planets

银河系所包含的

now do we expect our own

类似地球的行星

Milky Way Galaxy harbors.

的个数

And the number, as you might expect,

这个数目，正如你们期望的

is pretty staggering.

是十分惊人的

It's about 100 million such planets.

大约有一亿颗这样的行星

That's great news. Why?

这是个非常令人振奋的结果

Because with our own little telescope,

因为这意味着我们小小的望远镜

just in the next two years,

在接下来的两年内

we'll be able to identify at least 60 of them.

将能够分辨出至少60个类地行星

So that's great because then

这样的话，接下来

we can go and study them --

我们就能够着手研究它们

remotely, of course --

当然，只能在地球上进行

with all the techniques that we already have

利用我们在过去的五年内

tested in the past five years.

所检验过的所有技术

We can find what they're made of,

我们能探测出它们的成分

would their atmospheres have water, carbon dioxide, methane.

它们的大气是否有水有二氧化碳和甲烷

We know and expect that we'll see that.

我们相信我们能够探测到这些

That's great, but that is not the whole news.

这已经非常了不起了，但这还不是全部

That's not why I'm here.

这还不是今天我在这里进行演讲的原因

Why I'm here is to tell you that the next step

我今天站在这里，是想告诉你们我们接下来要做的

is really the exciting part.

绝对是令人振奋的

The one that this step

这一步

is enabling us to do is coming next.

将让我们有能力面对接下来的问题

And here comes biology --

那就是生物学

biology, with its basic question,

生物学方面的基本问题

which still stands unanswered,

仍然没有得到解决

which is essentially:

问题就是

"If there is life on other planets,

如果在其他行星上有生命存在

do we expect it to be like life on Earth?"

他们是否会类似于地球上的生命？

And let me immediately tell you here,

我需要说明的是

when I say life, I don't mean "dolce vita,"

我所说的“生命”不是指“愉快的生活”

good life, human life.

也不是指人生

I really mean life

我想表达的是

on Earth, past and present,

在地球上过去以及现在存在的生命

from microbes to us humans,

从微生物到我们人类

in its rich molecular diversity,

具有丰富的分子多样性

the way we now understand life on Earth

我们所理解的地球上的生命

as being a set of molecules and chemical reactions --

都是一系列的分子以及化学反应的结果

and we call that, collectively, biochemistry,

准确的说，我们称之为生物化学

life as a chemical process,

生命就是一个化学过程

as a chemical phenomenon.

一个化学现象

So the question is:

所以问题就是

is that chemical phenomenon universal,

这种化学现象在全宇宙都会发生，

or is it something

还是与

which depends on the planet?

所处的行星有关？

Is it like gravity,

是否就好像引力

which is the same everywhere in the universe,

在整个宇宙都适用

or there would be all kinds of different biochemistries

或者像是各种生物化学反应

wherever we find them?

因为地域得不同而改变？

We need to know what we are looking for

当我们努力解答这些问题的时候

when we try to do that.

我们要明白我们在寻找什么

And that's a very basic question, which we don't know the answer to,

这个最最基本的问题，我们却给不出答案

but which we can try --

但是我们努力尝试

and we are trying -- to answer in the lab.

尝试在实验室中寻找答案

We don't need to go to space

我们不需要去太空中

to answer that question.

探索答案

And so, that's what we are trying to do.

这就是我们努力的方向

And that's what many people now are trying to do.

这也是许多人正在努力的方向

And a lot of the good news comes from that part of the bridge

在这个我们不断探索的领域中

that we are trying to build as well.

也得到了很多好的成果

So this is one example

这只是我想要在这展示的

that I want to show you here.

一个例子

When we think of what is necessary

当我们考虑生命现象

for the phenomenon that we call life,

需要满足那些条件时

we think of compartmentalization,

我们往往会考虑到分离作用

keeping the molecules which are important for life

把那些对于生命来说重要的分子包裹在

in a membrane,

一个膜之内

isolated from the rest of the environment,

与外界的环境分隔开

but yet, in an environment in which

然而这些分子仍处于

they actually could originate together.

