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关于暗物质我们还知道什么?

What We (Don't) Know About Dark Matter

“暗物质”一词在过去笼统地指天文学家看不到
The phrase “dark matter” used to just be a catch-all term for anything astronomers
但他们知道确实存在的一些物质 比如说不对外辐射光线的星云之类
couldn’t see, but they knew had to be there, like a nebula that didn’t emit light.
但是现在 暗物质有了更具体的范畴:它是宇宙中占84%的那些
But these days, it’s something more specific: it’s the 84% of matter in the universe
我们所不知道的物质
that we don’t understand.
我们所有试图解释暗物质的理论都以失败告终
And all our best ideas to explain it have run straight into walls.
早在上世纪七十年代 天文学家是
Astronomers discovered dark matter back in the 1970s,
基于一些星系运动和旋转的方式而发现了暗物质
based on the way galaxies moved and rotated.
天文学家认为 如果恒星和气团的引力是使那些星系不会相互飞离的
They went way too fast for the gravity from the stars and gas astronomers saw to be the
唯一作用力 那么星系的运动速度过于快了
only thing keeping those galaxies from flying apart.
似乎这里一定有一些不可见的物质 而它无法被我们直接观察或探测得到
It seemed like there must be extra, invisible matter that we can’t see or detect directly
因为它既不产生光线 又不吸收或是反射光线
because it didn’t produce or absorb or reflect light.
我们观测到的只有它的引力作用
All we see is its gravitational pull.
有一段时间 一些人怀疑观测有偏差
For a while, some people doubted the observations,
而另一些人则开始思考也许我们弄错了引力的作用规律
and others started thinking maybe we were wrong about how gravity works.
但是在这一点上 大多数宇宙学家认为 我们必须接受
But at this point, most cosmologists agree that we just have to accept that there’s
在那里的不可见的物质构成了宇宙的主体部分 这一观点
invisible matter out there making up the majority of the universe.
因为证据不断堆积
Because the evidence keeps piling up.
每一件事物 从整个宇宙的演变到“大爆炸”之后残余信号
Everything, from the evolution of the entire universe to the leftover signals from the
似乎都在嚷嚷着 “暗物质”
Big Bang, seems to scream, “DARK MATTER.”
但是基于现存的所有证据
But despite all the evidence that exists,
我们仍然不知道暗物质的组成是什么
we still don’t know what dark matter is made of.
有部分科学家依然试图巧妙地微调我们所掌握的数学知识
There are some scientists still trying to subtly tweak the math we use
来描述引力作用使之符合所有的这些观测结果
to describe gravity so it fits all these observations,
而非假设这里有一堆不可见的物质
without assuming that there’s a bunch of invisible matter out there.
他们的研究内容被称作“MOND” 即“修正的牛顿动力学”
They work on what’s called MOND: MOdified Newtonian Dynamics.
他们已经能使用由他们修正过的物理学定律来解释
They’ve been able to use their reworked laws of physics to explain
部分作为暗物质存在证据的现象
some of the things that seem like evidence for dark matter.
但是像子弹星系团——两个对撞的星系——这样的物体
But objects like the Bullet Cluster, a pair of colliding clusters of galaxies where there
在这里 暗物质似乎与普通物质完全分离
seems to be dark matter completely separated from regular matter,
至少目前 超出了“MOND”理论的解释范围
really took the wind out of MOND’s sails, at least for now.
大多数宇宙学家承认 暗物质就在那里
Most cosmologists accept that dark matter is out there,
他们希望能够通过测算得出它是什么物质
and they want to figure out what it is.
通过审视 大爆炸后宇宙是如何演变 这一问题所模拟出的各类模型 他们已经
By looking at different models for how the universe developed after the Big Bang, they’ve
发现许多不同种类的物质 他们数量庞大而且足够黑暗
found lots of different kinds of objects that could be plentiful and dark enough
来解释这些观测结果
to account for the observations.
关于这个问题 这里有两种主要的思路
There are two main lines of thought on this,
