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世界上最成功的科学理论:标准模型

The Most Successful Scientific Theory Ever: The Standard Model

400 years ago,
四百年前
Galileo started piecing together the basic principles of reality—
伽利略开始厘清现实世界的基本原则
what we now call modern science.
即我们今天所说的现代科学
But the questions he was trying to answer are as old as humanity itself.
但他设法回答的这些问题 古老如人类本身:
What are we made of?
我们是由什么组成的?
What are the fundamental building blocks of the universe
构成了你 我 星辰 以及世间万物的
from which you, me, the stars, and everything else is constructed?
宇宙基本组成部分是什么?
In the centuries since Galileo,
自伽利略之后的几个世纪
thousands of theories and experiments have peered into smaller and smaller distances…
成千上万的理论和实验研究着越来越小的物质单位
converging on a single picture of the structure of matter.
最终汇成物质结构的单一图像
This somewhat daunting-looking formula is where we end up.
这个令人有些望而却步的公式 就是我们得出的结论
It gives the correct answer to hundreds of thousands of experiments,
它为成千上万的实验提供了正确的答案
in some cases with an accuracy that is unprecedented in science.
在某些情况下 其准确性甚至在科学界都是前所未有的
It is, by any measure,
无论用何种方式衡量
the most successful scientific theory of all time.
它都是有史以来最成功的科学理论
And yet for something so extraordinary,
但是 对于如此非凡的理论
we give it a rubbish name.
我们却给它起了一个蹩脚的名字
We call it the Standard Model.
我们称之为标准模型
I’m David Tong, a theoretical physicist at the University of Cambridge.
我是David Tong 剑桥大学的一名理论物理学家
And in this video, we’re going to build the Standard Model, piece by piece.
在这个视频中 我会带你们一步一步地建立标准模型
I hope that, by the end,
我希望 到视频最后
you’ll have some intuition for how all of the parts fit together
你们多少能感受到 所有的物质是如何组合起来
to create the fundamental building blocks of our universe.
从而创造出我们这个宇宙的基本构件的
This is the Standard Model.
这就是标准模型
It describes how everything in the universe
它描述了宇宙中的一切
is made of 12 different types of matter particles,
如何由十二种不同类型的物质颗粒组成
interacting with 3 forces,
与3种力互相作用
all bound together by a rather special particle
最后被一种非常特殊的希格斯玻色子颗粒
called the Higgsboson.
束缚在一起
Before we get going, some caveats.
在我们开始之前 有几件事要提醒大家
First…I said “three forces”.
首先 我刚刚说了“三种力”
While there are actually four fundamental forces at play in the universe.
但其实宇宙中有四种基本的作用力
This means that there’s something missing from this picture.
这意味着这张图中少了什么东西
And that something would be gravity,
而这个缺少的东西就是引力
the most obvious force at play in the world around us and yet,
它是我们身处的世界中最明显的力
in many senses, the one we understand least.
但从很多方面来说 也是我们最不理解的一个力
We do have a theory of gravity, a very successful theory.
我们的确有关于引力的理论 而且这一理论非常成功
It was given to us by Albert Einstein and goes by the name of general relativity.
它由阿尔伯特·爱因斯坦提出 被称为广义相对论
But there are two good reasons why it’s not included in the Standard Model.
但为什么标准模型并不涵盖它 这里有两大原因
The first is that, at the microscopic level,
第一 在微观层面上
the force of gravity is so weak
引力太过微弱
that it barely has any effect on a single subatomic particle.
以至于它对单个亚原子粒子几乎没有任何作用
The second is that we don’t really know how to incorporate general relativity,
第二 我们其实并不知道如何把广义相对论
which is a classical theory, into the quantum world.
这种经典理论 糅合到量子世界中
We have no idea how to peer into a black hole
我们不知道如何窥视黑洞
where quantum gravity effects are clearly at work.
量子引力效应显然在那里起作用
A second caveat
第二点要注意的是
is that the Standard Model is written in a language known as quantum field theory.
