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时光旅行有可能吗?

Is Time Travel Really Possible?

Imagine you own a watch that let’s you travel through time.
假设你有一块能穿越时空的手表
One day, you get the bright idea
一天 你脑子一热
to travel back to the 1920’s to mess with your grandparents.
想穿越回20世纪20年代 去给你祖父母捣乱
You press a few buttons,
你按了几个按钮
and suddenly you’re standing beside old Pappy
然后就突然站在了你年迈的祖父身边
who’s taking in the scenery at the precipice of the Grand Canyon.
他正沉浸在科罗拉多大峡谷险峻的风景里
Since you’ve never been the biggest fan of your grandfather,
因为你一直都不是很喜欢祖父
you decide to push him over the edge.
你决定把他推下悬崖
Gravity does its thing, and a few seconds later, no more Pappy.
在重力的作用下 短短几秒 你就再也没祖父了
But wait, if you killed your grandfather
但先等一下 如果你在你祖父
before he ever met your grandmother…
遇到你祖母之前就杀了他
you wouldn’t have been born to be able to go back in time and kill him!
那你就不可能出生 更不可能回到过去杀了他
Here’s the problem.
问题来了!
If you didn’t exist to kill your grandfather,
如果你不是来杀你祖父的
you couldn’t have killed him…
你就不会杀死他……
Because you didn’t kill him, he’s still alive.
你没有杀他 所以他还活着
but that would mean that you yourself would be alive
但这也就意味着你自己也还活着
and now you can go back in time to kill him.
现在你可以回到过去杀了他
And so the endless loop goes on.
如此便陷入了无尽的循环
This is called the Grandfather Paradox.
这被称为祖父悖论
And it’s part of what makes time travel so interesting.
这也是时间旅行很有趣的地方之一
The grandfather paradox deals with time travel on a significant scale.
祖父悖论从宏观层面解释了时间旅行
But why don’t we start with something a little smaller?
但我们为什么不从更细微处着手呢?
Let’s say you and I are wearing identical watches
假设你和我带着同一款手表
and we synchronize them right before I blast off into space.
并在我进入太空前 校对好了时间
In the space shuttle,
在航天飞机里
I’m traveling at roughly 28,000 kilometers per hour relative to the Earth.
我以约28000公里/小时的速度绕地球飞行
If I make a few orbits around the Earth before I return
如果我绕着地球轨道转几圈 再返回
when we compare watches, we’ll see that less time has passed for me.
当我们对表时 就会发现我手表的时间流逝得更慢一些
A very, very tiny amount of time, but is there nonetheless.
这只是很小 很小的一段时间 但时差是存在的
This is called time dilation,
这被称作时间膨胀
and it simply means that according to Einstein’s theory of Relativity,
它也简要说明了 根据爱因斯坦的相对论
Time measured along different trajectories is affected by differences in either gravity or velocity
不同轨迹上的时间会受到不同的地心引力或速度的影响
– each of which affects time in different ways.
——二者以不同的方式影响时间
One example of time dilation is
有一个例子可以验证时间膨胀
when we compare the passage of time on the ISS versus on Earth.
即 比较国际空间站和地球上时间的流逝速度
After spending six months on the Space Station,
宇航员在太空站待了6个月后
astronauts have aged approximately .005 seconds less than those of us here on Earth.
他的年龄比起地球上的我们 差不多会小0.005秒
Of course, this is a very insignificant amount of time,
当然 这段时间微不足道
but it would be much more apparent
但当他们的航速接近光速时
if the astronauts were able to travel to closer to the speed of light.
时间差会很显著
Interestingly, the effects of time dilation are fairly minor
有趣的是 即使速度达到了光速的70%
even up to around 70 % of the speed of light.
时间膨胀的作用仍非常小
However, once we reach 75% or so, the effects become dramatic.
但一旦达到光速的75%左右 作用将是戏剧性的
Now, bear with me here,
现在 请耐心听我说
because this is where things get a bit weird.
因为事情从这儿开始变得不可思议了
Possibly the strangest aspect of special relativity
或许狭义相对论最奇怪的地方就在于
is the distances shrink in the direction of motion.
运动中的物体在运动方向上的长度会缩短
