Have we reached the end of physics? | Harry Cliff

譯者: Christian Grey 審譯者: 瑞文Eleven 林Lim

A hundred years ago this month, a 36-year-old Albert Einstein

百年前的此月，

36 歲的愛因斯坦

stood up in front of the Prussian Academy of Sciences in Berlin

在柏林普魯士科學院前

to present a radical new theory of space, time and gravity:

發表有關時空與重力的 開創性理論：

the general theory of relativity.

廣義相對論。

General relativity is unquestionably Einstein's masterpiece,

這無疑是愛因斯坦的傑作，

a theory which reveals the workings of the universe at the grandest scales,

揭露大尺度世界的運行法則，

capturing in one beautiful line of algebra

以一則優美的公式囊括一切，

everything from why apples fall from trees to the beginning of time and space.

從為何蘋果會從樹上掉落

到時空的起源。

1915 must have been an exciting year to be a physicist.

1915 年是令物理學家 興奮的一年，

Two new ideas were turning the subject on its head.

兩個嶄新的觀念 在物理界掀起革命。

One was Einstein's theory of relativity,

一是愛因斯坦的相對論，

the other was arguably even more revolutionary:

另一個可說是 更革命性的量子力學。

quantum mechanics,

a mind-meltingly strange yet stunningly successful new way

這是一個十分艱深 但有效的新方法，

of understanding the microworld, the world of atoms and particles.

讓我們理解 原子與粒子的小尺度世界。

Over the last century, these two ideas have utterly transformed

上個世紀這兩個理論

完全顛覆我們對宇宙的認知。

our understanding of the universe.

It's thanks to relativity and quantum mechanics

多虧這兩個理論，

that we've learned what the universe is made from,

我們得以了解宇宙的 構成、形成與演進。

how it began and how it continues to evolve.

A hundred years on, we now find ourselves at another turning point in physics,

百年後的今日，

我們站在物理學新的轉捩點，

but what's at stake now is rather different.

但情況與當時卻相當不同，

The next few years may tell us whether we'll be able

未來幾年或許會告訴我們

是否可以進一步加深 對自然的認知，

to continue to increase our understanding of nature,

or whether maybe for the first time in the history of science,

抑或將是科學史上首次

we could be facing questions that we cannot answer,

人類面臨無法解釋的問題，

not because we don't have the brains or technology,

不是因為缺乏足夠才智或科技，

but because the laws of physics themselves forbid it.

而是物理定律阻止了我們。

This is the essential problem: the universe is far, far too interesting.

以下是主要問題：

宇宙實在太多采多姿，

Relativity and quantum mechanics appear to suggest

相對論與量子力學卻暗示：

that the universe should be a boring place.

宇宙應該是很空寂的，

It should be dark, lethal and lifeless.

應該是黑暗、致命、無生氣的。

But when we look around us, we see we live in a universe full of interesting stuff,

但當我們環顧四周，

會發現我們處於一個充滿

恆星、行星、樹木與 動物的新奇世界 。

full of stars, planets, trees, squirrels.

The question is, ultimately,

最終，問題是：

why does all this interesting stuff exist?

為什麼有這些有趣的萬物存在？

Why is there something rather than nothing?

為什麼是「有」，而不是「虛無」？

This contradiction is the most pressing problem in fundamental physics,

這個矛盾在基礎物理中 是最迫切的問題。

and in the next few years, we may find out whether we'll ever be able to solve it.

而在未來幾年，

我們也許會知道 是否有能力解決它。

At the heart of this problem are two numbers,

在這問題的核心是兩個數字，

two extremely dangerous numbers.

兩個極端危險的數字，

These are properties of the universe that we can measure,

關乎兩項可以量測的宇宙特質。

and they're extremely dangerous

它們非常危險，

因為假若它們之值 與現今有絲毫差異，

because if they were different, even by a tiny bit,

then the universe as we know it would not exist.

那我們所熟知的宇宙 便不復存在。

The first of these numbers is associated with the discovery that was made

第一個數字與在 距此數公里之外的

歐洲核子研究組織(CERN）裡，

a few kilometers from this hall, at CERN, home of this machine,

人類所建造最大的科學儀器──

the largest scientific device ever built by the human race,

大強子對撞機（LHC） 所做的發現有關。

the Large Hadron Collider.

The LHC whizzes subatomic particles around a 27-kilometer ring,

LHC 在長達 27 公里的環中，

getting them closer and closer to the speed of light

加速次原子粒子直至接近光速，

before smashing them into each other inside gigantic particle detectors.