标准模型是由一种被称为量子场论的语言写就的
This tells us that matter, at the fundamental level,
这意味着 物质在基本层面上
is not really made up of particles.
并不真正是由粒子构成的
Instead, it’s made up of fields:
相反 物质是由场构成的:
fluid-like objects which are spread throughout all of space.
场是流体一般的物质 遍布整个空间
These fields are engaged in an intricate, harmonious dance to a music
这些场伴随着我们称之为物理定律的音乐
that we call the laws of physics.
跳着复杂而和谐的舞蹈
The interactions between the fields produce the physical world in the form of particles.
场之间的相互作用以粒子形式创造了物质世界
To understand the Standard Model,
要理解标准模型
it’s more convenient to use the language of particles.
用粒子的语言来说明会更为便利
As we build up the Standard Model,
我们在建立标准模型的过程中
we’re going to meet lots of particles with an array of names
将会遇到许多粒子 它们的名字也千奇百怪
that can very quickly become bewildering.
很快就会让人眼花缭乱
But there is one classification that is, by far, the most important:
但有一种类别是迄今为止最重要的:
Every particle is either a fermion, which is a matter particle,
每一个粒子要么是费米子 一种物质粒子
or a boson, which is a force particle.
要么是玻色子 一种作用力粒子
The distinction between fermions and bosons lies in the quantum world.
费米子和玻色子的区别在于 量子世界中
Fermions must obey something that we called the Pauli exclusion principle.
费米子必须遵守我们所说的泡利不相容原理
Roughly speaking,
大致来说
this means that you can’t put two fermions on top of each other in space.
就是你不能让两个费米子挤在一个空间
As such, these are the building blocks of matter.
它们本身 就是物质的基石
Bosons, on the other hand,
另一方面 玻色子
can pile on top of each other as much as they want
可以随心所欲的占据同一个空间
because they’re not obliged to obey the Pauli Exclusion principle.
因为它们不必遵守泡利不相容原理
Bosons are the particles that mediate various forces
玻色子是传递各种作用力的粒子
and we’ll talk about them more later.
我们之后会详述
For now, let’s start by looking at the fermions.
现在 我们先来看看费米子
Everything that we’re made of can be reduced to just three matter particles:
构成我们的一切事物都能被简化为三种物质粒子:
this is the electron and two species of quarks that we call the up quark and the down quark
电子和两种夸克——上夸克和下夸克
The familiar proton and neutron each contain three quarks.
我们熟悉的质子和中子各包含三个夸克
The proton has two up quarks and a down,
质子有两个上夸克和一个下夸克
while the neutron has two down quarks and an up.
而中子有两个下夸克和一个上夸克
Put protons and neutrons together, and you have a nucleus.
把质子和中子放在一起 就得到了原子核
Add electrons into the mix and you have an atom.
再把电子加入其中 就得到了一个原子
Put a bunch of atoms together and that’s what we’re made of.
把一堆原子放一起 这就构成了我们
All the beauty and complexity that we see in the world around us
我们在世界上所看到的一切美丽与复杂的事物
can be traced to this same collection of three particles,
都能溯源到同样是这三种粒子构成的集合
rearranged over and over in different combinations.
只不过一次次组合的形式不同而已
Next comes the fourth type of matter particle.
接下来是第四种物质粒子
It’s called the neutrino and it’s not like the others.
它叫作中微子 而且跟其他粒子不同
Neutrinos are extremely light and barely interact with anything else.
中微子重量极轻 而且几乎不与其他粒子相互作用
For example, in the time it took me to say that,
例如 在我说出这句话的时间里
something like 100 trillion neutrinos passed through your body.
有大约100万亿的中微子穿过了你的身体
Most of them came from the sun,
其中大多数来自太阳
but millions of them have been streaming uninterrupted through the universe
但有数百万是从宇宙大爆炸后的几秒钟起
since the first few seconds after the Big Bang.
