(单词翻译:单击)
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 。