再使它們在巨型粒子探測器中對撞。

On July 4, 2012, physicists at CERN announced to the world

2012 年 7 月 4 日，

CERN 的物理學家 向全世界宣告，

that they'd spotted a new fundamental particle

探測到新的基本粒子。

being created at the violent collisions at the LHC: the Higgs boson.

在 LHC 的一場 劇烈對撞中產生：

希格斯玻色子。

Now, if you followed the news at the time,

如果你當時有關注這個消息，

you'll have seen a lot of physicists getting very excited indeed,

你會發現許多物理學家十分興奮。

and you'd be forgiven for thinking

而你也會覺得，

每次物理學家 發現新粒子都是如此，

we get that way every time we discover a new particle.

Well, that is kind of true,

沒錯。

but the Higgs boson is particularly special.

但希格斯玻色子格外特別，

We all got so excited because finding the Higgs

我們如此興奮是因為 發現希格斯玻色子，

proves the existence of a cosmic energy field.

意味著宇宙能量場的存在。

Now, you may have trouble imagining an energy field,

你可能無法想像一個能量場，

but we've all experienced one.

但我們都有這種經驗：

If you've ever held a magnet close to a piece of metal

如果你拿一個磁鐵靠近金屬片，

and felt a force pulling across that gap,

會感覺到之間有一股無形的拉力，

then you've felt the effect of a field.

那麼你就是感受到場的效應。

And the Higgs field is a little bit like a magnetic field,

希格斯場有點類似磁場，

except it has a constant value everywhere.

但它在任何地方都是常數，

It's all around us right now.

它就在我們四周，

We can't see it or touch it,

我們無法看或感受它，

but if it wasn't there,

但倘若它不存在，

we would not exist.

我們便不存在。

The Higgs field gives mass

希格斯場給予構成 我們的基本粒子質量，

to the fundamental particles that we're made from.

如果它不存在，

If it wasn't there, those particles would have no mass,

這些粒子便沒有質量，

原子無法形成，

and no atoms could form and there would be no us.

也就不會有你我。

But there is something deeply mysterious about the Higgs field.

但關於希格斯場有個謎團，

Relativity and quantum mechanics tell us that it has two natural settings,

相對論與量子力學說 它有兩種自然狀態。

a bit like a light switch.

有點像是電燈開關，

It should either be off,

不是關──

so that it has a zero value everywhere in space,

也就是說它到處的值都是零，

or it should be on so it has an absolutely enormous value.

就是開──

也就是說它到處都是個巨大定值。

In both of these scenarios, atoms could not exist,

在這兩個情況下原子都無法存在，

and therefore all the other interesting stuff

也因此這世上我們所見

that we see around us in the universe would not exist.

一切有趣事物將不存在。

In reality, the Higgs field is just slightly on,

事實上

希格斯場是稍稍打開的，

not zero but 10,000 trillion times weaker than its fully on value,

不是零，而是 開的值的一萬兆分之一，

a bit like a light switch that's got stuck just before the off position.

有點像是卡在 「關」前面一點的電燈開關。

And this value is crucial.

這個值十分重要，

If it were a tiny bit different,

若它與此值有絲毫不同，

then there would be no physical structure in the universe.

在宇宙中將不會有任何物理結構，

So this is the first of our dangerous numbers,

這就是第一個危險的數字，

the strength of the Higgs field.

希格斯場的強度。

Theorists have spent decades trying to understand

理論學家花了 幾十年的時間嘗試理解，

why it has this very peculiarly fine-tuned number,

為何是如此詭異精微的數值？

and they've come up with a number of possible explanations.

他們提出許多可行的解釋，

They have sexy-sounding names like "supersymmetry"

它們有酷炫的名字如

超對稱或巨大額外維度。

or "large extra dimensions."

I'm not going to go into the details of these ideas now,

我不會討論這些想法的細節，

but the key point is this:

但重點是：

if any of them explained this weirdly fine-tuned value of the Higgs field,

若它們真的解釋 怪異的希格斯場強度。

then we should see new particles being created at the LHC

那麼在 LHC 中我們應會觀察到

新粒子伴隨希格斯玻色子產生，

along with the Higgs boson.

So far, though, we've not seen any sign of them.

但至今為止我們一無所獲。

But there's actually an even worse example

然而還有關於這種

of this kind of fine-tuning of a dangerous number,

精細危險數字的更慘例子。

and this time it comes from the other end of the scale,

這次它來自另一個極端尺度：

from studying the universe at vast distances.

