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光子会投射阴影吗? – 译学馆
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光子会投射阴影吗?

Do Photons Cast Shadows?

There are plenty of objects that are good at blocking light and casting shadows,
有很多物体擅长阻挡光线和投射阴影
clouds, trees, birds, people, the moon.
比如云 树 鸟 人以及月亮
But what about light itself?
但是光本身呢?
Can photons cast shadows?
光子可以投射阴影吗?
At first glance, the answer appears to be no.
乍一看 答案似乎是否定的
Light, or photons, are electromagnetic waves
光或者光子是电磁波
and electromagnetic waves cann’t directly interact with themselves.
电磁波不会直接和自己相互作用
Other waves in nature, waves in shallow water, for example,
而自然界中的其他波 例如浅水中的波
can bounce directly off of or at least influence each other.
可以直接反弹或至少能互相影响
But not photons, they just pass right through.
但是光子并非如此 它们直接一穿而过
That’s why sunlight doesn’t block cell phone signals or human vision.
这也是阳光不会阻挡手机信号和人类视线的原因
However, there are three indirect ways that photons can interact with other photons.
然而 光子可以通过三种间接方式与其他光子相互作用
First, if a photon bumps into, say, an electron,
第一种 如果一个光子碰到一个电子
and that electron bumps into another photon,
这个电子又碰到另一个光子
the photons will technically have redirected each other.
理论上讲 两个光子将彼此重新定向
But this requires an electron to be in just the right place at the right time.
不过这需要电子出现在合适的地点 合适的时间
So I don’t think it really counts as a way for a photon by itself to make a shadow.
所以我认为这不能看作是光子真正产生阴影的一种方式
Second, just like how photons passing close to massive objects like the sun or a black hole
第二种 就像光子接近太阳或黑洞之类的庞然大物时
follow paths curved by gravity,
会沿因引力而弯曲的路径前进一样
a photon itself has energy and momentum,
光子本身具有能量和动量
and would technically gravitationally attract another passing photon.
并且从技术上来说 光子会用引力使另外一个经过的光子发生偏转
But the gravity from a photon is ridiculously tiny.
但是光子的引力非常小
Even the most energetic photon we’ve ever measured
即使是我们曾测量过的能量最高的光子
had a smaller gravitational field than a strand of DNA,
其引力场也比更小DNA链还要小
which won’t allow a photon to make a noticeable shadow.
以至于不会让光子产生可以观察到的阴影
But, third and finally,
但是 第三种也是最后一种方式
super high energy photons can spontaneously turn into particle-antiparticle pairs,
超高能光子可以自发地变成正反粒子对
like an electron and positron, and then back again
比如电子和负电子 然后再变回来
and these particles can deflect other photons,
这些粒子可以使其他光子发生偏转
resulting in legit photon-on-photon scattering.
从而导致合法的光子对光子的散射
I say “legit” because
我说“合法的”是因为
the key here is that you don’t need to lock out and have an electron happen to be passing by.
这里的关键在于 不需要运气好到碰巧有电子经过
Two solitary high-energy photons
两个孤立的高能光子
can spontaneously generate their own means of crashing into or bouncing off each other.
可以自发地用自己的方式彼此碰撞或反弹
So what kind of shadow do we get?
所以会得到什么样的阴影呢?
Well, photons only bounce off each other exceedingly rarely.
光子之间极少互相反弹
Even very very carefully controlled experiments with ridiculously high powered lasers
甚至使用非常高功率的激光 进行非常非常仔细控制的实验
have a hard time observing any interaction between photons,
也很难观察到光子之间任何的相互作用
Which doesn’t sound promising for noticing a shadow.
这听起来似乎没有发现阴影的希望
But, there is one very real way that photons cast shadows.
但是 光子有一种非常直观的方式来投射阴影
Because space is so huge,
由于宇宙非常巨大
super high energy photons travelling through it
穿过它的超高能光子
do eventually crash into
最终会撞上
one of the many low energy photons of the cosmic microwave background radiation,
宇宙微波背景辐射中的许多低能光子中的一个
that are present pretty much everywhere in the universe.
这种低能光子几乎在宇宙中无处不在
And so, right now, you are literally being shadowed from ultra high energy gamma ray photons
所以 现在你实际上正处于大爆炸留下的
by the photons left over from the big bang.
超高能伽马射线光子的阴影里
All right, it’s sponsor time,
好了 现在是赞助时间
which means Particle Fever promotion time.
也就是说这是《狂热粒子》的推广时间
I’ve recommended it before because it’s an amazing documentary about particle physics
我之前推荐过它 因为这是一部很棒的关于粒子物理学的纪录片
and I’m gonna recommend it again
我想要再推荐一次
because I know not all of you have watched it on Curiosity Stream yet,
因为我知道不是所有人都到Curiosity Stream看过它
otherwise why would they still be sponsoring Minute Physics videos?
不然他们为什么还赞助《分钟物理》视频?
Anyway, in addition to Particle Fever, Curiosity Stream has a deal going on right now.
无论如何 除了《狂热粒字》 Curiosity Stream正在进行一项促销
If you get a Curiosity stream subscription, which costs less than a cup of coffee,
如果你用不到一杯咖啡的钱订阅Curiosity Stream
you now also get a bundled subscription to Nebula,
你还可以获赠订阅Nebula
the streaming service made by and for educational youtube video creators
这是由教育类YouTube视频创作者提供的流媒体服务
with ad-free viewing and exclusive originals,
无广告 内容全部是独家原创
like Real Engineering’s series on the insane logistics of D-Day.
就像《真实工程》中讲述的诺曼底登陆战的疯狂物流一样
So go to curiositystream.com/minutephysics and use offer code minutephysics
来吧 使用我们的优惠码minutephysics访问curiositystream.com/minutephysics
to get your first month of curiosity stream and nebula for free.
免费使用Curiosity Stream和Nebula一个月
Just think how many times you can watch Particle Fever in a month!
想想在一个月里你能观看多少次《狂热粒子》吧!

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视频概述

讲述光子如何通过3种间接的方式投射出阴影

听录译者

收集自网络

翻译译者

LawrenceWang

审核员

审核员BY

视频来源

https://www.youtube.com/watch?v=Fv1JJ227CQk

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