To answer this question,

為了回答這個問題，人們想了各種模型來描述這個世界

humans come up with stories to describe the world.

我們測試這些模型

We test our stories and learn what to keep and what to throw away.

並知道了到哪些該保存下來，哪些該捨棄

But the more we learn,

00:00:14,465 --> 00:00:18,980 但當我們知道了更多，模型就變得更加奇怪且複雜

the more complicated and weird our stories become.

有些甚至困難到，相當難以精確說明它

Some of them so much so,

就像弦理論

that it's really hard to know what they're actually about.

一個著名的，充滿爭議的，並且常被誤解的理論

Like string theory.

為何會有人想出這套理論，而它的描述是正確的嗎?

A famous, controversial and often misunderstood story,

或只是一個不值得重視的想法?

about the nature of everything.

♪~好聽的開場音樂~♪

Why did we come up with it and is it correct?

為了知道自然的樣貌

Or just an idea we should chuck out?

我們近距離觀察各種事物，並且驚奇於其中深藏的奧妙

To understand the true nature of reality,

微小世界的奇妙景觀

we looked at things up close and were amazed.

一群群奇妙的生物

Wonderous landscapes in the dust,

複雜的蛋白質機械

zoos of bizarre creatures,

他們全由分子所構成

complex protein robots.

並且又由更小的原子所構成

All of them made from structures of molecules

我們曾經認為它們就是世界的基本單元

made up of countless even smaller things:

直到我們將它們強力相撞

Atoms.

並發現了完全不可再切割的物質

We thought they were the final layer of reality,

【基本粒子】

until we smashed them together really hard

但現在有個問題

and discovered things that can't be divided anymore:

基本粒子太小，我們不能直接觀測到它

Elementary particles.

試想一下，什麼是觀測呢?

But now, we had a problem:

想要做觀測，我們需要光，也就是電磁波

They are so small that we could no longer look at them.

這道波撞擊物體的表面，並反射至你的眼睛裡

Think about it: what is seeing?

光波攜帶著物體的資訊

To see something, we need light, an electromagnetic wave.

讓你的大腦能建構影像

This wave hits the surface of the thing

所以你不能在沒有某種交互作用的情況下做觀測

and gets reflected back from it into your eye.

看到，便能有所了解，這是一個主動而非被動的過程

The wave carries information from the object

對大多數的物體來說這都不是問題

that your brain uses to create an image.

但基本粒子非常非常非常的小

So you can't see something without somehow interacting with it.

它小到我們過去所能看到的電磁波根本碰不到

Seeing is touching, an active process, not a passive one.

可見光只會穿過它們

This is not a problem with most things.

我們可以藉由縮小電磁波波長來解決問題

But particles are

但波長越小，意味著能量越大

But particles are very,

所以，當我們用一道高能量的光去照射粒子

But particles are very, very,

光會改變粒子的位置

But particles are very, very, very small.

為了觀測它，我們改變了它的性質

So small that the electromagnetic waves we used to see

結論是，我們無法精確地量測基本粒子

are too big to touch them.

這現象重要到被命名為

Visible light just passes over them.

【海森堡測不準原理】

We can try to solve this by creating electromagnetic waves

一切量子物理學的基礎

with more and much smaller wavelengths.

所以，粒子看起來是什麼樣子?

But more wavelengths, means more energy.

它的本質是怎樣?

So, when we touch a particle with a wave that has a lot of energy

我們其實並不知道

it alters it.

如果我們盡可能去觀測它

By looking at a particle, we change it.

我們可以看到一團模糊的物體

So, we can't measure elementary particles precisely.

但這不是粒子本身

This fact is so important that it has a name:

我們只知道它們存在

The Heisenberg uncertainty principle.

這種情況下，我們要對它們怎麼做科學研究呢?

The basis of all quantum physics.

就像前人一樣

So, what does a particle look like then?

我們提出了新的數學模型

What is its nature?