能让它们共同产生的环境之中

And in one of our labs,

在我们的一个实验室

Jack Szostak's labs,

Jack Szostak的实验室中

it was a series of experiments

过去的四年间

in the last four years

我们进行了一系列实验

that showed that the environments --

发现在一些特定环境下

which are very common on planets,

一些在地球这类行星上

on certain types of planets like the Earth,

常见的环境

where you have some liquid water and some clays --

这样的环境中一般都存在水和粘土

you actually end up with

实际上你会得到

naturally available molecules

自然形成的分子

which spontaneously form bubbles.

自然地形成了泡

But those bubbles have membranes

但是这些泡都有膜

very similar to the membrane of every cell

这些膜与地球上所有生物的细胞膜

of every living thing on Earth looks like,

都非常相似

like this.

如同这样

And they really help molecules,

这些膜使得

like nucleic acids, like RNA and DNA,

像核酸，RNA、DNA之类的分子

stay inside, develop,

能够在膜内演化

change, divide

转变，和分化

and do some of the processes that we call life.

这其中的一些过程，就是我们所说的生命现象

Now this is just an example

这仅仅是一个例子

to tell you the pathway

用来说明我们如何

in which we are trying to answer

解决一个重要的问题：

that bigger question about the universality of the phenomenon.

关于这种现象的普遍性

And in a sense, you can think of that work

在某种意义上，你可以把这个领域内

that people are starting to do now around the world

人们正在开始着手的工作

as building a bridge,

看作是建造一座桥

building a bridge from two sides of the river.

在河的两岸建造

On one hand, on the left bank of the river,

河的左岸

are the people like me who study those planets

是像我一样，研究这些行星的人

and try to define the environments.

尝试定义生命存在的环境

We don't want to go blind because there's too many possibilities,

有太多的可能性，我们不能盲目的尝试

and there is not too much lab,

因为实验室资源并不多

and there is not enough human time

并且个人的时间也不足以

to actually to do all the experiments.

完成所有的实验

So that's what we are building from the left side of the river.

这就是我们在河的左岸所建造的

From the right bank of the river

而在河的右岸

are the experiments in the lab that I just showed you,

就是我刚刚展示的实验室里的实验

where we actually tried that, and it feeds back and forth,

我们尝试互通有无

and we hope to meet in the middle one day.

我们希望有一天能够在桥中间回合

So why should you care about that?

那么，我凭什么让你们听我的演讲

Why am I trying to sell you

我凭什么在这里兜售

a half-built bridge?

一座没有完成的桥

Am I that charming?

我有那么大的魅力么？

Well, there are many reasons,

其实原因有很多

and you heard some of them

你们从今天的演讲中

in the short talk today.

了解了其中的一些

This understanding of chemistry

这些对于化学的理解

actually can help us

实际上能够在日常生活中

with our daily lives.

帮助我们

But there is something more profound here,

但是还有更深层次的

something deeper.

意义存在

And that deeper, underlying point

其更深层次的意义

is that science

在于科学

is in the process of redefining life

正在重新定义生命

as we know it.

如我前面所介绍的

And that is going to change

这同样也将深刻地改变

our worldview in a profound way --

我们的世界观

not in a dissimilar way

就如同

as 400 years ago,

400年前

Copernicus' act did,

哥白尼的发现那样

by changing the way

改变了我们

we view space and time.

对空间与时间的认识

Now it's about something else,

而现在转变的，尽管并非对时间与空间观念

but it's equally profound.

但是它的意义也同样深远

And half the time,

最重要的

what's happened

是关于

is it's related this kind of

它让我们

sense of insignificance

作为人类

to humankind,

面对地球，面对更广阔的宇宙时

to the Earth in a bigger space.

产生的渺小感

And the more we learn,

我们知道的越多

the more that was reinforced.

这种感觉也就越强烈

You've all learned that in school --

我们在学校时就已经知道

how small the Earth is

与整个宇宙相比

compared to the immense universe.

地球是多么渺小

And the bigger the telescope,

而我们的望远镜造的越大

the bigger that universe becomes.

