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莱戈拉斯能看多远 – 译学馆
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莱戈拉斯能看多远

How Far Can Legolas See?

《指环王》中有个著名的场景 精灵莱戈拉斯声称
There’s a famous scene in the Lord of the Rings where the elf Legolas claims to be able
他能看到5里格远的骑士团 在此之上
to count the exact number of horsemen 5 leagues away, and on top of that
还能辨认出他们的首领特别的高
he can tell that their leader is very tall.
但是即便拥有最完美的视力
But even with the most perfect eyes possible,
真的有人能看到那么远吗
would anyone be able to see that far?
当我们在看的时候 我们看到的是由光源发出
When we see, we’re looking at light that’s traveled outwards
经过物体反射的光线 通过眼睛内的晶状体
from a light source, bounced off an object, passed through the lens in the eye,
最终在视网膜聚焦成像
and been focused into an image on the retina.
另外……光线的传播过程并非完美的直线
Except… light isn’t a particle traveling in perfectly straight lines – it
而是波 因此对我们和莱戈拉斯来说就有个问题
is a wave. And therein lies the problem, both for us, and for Legolas.
因为任何波 无论是水波 声波还是光 当它
Because any wave – whether water, sound or light
通过一个狭窄的出口时会发生所谓的衍射
traveling through a small opening will become spread out by a process known as diffraction,
对于光来说 其实质就是图像模糊了
which for light, essentially blurs the image.
你可以使用长焦镜头来观察
You can see this with a telephoto camera lens,
这种相机的光圈可以调得非常非常小
where the camera aperture has been made very very small,
小到连图像都变得扩散模糊 甚至无法分辨
small details in the photograph start to become spread out, blurred, and even indistinguishable!
或者 如果你把一张纸贴在眼前
Or, if you hold the edge of a piece of paper in front of your eye and
透过边缝去阅读 微小的字会变得模糊不清
try to read past it, small words will become blurry!
这个由光点扩散而成的光斑叫做“艾里斑”
The blur that a small point of light spreads out to become is called an Airy disk, and
由远处微小物体形成的艾里斑
the size of the Airy disk for distant tiny objects
其大小仅取决于光的波长和透光孔径
depends only on the wavelength of light in question and the size of the opening you’re looking through.
因此就可见光和人类瞳孔来说
So for visible sunlight and a human-sized pupil,
衍射现象使我们最多只能看清
diffraction limits us to at best be able to distinguish objects
大于7个千分度的物体
that are bigger than seven one-thousandths of a degree,
比如 一个1公分大小的物体在一百米开外
for example, an object one centimeter in size a hundred meters away,
另外100米开外放置任何小于1公分的物体就会模糊
another way of putting this is that everything 100m away and smaller than 1cm gets blurred
所以可分辨的大小就是1公分
so that it appears to be about 1cm in size,
不管你放多小的物体 只要小于1公分就会模糊
no matter how small it really is – subtle details smaller than 1cm blur away.
所以这位莱戈拉斯 瞳孔与人类近似
So when Legolas, who has very human-sized pupils,
当他看着24千米远的罗翰骑士团时
looked at the riders of Rohan 24 km away,
衍射现象告诉我们任何小于3米的物体
diffraction tells us that everything smaller than 3 METERS
都会模糊成斑点
would have been blurred to about three meters in size.
也许他还能点清骑兵人数
perhaps he could still count the number of horsemen,
但他绝对无法分辨几厘米的斑点的身高差
but he definitely couldn’t distinguish their heights to within a few centimeters…
除非莱戈拉斯能看到紫外光
Unless Legolas could see in ultraviolet,
也就是光波长越短 衍射越少
shorter wavelength light diffracts less,
如果他真能看到紫外光区
so if he could see in the extreme UV, then
那么他就能分辨10厘米大小的物体
he’d be able to distinguish objects 10 cm in size,
这样就足够他辨别那些人的身高差了
almost enough to discern the height of a man.
除此之外 很多气体会吸收紫外光线
Except that pretty much any kind of air absorbs extreme UV light,
所以如果他能看到紫外光
so even if he could see UV,
莱戈拉斯将会迷失在黑暗中
Legolas would have been left in the dark.
或许人家有某种魔力吧
Or maybe it’s just… magic.
本视频部分内容来自于听书网
So this video is brought in part by audible.com,
该网站的有声书涵盖了各种文学作品
leading provider of audiobooks across all types of literatures
包括小说类 纪实类以及期刊杂志
including fiction nonfiction and periodicals.
如果你去audible.com/minutephysics网站
If you go to audible.com/minutephysics
你可以免费选取一本有声书下载
you can try out audible by downloading a free audio book of your choice like
比如J.R.R.托尔金写的《双塔奇兵》
The Two Towers the second book in J.R.R. Tolkien
它是指环王三部曲的第二部 精彩但有物理漏洞
excellent but potentially physically inaccurate the Lord of the Rings trilogy.
如果你只看过电影就太可惜了
If you’ve only ever seen the movies you’re missing out,
去读一读或听一下有声书吧
read or listen to the books.
总之 感谢听书网给了我继续出视频的机会
Anyway, thanks to audible for helping me continue to make these videos
别忘了在听书网下载免费有声书哦
and don’t forget to download your free audio book at audible.com/minutephysics.

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视频概述

《指环王》中有一个著名的场景,精灵族莱戈拉斯能看到千里之外的每个骑兵。现实之中我们真的能看清楚吗?是什么因素决定了我们的视力的极限?

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视频来源

https://www.youtube.com/watch?v=Rk2izv-c_ts

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