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Most everyday phenomena happen equivalently in a mirror as they do normally - at least, from a physics perspective.
大多数日常现象在镜子里的表现和镜外表现是一样的——至少从物理学的角度来看是这样的。
Unlike when you play a video backwards in time (where it's pretty obvious that something weird is going on),
和你倒着播放一个视频不一样（很明显倒播视频会发生奇怪的事情），
when compared with a normal video, motion in a mirrored video still looks totally physically normal - just mirrored.
与正常的视频相比，镜像视频中的运动在物理学上看起来还是完全正常的——只是镜像而已。
In fact, without outside context, there's no way to tell which was the original and which was mirrored!
事实上，如果没有外部环境，就无法分辨哪个是本体，哪个是镜像！
Which is why horizontally flopped shots are used in movies all the time.
这就是为什么在电影中总是使用水平镜头。
In fact, as far as we know, everything in the universe governed by electromagnetism and gravity
事实上，据我们所知，宇宙中的一切都是由电磁力和引力
and the strong nuclear force behaves this way - if you set up two experiments that are mirror images of one another,
以及强大的核力控制的——如果你设置两个互为镜像的实验，
they'll produce results that look like mirror images of each other.
它们的结果就会看起来像互为镜像。
Which presents a problem if we ever need to communicate with aliens from afar:
这样有一个问题，如果我们需要与远方的外星人交流：
if all physics is mirror-symmetric, that would mean left handed and right handed are relative
如果所有的物理都是镜像对称的，那就意味着左手边和右手边是相对的，
just like up and down and forward and back,
就像上下前后一样，
so if we were communicating with aliens and didn't have any shared reference objects,
因此，如果我们与外星人通信，并且没有任何共享的引用对象，
we'd we have no way of explaining what we mean by left-handed and right-handed using physics.
我们无法用物理学来解释什么是左手边，什么是右手边。
This Left/Right ambiguity is called "the Ozma Problem". And the distinction between left and right is important,
这种左/右不确定性被称为“奥兹玛问题”。左和右之间的区别很重要，
because earth-based life mostly relies on sugars with right-handed symmetry and amino acids with left-handed symmetry.
因为地球上的生命主要依赖于右旋对称的单糖和左旋对称的氨基酸。
This isn't a physics constraint - it just as easily could have been the other way around -
这不是物理限制——反过来也很容易——
but the point is, the molecules in our food and our bodies do have a specific orientation,
但问题在于我们食物和身体中的分子确实有一个特定的方向，
so not knowing left from right could impair intergalactic culinary relations.
无法区分左右可能会损害星系间的烹饪关系。
However, there is a solution: the weak nuclear force, which governs the decay of subatomic particles
但有一种解决办法：支配亚原子粒子衰变的弱核力
doesn't always play nicely when mirrored.
在镜像时并不总是能很好地发挥作用。
For example, when uranium nuclei beta decay they emit mostly electrons spinning like left-handed corkscrews,
例如，当铀原子核衰变时，它们发射出的大部分电子像左旋开瓶钻一样旋转，
but if you perform the mirror image of the experiment using a mirror-image uranium nucleus,
但如果你用镜像铀原子核进行镜像实验，
the nucleus still emits electrons spinning like left-handed corkscrews rather than right-handed, as they would in a mirror.
原子核仍然像左旋开瓶器那样释放电子，而不是像在镜子里那样向右旋。
It turns out that in our universe, the mirror-image of a physical process doesn't always result in the mirror image of the outcome -
事实证明，在我们的宇宙中，物理过程的镜像并不会导致结果的镜像
uranium always decays more into left-handed electrons, no matter how you look at it.
不管你怎么看，铀总是更容易衰变成左旋电子。
So we'd tell the aliens "you know how electrons spin when uranium decays? That direction is what we call 'left'".
所以当我们告诉外星人“你知道铀衰变时电子是如何旋转的吗？那个方向就是我们所说的‘左’。”
Which would solve the Ozma problem - except our universe has a next level Ozma problem of its sleeve.
这将解决奥兹玛问题—除了我们的宇宙还有一个更高级的奥兹玛问题。
Because what if the distant aliens were made entirely of antimatter? I mean, in principle they could be and we wouldn't know.