點粒子模型

We don't know.

我們決定假設，粒子在空間中只是一個點

If we look really hard,

任何電子都只是空間中有特定電荷量和特定質量的點

we can see a blurry sphere of influence,

而且所有電子都無法被區分

but not the particles themselves.

這樣物理學家便可定義它們，並計算它們之間的交互作用

We just know they exist.

這套理論叫【量子場論】，並且解決了許多問題

But if that's the case,

粒子物理中的標準模型都是建立在這上面的

how can we do any science with them?

而粒子物理實驗的精確值也相當高

We did what humans do and invented a new story:

有些電子的量子性質被量測出來了

A mathematical fiction.

而精確值可以到0.0000000000002% (2*10^-13%)

The story of the point particle.

所以，就算粒子並不真的是個點

We decided that we would pretend that a particle is a point in space.

這樣的假設讓我們可以相當精確地去描繪宇宙

Any electron is a point with a certain electric charge and a certain mass.

這樣的想法不僅讓科學進步

All indistinguishable from each other.

它也帶給我們許多每天都在用的科技成就

This way physicists could define them

但有一個重大的問題

and calculate all of their interactions.

【重力】

This is called Quantum Field Theory, and solved a lot of problems.

在量子力學裡，所有的力都由特定的粒子產生

All of the standard model of particle physics is built on it

但根據愛因斯坦的廣義相對論

and it predicts lots of things very well.

重力並不像宇宙中其他作用力一樣

Some quantum properties of the electron for example

如果宇宙是場戲劇，粒子就是演員

have been tested and are accurate up to

而重力則是舞台

0,

簡單來說，重力是種幾何學

0,00

時空間的幾何學

0,0000

所以我們必須定義出絕對的距離

0,000000

但在量子物理的世界中，我們無法明確量測事物

0,00000000

重力模型與量子物理模型彼此並不相容

0,0000000000

當物理學家試圖增加新的粒子來描述重力時

0,000000000000

他們的數學系統卻崩潰了

0,0000000000002 %.

這是個相當重要的問題

So, while particles are not really points,

如果我們可以結合重力與標準模型

by treating them as if they were,

我們可以得到一切的萬有理論

we get a pretty good picture of the universe.

所以天才們開始想新的模型

Not only did this idea advance science,

他們問到:「比一個點更複雜的事物是什麼?」

it also led to a lot of real-world technology we use everyday.

一條線? 或是一條弦?

But there's a huge problem:

弦理論就這樣誕生了

Gravity.

弦理論之所以會如此精美

In quantum mechanics, all physical forces are carried by certain particles.

是因為其用了各異的震盪模式描述了基本粒子

But according to Einstein's general relativity,

就像小提琴不同的琴弦震動，能夠發出各異的樂音，

gravity is not a force like the others in the universe.

弦的各種震盪模式就能產生不同的粒子

If the universe is a play,

最重要的是

particles are the actors,

弦理論也能描述重力

but gravity is the stage.

弦理論可以統合宇宙中所有的基本作用力

To put it simply, gravity is a theory of geometry.

這造成了群情激奮與大肆炒作

The geometry of space-time itself.

弦理論很快的成為了可能解釋一切的理論

Of distances, which we need to describe with absolute precision.

不幸的是，弦理論有許多特殊的限制

But since there is no way to precisely measure things in the quantum world,

在我們這由三維空間與一維時間組成的宇宙中

our story of gravity doesn't work with our story of quantum physics.

弦理論不能保持數學上的一致性

When physicists tried to add gravity to the story by inventing a new particle,

弦理論需要以十維的世界來運作

their mathematics broke down

所以，弦理論確實能在理論中的宇宙運作

and this is a big problem.

而物理學家想要找出去除剩餘六維的數學模式來探究我們所處的宇宙

If we could marry gravity to quantum physics and the standard model,

但直到現在，沒有能人成功達成這個任務

we would have the theory of everything.