就在宇宙中不断地流动
So, there we have it: four matter particles.
现在 我们认识了四种物质粒子
Three that make up you, me, and everyone we know,
其中三种构成了你 我和所有其他人
and one very peculiar cosmic ghost flowing through us all.
还有一种就如奇异的宇宙幽灵在我们之中流动
But here’s where things start to get weird.
但是 事情开始变得古怪了
Because Nature didn’t stop there.
因为自然并没有止步于此
For reasons that we don’t understand,
出于某种我们无法理解的原因
she took this collection of four particles
她创造了这四种粒子
and made two further copies.
然后又制造了两份副本
This means that there are actually three different kinds of electron-like particles.
这意味着实际上有三种不同的类电子粒子
In addition to the original electron that we know and love,
除了我们所了解和喜爱的原始电子
there are particles called the muon and the tau.
还有两种叫做μ子和τ中微子
The muon and the tau behave exactly like an electron,
μ子和τ中微子的行为极像电子
with one important exception:
但有一个重要区别:
they’re heavier.
它们质量更大
The muon is about 200 times heavier than the electron,
μ子的质量是电子的200倍
the tau almost three and a half thousand times heavier.
τ中微子的质量是电子的3500倍
The same generational pattern then repeats for the quarks.
同样的代际模式也出现在夸克之中
There are two heavier versions of the down quark,
有两种质量更大的下夸克
that we call the strange, and bottom quarks
我们称之为奇异夸克和底夸克
and two heavier versions of the up quark called charm and top
还有两种质量更大的上夸克 称为魅力夸克和顶夸克
And then there are also two more neutrinos:
另外 还有两种中微子:
we become a little bit unimaginative in our naming
我们的命名有点缺乏想象力
and call the full collection the electron neutrino, the muon neutrino, and the tau neutrino.
这整个集合中有电子中微子 μ子中微子和τ中微子
Now, we don’t see the second and the third generations of particles in everyday life.
现在 我们在日常生活中看不到第二代和第三代粒子
We can create these heavier particles
我们可以制造这些质量更大的粒子
but they are unstable,
但是它们不太稳定
which means that they quickly decay to the first generation of particles that we’re made of.
这意味着它们会很快衰变为构成我们的第一代粒子:
Nonetheless, we know they exist.
虽然如此 我们知道它们是存在的
We can detect them in particle accelerators.
我们可以在粒子加速器中探测到它们
In some cases, we’ve even been able to take photographs of the tracks they leave behind.
某些情况下 我们甚至能拍下它们留下的痕迹
This is the collection of particles that makes up our world.
这就是构成我们世界的粒子集合
Three sets of four.
三组集合 每组四种物质粒子
Now some of this we understand very well.
其中一些 我们非常了解
In particular, we understand why particles have to come in a set of four.
特别是 我们理解为什么粒子必须以四个一组的形式出现
There is a mathematical consistency condition in the Standard Model
标准模型中有一个数学一致性条件
that tells us that you can’t have one particle without the other three.
它告诉我们 没有其他三种粒子时 粒子不能单独存在
In contrast
相对而言
we don’t understand at all why there are three generations rather than any other number.
我们完全不懂 为什么有三代 而不是其他数字
That remains a complete mystery.
这仍然是个未解之谜
There is, however, a surprising aspect of mathematical unity here:
然而 数学统一性令人惊讶的一个方面是
all particles are described by exactly the same equation.
所有的粒子都由完全相同的方程描述
This equation was written down in the 1920s by the physicist Paul Dirac
20世纪20年代 物理学家保罗·狄拉克写下了这一等式
originally to describe the electron.
最初 它是用来描述电子的
But, as we discovered more and more particles (quarks and neutrinos)
但是 随着我们发现了越来越多的粒子(夸克和中微子)
we realized the Dirac equation or variants of it.
我们认识到 狄拉克的等式或它的变体
also describles them.
同样适用于它们
So, that’s the stuff we’re made of.