When we think of traveling to a point 10 light years away at 90 % of light speed,
当我们设想以光速的90%穿越到10光年外的一个地方
you’d expect it to take 11 years, right?
你估计会花上11年 对吧?
That’s not exactly the case.
事实并非如此
To a stationary observer,
从静止的角度来说
it would indeed seem to take your vessel 11 years.
确实看起来 你的飞机要花11年
But to the people inside the vessel, not only time,
但对于飞机里的人来说 不光是时间
but distance would dilate
连距离也会膨胀
and you would reach that point in only 4.4 years.
你只需要4·4年就能到达目的地
Want to play with time dilation yourself?
想自己试试时间膨胀吗
I’ve added a link down below to a time dilation calculator.
我在下方添加了时间膨胀计算器的链接
Okay, that’s all really fascinating,
这些真的太有趣了!
But is it really time travel?
但这真的是时间旅行吗?
Perhaps not in the sense that we usually think of it
也许并不像我们通常认为的那样
but according to the nature of space-time, it is.
但是根据时空的本质 确实如此
If you were to return home from your 90 % light speed trip,
如果你结束了光速90%的时间旅行 回到家
you would be almost 9 years older.
你差不多会老9岁
But everyone back on Earth would have aged 22 years.
但是每个地球人都会变老22岁
So in essence, you’ve traveled 13 years
所以本质上 相对于太空中的时间来说
into the future relative to your time in space.
你已经在未来旅行了13年
let’s look at another example.
我们来看另一个例子
In the film Interstellar,
在电影《星际穿越》中
Cooper and his team land on a large watery planet,
库珀和他的团队着陆在一颗巨大的水行星上
on which gravity is 30% stronger than on Earth.
上面的重力相当于地球上的130%
This planet is situated very close to a supermassive black hole called Gargantua,
这颗行星非常靠近一个名为Gargantua的超大质量黑洞
which it orbits at 55 % speed of light.
它以光速的55%绕黑洞的轨道运行
Gargantua’s mass is equal to that of 100,000,000 suns
Gargantua的质量相当于一亿个太阳
and spins at 99.8 % the speed of light.
并以光速的99.8%在自转
The combination of all these factors have the effect of slowing down time
所有这些因素综合起来导致时间
relative to the astronaut left abord the ship, by a staggering 61,000 times.
相比于宇航员离开飞机的时间慢了惊人的6万1千倍
That means that 1 hour on the planet is equal to seven years aboard the ship.
也就是说这颗行星上的1小时相当于飞机上的7年
When the team makes it back to the vessel after a little over three of their hours,
当团队三个多小时后回到飞机时
their friend had aged by 23 years.
他们的朋友老了23岁
The craziest part is that this isn’t just science fiction.
最不可思议的是 这并不只是科幻小说
Those calculations all check out.
那些计算数据都是正确的
That’s exactly how it would happen in real life.
这确实是会在现实生活中发生的
So in essence, the crew had traveled 23 years into the future.
所以本质上说 宇航员在未来旅行了23年
Now so far, we’ve only explored traveling into the future.
到目前为止 我们只探索了未来的旅行
Is it possible to travel backwards in time?
那是否可以回到过去呢?
According to some theories,
根据某些理论
specific types of motion in space might allow time travel into the past and future,
特定类型的空间运动可能允许时间穿越到过去和未来
if these geometries and motions were possible.
前提是这些坐标和位移是真实发生的
However, that’s a big if.
不过 这只是一个大的假设
It would require something called a closed timelike curve, or CTC for short.
它必须要满足封闭类时曲线 简称CTC
A CTC is a closed loop in space time
CTC是一个时空闭环
which could theoretically allow an object to return to its own past.
理论上能够使物体回到过去
The science behind time travel to the past, is incredibly complex and speculative
回到过去的时间旅行 背后的科学技术是具有复杂性和投机性的
and many scientists suspect that it is not possible at all,
基于因果关系
because of the issue of causality.
很多科学家怀疑这根本不可能
That bring us back to the Grandfather Paradox,
这让我们又回到了“祖父悖论”的问题
if in fact these scientists are correct and
如果这些科学家是正确的
assuming traveling to the past would cause a paradox