並且弦理論中的預測全部都尚未被實驗證實

So, very smart people came up with a new story.

所以，弦理論並沒有真正透露出宇宙的真實樣貌

They asked: What is more complex than a point?

所以有人指出

A line-

弦理論可能完全不實用

A line or a string.

科學是由一連串的實驗和預測所組成

String theory was born.

如果我們無法證明

What makes string theory so elegant,

那麼我們為何要費心於弦理論呢

is that it describes many different elementary particles

它與我們如何去使用它息息相關

as different modes of vibration of the string.

物理是建立於數學規則

Just like a violin string vibrating differently can give you a lot of different notes,

2+2=4

a string can give you different particles

這就是事實，不論你有什麼想法

Most importantly, this includes gravity.

而弦理論中的數學推導是可行的

String theory promised to unify all fundamental forces of the universe.

這就是為什麼弦理論仍然是非常實用的

This caused enormous excitement and hype.

想像你打算造一艘巨大的郵輪

String theory quickly graduated to a possible theory of everything

但你只有一張划槳小船的藍圖

Unfortunately, string theory comes

它們顯然有諸多不同之處

with a lot of strings attached.

引擎，材料，大小

Much of the maths involving a consistent string theory

但他們的原理基本上是一樣的

does not work in our universe with its three spatial and one temporal dimensions.

會飄浮在水上的東西

String theory requires ten dimensions to work out.

所以，透過研究划槳小船的藍圖

So, string theorists did calculations in model universes.

你最終可能還是可以學到怎麼去造一艘遊輪

And then try to get rid of the six additional dimensions and describe our own universe

有了弦理論

But so far, nobody has succeeded

我們可以試著去解釋一些困擾物理學家數十年的量子重力論的難題

and no prediction of string theory has been proven in an experiment

像是黑洞如何運行或是它的訊息悖論

So, string theory did not reveal the nature of our universe.

弦理論可能可以成為指引我們方向的一盞明燈

One could argue that in this case

有了這個想法

string theory really isn't useful at all.

弦理論就變成了一個理論物理學家的珍貴工具

Science is all about experiments and predictions.

並且可以幫助他們去探索量子世界的新層面

If we can't do those,

以及一些美麗的數學理論

why should we bother with strings?

所以，雖然弦理論可能無法解釋一切事物

It really is all about how we use it.

不過就如同點粒子模型一般，

Physics is based on maths.

弦理論可以是一個非常實用的理論

Two plus two makes four.

我們還不知道現實世界的真實樣貌到底是如何

This is true no matter how you feel about it.

不過我們會繼續想出更多理論來試著探究

And the maths in string theory does work out.

直到將來的某天

That's why string theory is still useful.

希望我們能真正了解其中的奧妙

Imagine that you want to build a cruise ship,

這部影片由瑞士國家科學基金會所贊助

but you only have blueprints for a small rowing boat.

並且由Alessandro Sfondrini提供科學上的諮詢

There are plenty of differences:

the engine,

the engine, the materials,

the engine, the materials, the scale.

But both things are fundamentally the same:

Things that float.

So, by studying the rowing boat blueprints,

you might still learn something about how to build a cruise ship eventually.

With string theory,

we can try to answer some questions about quantum gravity

that have been puzzling physicists for decades.

Such as how black holes work

or the information paradox.

String theory may point us in the right direction.

When used in this spirit,

string theory becomes a precious tool for theoretical physicists

and help them discover new aspects of the quantum world

and some beautiful mathematics.

So, maybe the story of string theory

is not the theory of everything.

But just like the story of the point particle,

it may be an extremely useful story.

We don't yet know what the true nature of reality is

but we'll keep coming up with stories to try and find out.

Until one day,

Until one day, hopefully

Until one day, hopefully, we do know.

This video was supported by the Swiss National Science Foundation

and realized with the scientific advice of Alessandro Sfondrini.