因为如果遥远的外星人完全由反物质构成呢？我的意思是，原则上它们可能是，但我们不知道。
Antimatter interacting with itself behaves exactly like matter interacting with itself:
反物质与自身的相互作用就像物质与自身的相互作用一样：
antihydrogen has the same atomic spectrum as hydrogen,
反氢原子与氢原子具有相同的原子光谱，
and antimatter-you looks and behaves exactly like matter-you until it interacts with matter.
而反物质——你的外表和行为与物质完全一样——除非它与物质相互作用。
And here's the problem: while the matter version of a uranium nucleus
问题就来了：尽管铀原子核的物质形式
always decays into left-handed electrons whether it's in a mirror or not,
总是衰变为左旋电子，无论它是否在镜子里，
the anti-matter version always decays into right-handed anti-electrons whether it's in a mirror or not.
但反物质总是衰变为右旋反电子，不管它是不是在镜子里。
So if we told the aliens "look at the beta decay of the nucleus with atomic weight 239
所以如果我们告诉外星人“看看原子核的衰变，它的相对原子质量是239，
- that's always the orientation we call left-handed", that would be wrong: for aliens made of antimatter,
这就是我们所说的左边”，这就是错的：对于由反物质组成的外星人，
it would in fact be what we call right handed. And you definitely don't want to shake either hand of an alien made of antimatter.
这其实是我们所说的右边。你绝对不想和反物质构成的外星人握手。
So how can you figure out, from afar, whether or not a distant alien is made of antimatter? This is the Ozma problem, level 2.
那么你怎么才能知道，遥远的外星人是否由反物质构成呢？这就是奥兹玛问题的第二阶段。
Essentially, antimatter is another kind of mirror we can hold up to the universe,
从本质上讲，反物质是另一种我们可以用来反映宇宙的镜子，
which combined with the possibility of regular mirroring means we can't use beta decay to define left vs right.
它结合了常规镜像的可能性，意味着我们不能用衰变来定义左和右。
But luckily, there's a next level solution, again thanks to the weak nuclear force.
但还好，还有下一个阶段的解决办法，再次感谢弱核力。
Enter the Kaon, a fast-decaying subatomic particle.
进入到K介子，一种快速衰变的亚原子粒子。
Whether they're mirrored or not, around 20.3% of the time Kaons decay into right-handed anti-electrons,
无论它们是否是镜像，大约20.3%的时间介子衰变为右旋反电子，
while around 20.1% of the time - slightly less often - they decay into left-handed electrons.
而大约20.1%（稍微少一些）的时间介子衰变为左旋电子。
And the key is this: if you instead take antimatter Kaons, whether mirrored or not,
关键在这里：如果你用反物质的介子，无论是否镜像，
they still decay slightly less often into left-handed electrons,
它们仍然会以较少的频率衰变为左旋电子，
rather than right-handed anti-electrons as you might have expected from the way antimatter-uranium decays.
而不是你所期望的从反物质-铀衰变的方式中得到的右旋反电子。
That is, normal kaons - whether mirrored or not - and anti-kaons -
也就是说，正常的K介子（无论是否镜像）和反K介子
whether mirrored or not - both decay less often into left-handed electrons.
（无论是否镜像）都不太容易衰变为左旋电子。
And this is how distant aliens could figure out if they're made of matter or antimatter
不管遥远的外星人是由物质还是反物质组成
and whether or not they're using the same concept of "left" and "right" as us: simply build a particle accelerator
不管它们左右的概念和我们是否相同，向它们解释左右很简单：建立一个粒子加速器
and look at the decays of neutral kaon particles; the electron-like thing
并观察中性K质子粒子的衰变；衰变得不那么频繁的电子一样的东西，
that they decay into slightly less frequently is made of what we call matter, and it'll be moving in what we call a left-handed way.
像电子一样的东西是由我们所说的物质构成的，它会以我们所说的左旋方式运动。
The universe doesn't distinguish between left and right or matter or antimatter
宇宙无法区分左右也不区分电磁、
for electromagnetism, for gravity, and for the strong nuclear force.
重力和强核力是物质或反物质。
But for some reason, the weak force allows us to tell the difference.
但由于某种原因，弱力让我们能够分辨出它们的区别。