并假设回到过去会引起悖论
then we have our answer, time travel to the past is impossible.
那我们就有了答案 回到过去是不可能的
If however, the Novikov Self-Consistency Principle is correct,
但是如果 诺维科夫自洽性原则是正确的
then there is still a chance.
那还是有机会的
The Novikov Principle states
诺维科夫自洽性原则指出
that if an event exists that would cause a paradox or
如果一个事件的存在引起了悖论
any change to the past whatsoever,
或者导致过去发生了任何变化
then the probability of that event is zero.
那这个事件发生的概率就为0
It would thus be impossible to create time paradoxes.
因此 也就不会产生时间悖论
Unfortunately, for any would-be time travelers,
不幸的是 对于任何想穿越时空的人来说
the Novikov Principle is not widely accepted.
诺维科夫自洽性原则并没有被广泛认同
Another possibility would be the existence of wormholes,
另一个可能性是虫洞的存在
which are technically permitted by general relativity.
广义相对论认为这在技术上是可行的
– In order to travel through time using a wormhole,
即 通过虫洞进行时光穿梭
it would have to be what is known as a Transversable Wormhole.
这就是所谓的“可穿越的虫洞”
Brace yourself for more strange space-time shenanigans here.
打起精神来 了解更多离奇的时空穿越诡计吧!
In order to be able to travel through time using a Transversable Wormhole,
为了能够借助 “可穿越虫洞”进行时光旅行
its creation would have to be in one of two ways.
那就要选择以下两个方法中的一个
Option one
选择1
one end of the wormhole would have to be accelerated to a significant portion of the speed of light,
虫洞的一端必须加速 使之无限接近光速
then brought back to the origin point.
然后回到原点
time dilation would result in an accelerated wormhole entrance
时间膨胀将会导致加速的虫洞入口的时间
aging less than the stationary one
比静止的入口时间流逝得慢
as seen by an external observer
这是从外部观察者的角度来说的
Option 2 requires one end of the wormhole to be placed
选择2 需要将虫洞的一端
within the gravitational field of an object with higher gravity than the other entrrance
置于一个物体的引力场内 这里的引力比另一端入口的引力大
and then returned to a position near the other entrance
然后回到接近另一端入口的某个位置
This is a difficult concept to grasp So think of it this way,
这是个很难理解的概念 你就这样想
imagine you and I synchronize our watches to both display the year 2000
设想一下 你跟我同时将手表设置为2000年
I hop in my ship and accelerate one entrance to the wormhole to near light speed
我跳上飞机 将虫洞的一端的入口加速至接近光速
and then bring it back
然后把手表带回来
my watch now reads 2004 and yours reads 2012
现在我的手表显示的时间是2004年 而你的是2012年
If someone were then to enter the accelerated entrance
如果有人进入了加速的入口
they would now exit the stationary entrance in the year 2004
并从静止的入口出去 出去的时间将是2004年
the same location, but 8 years in their past
但同一位置的时间 却已经过去了8年
It’s incredibly complicated stuff
这是个超级复杂的概念
But an easier way to look at it is by picturing by a piece of paper
理解它的一个更简单的办法就是借助一张纸
This paper represent space time,
假设这张纸代表了时空
a wormhole is an area of warped spacetime with an entrance and an exit
虫洞是一个有入口和出口的扭曲时空区域
which you can imagine
你可以想象
as the paper being folded back on itself with a hole poked through it
这纸张折叠了 上面有个洞穿过
essentially you’re simply skipping all the time and distance between the two points
本质上 你只是跳过了两点之间的时间和距离
The problem with transversable wormholes
可穿越虫洞的问题是
is that you can’t possibly travel back further than the initial creation of the wormhole
你不可能穿越到 比虫洞最初创建的点更远的地方
So…really it’s more a path through time rather than
所以…实际上 这更像是一条时光隧道
a device propels itself back and forth through the years at will
而不是一个可以在岁月间任意穿梭的装置
It could be useful for the people in the distant future wanting to come observe our time
它可能对那些在遥远的未来想要来观察我们现在时间的人类有用
but if we created such a portal today
但如果我们今天就创建这样一个门户