这就是组成我们的基本物质
But still we’re missing something crucial!
但我们仍然漏了一些重要的东西!
We are missing the forces.
我们遗漏了“力”
Without the forces, the universe would be boring.
没有这些力 宇宙将会变得无趣
All of the particles would wander around the cosmos like lost souls,
所有粒子都会像迷失的灵魂一样在宇宙游荡
never interacting, never doing anything interesting.
不会相互作用 也不会发生任何有趣的事
There are three fundamental forces in the Standard Model
标准模型中有三种基本力
the electromagnetism,
电磁力
the strong force,
强力
and the weak force.
和弱力
Each of these forces comes with an associated particle.
每一种力都伴随着一个相关的粒子
These particles are what we called bosons,
这些粒子就是我们所说的玻色子
the other half of our particle family.
我们粒子家族的另一半
Bosons are force-carrying particles.
玻色子是携带力的粒子
In one way of viewing things,
从一个角度来看
you can think of the fermions as constantly swapping bosons between them
你可以理解为费米子在不停地交换玻色子
affecting their motion
影响它们的运动
and giving rise to what we call a force.
并产生我们所说的力
Let’s begin with the most familiar of these forces.
让我们从最熟悉的力开始
Electromagnetism is responsible for the chemical properties of the elements
电磁力决定了元素的化学性质
and we’ve harnessed it to create much of modern technology.
我们利用它创造了许多现代科技
It acts on anything that carries electric charge.
它对任何带电荷的东西都起作用
That means that it acts on the electron-type particles and the quarks,
这意味着它作用于电子型粒子和夸克
but not on the neutrinos
但对中微子没有影响
because neutrinos are electrically neutral.
因为中微子是电中性的
An electron sitting in space will give rise to an electric field
位于空间中的电子会产生一个电场
which spreads radially outwards,
呈辐射状扩散
and attracts or repels all other electrically charged particle in its neighborhood.
并吸引或排斥其附近所有其他带电粒子
But if you look more closely at that electric field,
但是如果你仔细观察那个电场
you will find that it’s comprised of the particles of electromagnetism
你会发现它是由电磁粒子组成的
These particles we call photons.
这些粒子我们称之为光子
Next is the strongest fundamental force in nature,
接下来是自然界中最强的基本力
aptly named the strong force.
它被恰当地命名为强力
This force acts only on quarks and, subsequently, on particles like protons and neutrons that
这种力只作用于夸克 随之作用于质子和中子
are made of quarks.
这些由夸克组成的粒子
it is the strong force that holds together the nuclei of atoms.
正是强力 使得原子核结合在一起
It’s also this force that is responsible for nuclear fission
也正是这种力量导致了核裂变
and gives the energy that is released in an atomic explosion.
并产生了原子爆炸释放的能量
Just as the photon is associated to electromagnetism,
正如光子与电磁力联系在一起一样
there is a particle associated to the strong force.
也有这样一个粒子与强力有关
We call it the gluon because it literally sticks quarks together.
我们称之为胶子 因为实际上是它将夸克粘在一起
As the electron gives rise to an electric field,
正如电子会产生电磁场一样
so a quark sitting in space will give rise to a gluon field.
空间中的夸克也会产生一个胶子场
But now something different happens:
但是这回发生的事有些不同:
unlike electromagnetism, the field doesn’t spread out radially.
与电磁学不同 胶子场不会呈放射状扩散
Instead, the quark produces a thin flux tube,
相反 夸克产生了一个薄通量管
a string-like object, which can only end when it finds a different kind of quark.
类似于弦 只有遇到不同种类的夸克时才会停下来
This is what makes the strong force strong.
这就是强力之所以强的原因
Because the quarks are joined by a flux tube,
因为夸克是由通量管连接在一起的
it takes more and more energy to pull them apart.
要把它们拉开就需要更多的能量
This is why we never see quarks on their own.
这就是我们看不到单独的夸克的原因
They’re always bound together by the strong force inside bigger particles,
它们总是被较大粒子内部的强力束缚在一
like protons and neutrons.
