评论
打印
Generally speaking, astronomers tend to study the biggest stuff in the universe, while particle physicists study the smallest.
一般来说，天文学家倾向于研究宇宙中最大的物质，而粒子物理学家则研究最小的物质。
But over the last few years, astronomers have done more and more research on a certain prediction made by string theory --
但在过去的几年里，天文学家们对弦理论做出的预测做了越来越多的研究
one of the most popular unproved ideas in all of physics.
弦理论是物理学中最流行的未经证实的观点之一。
And let’s just say their results haven’t been very encouraging so far.
我们只能说研究结果不尽如人意。
The hope was that this might change after a new study from NASA’s Chandra X-Ray Observatory,
希望美国宇航局钱德拉X射线天文台的一项新研究能够改变这一点，
which tried to find evidence for string theory using galaxy collisions.
他们试图利用星系碰撞来寻找弦理论的证据。
But so far, things aren’t looking promising.
但到目前为止，情况看起来并不乐观。
This new study was published last month in The Astrophysical Journal, and it has three key pieces.
上个月，这项新研究发表在《天体物理学杂志》上，它有三个关键部分。
There’s the string theory. There’s the astronomy.
有弦理论。有天文学。
And there’s the family of hypothesized particles that ties them all together: a group called axion-like particles.
还有把它们联结在一起的假设粒子:一类叫做类轴粒子的物质。
But first, the string theory.
首先来说弦理论。
String theory is one of the major candidates for what’s called a “Theory of Everything”:
弦理论是所谓“万物理论”的主要候选理论之一:
a single framework that could predict the results of any experiment we could ever do.
“万物理论”是指一个可以预测我们能做的任何实验结果的单一框架。
Our best theories currently split the universe into the big stuff that’s governed by gravity, and small stuff that’s modeled by quantum mechanics.
目前，我们的最佳理论把宇宙分成由引力控制的大物质和由量子力学模拟的小物质。
Both models are great in their own domains, but try to make them overlap, and funky things can happen.
这两种模式在各自的领域都很出色，但如果让两者重叠，就会发生一些奇怪的事情。
For instance, if you try to study gravity on the tiniest scales, any little bit of gravity should make more gravity around it.
例如，如果你试图在最小的物质上研究重力，那么任何一丁点儿重力都会使它周围产生更多重力。
So gravity should make more gravity, should make more gravity --
所以重力会产生更多的重力，再产生更多的重力
until you end up with an infinitely dense point where math doesn’t work.
直至达到一个无限稠密的点，连数学都不起作用了。
But in string theory, that can’t happen.
但在弦理论中，这是不可能的。
String theory supposes that all particles are actually made of tiny, vibrating strings.
弦理论认为所有的粒子实际上都是由微小、振动的弦构成的。
And to make a simplification, since those strings have a sort of length, their interactions can never create a single, infinitely dense point.
简单来说就是，因为这些弦有一定的长度，它们的相互作用永远不会产生一个单一、无限密集的点。
And that stops the chaos.
这样就不会出现混乱。
Different theorists find different ways to go from this stringy foundation to a universe like ours,
不同的理论学家有不同的方法，从这种稠密的基础到我们的宇宙，
so there are multiple versions of string theory out there.
所以弦理论有很多种说法。
But many of them require certain kinds of new, unobserved particles to work.
但是它们中的许多说法都需要有某种新的、未观察到的粒子来运作。
Including some small, super-light ones.
包括一些特别小、超级轻的粒子。
They’re known as axion-like particles, or ALPs.
它们被称为类轴粒子，简称ALP。
If they exist, ALPs would be so light that they’d hardly ever bump into any other kind of matter,
如果它们真的存在，ALP会非常轻，轻到几乎不会撞上任何其他物质，
which would explain why we’ve never seen one in an experiment.
这就解释了为什么我们从来没有在实验中看到过它。
But a lot of researchers still think they’re out there,
但很多研究人员依然认为它们是存在的，
because ALPs seem like the perfect missing pieces to many puzzling aspects of the universe.
因为对宇宙中许多令人困惑的方面来说，ALP似乎是完美缺失的那一部分。
They’re good candidates for dark matter, they could be why the universe has more matter than antimatter,
它们是暗物质很好的候选者，它们也可以解释为什么宇宙中的物质多于反物质，
and they might even explain why time only ticks in one direction!
它们甚至还能解释为什么时间只在一个方向上走动!
But we still haven’t seen them.
但我们仍然从来没有见过ALP。
The good news is, human-run experiments aren’t the only places to look.
