本视频由YouTube Red科幻系列“生命线”赞助播出
This video is sponsored by the YouTube Red Sci-Fi Series “Lifeline”.
很久以前我就想做一个视频
For ages I’ve been wanting to
分析科幻作品中的时间旅行
make a video analyzing time travel in fiction –
不是分析如何通过魔法的或物理的原理实现时间旅行
not the magical or physical mechanisms by which the time travel is supposedly achieved,
而是分析在每个故事世界中不同的时间旅行方式
but rather, the different ways time travel can influence causality (and thus the plot)
如何影响因果关系和故事情节
within the universe of each story.
不消说 前方有剧透
Needless to say, there are spoilers ahead!
让我们从奥森·斯科特·卡德的书
Let’s start with Ender’s Game
《安德的游戏》开始吧
by Orson Scott Card –
该书中时间旅行是完全现实的：
time travel in this book is actually 100% realistic:
书中人物以接近光速的速度旅行时
the characters experience slower passage of time
就会经历较慢的时间轨道
when they travel close to light speed,
也就是说地球或其它星球已过去了好几年
allowing just a few days or months to pass for those traveling
而那些进行时光旅行的人仅度过几天或几个月
while years pass on earth or other planets.
他们的时间和我们一样向前流逝
It’s traveling forward through time like we normally do,
只是速度不同
but at different rates.
这种时间旅行不能“改变过去”
This kind of time travel doesn’t ”change the past”
也不允许人物改变已做出的决定
or allow characters to make different decisions than the ones they already did –
历史时间轴具有一致性
it’s all one consistent historical trajectory.
原版电影《人猿星球》中也有类似场景
The original Planet of the Apes film is similar,
宇航员经历了极度的时间膨胀
where astronauts experience extreme time dilation
坠落到一个由人猿统治的奇怪星球上
and then crash land on a strange ape-ruledplanet that
（猛料）却发现这里是很久以后的地球
(major spoiler) turns out to just be earth in the distant future.
时间旅行到底是怎么一回事呢？
But what about actual time-travel time travel?
我觉得在科幻作品中不同类型的时间旅行
Well, I would say there are two big distinguishing features
可以分为两大类
between different types of time travel in fiction.
第一种 无论时间旅行者身处何地
The first is whether or not the time traveler is there
故事总是按“既定现实”开展
when history happens the ”first time around” –
即某种“自我一致性”
that is, is there a kind of “self-consistency “
也就是当时间旅行把你带回过去
where, since time travel takes you to the past, when the past happened the first time,
然后再把你从过去带回原来的时间轨道
the time-traveling version of you was always there to begin with?
或者回到过去的时间旅行改变了既定事实
Or does the very act of time traveling to the past change
使世界朝着与既定轨道不同的
what happened and force the universe onto a different trajectory
时间轨道演进
of history from the one you experienced prior to traveling?
第二种不同类型的时间旅行是：
And the second distinguishing feature is:
进行时间旅行的某些人拥有自由意志
who has free will when somebody is time traveling.
也就是 某些人的行为可以改变时间轨道
Like, whose actions are allowed to move history
而其他人的行为则不能
onto a different trajectory, and whose aren’t?
一个最简单的时间旅行就是“反复”
One of the simplest time travels is “do-over” time travel,
基本上就如同你在玩电子游戏
It’s essentially like playing a video game where
你能反复从一个关卡开始
you can start a level over with the foresight of
并预先知道自己第一次犯了什么错误
what you did wrong the first time.
以《土拨鼠之日》里比尔·莫里饰演的角色为例
For example, in Groundhog Day Bill Murray’s
该角色反复地过着同一天
character relives the same day over and over
虽然每次他都可以做出不同的选择
again, and though he can make different choices each time,
但他总是回到同一个起点
he always starts back at the same point
（不过之前的选择他都记得）
(except with new memories of his previous choices).
也就是说 只有弄明白这套严密的选择集合
That is, until he figures out the one exact set
他才能够跳出这个循环
of choices that frees him from the loop.
我认为电影《圣诞颂歌》也是这个道理
I consider “A Christmas Carol” to be in this vein, too,
尽管它看起来可能不太像时间旅行
even though it may not seem like time travel.
守财奴必须按照目前的时间轴旅行到未来
But because Scrooge gets to visit the future of his current timeline,
尽管时间旅行时他不能直接影响时间轴
even though he has no ability to affect the timeline directly while “visiting”,
但他仍然可以基于已有的认知来改变当前的行为
he can still change his actions in the present based on what he learns,
这本质上就是“反复”
essentially getting a “do-over.”
电子游戏《时空幻境》也是基于“反复”的理念
The video game Braid is built on the idea
你可以往回倒几秒钟
of “do-overs”, where you get to rewind
试一条新路子
a few seconds and try something different
不过有些物件不受时光倒流的影响
(though there are some things that are immune
它们不会发生变化
to going back in time and don’t “rewind”,
这也是该游戏的有趣之处
which is what makes the game interesting).