we couldn’t use it to go visit the dinosaurs
我们并不能用它去看到恐龙
One final method that could potentially
最后一种可能
One final method that could potentially allow an individual to more or less travel through time is cryopreservation
让一个人或多或少能穿越时间的方法是冷冻保存
The branch of science concerned specifically with preserving human is called cryonics
专门研究保存人体的科学分支叫做人体冷藏学
and the practice has been around since the late 1960s.
这种方法可以追溯到20世纪60年代末
Cryonics is on the speculative edge of medicine
人体冷藏学的研究现在属于医学边缘学科
as its proponents suggest that Death is not a singular event, but a process
正如它的支持者所说 死亡不是一个单一的事件 而是一个过程
it would have to be for the practice to be successful
也只有这样 实践才能成功
because it’s currently illegal for a human to be frozen before they die
因为在现阶段 人类在死前被冷冻是违法的
When a person opted to be cryo-preserved
当一个人选择了人体冷冻
their bodies prepared minutes after official death
他们的尸体要在宣布死亡几分钟后就准备就绪
the theory is that by reducing the patient’s body temperature to around -130 degrees celcius
理论上通过把病人的体温降到零下130摄氏度
enough brain information will be retained in an accessible state
足够的大脑信息将以可达的状态被保留
for doctors and scientists of the far future to revive the patient
从而使未来的医生和科学家 能够唤醒病人
temperatures of that low inevitably cause significant damage to the human body
无论之前是否做了保护措施 如此低的温度不可避免地
regardless of prior-preservation safeguards
会对人体造成严重的伤害
so the doctors of today are relying on the development of future technology
所以今天的医生都依赖于未来技术的发展
that will allow the brain to be repaired at the molecular level
让大脑在分子层面上得以修复
and restored to functioning condition
并恢复到正常状态
if someday technology has advanced far enough
如果有一天科技进步到一定程度
to revive cryo-preserved humans
可以让冷冻保存的人类复活
they will have essentially time traveled to the future
从本质上说 他们就穿越到了未来
it’s not quite as easy as shows like futurama make it seem
这并不像《飞出个未来》 里展示的那么容易
but it is theoretically possible
但在理论上是可行的
and that’s time travel in a nutshell
简而言之 这就是时间旅行
you really can move forward through time by
你真的可以
traveling at an immense speeds or through cryo-preservation
通过极快的速度或人体冷冻技术穿越到未来
But travel to the past is likely impossible
但回到过去似乎就不可能了
of course the science of quantum physics and time travel is incredibly vast
当然 量子物理和时间旅行的科学是非常广阔的
and well beyond the grasp of most normal people
远远超出了大多正常人的想象
so we may be missing just one crucial element
因此 我们可能只是遗漏了来理解
to understanding exactly how spacetime works
时空具体是如何运作的某个关键因素
but who knows?
但谁知道呢?
maybe someone from the far future will show up in our time
也许来自遥远未来的某个人会出现在我们的时代
and give us the key to unlocking the mystery or…would that cause a paradox
给我们解开谜团 或者又会引起悖论?
as always, I’ve included sources and links for further reading in the description
和之前一样 我会留下资源和链接 您可以进行更深入的阅读
if you enjoy this video please
如果您喜欢这个节目
take a moment to subscribe my channel
请您花一点宝贵的时间订阅我的频道
your support helps me keep releasing two videos every week
您的支持会让我每周坚持更新2个视频
feel free to leave a like or dislike as you please
请留下您喜欢或不喜欢的评价
and share your thoughts on time travel in the comments
并在留言中分享有关时间旅行的想法
thanks for watching! And I’ll see you in the next video
感谢您的收看 下期节目再见

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视频概述

本文简要介绍了时光旅行的可行性以及时光旅行的方法和未来设想

听录译者

收集自网络

翻译译者

紫琳轩

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审核员XY

视频来源

https://www.youtube.com/watch?v=pQC3ErD1YwE

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