评论
打印
The video game Portal is built around a sci-fi device
电子游戏《传送门》是是围绕科幻设备构建的，
that can create a portal connecting one place on the wall or ceiling or floor to another,
可以创造将墙壁、天花板或地板上的一个地方连接到另一个地方的传送门，
and objects in the game, or the player themselves
游戏中的物体，或者玩家本身
can pass essentially instantaneously from one end of the portal to the other.
可以从传送门的一端传递到另一端。
In particular, an object entering one end of a portal with a certain speed
特别地，以一定速度进入传送门的一端的物体
leaves the other end with the same speed,
以相同的速度离开另一端，
though if the portals aren't oriented in the same direction,
即使传送门的朝向不相同，
then the object will exit in the new direction.
物体也还是会从新的方向穿出。
But the speed will be the same.
但速度是一样的。
And this leads to an apparent paradox:
这就引出了一个明显的悖论：
what happens if one of the ends of the portal is itself moving?
如果传送门的一端自身在移动，会发生什么？
Does a stationary object plop out the other end of the portal with zero speed,
一个静止的物体是否会因为在进入传送门之前没有速度，
since it had no speed before entering?
而以速度为零的状态弹出传送门的另一端？
Or if the orange portal moves quickly downwards,
或者假如橙色的传送门快速下降
does the cube shoot out of the blue portal with the corresponding relative speed?
那小方块是否会以相应的相对速度从蓝色的传送门射出？
It's easy to argue in favor of either case,
支持这两种情况都是很容易的，
which I suspect is why this puzzle is so popular on the internet!
我怀疑这就是为什么这个谜题在互联网上如此流行！
Of course, as far as we know such portals don't exist,
当然，就我们所知这样的传送门并不存在，
but supposing they did, and obeyed the laws of physics,
但假设它们确实存在，并且遵守了物理定律，
then the question really boils down to this:
那么问题就可以归结为：
if objects have to enter and exit the portals with the same speed,
如果物体必须以相同的速度进出传送门，
then what's that speed being measured relative to?
那么测量的速度是相对于什么而言的呢？
Because in our universe there's no absolute reference frame
因为在我们的宇宙中没有绝对的参照系
from which to measure speeds and velocities on their own.
来测量它们自己的速度和速率。
Velocities can only be determined relative to another object.
只能确定相对于另一物体的速度。
So here are a few options: perhaps when passing through a portal,
这里有几个选项：可能当通过传送门时，
the object maintains the same speed relative to the environment, This one's option A.
物体相对于环境保持相同的速度，这个选择A选项。
Or perhaps objects maintain the same speed relative to the average position of the portals themselves.
或者物体相对于传送门本身的平均位置保持相同的速度。
Except that's mathematically the same as measuring relative to the environment,
但这在数学上与相对于环境的测量是一样的，
as long as the portals aren't accelerating – so option A.
只要传送门没有加速--所以选择A。
Or perhaps the speed of an object has relative to the portal it enters
或者，物体相对于其进入的传送门的速度
is the same as the speed it has relative to the portal it exits. This one is option B.
与其相对于其退出的传送门的速度相同。这个选择B选项。
Or perhaps objects enter and exit at a constant speed
或者物体以相对于它们当前不使用的传送门的
relative to the end of the portal they're NOT using at the moment.
末端恒定的速度进入和离开。
It's a valid possibility, although it's kind of weird.
很有可能，不过，有点奇怪。
The thing is, all of these options are consistent with what you see in the video game,
问题是，所有这些选项都与你在电子游戏中看到的一致，
Because in the game the portals pretty much never move relative to the environment.
因为在游戏中传送门几乎从不相对于环境移动。
My personal opinion is that the most physically natural option is B,
我个人认为B选项是最符合物理常识的，
where the velocity is locally measured relative to the individual ends of the portals,
其中速度是相对于传送门的各个末端局部测量的，
and so the cube shoots out of the blue portal.
因此小方块从蓝色传送门射出。
This would be roughly what you'd expect if the portals were wormholes bending spacetime,
这大概就是你所期望的，如果传送门是弯曲时空的虫洞，
because the objects then would obey conservation of momentum in a curved spacetime,
因为物体在扭曲的时空中也遵守动量守恒，
or if the portals were more of a teleportation device
或者，如果传送门更像是一个传送装置，
that scans the matter coming in one end and reconstructs it,
它扫描来自一端的物体，并在另一端重建它，
kind of like a 3D printer, at the other end. So I think B is more natural.
就像3D打印机一样。所以我认为B选项更自然。
It's also tempting to think that there's simply no way it can be option A,
所以我也很想认为选项根本不可能是A，
the one where objects keep their same speed relative to the environment.
物体相对于环境保持相同的速度。
Because how could a stationary object exit a stationary portal while remaining stationary?
