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Mirrors are amazing. They turn walls into portals to another world.
镜子是令人惊异的东西。它们把墙变成通往另一个世界的入口。
Well our world only slightly different, like you've probably noticed that words look backwards in a mirror,
我们的世界只有一点点不同，你可能已经注意到文字在镜子里是反向的，
But they aren't upside down, which is weird because how would a mirror know to flip left and right but not up and down.
但它们不是上下颠倒的，这很奇怪，因为镜子怎么知道左右颠倒，却不知道上下颠倒呢？
Well the short answer is that mirrors don't flip left and right or up and down.
简而言之，镜子不会左右翻转或上下翻转。
If you look very carefully at a scene in a mirror,
如果你非常仔细地观察镜子中的场景，
You'll notice that everything on the left stays on the left,
你会注意到所有在左边的东西都在左边，
everything on the right stays on the right, everything up stays up and everything down stays down.
右边的东西都在右边，上面的东西都在上面，下面的东西都在下面。
What does get flipped is the direction into or out of the mirror, the things closest to us and up farthest away
真正翻转过来的是进入或离开镜子的方向，也就是离我们最近和最远的东西。
and the things farthest from us and up closest.
以及离我们最远和最近的东西。
Mirrors flip not left and right nor up and down, but depth they flip in and out.
镜子不是左右翻转，也不是上下翻转，而是深度的翻转。
And mirrors invert in and out because they reflect light according to the principle of specular reflection.
镜子是反射光的，因为它们根据镜面反射的原理反射光线。
Light coming into the mirror at a given angle bounces back out at an equivalent angle.
光线以一个给定的角度射入镜子，然后以一个相等的角度反射回来。
This means that after bouncing off a mirror, light is behaving no differently than it would have if instead of a mirror.
这意味着，光线在被镜子反射后，其表现与在镜面反射后没有什么不同。
There were a window into a parallel universe on the other side,
在另一边有一扇通往平行宇宙的窗户，
just like ours in every way except with in and out reversed.
就像我们的一样，除了内外是颠倒的。
That's why mirrors feel like windows into another world.
这就是为什么镜子给人一种进入另一个世界的感觉。
Light reflecting off them behaves in literally the same way as if they were windows into another world.
光线从它们身上反射出来，就好像它们是通向另一个世界的窗户一样。
Ok, but then what about the whole left-right flip question?
那么关于左右翻转的问题呢？
How does it make sense if mirrors don't flip left and right?
如果镜子没有左右翻转，这怎么能说得通呢？
Well you can literally see the answer for yourself by writing on something transparent.
在透明的东西上写一些东西，你就知道答案了。
When the word is readable left to right, its mirror image is also readable left to right.
当单词从左到右可读时，它的镜像也从左到右可读。
The reason words are usually flipped in mirrors isn't because mirrors flip them. We flip them.
词语在镜子里经常翻转的原因并不是因为镜子会翻转它们。是因为我们翻转他们。
Words it turns out tend to be printed on or attached to objects
事实证明，文字往往被印在物体上或附着在物体上，
that we have to turn to face the mirror in order to see them in the mirror.
我们必须面对镜子才能在镜子里看到他们。
We flip the words and we normally do it left and right.
我们翻转单词，通常是左右翻转。
We could just as well turn them vertically,
我们也可以让它们上下旋转，
in which case the word would look flipped top bottom in the mirror, not left right.
在这种情况下，这个单词在镜子里看起来是上下颠倒的，而不是左右颠倒。
Again, not the mirrors doing.
再说一次，不是镜子在起作用。
Here's the deal: if a word is flipped in a mirror, it's probably flipped outside the mirror too.
事情是这样的：如果一个词在镜子里翻转了，它在镜子外面很可能也会翻转。
We just don't normally notice that the word got flipped outside because we can't see through solid objects.
我们只是通常不会注意到这个词被翻了过来，因为我们不能透过固体看到东西。
In order to see the word without looking in the mirror,
为了不用照镜子就能看到这个词，
We'd have to go around to the other side of the object and turn ourselves around,
我们必须绕到物体的另一边，然后转个身，
unless you have multiple mirrors.
除非你有多个镜子。
In that case, in and out get flipped along two different directions
在这种情况下，输入和输出会沿着两个不同的方向翻转，
which combines to mean that things on the left indeed show up on the right and things on the right show up on the left.
结合起来后，左边的东西确实会出现在右边，右边的东西会出现在左边。
Or if we rotate the mirrors up gets flipped with down and down with up.
或者如果我们向上旋转镜子，它会随之向下和向上翻转。
So if somebody tells you that mirrors don't flip left and right. Well, mirrors actually can, but not mirror.
如果有人告诉你镜子不会左右翻转。其实多个镜子可以，但单个镜子不行。
A lone single mirror has to get us to do the flipping for it.
只有一面镜子的话，得需要我们翻转它。
