How to build a dark matter detector - Jenna Saffin

翻译人员: Lipeng Chen

More than two kilometers below the surface of northern Ontario,

在安大略湖北部湖面以下超过2000米处，

suspended in 345,000 liters of ultra-pure water,

345000升超纯净的湖水中，

there’s a perfect sphere.

悬浮着一个完美球体。

It contains 3600 kilograms of liquid argon,

这个球体中含有3600千克的液态氩，

cooled to -180 degrees Celsius.

已被冷却至零下180摄氏度。

Scientists continuously monitor this chamber from above ground,

科学家们在地面上 持续不断地监控着这个球体，

looking for a glimmer of light in the darkness.

期望在黑暗之中寻找到丁点儿光亮。

Because down here,

因为在水下，

deep beneath the Earth’s surface and cocooned in a watery shield,

在地下深处被水包裹的地方，

that light would indicate the presence of one of the universe’s greatest mysteries:

亮光将有可能意味着 宇宙间最神奇的物质之一，

dark matter.

暗物质的存在。

All the matter we can see, planets, stars and galaxies,

我们能看见的所有物体，星球、星星以及星系，

doesn’t create enough gravitational pull

所产生的引力

to explain the universe’s larger structure.

都不足以解释宇宙更为宏大的结构。

It’s dark matter, which is estimated to make up 25% of the known universe.

据猜测，暗物质构成了我们所知宇宙的25%。

But despite its prevalence,

虽然暗物质普遍存在，

so far we haven’t been able to detect it directly.

但是时至今日， 我们都未能直接探测到暗物质。

It’s no small challenge.

这并非一个轻松的挑战。

Dark matter was so named because it doesn’t interact with any type of light,

暗物质之所以叫做暗物质， 是因为它并不和任何光源产生作用，

visible or otherwise,

否则它就能被看见，

which means our usual observation tools

这也意味着我们通常的探测工具

simply don’t work when trying to observe it.

在探测暗物质时并不适用。

But while dark matter may not be visible in the electromagnetic spectrum,

虽然暗物质不能在电磁频谱下被观测到，

it’s still matter,

它仍然是一种物质，

so we should be able to measure its interactions with other matter.

我们应该可以探测到它与其他物质之间的互动。

And if our current model of physics is correct,

如果我们当前的物理模型是正确的，

billions of sub-atomic dark matter particles

那么数百万的亚原子暗物质粒子

are passing through the Earth every second.

每分每秒都在地球上穿行。

Despite the prevalence of dark matter,

虽然暗物质普遍存在，

its interactions are predicted to be rare and extremely weak.

据预测它们与外界的互动十分罕见， 即便是有也很微弱。

To detect these interactions,

为了探测这类互动，

dark matter experiments need to be incredibly sensitive.

暗物质实验也将十分细微。

With such sensitive equipment,

实验采用的装置也将十分敏锐，

the ever-present background radiation on Earth’s surface

地球表面一直存在的背景辐射

would create so much noise in the data

将会对数据产生巨大的噪音干扰，

that any dark matter particles would be completely overwhelmed.

如此一来，任何暗物质粒子都会被彻底掩盖。

It would be like trying to hear a pin drop on a busy city street.

这就像是要在喧嚣的街道上 听到一枚针掉落的声音。

To solve this problem,

为了解决这个问题，

scientists have had to dig deep into the Earth.

科学家们只能深深探索地表以下。

Dark matter experiments are set up in specialized underground labs,

暗物质实验场所建立在专门的地下实验室中，

either in mines or inside mountains.

或在矿场中，又或在深山里。

The rock that makes up the Earth’s crust works like a filter,

组成地壳的岩石就像是过滤器一样，

absorbing radiation and stopping disruptive particles.

它们吸收辐射并防止对粒子产生破坏。

The ultra-pure water in which the detector is suspended

而探测器悬浮在水中，

adds an additional layer of radiation filtering.

这些水相当于又增加了一层辐射过滤网。

This shielding ensures that only the particles scientists are looking for

这些防护能够保证 只有科学家们想要寻找的粒子

can make their way into the detectors.

才能够被探测器捕捉到。

Once these particles reach an experiment’s inner vessel,

当这些粒子进入到实验容器内时，

scientists have a chance of detecting them.

科学家们就有机会检测它们。

The detector media are chosen because they’re exquisitely sensitive detectors

这些探测媒介十分敏锐，

that can be purified extremely well.

可以得到十分纯净的结果。

These could be a liquid noble gas,

这些可能是液态惰性气体、

germanium

锗、

and silicon crystals,

晶体硅、

a refrigerant,

制冷剂、

or other materials.

或是其他材料。

When radiation interacts, it leaves tell-tale signs,

辐射作用会释放出一些信号，

such as light or bubbles,

例如光亮或气泡，

which can be picked up by the sensors inside the detector.

这些信号就会被探测器中的传感器捕捉到。

The detector media are held in a central chamber made of glass

探测媒介被放置于一个由玻璃

or a special type of acrylic.

或某种特殊丙烯酸树脂制成的容器中。

These chambers have to be able to hold the substance inside

这些容器可以存放物质，

without interacting with it

但又不同其中的物质发生反应，

while withstanding incredible pressure from the water outside.

同时还能承受外界水源的巨大压力。

The inner vessel is surrounded by powerful sensors

容器内到处都是强大的传感器，

designed to detect even the tiniest blips of light,

这些传感器甚至可以 探测到最微弱的一丝亮光，

or the sound vibrations caused by a single bubble.

或者又一个气泡造成的声音振动。

Each sensor records data 24/7,

每个传感器都全天候地记录数据，

and experiments run for months and years at a time,

每次实验将持续数月甚至数年，

generating terabytes of data every day.

实验每天都会产生兆兆字节级别的数据。

Building dark matter detectors is as much a feat of engineering

打造暗物质探测器需要极为精巧的工程，

as it is a feat of physics.

正如暗物质本身也是 物理中极为精巧的一部分。

By the time an experiment is ready to start collecting data,

在投入数年甚至数十年的研究工作之后，

years or decades of work and investment have already gone into it,

实验才能做好准备，可以开始收集数据，

to the tune of tens of millions of dollars.

而此实验的投资都需要数千万美元。

As of 2017, no dark matter particles have been directly detected.

2017年，还没有暗物质被直接检测到。

That’s not entirely surprising.

这一点都不令人感到意外。

Physicists expect these interactions to be incredibly rare and difficult to detect.

物理学家们认为暗物质与外界的 互动极其稀少并且很难被检测到。

In the meantime,

与此同时，

scientists continue to develop new technologies

科学家们继续开发新的科技，

and increase detector sensitivity,

提升探测器的灵敏度，

closing in on where dark matter is hiding.

越来越向暗物质靠近。

And when they find it,

当他们寻找到暗物质时，

we’ll finally be able to bring the universe’s darkest secrets into the light.

我们则终于云开见日， 揭开了宇宙间最神秘的谜团。