《时空幻境》里还有另一种时间旅行
Braid also has another kind of time travel,
你可以作为分离的个体回到过去
where you go back to your past as a separate individual,
而你的过去版将不再拥有自由意志
and the past version of you is there with no free will,
过去版的你将完全根据你的首次行动来行动
just does exactly what you did the first time around,
而时间旅行中的你能改变时间轨道
while “time-traveling you” can change the course of history.
这也是YouTube频道Corridor Digital制作的视频《Clock Blockers》所基于的原理
This is also how the video “Clock Blockers” by the Corridor Digital youtube channel works.
还有一种时间旅行就是
And then there’s time travel where the very act
你穿到过去或未来的行为
of going to the past or future creates
将产生一个全新的时间轨迹
a fully new trajectory of history
因为你通过时间旅行去了
because time-traveling you weren’t there the first
你第一次并没去过的地方
time around, and now you are.
这就是典型的“怎样都行”式时间旅行
This includes the typical “anything goes” time travel movies
就像电影《比尔和泰德历险记》
like Bill & Ted’s Excellent Adventure,
《回到未来》《星际迷航：第一次接触》等等
Back to the Future, Star Trek First Contact, and so on,
这类时间旅行中 你可以随心所欲地穿来穿去
where you can kind of instantly jump back and forth to any point in time you want,
有可能会出现多个版本的你自己
potentially resulting in multiple versions of yourself.
从因果关系的角度看
From a causality perspective,
你过去的所作所为（甚至你回到过去这件事本身）
anything you do in the past (and even just the act of going back in time )
都会改变时间轨道 重建新的时间轴
redirects the course of history onto a new timeline –
朝着新的方向发展 电影《回到未来》
in Back to the Future,
马蒂介入了他父母的相爱史
Marty’s interference with his parents falling
使得历史走向
in love results in the timeline of history
朝着另一方向发展
being redirected towards a version
而他并不存在于这一时间线的未来当中
of the future where he doesn’t exist
他开始从照片中 从现实生活中消失
and so he starts to disappear from photos and real life.
即使矫正了历史的重大偏离
And even after correcting that major deviation,
还是导致
his interactions with his parents while he’s in the past result
当他回到现在时 他的父母变成了完全不一样的人
in them being very different people when he returns to his present time;
一不小心 他就让历史进程稍稍不一样了
he accidentally caused history to progress in a slightly different direction.
电影《环形使者》也是如此
The movie “Looper” is similar,
但是要稍微复杂些 因为
but there’s a little more circularity
当你回到过去的时候
because when you jump to the past,
你改变了历史轨迹 而这个未来中的那个你
you cause history to branch onto on a trajectory where, in the future,
也和你一样回到了那个时间
the younger you also goes back in time the same way you just did.
你和过去的你
Both you and your past self still have
都有自由意志改变历史走向
enough free will to change that forward course of
但是 不可思议的是
history, though, which results in weirdness
当过去的你做一些你没做过的事
like you getting new memories when your past
你也会获得那部分记忆
self does things you yourself didn’t do,
如果他失去了身体的某个部分 你也会突然间
or if they lose a body part, suddenly you’ll lose it too
失去那部分身体 取而代之的是你身上的旧疤痕
and find it immediately replaced by an old scar.
所以 现在的变化不仅会影响未来的时间线
So, changes to the present affect not just future timelines,
还会影响回到现在
but also future timelines
产生的时间线的未来
that wrap back around to the present!
独立电影《初始者》这是这个套路
The indie film Primer is in the same vein,
该影片在剧情方面并未将时间旅行演绎到极致
except that it takes the plot device of time travel to the extreme,
反而是时间旅行形成环环相套的结构
with time travel within time travel within time travel,
比如时间旅行者可以和正在时间旅行的另一个自己交流
with time-traveling characters interacting with other time-traveling versions of themselves,
带着时间机器回到过去 再进入其它时间机器中
bringing time machines with them to the past inside other time machines, and so on.
除了复杂性 还有两个使《初始者》脱颖而出的特点：
But beyond the complexity, there are two things that make Primer stand out:
首先 回到过去的时间旅行不是瞬间一跃就能完成的
first, time travel to the past isn’t an instantaneous jump,
而要花费时间：回到过去6个小时
but actually takes time: to go back 6 hours,
你就得在时间机器里坐上6个小时
you sit in the time machine for what feels like 6 hours.
时间机器的时间被初步激活以前
And time travel can’t take you back to a time
你是不能回到过去某一时间点的
before a given time machine was initially activated, since of course,
只有打开时间机器并进入 它才会将你带回过去
the machine can only be taking you back in time inside it if it’s turned on,
所以时间机器首次打开的时间就是你能回到过去的最远时间
so the first time it was turned on is the farthest back in time you can go in a given machine.
逻辑性很妙
There’s a nice logic to it.