我们只需将它们称作“旧物理学”和“新物理学”
which we’ll just call “old physics” and “new physics”.
“旧物理学”团队想要解释的是暗物质是由我们已知存在的物质组成的
The “old physics” crew wants to explain dark matter with stuff we already know exists.
他们中的某些人认为暗物质就同其字面意思一样:即黑暗的常规物质 像
Some of them think that dark matter is literally that: Regular matter that’s dark, like black
黑洞或是中子星或是被称为“失败的恒星”的褐矮星
holes or neutron stars or failed stars known as brown dwarfs.
这些都被称作“MACHO”
All of these are called MACHOs, with an M. Not the delicious snack.
它指的是“巨型密集晕状物”
It stands for MAssive Compact Halo Objects.
“MACHO”自身不发光 如果有 也很少
MACHOs produce little, if any, light of their own,
所以这就能说得通 我们所能观察到的只有它们的引力
so it would make sense if all we could see was their gravity.
但事实是 当研究者运用精密的望远镜进行更加细致的观察时 他们
Thing is, when researchers have looked more carefully with sensitive telescopes, they
没能发现附近任何地方有足够的“MACHO”来解释所有的暗物质
haven’t seen anywhere near enough MACHOs to explain all of the dark matter out there.
在“旧物理学”阵营里的其他人曾认为 暗物质是由中微子构成的
Other people in the “old physics” camp used to think dark matter was made of neutrinos:
中微子是一种如鬼魅般无形的亚原子粒子 一般产生于
ghostly subatomic particles that come out of processes
比如说 恒星内部发生的核反应
like the nuclear reactions that happen in stars.
中微子不发光 而且它们几乎不与其它物质相互作用
Neutrinos don’t produce light, and they barely interact with other matter at all,
这使得它们成为暗物质的完美候选品
which made them a great candidate for dark matter.
而且他们几乎没有质量 但即便每个中微子个体非常轻
They also have almost no mass, but even though each individual neutrino is incredibly light,
当它们数量很多时 其质量也会叠加
the mass would add up, as there are a lot of them.
如果有足够的中微子在那里 它们可以说明所有这些额外的引力
If there are enough neutrinos out there, they could explain all that extra gravity.
但是这里有一个问题:我们所知的中微子运动速度过快以至于无法聚集成团
But there’s a problem: the neutrinos we know about move way too fast to clump together
而我们观察到的暗物质则是聚集在一个巨大的结构内 就像星系一样
the way we’ve seen dark matter clumped together in huge structures like galaxies.
这使我们来到“新物理学”阵营:这些科学家正在寻找
Which brings us to the “new physics” camp: scientists who are looking for
新的微粒种类 并用它们来预测我们所观察到的现象
new kinds of particles that predict what we see.
他们中的许多人正在寻找“WIMP” 或者说是“弱相互作用大质量粒子” 如此取名
A lot of them are looking for WIMPs, or Weakly Interacting Massive Particles, so named because
的原因是它们和常规物质的相互作用十分微弱
they only interact very weakly with normal matter.
这将解释了为什么我们很难探测到它们的存在
Which would explain why it is so hard for us to detect them.
在研究者们看来 许多种类的“WIMP”都有可能是暗物质
There are lots of types of WIMPs that researchers think could be dark matter,
而且他们通过不断做实验来寻找它们
and they keep doing experiments to look for them.
但是他们从未找到任何这样的物质 并且随着每一个实验的进行
But they’ve never found any, and with every experiment,
他们排除了越来越多种类的“WIMP”
they keep ruling out more and more types of WIMPs.
另一种可能性是 我们错过了某些有关中微子的事情
Another possibility is that we’re missing something about neutrinos.
一些科学家认为 这里可能存在着某种新型超重中微子 而我们只是
Some scientists think there might be a new kind of super-heavy neutrino that we just
尚未发现而已 因为这样 你就不需要数量和轻型中微子相同的
haven’t detected yet, because you wouldn’t need as many heavy neutrinos
超重中微子来解释暗物质的存在
to account for dark matter as you would light neutrinos.