大尺度下的宇宙學。

One of the most important consequences of Einstein's general theory of relativity

愛因斯坦廣義相對論，

最重要的結論之一是

was the discovery that the universe began as a rapid expansion of space and time

發現在 138 億年以前， 因時空急速膨脹而生成宇宙，

13.8 billion years ago, the Big Bang.

這就是大霹靂。

Now, according to early versions of the Big Bang theory,

根據大霹靂學說的早期版本，

the universe has been expanding ever since

宇宙一直在膨脹，

with gravity gradually putting the brakes on that expansion.

而重力使其膨脹速逐漸減緩。

But in 1998, astronomers made the stunning discovery

但在 1998 年，

天文學家發現一件驚人的事實：

that the expansion of the universe is actually speeding up.

宇宙正在加速膨脹！

The universe is getting bigger and bigger faster and faster

宇宙之所以加速擴張，

driven by a mysterious repulsive force called dark energy.

乃是受一種稱為暗能量的 神祕斥力所驅使。

Now, whenever you hear the word "dark" in physics,

在物理學當你聽到「暗」時，

you should get very suspicious

你要有警覺心，

because it probably means we don't know what we're talking about.

因為這很可能意味著

我們不知道自己在說什麼。

（笑聲）

(Laughter)

我們不知道什麼是暗能量，

We don't know what dark energy is,

but the best idea is that it's the energy of empty space itself,

但最好的解釋是： 它是空無空間的能量、

the energy of the vacuum.

真空的能量。

Now, if you use good old quantum mechanics to work out

如果你用舊的量子力學

how strong dark energy should be,

計算暗能量的強度，

you get an absolutely astonishing result.

你會得到驚人的結果。

You find that dark energy

你會發現它的值應該是

should be 10 to the power of 120 times stronger

我們在天文學觀察到的值， 再乘以10 的 120 次方。

than the value we observe from astronomy.

That's one with 120 zeroes after it.

就是 1 後面加 120 個 0。

This is a number so mind-bogglingly huge

這個數字如此龐大，

that it's impossible to get your head around.

以至於你的腦袋會當機。

We often use the word "astronomical" when we're talking about big numbers.

我們常用「天文數字」 來描述巨大數字，

Well, even that one won't do here.

但在這兒卻不管用，

This number is bigger than any number in astronomy.

因為它比天文學裡的任何數字還大。

It's a thousand trillion trillion trillion times bigger

它是整個宇宙原子數量的 一千兆兆兆倍，

than the number of atoms in the entire universe.

So that's a pretty bad prediction.

所以這是個很差勁的預估。

In fact, it's been called the worst prediction in physics,

事實上它被稱為 物理史上最糟的預估。

and this is more than just a theoretical curiosity.

而這不單是理論上的事，

If dark energy were anywhere near this strong,

若暗能量到處都是如此強，

then the universe would have been torn apart,

宇宙早就被撕碎了，

stars and galaxies could not form, and we would not be here.

星星與星系也不會形成，

我們也不會存在。

So this is the second of those dangerous numbers,

這就是第二個危險的數字：

the strength of dark energy,

暗能量強度。

and explaining it requires an even more fantastic level of fine-tuning

解釋它需要比我們在 希格斯場見到的

than we saw for the Higgs field.

更加精細的微調。

But unlike the Higgs field, this number has no known explanation.

但與希格斯場不同的是，

對於這個數字 沒有任何已知的解釋，

The hope was that a complete combination

而希望繫於：

愛因斯坦的相對論──

of Einstein's general theory of relativity,

which is the theory of the universe at grand scales,

即大尺度描述宇宙的理論，

with quantum mechanics, the theory of the universe at small scales,

與量子力學──

小尺度描述宇宙的理論，

might provide a solution.

兩者的大一統可以提供解答，

Einstein himself spent most of his later years

愛因斯坦晚年大多時間致力於

on a futile search for a unified theory of physics,

大一統論的尋找，但並未成功。

and physicists have kept at it ever since.

而往後的物理學家也是如此。

One of the most promising candidates for a unified theory is string theory,

其中一個較有希望的候選者是弦論，

and the essential idea is,

它的主要思想是：

if you could zoom in on the fundamental particles that make up our world,

如果你能極近觀察 構成世界的基本粒子，

you'd see actually that they're not particles at all,

你會發現它們根本不是粒子，

but tiny vibrating strings of energy,

而是細小振動的能量弦。

with each frequency of vibration corresponding to a different particle,

不同的振動頻率對應不同的粒子。

a bit like musical notes on a guitar string.

有點像是吉他弦的音階，

So it's a rather elegant, almost poetic way of looking at the world,

這是以極高雅甚至如詩的方式

來看這個世界。

but it has one catastrophic problem.

