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If you like cosmology, you've probably seen this picture before.
如果你对宇宙学感兴趣，那你应该看过我接下来描述的这个景象：
It's called the Cosmic Microwave Background, or the CMB, and it's a false color image of the oldest light in the universe that physics allows us to see.
也就是宇宙微波背景辐射(CMB)，它是宇宙里年头很长的光线所产生的彩色图像的假象，由于物理学的原理，可以被人类看到。
It's a baby photo from when space was around 400,000 years old.
宇宙微波背景辐射是宇宙走过了大概40万年时候的一张婴儿照片。
But it is not the oldest image we might one day capture.
但它可能并不是人类可以捕捉到的年头最长的图像。
There's another, elusive cosmic background created by some of the most mysterious particles physics has described: neutrinos.
还有另一种难以捉摸的宇宙背景辐射，它与最为神秘的粒子物理学有关：中微子。
Appropriately, it's called the Cosmic Neutrino Background.
这种情况叫做宇宙中微子背景辐射。
And if astronomers are able to snap a photo of it, well, it'll open up a treasure trove of knowledge about the universe when it was only a second old.
如果天文学家能够拍摄这种辐射的图像，就可以让我们了解到许多有关宇宙的情况，比如宇宙只有现在一半大时候的情况。
Both the CMB and its neutrino counterpart have to do with a phenomenon called decoupling.
无论是宇宙微波背景辐射还是宇宙中微子背景辐射都与一种叫做去耦合的现象有关。
These were moments when certain particles stopped interacting with the rest of the matter in the universe, and could stream through space without, for the most part, hitting anything.
有时候，一些特定的粒子会不再与宇宙里的其他物质相互作用，它们可以穿梭宇宙而不会撞击到任何物体。
See, at the moment of the universe's birth, it was so hot that everything was just a soup of fundamental subatomic particles and light.
在宇宙混沌之初，温度极高，所以任何事物都像是一锅由亚原子粒子和光线组成的汤。
Then, as space expanded, temperatures started dropping, and particles started slowing down.
随后，随着宇宙的扩张，温度开始下降，粒子也开始减速。
Eventually, that allowed the formation of protons and neutrons, then atomic nuclei, and then atoms as a whole. And so on and so forth.
最后，就促成了质子和中子的形成，然后是原子核，再然后是原子，等等。
The Cosmic Microwave Background formed when photons separated from this soup.
宇宙中微子背景辐射会在质子脱离出这锅汤的时候形成。
For the first several hundred thousand years, there were so many lone electrons zipping around that the universe was opaque, because photons couldn't travel very far before getting scattered.
在宇宙形成后的头几百年间，有很多单独的电子在宇宙里快速移动，导致宇宙变成了不透明的，因为质子只有在分散的情况下才能走得很远。
Then, as the universe grew, the density of these free electrons decreased.
随后，随着宇宙的扩张，这些自由质子的密度变小。
Many also started getting locked up into newly-formed atoms, so the average time between photon scattering increased.
很多质子就被锁在了新形成的原子中，所以质子分散的平均时耗就加长了。
And 380,000 years after the Big Bang, light was able to stream unimpeded through the universe.
宇宙形成38万年后，光线终于可以不受阻碍的穿梭宇宙间。
Scientists say that this is when photons decoupled from matter.
科学家认为，这时候正是质子与宇宙里的物质发生去耦合作用的时候。
And images of the CMB show us that moment.
宇宙微波背景辐射的图像向我们展示了这一时刻。
But photons weren't the first particles to separate from the primordial soup.
但质子并非与这锅汤分离的唯一粒子。
When the universe was only a second old, neutrinos high-tailed it outta there, freely flying through space.
当宇宙只有现在一半大的时候，中微子发生了迅速逃离，并在宇宙间自由穿梭。
They produce their own background radiation distinct from the CMB, called the CνB, or CNB. The Cosmic Neutrino Background.
中微子产生了自己的背景辐射，这种辐射与宇宙微波背景辐射不同，它的名字叫CνB，也就是CNB——宇宙中微子背景辐射。
Neutrinos are in the same family of particles as electrons.
中微子跟电子一样，同属粒子的大家族。
But unlike electrons, they're really hard to detect because they almost never interact with anything.
但跟电子不同的是：中微子很难被我们探测到，因为中微子几乎不与任何事物接触。
Like, you literally have trillions of them streaming through your body right now.
比如，中微子可以在人毫不察觉的情况下穿过人的身体。
To neutrinos, even entire planets mean nothing.
对中微子来说，即便是行星摆在面前，它也不会放在眼里。
This is why they were able to decouple from matter much faster than photons did.
因此，中微子可以与物质发生去耦合作用，速率要比质子的去耦合作用更快。
They only had to wait for the universe to cool to 35 billion Kelvin, as opposed to a few thousand.
唯一的条件是：中微子需要等到宇宙的温度降低到350亿开氏度的时候才行，几千度根本不够
At that point, things were moving slowly enough, relatively speaking, that neutrinos stopped crashing into other particles all the time.
一旦这个条件达到，物体的移速就会变得非常之慢，这样的话，相对而言，中微子就不会一直撞击到其他粒子的身上。
Now, it's worth noting that not all neutrinos were made in the Big Bang.
现在有一点值得注意：并非所有的中微子都是由宇宙大爆炸产生的。
They're also produced by stars as they undergo nuclear fusion, and by your own body as certain radioactive atoms decay.
恒星在经历核聚变的时候以及人体在放射性原子腐朽的时候也会产生中微子。
But cosmic neutrinos are a lot sneakier.
但宇宙里的中微子更神秘一些。
And right now, we don't have technology sensitive enough to find direct evidence of them.