例如质子和中子
The third and final force is the most intricate and subtle of them all.
第三种也是最后一种力是所有力中最复杂和最微妙的
This is the weak force.
这就是弱力
Like the strong force, the weak force acts only on subatomic distances.
像强力一样 弱力只作用在亚原子的距离上
But rather than bind particles together, the weak force is all about decay.
但是弱力不是将粒子结合在一起 而是衰变
We just learned that the strong force binds quarks together to form protons and neutrons,
我们刚刚了解到强力将夸克结合在一起形成质子和中子
creating the atomic nucleus.
创造了原子核
The weak force has the astonishing ability to allow quarks to switch their identity.
弱力的惊人力量可以使夸克转换身份
A down quark can turn into a up quark,
一个下夸克可以变成上夸克
releasing an electron and neutrinoin the process.
在这个过程中释放出一个电子和中微子
This means that a neutron can morph into a proton.
这意味着一个中子可以变成一个质子
What we call radioactive beta decay.
我们称之为放射性β衰变
In this way, the weak force is responsible for the nuclear fusion reactions
这样的话 弱力负责核聚变反应
that power the sun and produce the energy required for life on Earth.
为太阳提供动力 并产生地球生命所需的能量
Finally, the weak force is also the reason that heavier matter particles
最后 弱力也是较重物质粒子
quickly decay into the three lighter and more stable fermions
迅速衰变为三个更轻更稳定的费米子的原因
that make up matter we know it.
这三种费米子构成了我们所知道的物质
There are particles associated to the weak force
也有与弱力相关联的粒子
we call these the W and Z bosons.
我们称之为W玻色子和Z玻色子
The weak force is the only one of the three forces to act on all the particles.
弱力是三种力中唯一作用于所有粒子的力
In particular, it’s the only force that neutrinos feel.
特别的是 它是唯一能作用于中微子的力
Finally It’s time to meet the last piece of the jigsaw:
终于到了拼图的最后一块了:
the particle that in many ways ties the whole Standard Model together.
从多个方面将整个标准模型联系在一起的粒子
This is the Higgs boson.
那就是希格斯玻色子
To explain why the Higgs boson is so special,
为了解释希格斯玻色子的特殊之处
I should first tell you a striking fact:
我要先告诉你一个惊人的事实:
none of the fundamental particles in the world have a mass.
世界上的基本粒子都没有质量
This is where the Higgs boson comes in.
这就是希格斯玻色子的用武之地
Its role is to endows all fermions with a mass.
它的作用就是赋予所有费米子质量
I’d love to be able to give you a clear explanation of why this happens.
我很想给你们解释清楚 为什么会发生这种情况
But sadly it’s difficult to come up with good analogies for the Higgs field.
但遗憾的是 要给希格斯场找到好的类比真是太难了
Here is what I would say as a so-so analogy
所以我只能讲一个一般的类比
you should view the Higgs field as something like a cosmic molasses,
你应该把希格斯场看作类似宇宙糖浆的东西
speard through out the universe
弥漫在整个宇宙中
trapping matter particles as they travel through space
在物质粒子穿越空间时捕获它们
and giving them what appears to us, to be a mass
并赋予它们我们都拥有的东西 那就是质量
So this is the Standard Model:
这是标准模型:
12 matter particles, interacting with 3 forces and a Higgs field.
12种物质粒子与3种力和一个希格斯场相互作用
It’s a beautiful picture, the pinnacle of 400 years of science.
这是一幅美丽的图画 是400年来科学的顶峰
But it’s clear that the Standard Model is not the last word in physics.
但是很明显 标准模型并不是物理学的最终结论
Since the discovery of the Higgs boson,
自从发现希格斯玻色子以来
physicists like me feel that in many ways
像我这样的物理学家都觉得在很多方面
the Standard Model is too successful.
标准模型都过于成功了
It gives the right answer to every experiment that we can do.