我们所发现的宇宙就越大

And look at this image of the tiny, blue dot.

看看这个图像上的小蓝点

This pixel is the Earth.

这个像素就代表地球

It is the Earth as we know it.

这就是在

It is seen from, in this case,

土星轨道外

from outside the orbit of Saturn.

看我们熟悉的地球的样子

But it's really tiny.

它真的很小

We know that.

我们知道

Let's think of life as that entire planet

现在我们把生命当作一个行星

because, in a sense, it is.

因为在某种程度来说的确如此

The biosphere is the size of the Earth.

地球有多大生物圈就有多大

Life on Earth

地球上的生命

is the size of the Earth.

就是地球的大小

And let's compare it to the rest of the world

现在让我们在空间上将它

in spatial terms.

与宇宙的其他部分比较

What if that

如果

Copernican insignificance

哥白尼带给我们的渺小感

was actually all wrong?

是完全错误的

Would that make us more responsible

我们会不会对当今世界所发生的一切

for what is happening today?

更具有责任感？

Let's actually try that.

我们也许应该尝试一下

So in space, the Earth is very small.

在宇宙中，地球非常的小

Can you imagine how small it is?

你能想象它有多小么？

Let me try it.

我们来看看

Okay, let's say

比如说

this is the size

这是可观测宇宙

of the observable universe,

的大小

with all the galaxies,

包括所有的星系

with all the stars,

以及恒星

okay, from here to here.

从这里到这里

Do you know what the size of life

你知道生命在这条领带上

in this necktie will be?

占多大尺寸么？

It will be the size

它的尺寸将会是

of a single, small atom.

一个原子的大小

It is unimaginably small.

不可思议的小

We can't imagine it.

我们无法想象

I mean look, you can see the necktie,

我的意思是，你能看到这条领带

but you can't even imagine seeing

但是你根本想象不到能够看到

the size of a little, small atom.

单个原子的尺寸

But that's not the whole story, you see.

但这还不是全部

The universe and life

宇宙与生命

are both in space and time.

都存在于时空当中

If that was

如果这是

the age of the universe,

宇宙的年龄

then this is the age of life on Earth.

那么这就是地球上生命的年龄

Think about those oldest living things on Earth,

想象一下地球上最古老的生命

but in a cosmic proportion.

再对比宇宙的时间尺度

This is not insignificant.

就显得不那么渺小了

This is very significant.

而是非常显著的

So life might be insignificant in size,

所以生命在空间上是十分渺小的

but it is not insignificant in time.

但是在时间上却不是这样

Life and the universe

生命与宇宙

compare to each other like a child and a parent,

对比起来就像是孩子和父母

parent and offspring.

父母与子女

So what does this tell us?

这告诉我们什么？

This tells us that

这告诉我们

that insignificance paradigm

从哥白尼时代

that we somehow got to learn

我们就被灌输的

from the Copernican principle,

渺小感

it's all wrong.

是错误的

There is immense, powerful potential

生命在宇宙之中

in life in this universe --

是巨大的，有力的，有潜能的

especially now that we know

特别在现在我们知道

that places like the Earth are common.

像地球这样的星球还有很多

And that potential, that powerful potential,

这种潜力，这种巨大的潜力

is also our potential,

也是我们的潜力

of you and me.

包括你和我

And if we are to be stewards

如果我们都成为

of our planet Earth

我们地球

and its biosphere,

与生物圈的管理员

we'd better understand

我们也许能够更加理解

the cosmic significance

生命对于宇宙的意义

and do something about it.

能够为此做点什么

And the good news is we can

好消息是我们

actually, indeed do it.

确实能够做些事情

And let's do it.

让我们开始行动

Let's start this new revolution

在前一场革命的末端

at the tail end of the old one,

开始一场新的革命

with synthetic biology being

人工生物学已经成为

the way to transform

改造我们环境

both our environment

以及未来

and our future.

的手段

And let's hope that we can build this bridge together

希望我们能够一起建造这座桥

and meet in the middle.

在中间回合

Thank you very much.

非常感谢

(Applause)

掌声