好消息是，人类实验并不是唯一值得关注的地方。
According to string theory, ALPs should occasionally turn into photons, or particles of light, as they travel through a magnetic field, and vice versa.
根据弦理论，在穿过磁场时，ALP偶尔会变成光子，或光粒子，反之亦然。
And for astronomers, that’s pretty convenient, because space is full of light and magnetic fields.
对天文学家来说，这很方便，因为太空中充满了光和磁场。
So, if you looked at light after it went through one of these fields, you could look for distortions created by ALP interference.
所以，如果你观察光穿过某个磁场的时候，可以寻找因ALP干涉产生的扭曲。
And if you saw that -- well, you’d provide the evidence physicists have been looking for.
如果你看到了——那你就能提供物理学家一直在寻找的证据了。
Recently, this is exactly what a team of astronomers and cosmologists tried to do using the Chandra X-Ray Observatory.
最近，一群天文学家和宇宙学家试图利用钱德拉X射线天文台实现这一点。
They weren’t the first to look for ALPs this way, but their observations let them look more closely than anyone had before.
他们并不是第一群用这种方式寻找ALP的人，但他们的观察让他们比以往任何人都能更近距离地看到。
They used Chandra to look at light from a galaxy called NGC 1275.
他们利用钱德拉天文台观测了一个名为NGC 1275的星系发出来的光。
It’s about 230 million light-years away, and it’s a galaxy that eats other galaxies.
它离我们约2.3亿光年远，它会吞噬其他星系。
Collisions like that release tons of X-rays, and we can use models to predict what those rays should look like in an ALP-free universe as they escape the galaxies’ magnetic fields.
这样的碰撞会释放出大量的X射线，我们可以利用模型来预测当这些射线逃离星系的磁场时，它们在一个没有ALP的宇宙中会是什么样子。
In their study, the team compared what they saw from NGC 1275 with a range of ALP models -- because, remember, there’s no one model.
在他们的研究中，研究小组将他们从NGC 1275中看到的数据与一系列的ALP模型进行了比较——因为，记住，没有任何固定模型。
Some say ALPs should interact with light a lot; others say it should be pretty rare.
有人说ALP应该经常与光线互相作用；其他人则认为这种情况很少见。
And in the end… well, The light from the galaxy looked exactly like we’d expect.
最后，来自星系的光看起来和我们预期的一模一样。
The team saw no evidence of ALPs in their data.
研究小组在他们的数据中没有发现ALP存在的证据。
This doesn’t mean they aren’t out there, but the fact that even a super-sensitive telescope like Chandra couldn’t find them does effectively eliminate a big range of possible models.
这并不意味着它们不存在，但事实上，即使是像钱德拉这样超灵敏的天文台也无法找到它们，这确实有效排除了大量可能的模型。
Maybe an even more advanced telescope could change things in the future.
也许未来更先进的望远镜可以改这一切。
But again, this Chandra study isn’t the only one of its kind.
但钱德拉的研究并不是唯一的。
Over the last couple decades, astronomical teams around the world have looked for evidence of ALPs in their data, and none have found anything.
在过去的几十年里，世界各地的天文团队都在他们的数据中寻找ALP存在的证据，但都没有找到。
There are still models out there that fit everyone’s observations, but the field is thinning out fast -- making some scientists increasingly skeptical about ALPs and some of the string theories that predict them.
目前仍有一些模型符合所有人的观察，但这个领域正在迅速缩小，这使得一些科学家越来越怀疑ALP和一些预测它们的弦理论。
So axion-like particles might still exist.
所以类轴粒子也许还是存在的。
But if they do, they probably look pretty different from what we first expected.
但如果它们真的存在，那看起来可能与我们最初的预期大相径庭。
And as we eliminate model after model that resuires them, some physists may start looking for a theory with a few less strings attached.
当我们排除一个又一个需要ALP的模型时，一些物理学家可能会开始寻找一些不那么需要弦理论的理论。
Thanks for watching this episode of SciShow Space News!
感谢收看本期的太空科学秀!
If you’re interested in astronomy and want to learn more about the field as a whole, you might enjoy a series from one of our sister channels, Crash Course.
如果你对天文学感兴趣，想要更多地了解这个领域，你可以从我们的同系列频道之一《速成课程》(Crash Course)中收看更多节目。
Their Crash Course Astronomy series covers everything from stars to eclipses to big questions about things like dark energy.
那里的天文学系列速成课程涵盖了从恒星到日食再到暗能量等大问题的所有内容。
It’s hosted by the amazing Phil Plait and is just a great time.
它由超棒的菲尔·普莱特主持，内容很赞。
You can check it out after this!
大家可以去看看哦!