因为静止物体怎么可能在静止状态下通过静止的传送门？
The object would have to move, right? However, there is a way for option A to work.
物体必须移动，对吗？但是，A选项有一个可行办法。
Precisely because the cube doesn't enter the orange portal all at once. It goes in bit by bit.
正因为小方块不会同时进入橙色传送门。而是一点一点地进入。
And if those bits come out of the blue portal not moving,
如果这些点从蓝色的传送门出来，不动，
then they all appear exactly in the plane of the portal stationary,
那么它们都会准确地出现在传送门静止的平面上，
and they would keep on piling up against each other,
它们会不断地互相堆积，
squishing the cube into a flat square which is not moving.
把小方块压扁成一个不动的正方形。
Or, if the cube were rigid and couldn't be squished,
或者，如果小方块是刚性的，不能被压扁，
then it simply couldn't enter the orange portal in the first place,
那么它一开始就不能进入橙色的传送门，
The blue end of the portal will act like a wall
传送门的蓝色末端会像一堵墙，
and the orange portal would bounce off of it!
橙色的传送门会从上面弹开！
And I suspect option A is actually how the portals are programmed in the video game itself,
我怀疑选项A实际上是如何在视频游戏中对传送门编程的，
both because measuring speeds relative to the global environment
因为测量相对于全球环境的速度
as opposed to relative to a particular object is typically the easiest thing to program.
而不是相对于特定对象的速度，这个通常是最容易编程的。
And because people who've done experiments within the game engine
那些在游戏引擎中做过实验的人
to try to see what happens have discovered that the game glitches
发现游戏发生故障，
and doesn't let solid objects pass through a portal moving towards them.
并且不会让实体物体通过一个向它们移动的传送门。
Which is perhaps unsatisfying answer to a paradox,
这可能是一个令人不满意的答案，自相矛盾，
and not how you think the portals should work. But that's ok!
也并非你所认为的传送门的工作方式。但是这也不错！
We don't have to agree with the game designers.
我们不必同意游戏设计者的观点。
To me, the moral is that the portal paradox is not a paradox.
对于我来说 传送门悖论并不是悖论。
The answer depends on how the portals themselves actually work,
答案取决于传送门本身是如何工作的，
which, since they're fictional, is up to you to decide.
这取决于你的决定，因为它们都是虚构的。
What you think should happen says more about you:
你认为应该发生的事更能说明你：
and whether you think more like a programmer, or more like a physicist!
你的思维方式更像程序员还是更像物理学家！
And so, I leave you with a final portal puzzle to ponder:
所以，我留给你们最后一个需要思考的传送门谜题：
what if instead of moving down towards the cube,
如果橙色的传送门不是向下朝小方块移动，
the orange portal is moving sideways on the ground,
而是在地面上横向移动，
and you drop the cube through it.
你就会把小方块从这里扔进去。
Does the cube shoot straight up through the blue portal?
小方块是直接从蓝色的传送门射出的吗？
Does it bounce off the orange portal?
它会从橙色的传送门弹回来吗？
Or does it shoot out of the blue portal at an angle?
或者它是以一个角度从蓝色的传送门射出？
This MinutePhysics video was supported by CuriosityStream,
《分钟物理》频道得到了CuriosityStream的支持，
an affordable subscription streaming service
这是一个收费低廉的流媒体服务，
that's all about science, documentaries and non-fiction.
涉及科学、纪录片和非小说类内容。
Look, I'm not going to beat around the bush,
听着，我不会拐弯抹角的，
CuriosityStream has in their collection what in my opinion
我认为CuriosityStream有
is the best documentary about physics I've ever seen,
我见过的关于物理学的最好的纪录片，
"Particle Fever", and you can watch it right now
你现在可以登录网址curiositystream.com/minutephysics
by heading to curiositystream.com/minutephysics,
观看《粒子狂热》这个节目，
and signing up with the promo code "minutephysics",
同时在注册的时候输入优惠码"minutephysics"，
which gets you the first 30-days completely free.
这样你就可以在头30天完全免费观看。
After that, a subscription to CuriosityStream is
之后，订阅CuriosityStream
just $ 2.99 a month for you to have unlimited access to
只需每月2.99美元，你就可以无限制地
over 2400 other documentaries and nonfiction programs,
观看2400多部其他纪录片和非小说类节目，
including some from people you might recognize.
包括一些你可能认识的名人。
But seriously, just go watch Particle Fever
但说真的，去看《粒子狂热》吧。
by heading to curiositystream.com/minutephysics,
前往curiositystream.com/minutephysics，
and using the promo code ‘minutephysics'.
到时候用这个优惠码"minutephysics"。
Particle Fever is so good!
《粒子狂热》真的很棒！