我们做的每个实验 它都给出了正确答案
Our current hope is that we will eventually find an experiment
我们当下的愿望是 最终做出一个
that it gives the wrong answer to.
标准模型无法给出正确答案的试验
And there are some hints that this is happening.
有一些迹象表明这一切正在实现
Because only then can we get clues about what lies beyond.
因为只有这样我们才能得到关于更多未知领域的线索
One of the open questions about the Standard Model
关于这个模型的一个悬而未决的问题是
is whether the three fundamental forces are actually different
这三种基本力量是否是本质不同的
or whether they are a manifestation of a single all-encompassing force.
或者 是否存在一种包罗万象的力 可以囊括这三者
This is the dream of a Grand Unified Theory.
这就是大统一理论的理想情况
There are some theoretical signs that this may be the way things work out
某些理论表明 事情可能就是这样的
but so far no experimental confirmation.
但到目前为止还没有实验可以证实
Of course, we’re also left with the obvious thing that’s missing:
当然 我们还缺了一个显而易见的东西
that’s gravity
那就是引力
At the beginning of the video, I talked about the problem of quantum gravity.
视频一开始 我就谈到了量子引力的问题
In recent years we’ve discovered gravitational waves
近些年 我们发现了引力波
which are ripples of space and time itself.
它是空间和时间本身的涟漪
And, if we look closely,
如果我们仔细观察
there are good reasons to believe that these waves are made of quantum particles
就有足够的理由相信 这些波是由量子粒子组成的
that we call gravitons
我们称之为引力子
just like light waves are made out of photons.
就像光波是由光子组成的一样
There are other things missing too.
缺漏的地方还有一处:
the Standard Model doesn’t include the invisible realm of dark matter and dark energy
标准模型不包括暗物质和暗能量这些不可见领域
which means that we’re missing an explanation
这意味着我们对宇宙中
for a whopping 95% of the energy in the universe.
高达95%的能量的无法给出解释
Dark matter is almost certainly made up of additional particles
几乎可以肯定 暗物质由别的粒子组成
that don’t interact with electromagnetism.
它们不与电磁相互作用
Perhaps these particles have their own forces and their own messenger bosons.
也许这些粒子有自己的力和自己的信使玻色子
And there are still more questions about the Standard Model
关于标准模型还有很多问题
that we just don’t know how to answer.
我们尚不知如何解答
Why is the muon 200 times heavier than the electron,
为什么μ子质量是电子的200倍
while the top quark is almost 350,000 times heavier than the electron?
而顶夸克的质量几乎是电子的35万倍?
Why are the neutrinos a million times lighter?
为什么中微子要轻一百万倍?
We have no idea.
我们完全不知道
We have no way of predicting the masses of these particles
我们没有办法预测这些粒子的质量
other than going out and measuring them in experiments.
除非我们在实验中去测量
But there are clearly patterns within these masses of particles
但是显然 这些大量的粒子存在某种模式
which strongly suggest that there is some underlying structure just waiting to be uncovered.
这是存在潜在结构的有力信号 有待进一步揭示
The hope is, with experimental results going hand in hand with new theoretical ideas
我希望随着实验结果与新的理论观点携手并进
we will ultimately be able to reveal the next layer of reality
我们最终将能够揭示下一层现实的面纱
and understand what lies beyond the Standard Model.
理解标准模型之外更多的世界
Until then, we continue Galileo’s journey,
在那之前 我们会继续伽利略的旅程
with the ultimate goal
致力于他的终极目标:
a theoretical framework to explain the universe and everything in it.
一个能够解释宇宙万物的理论框架
a theory of everything.
一个万物理论

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视频概述

你,我,日月星辰都是怎么构成的?宇宙的基本组成部分是什么?这些人类自诞生之日起就不断探索的谜团,一个公式就能解答!

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翻译译者

金香木花

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审核员IBRT

视频来源

https://www.youtube.com/watch?v=Unl1jXFnzgo

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