但它有個致命傷：

It turns out that string theory isn't one theory at all,

弦論根本不是一個理論，

but a whole collection of theories.

而是許多理論的集合，

It's been estimated, in fact,

事實上估計約有

that there are 10 to the 500 different versions of string theory.

十至五百個不同的弦論，

Each one would describe a different universe

每一個都描述不同的宇宙

with different laws of physics.

與不同的物理定律。

Now, critics say this makes string theory unscientific.

批評者表示這使弦論不科學，

You can't disprove the theory.

你無法證明它的對錯。

But others actually turned this on its head

但有人腦筋一轉說：

and said, well, maybe this apparent failure

或許這顯見的失敗是

is string theory's greatest triumph.

弦論最大的成功。

What if all of these 10 to the 500 different possible universes

若這十至五百個理論描述的宇宙，

actually exist out there somewhere

確實在多重宇宙的某處存在，

in some grand multiverse?

Suddenly we can understand

剎那間我們就可以解釋

the weirdly fine-tuned values of these two dangerous numbers.

那兩個怪異精細的危險數字。

In most of the multiverse,

在多重宇宙大多地方，

暗能量太強以致宇宙會被撕裂，

dark energy is so strong that the universe gets torn apart,

或希格斯場太弱以致原子無法形成。

or the Higgs field is so weak that no atoms can form.

We live in one of the places in the multiverse

我們在多重宇宙的一隅，

where the two numbers are just right.

剛好這兩數字是恰當的。

We live in a Goldilocks universe.

我們住在「金髮宇宙」 （適當的宇宙）。

Now, this idea is extremely controversial, and it's easy to see why.

這個想法十分具爭議性，

原因十分簡單，

If we follow this line of thinking,

如果我們順著這條思路，

then we will never be able to answer the question,

那我們永遠無法回答以下問題：

"Why is there something rather than nothing?"

為什麼是「有」而不是「虛無」？

In most of the multiverse, there is nothing,

在多重宇宙大多處什麼也沒有，

and we live in one of the few places

我們住在其中一個少數地方，

where the laws of physics allow there to be something.

剛好物理定律允許存在物質。

Even worse, we can't test the idea of the multiverse.

更糟的是我們無法 檢驗多重宇宙的想法，

We can't access these other universes,

我們無法去其他宇宙，

so there's no way of knowing whether they're there or not.

所以無法得知它是否存在。

So we're in an extremely frustrating position.

所以我們處於一種令人氣餒的狀況。

但那不代表多重宇宙不存在，

That doesn't mean the multiverse doesn't exist.

There are other planets, other stars, other galaxies,

既然有其他行星、恆星與星系，

so why not other universes?

為何其他宇宙不行？

The problem is, it's unlikely we'll ever know for sure.

問題是我們不太可能 證實它的真實性。

Now, the idea of the multiverse has been around for a while,

多重宇宙的想法已經出現一陣子。

but in the last few years, we've started to get the first solid hints

在最近幾年

我們開始有幾個較具體的跡象，

that this line of reasoning may get born out.

顯示這條思路或許行得通。

Despite high hopes for the first run of the LHC,

儘管對第一次 LHC 運行的高度期待，

what we were looking for there --

我們在尋找新的物理理論：

we were looking for new theories of physics:

超對稱或巨大額外維度，

supersymmetry or large extra dimensions

以解釋詭異精細的希格斯場強度。

that could explain this weirdly fine-tuned value of the Higgs field.

But despite high hopes, the LHC revealed a barren subatomic wilderness

但儘管高度期待，

LHC 顯示出只有希格斯波色子的

populated only by a lonely Higgs boson.

荒涼次原子世界。

My experiment published paper after paper

我的實驗報告 一篇接著一篇都寫著，

where we glumly had to conclude that we saw no signs of new physics.

我們遺憾宣布沒有新物理的跡象。

The stakes now could not be higher.

危機指數已經到達頂端。

This summer, the LHC began its second phase of operation

這個夏天 LHC 開始第二次運作，

能量幾乎是第一次的兩倍。

with an energy almost double what we achieved in the first run.

What particle physicists are all desperately hoping for

粒子學家迫切希望的

are signs of new particles, micro black holes,

是新粒子、微型黑洞

or maybe something totally unexpected

或完全意料之外的訊號，

emerging from the violent collisions at the Large Hadron Collider.

從 LHC 激烈碰撞中產生。

If so, then we can continue this long journey

倘若如此，我們便可以繼續這趟

that began 100 years ago with Albert Einstein

由愛因斯坦開始的、 超過百年的旅程，

towards an ever deeper understanding of the laws of nature.