我对下面这部电影里的科幻时间旅行情有独钟：
Which brings us to perhaps my all time favorite of all fictional time travel:
《哈利·波特与阿兹卡班的囚徒》
Harry Potter and the Prisoner of Azkaban.
影片中的时间旅行属于那种
It’s a kind of time travel
你可以穿越到过去且能与现实中的自己取得联系
where you instantly jump back in time and can interact with yourself,
但并不能产生新的时间轴
but it doesn’t generate new timelines.
这样安排是因为在哈利·波特世界中
It manages this because in the Harry Potter universe,
你经历了你的初始时间轨道
while you were experiencing your initial,
这个时间旅行轨道经过了某个特殊的点
pre-time-travel passage through a particular point in history,
所以你的“克隆时间旅行”路线是既定的
your “time-traveling clone” was also already there,
所以时间旅行者最终会按既定路线做完一切
doing everything you’ll eventually do when you time travel yourself.
比如 时间旅行者哈利和他的朋友救了他们自己
For example, Harry and friends are saved from dying by their time-traveling selves,
这里的初始时间轨道很重要
the first time history gets to that point.
在此基础上 如果你穿回过去
It makes so much sense –if you go back in time,
当然了 在那时那地
and of course you really and truly were
你是实实在在存在着的
at that location in time at that time.
这也意味着重叠时间内
This also means that during the period of overlap,
你作为时间旅行者没有自由意志
the time-traveling you has no actual free will,
因为你做的一切在某种程度上已经被做过了
since everything you do has in some sense already been done,
所以哈利知道自己不得不拯救过去的自己
which Harry comprehends when he realizes he has to save his past self
因为过去的自己
because he was already saved
已经被未来的自己拯救了
by his future self when he was in the past.
我比较欣赏这种时间旅行是因为它印证了逻辑上的一致性
I think I love this kind of time travel because it manages to be logically consistent:
回到过去却不能改变过去
it’s time travel to the past where you can’t change the past,
因为过去已经发生了
because the past already happened.
而时间轴只有一条：
And there’s only one timeline –
时间旅行者从未来而来
the one in which time travelers arrive from the future,
做了一些事 一段时间后
do stuff, and at some later date,
又回到了过去
leave to go to the past.
逻辑兼容是至关重要的
Logical consistency is a primary thing that,
你可能注意到了
you may have noticed,
我认为逻辑兼容是好的时间旅行故事的基础
I think lays the foundation for good time travel stories –
不仅因为逻辑兼容本身的重要性
not because logical consistency is important in an of itself,
还因为 在大多数情况下
but because, most of the time,
故事中的人物要想塑造得成功
in order to care about the characters in a story,
必须使其行为不能前后矛盾
we have to believe that actions have consequences.
如果发生的一切都是毫无意义的事件序列
If everything is just a meaningless series of events,
就不能成为一个完整的故事
then we almost don’t have a story.
所以如果故事世界有一定的规则
So it’s really helpful if there are rules
那就再好不过了
by which the universe of the story functions,
不管是什么规则
whatever those rules may be.
说到行为的因果性
Speaking of actions with consequences,
容我透露一下我将参与制作的视频
I finally got the kick in the pants I needed to make
该视频来自YouTube频道Corridor Digital中我的一些朋友
this video from my friends at the Corridor Digital YouTube channel.
他们请我帮忙推出新的YouTube Red原版视频系列Lifeline
They’ve asked me to help promote their new YouTube Red Original Series,
先来个小小的剧透吧
”Lifeline”, which, minor spoilers ahead…
该科幻动作惊悚视频涉及时间旅行元素
is a Sci Fi action thriller with time travel in it.
你会问 哪种时间旅行呢？
What kind of time travel, you ask?
也就是如果某人未来会死
Essentially, if somebody dies in the future,
而他给现在的世界发送了消息
that sends a message back to the present,
这样现在的他就能穿到死亡前的那一刻
which allows people to jump forward to just before the time the person dies
然后改变继续发展的时间轨道
and change the trajectory of history from that point onwards,
阻止他们的死亡
averting their death.
但你可以想象到 最后的结局不太妙
But as you might imagine, things eventually go awry.
我强烈推荐你们进入Corridor Digital频道的Lifeline版块
I highly recommend you check out the first episode
观看这个视频
of Lifeline for free on the Corridor Digital
点击屏幕上和简介中的链接也能进入观看
channel or by following the links onscreen or in the description.
告诉你们个小趣闻：
And fun facts:
其实我在“分钟物理”这个节目之前就认识Corridor频道里的朋友们了
I actually know the Corridor guys from back before MinutePhysics,
当时我还在做freddiew这个频道
when I was doing special effects for the “freddiew” channel.
我们成长于明尼苏达州相邻的城镇
We also all grew up in neighboring towns
还在高中运动会上打过对手赛
in Minnesota and even competed against each other in high school sports,
不过那时候我们还彼此不认识
though we didn’t know each other at the time.
闲话不多说啦 请去观看Lifeline频道吧
But enough trivia – go check out Lifeline!