而现在，我们还没有足够灵敏的技术，所以无法找到中微子在宇宙存在的直接证据。
Our current detectors can isolate neutrinos with energies on the order of 0.1 Megaelectron volts, but that's over a billion times more energetic than cosmic neutrinos.
我们当前的探测器可以将中微子与能量隔绝在0.1兆电子伏的级别，但这样的能量是宇宙中微子的10亿多倍。
So we're working on indirect detection.
所以我们还在寻找间接探测的方式。
And there are a couple ways we can do that.
有几种途径可以实现间接探测：
First, there's studying the CMB for any subtle imprints the CnuB may have made.
也有科学家在研究宇宙微波背景辐射，想通过这种方式来了解宇宙中微子背景辐射是否留下了某些痕迹。
Basically, after neutrinos decoupled but before photons did, the neutrinos would have created tiny sonic booms in the primordial soup.
中微子在发生去耦合作用以及质子发生去耦合作用之前，中微子会在宇宙的这一大锅汤里产生小型音爆。
They would've produced regions that were slightly hotter or colder than others nearby.
音爆会产生一些区域，这些区域的温度比其他区域高或者低。
So far, some papers have reported detecting cosmic neutrinos' influence on the CMB.
目前为止，一些论文已经报道过探测到宇宙中微子对宇宙微波背景辐射的影响。
A 2005 report in Physical Review Letters used data from the WMAP satellite and the Sloan Digital Sky Survey.
2005年，《物理评论快报》上发表了一篇报道，其中用到了微波各向异性探测器以及史隆数位巡天探测到的数据。
And Planck telescope data provided less ambiguous results a decade later.
10年后，普朗克望远镜提供的数据更加准确。
It doesn't confirm anything for sure yet, but it is a promising start.
但准确的数据无法为我们证实什么，只能说明这是一个良好的开始。
The other indirect detection method requires monitoring the radioactive decay of tritium.
其他不直接探测的方式都需要监控氚的放射性衰变。
That's a hydrogen atom with two extra neutrons in its nucleus.
这是一种氢原子，其原子核里有2个额外的中子。
Tritium naturally decays by emitting an electron, but it can be forced to decay faster than usual if it absorbs a neutrino.
氚在发生自然衰变的时候会放射电子，但它在吸收了中微子后，会不得已以比往常更快的速度发生衰变。
In that case, the electron it emits has a measurably different energy.
这样的话，它释放的电子就会产生完全不同的能量。
That energy actually depends on the energy of the neutrino that was absorbed.
这个能量大小实际上取决于所吸收中微子的能量。
So by tracking it, physicists would be able to tell the difference between the tritium absorbing a cosmic neutrino, or one from another source.
所以，如果能跟踪这一点，物理学家就能发现吸收宇宙中微子和未吸收宇宙中微子的氚之间的区别。
The problem with this method, though, is scale.
这种方法存在的问题也不小。
Because the energy of cosmic neutrinos is so low, and our detectors aren't very large or sensitive, we can only hope for a single detection a month. If that.
由于宇宙中微子的能量很低，而我们的探测还不够大，也不够灵敏，所以探测工作每个月最多也只能做一次。
The KATRIN experiment in Germany, for example, uses 20 micrograms of tritium.
比如，德国卡尔斯鲁厄氚中微子就使用了20毫克的氚。
And under the most ideal of conditions they estimate they'll get 1.7 hits a year.
他们估测，在最理想的情况下，每年可以得到1.7次撞击。
The PTOLEMY experiment at Princeton, on the other hand, is currently operating a prototype device to track even more neutrinos.
而普林斯顿的托勒密试验正在通过一种标准仪器来追踪更多的中微子。
It involves a detector the size of a postage stamp made of a single, atom-thick layer of tritium on top of an atom-thick layer of carbon.
试验中要用到的探测器，其大小跟邮票差不多，它是由一个单独的、只有原子薄厚的一层氚摞在一个只有原子薄厚的碳层上组成的。
Ultimately, they hope to expand their amount of tritium up to 100 grams, where they might capture 10 cosmic neutrinos a year.
他们的最终目标是将氚的质量提高到100克，这样的话，每年就能捕捉到10个宇宙中微子了。
So we'll see.
让我们拭目以待吧。
There's a ton of effort and money going into these techniques, but scientists aren't doing it just for the thrill of the hunt.
这些技术都需要倾注大量的工作和资金，但科学家做这些并不只是为了探险。
Finding cosmic neutrinos would push back how far into the universe's history we can actually observe.
如果能找到宇宙中微子，就能再将人类可以探究的宇宙历史跨度扩大一些。
Right now, math can take us back further than the CMB, but we don't have the experimental data to confirm it.
目前，数学手段让我们可以探究到宇宙微波背景辐射之外的物体，但我们没有实验数据来证实这些。
It's all hypothetical.
这些都只是我们的假设而已。
The CnuB would push us back to a time where matter and light readily interacted.
宇宙中微子背景辐射可以将我们带回一个物质与光线容易发生作用的时段。
And knowing more about these cosmic neutrinos would inform astronomers how what we normally think of as anti-social particles actually affected the structure of the universe.
如果能对宇宙中微子了解得更多，天文学家就能知道我们眼中的反社会粒子是如何影响宇宙结构的。
So thanks, cosmic neutrinos currently flying straight through my… yep. There they go. Through the entire planet.
所以，还是要感谢宇宙中微子，没准他们现在就在不断穿过我的身体、穿过整个宇宙……没错，一定是这样。
What are you going to do?
大家怎样看呢？
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
If you'd like to learn more about the Big Bang, you can watch our episode about the first few moments of the universe that physics can't quite explain.
如果您想了解与宇宙大爆炸有关的内容，我们有一集是有关宇宙初期一些物理学无法解释的现象。