朝著對自然律更深刻的認知邁進。

But if, in two or three years' time,

但若兩三年下來，

when the LHC switches off again for a second long shutdown,

在 LHC 第二次長期關機前，

我們除了希格斯玻色子外一無所獲。

we've found nothing but the Higgs boson,

then we may be entering a new era in physics:

那麼我們或許 就進入新的物理紀元：

an era where there are weird features of the universe that we cannot explain;

一個有我們無法解釋現象的時代。

an era where we have hints that we live in a multiverse

一個有跡象顯示我們活在

我們能力範圍外的多重宇宙時代。

that lies frustratingly forever beyond our reach;

an era where we will never be able to answer the question,

一個我們永遠無法回答

為什麼是「有」 而不是「虛無」的時代。

"Why is there something rather than nothing?"

Thank you.

謝謝！

(Applause)

（掌聲）

Bruno Giussani: Harry, even if you just said

布魯諾：哈利，即使你剛有說

the science may not have some answers,

科學或許有無法解釋的事情，

我還是想問你幾個問題：

I would like to ask you a couple of questions, and the first is:

第一個是

建造像 LHC 是一個世代的計畫，

building something like the LHC is a generational project.

I just mentioned, introducing you, that we live in a short-term world.

剛介紹你時我有提到，

我們活在短週期的世界裡，

How do you think so long term,

你對這個世代的人花這麼多時間

projecting yourself out a generation when building something like this?

建造這樣的機器有什麼看法？

Harry Cliff: I was very lucky

哈利：我很幸運在 2008 年

that I joined the experiment I work on at the LHC in 2008,

當一切剛開始起步時，

just as we were switching on,

便加入這個研究團隊。

and there are people in my research group who have been working on it

這個團隊中有研究它 超過三十年的人，

for three decades, their entire careers on one machine.

他們人生全投入在這機器上。

我想第一次有關 LHC 的談話

So I think the first conversations about the LHC were in 1976,

是在 1976 年。

and you start planning the machine without the technology

在沒有所需科技來建造它的狀況下，

that you know you're going to need to be able to build it.

人們開始設計它。

90 年代初期 設計工作認真開始時

So the computing power did not exist in the early '90s

電腦運算能力還嚴重不足，

when design work began in earnest.

One of the big detectors which record these collisions,

其中一個偵測這些碰撞的偵測器，

當時他們不認為有科技

they didn't think there was technology

that could withstand the radiation that would be created in the LHC,

可以抵抗 LHC 內部 形成的輻射，

so there was basically a lump of lead in the middle of this object

所以原本在這中間有一塊鉛，

with some detectors around the outside,

偵測器則散佈四周，

但後來我們有發展出新科技。

but subsequently we have developed technology.

我們必須依賴人們的聰慧，

So you have to rely on people's ingenuity, that they will solve the problems,

一切問題會被解決，

只是可能是十年或更久之後。

but it may be a decade or more down the line.

布：兩三個星期前中國宣布

BG: China just announced two or three weeks ago

that they intend to build

他們計畫建造一個

a supercollider twice the size of the LHC.

比 LHC 大兩倍的超級對撞機，

I was wondering how you and your colleagues welcome the news.

我想知道你與同事們 對這新聞的看法。

HC: Size isn't everything, Bruno. BG: I'm sure. I'm sure.

哈：布魯諾，大小不代表一切。

布：我知道、我知道。

(Laughter)

（笑聲）

It sounds funny for a particle physicist to say that.

聽粒子物理學家這樣說蠻有趣的。

But I mean, seriously, it's great news.

不過認真地，它是個好消息！

So building a machine like the LHC

建造像 LHC 的機器

requires countries from all over the world to pool their resources.

需要全世界國家的投入，

No one nation can afford to build a machine this large,

沒有國家可以負擔如此的花費，

apart from maybe China,

或許除了中國。

because they can mobilize huge amounts of resources,

因為他們可以動用

大量資源、人力、金錢

manpower and money to build machines like this.

來建造這樣的機器。

So it's only a good thing.

所以這是好消息吧！

What they're really planning to do is to build a machine

他們計畫建造的是

可以詳細研究 希格斯玻色子並給我們

that will study the Higgs boson in detail and could give us some clues

as to whether these new ideas, like supersymmetry, are really out there,

像是超對稱的新想法 是否為真的線索。

so it's great news for physics, I think.

所以我想對物理界來說是好消息。

BG: Harry, thank you. HC: Thank you very much.

布：謝謝 哈：謝謝

（掌聲）

(Applause)