这有点像如何只用少量大的炸土豆片伴以许多配料
Sort of like how it only takes just a few large chips with lots of toppings to fill
而非用一大堆小的炸土豆片来填饱你的肚子
you up instead of just a bunch of little tiny chips.
我不知道我们怎么就回到了烤干酪辣味玉米片
I don’t know how we got back to nachos.
是我饿了吗?
I’m hungry?
不管怎样 如果这里一开始就不存在大量超重中微子
Anyway, if there aren’t as many heavy neutrinos out there to begin with,
之后这就能说得通 我们为何尚未发现这种微粒
then it would make sense that we haven’t spotted any yet.
支持“新物理学”的人们还认为 轴子可能是关键
There are also “new physics” people who think axions might be the key.
轴子是1970年代预测的微粒
Axions are particles that were predicted back in the 1970s
用来解决物理学上的一个同暗物质毫不相关的问题
to solve a completely unrelated problem in physics.
但和中微子一样 它们也几乎没有重量而且难以发现 而且一些模型
But like neutrinos, they’d also be almost weightless and hard to detect, and some models
显示 部分或甚至全部的暗物质可能是由轴子构成的
suggest that some or even all dark matter could be made of axions.
随后 一些真正思想活跃的物理学家着手研究一个想法叫做超对称性
Then there are the really creative physicists who are working on an idea called supersymmetry,
在此 宇宙中的每一个微粒都对应一种孪生的重型粒子
where every particle in the universe has a kind of heavy twin,
而这其中的某一种孪生粒子将会是暗物质
and one of those twins would be dark matter.
一些研究者甚至认为
There are even some researchers who think
我们所看到的不过是平行宇宙对我们进行干扰的结果
we’re seeing the effects of parallel universes messing with ours.
但是 又一次 这里没有任何直接证据证明任何这些新想法
But, again, there is no direct evidence for any of these new ideas.
没有人见过超重中微子 也没有人见过轴子
No one has seen a super-heavy neutrino, no one has seen an axion,
没有人见过超对称的孪生粒子 同样也没有人见过平行宇宙
no one’s seen a supersymmetric twin, and no one has seen a parallel universe.
实验已经排除了超重中微子和超对称性的最简单的模型
Experiments have ruled out the simplest models of heavy neutrinos and supersymmetry,
而且实验还排除了轴子这一解释
and they’ve ruled out axions as an explanation
至少对暗物质的主要组成部分而言 无此可能
for at least the majority of dark matter out there.
所以现在 我们卡住了
So for now, we’re stuck.
全世界的科学家尽全力工作
Scientists around the world are working as hard as they can
来更好地了解暗物质 从那些整日熬夜在望远镜下的
to understand dark matter better, from the ones staying up all night at the telescope
到那些整日熬夜在黑板前的科学家
to the ones staying up all night at the blackboard.
但是正如它现在所表明的 宇宙中占绝大多数的物质
But as it stands right now, the vast majority of the matter in the universe
仍然是一个完完全全的谜团
remains a complete mystery.
本期节目灵感和内容皆源于《我们不知道》
This episode was inspired by and brought to you by We Have No Idea,
这是一本由豪尔赫·可汗和丹尼尔·怀特森所作的新书
a new book by Jorge Cham and Daniel Whiteson.
《我们不知道》一书将卡通和幽默同严肃的科学相结合 探究了暗物质的
Mixing cartoons and humor with serious science, We Have No Idea explores the mysteries of
谜团以及许多其它有关宇宙的开放性问题
dark matter and lots of other open questions about the universe.
如“这里有多少种维度?”或是“为什么我们不由反物质组成?”
Like “How many dimensions are there?” or “Why aren’t we made of anti-matter?”
这本书已经发售 你可以在wehavenoidea.com上订购
The book is available now, and you can get your copy at wehavenoidea.com.

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视频概述

有关暗物质的几种设想,及其相关的外延知识

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视频来源

https://www.youtube.com/watch?v=1pq9hovXI44

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