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Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to learn more.
感谢Brilliant对本期节目的支持。登录Brilliant.org/SciShow了解更多。
In nature, most of our basic forces both attract and repel. In fact, gravity is the only exception.
在自然界中，我们的大多数基本力量既相互吸引又相互排斥。事实上，重力是唯一的例外。
As far as we can tell, anything gravity acts on just goes one way: down. As long as there's no other forces involved, anyway.
据我们所知，重力作用的任何东西都是单向的：向下。只要没有其他力量参与。
But there is actually an exception to the exception. On a teeny-tiny scale, we're exposed to negative gravity every day.
但有一个例外中的例外。在极小的范围内，我们每天都暴露在负重力下。
Because, according to theorists, sound waves, of all things, have negative gravity.
因为，根据理论学家的理论，在所有的事物中，声波具有负重力。
And what's even more amazing is that you don't need fancy science like quantum mechanics or general relativity to understand why.
更令人惊奇的是，你不需要像量子力学或广义相对论这样神奇的科学来理解其原因。
You can understand real-life negative gravity using classical physics; the stuff you probably learned in high school.
你可以用经典物理学来理解现实生活中的负重力；你可能在高中学过。
Now, I know the idea that gravity acts on sound at all might seem a little sketchy, because sound waves aren't some special kind of matter.
我知道重力作用于声音的想法可能看起来有点粗略，因为声波不是某种特殊的物质。
They're just vibrations: the scrunching up and stretching out of molecules like those in the air.
它们只是振动：就像空气中的分子一样，会弯曲和伸展。
Still, scientists argue that you can think of them as particles. Kind of like you can think of light as particles, or photons.
尽管如此，科学家认为，你可以把它们看作粒子。就像你可以把光想象成粒子，或者光子。
In sound, though, they're called phonons. Phonons aren't like electrons or molecules or any other particles you're familiar with.
在声音中，它们被称为声子。声子与电子或分子或其他你熟悉的粒子不同。
They're essentially packets of energy moving at a similar speed.
它们本质上是以相似速度运动的能量包。
As a sound wave passes through the air, molecules speed up as they squish together and slow down as they spread out.
当声波通过空气时，分子在挤压时加速，在扩散时减速。
And a phonon is a tiny packet of those vibrations. So it's not exactly a single physical particle. It's more like a flock of birds.
而声子就是这些振动的一小部分。所以它不是一个单一的物理粒子。它更像是一群鸟。
A flock is just a bunch of individual birds, but you can still identify it as its own unit.
鸟群是一群单只的鸟，但你仍可以将它定义为单位。
And that's the idea with phonons as well. It's like a "flock" of vibrations that emerge from a sound wave.
声子也是如此，就像一群由声波产生的振动。
The weird thing about these phonons is, according to theory, they move upward in a gravitational field.
这些声子的奇怪之处在于，根据理论，它们在重力场中向上运动。
It might seem like that just shouldn't happen; that's not how gravity works.
这似乎是不应该发生的，重力不是这样的。
But the reason is actually pretty straightforward. Picture a sound wave moving through the air.
但原因其实很简单。想象一个声波在空气中移动。
Air pressure is slightly greater at the bottom of that wave than at the top, because the lower air is denser.
声波底部空气压力比顶部稍高，因为底部的空气密度更大。
It's just like how water pressure is greater near the ocean floor than it is near the surface.
就好像海底附近的水压比海面附近的水压大一样。
Since sound vibrations travel faster through denser fluids,
由于声音振动在密度更大的流体中传播得更快，
the bottom of the sound wave, where the air is under a lot more pressure, travels faster.
所以在空气压力更大的声波底部传播得更快。
And that makes the whole thing bend up. Just ever-so-slightly.
所以所有事物向上弯曲，轻微弯曲。
That means the sound wave, and the phonons that make it up, are going against gravity.
这意味着声波以及组成声波的声子，都是反重力的。
In other words, phonons have negative mass. Because anything with a positive mass would get pulled down.
换句话说，声子有负质量。因为任何质量为正的物体都会被向下拉。
This is an actual, physical effect, not just an illusion. It's not like an airplane taking off, or a bird flying, either.
这是真实的物理效应，不是幻觉。它不像飞机起飞，也不像鸟儿飞翔。
Gravity is still pulling down on those things, even as they move up. But sound waves are actually falling up.
重力仍然在向下，即使它们向上运动。但声波实际上是上升的。
And that comes with some pretty wild consequences.
这带来了一些非常严重的后果。
The first thing is, over large enough distances, all sound waves should curve upward.
首先，在足够长的距离内，所有的声波都应该向上弯曲。
This probably wouldn't have any real-world impacts, like, it's not going to change how we communicate.
这可能不会对现实世界产生任何影响，比如，它不会改变我们交流的方式。
The amount of predicted curving is so small that we don't even have instruments sensitive enough to detect it.
预测曲线的数量是很小，我们甚至没有足够灵敏的仪器来检测它。
But scientists think this effect could be more relevant in objects like neutron stars,
但科学家认为这种效应可能与中子星等物体更相关，
where sound waves travel through super-dense fluids. There, phonons could significantly affect the star's behavior.
在中子星中，声波穿过超密流体。在那里，声子可以显著地影响恒星的行为。
But that's not the end of the story, either.
但故事还没完。
Because on top of defying gravity themselves, sound waves should also push away anything with mass.
因为声波除了自身对抗重力之外，还会把任何有质量的物体推开。
See, anything with mass has gravity. And not just big things, like, you have your own gravitational field.
任何有质量的东西就有重力。不只是大的东西，比如，你也有自己的重力场。
And so do phonons. Except, since phonons have negative mass, they also have negative gravity.
声子也一样。除了，因为声子的质量是负的，所以它们的重力也是负的。
Meaning they should repel anything with mass.
这意味着它们应该排斥任何有质量的物体。
Again, we don't have the technology to measure this kind of effect yet, since gravity is pretty weak on a microscopic level.
我们没有技术可以测量这种效应，因为重力在微观层面上非常弱。
But this is still fascinating. And this weird behavior is all based on pretty simple, old-school physics;
这仍然令人惊叹。并且这种奇怪的行为基于非常简单的，老派的物理理论
stuff that's been sitting right in front of us for literally hundreds of years.
这些理论已经存在好几百年了。
So, what do you know? It turns out, now and then, old physics can do new tricks.
事实证明旧的物理学有时也能变出新花样。
If you're the kind of person who likes using what you know to figure out new things about the world, you might also like courses offered by Brilliant.
如果你是那种喜欢用知识探索世界新事物的人，那么你或许会喜欢Brilliant的课程。
Brilliant offers courses in science, engineering, and math, and they're designed by professors at institutions like MIT, Caltech, and Duke.
Brilliant提供科学、工程和数学课程，均由麻省理工学院、加州理工学院和杜克大学的教授设计。
The courses are hands-on, with interactive quizzes and guided problems with explanations.
这些课程是实践性的，包括互动测验和带解释的指导性问题。
Brilliant courses are also available offline on their iOS and Android app, so you can keep learning when you're on the go.
Brilliant的课程还能在他们的iOS和Android应用程序上离线学习，所以你可以在忙碌的时候继续学习。
To find out more, head over to Brilliant.org/SciShow.
登录Brilliant.org/SciShow了解更多。
If you're one of the first 200 people to sign up at that link, you'll get 20 percent off an annual premium subscription!
前两百米注册的用户，可获得年度会员八折优惠！
And as always, thanks for watching SciShow.
一如既往，感谢收看。
