与摩根·弗里曼一起穿越虫洞（2010）

我们也许会认为现在发生的事情会改变他们最终的状态
We may think what happens now changes their final state,
但实际上，成品巧克力中的成分
but actually, what's inside the finished chocolates
决定了可以放进去的原料
determines the ingredients that can be put in.
也许有某种巧克力原料
There may be certain chocolate ingredients
与成品的状态不一致
that are simply inconsistent with this final state.
在生产线的中间
In the middle of the production line,
看起来机器可以添加奶油原料
it may appear the machines can add a cream filling
或者覆盆子原料
or a raspberry filling,
但由于成品巧克力含有覆盆子
but since the finished chocolates contain raspberry,
只有粉色的原料可以进入生产线
only the pink filling can possibly enter the line.
终点限制了现在的可能
The end limits what is possible now.
保罗认为类似的限制
And Paul thinks there's a similar limiting effect
从宇宙终极的未来
radiating back to our present
辐射到了我们的现在
from the ultimate future of the universe.
如果我们想象宇宙的最终状态
If we imagine the final state of the universe
被自然以某种方式固定
being fixed by nature in some way,
可以牵连到
then that would have implications
我们现在看到的生产线
for the production line that we're seeing now.
与巧克力的一大差别是
The big difference with the chocolates
无论发生了什么
is that whatever happens,
巧克力都会有一个最终的状态
there will be a final state of the chocolates.
这在机器的内部提前决定好了
That is determined in advance by the internal machinery.
但是在真实的宇宙中，就连大自然
But in the real universe, nobody, not even nature,
也无从知道最终状态将会是怎样的
knows what that final state will be.
尽管没有人可以确定
Although no one can say for sure,
但大多数的科学家认为
most scientists think
宇宙遥远的未来将来是寒冷、黑暗
the far future of the cosmos will be cold, dark,
空空如也的
and completely empty of all particles.
保罗认为我们也许能够发现
Paul thinks we might be able to detect
未来对于我们此时此地
the effects of this future on certain experiments
的某个实验的效果
we perform here and now.
一个主意是向深邃的太空中发射一束激光
One idea is to fire a laser into deep space.
只要保罗的激光束最终遇到了什么东西
As long as Paul's laser beam eventually runs into something,
比方说一颗行星
like a planet,
激光可以正常发射
then the laser will fire as normal.
然而，保罗把激光对准
However, if Paul directs his laser
空间中完全空荡的路径
into a completely empty patch of space,
没有什么东西可以阻挡它
where nothing would ever block it
理论上它就能永远传播下去
and it could, in theory, travel forever,
激光也许不工作
the laser might not work.
所以你可以将激光指向天空中黑暗的部分
So you can point a laser at the dark parts of the sky,
你会注意到那里没有任何光传来
and you can notice there wasn't any light coming out
或者没有多少光
or there's not much light.
光不会传来
Light wouldn't come out
因为宇宙遥远的未来不允许任何光存在
because no light is allowed in the far future of the universe.
如果宇宙的终点状态确实是黑暗而空洞的
If the end state of the universe is, indeed, dark and empty,
没有任何现在的东西，像是激光束的光子
nothing from the present, like photons from the laser beam,
被允许到达那里
can be allowed to reach it.
寻找未来影响现在的证据
Finding evidence that the future influences the present
产生了有趣的可能性
creates an intriguing possibility.
我们现在，可以穿越并影响我们的过去吗？
Can we, right now, reach back and affect our own past?
量子力学表明，未来可以控制过去
Quantum mechanics suggests the future can control the past.
也许有一天，我们将把理论变成实践
Maybe some day, we'll turn theory into practice,
但是有什么限制呢？
but what are the limits?
有人能回到过去，改变历史吗？
Could someone go back in time and change history,
在希♥特♥勒♥发起战争之前阻止他
stop Hitler before he starts a war
或者从刺客的子弹下解救肯尼迪？
or save JFK from an assassin's bullet?
托德·布龙喜欢想象生活在过去
Todd brun likes to imagine what it would be like
会是怎样一番体验
to live in the past.
作为南加州大学的一名物理学
And as a professor of physics and electrical engineering
和电子工程学教授
at the university of Southern California,
他正在尝试搞清
he's actually trying to work out
回到过去是否可能
whether traveling back in time is possible.
时间的方向是一个谜
The direction of time itself is something of a mystery.
在物理学的公式里，看起来好像
In the equations of physics, it seems like
你既可以向前又可以向后
you could run them either forwards or backwards.
但我们观察到的周围的一切
But everything we observe in the world around us
都指出时间只有一个可能的方向——向前
points to time having only one possible direction -- forwards.
任何东西都在变老、衰败
Everything grows older, everything decays.
当我们在黑板上写字
When we write on a chalkboard,
我们留下的印迹是粉笔灰
the marks that we leave are chalk dust
从粉笔的一端变成碎屑
that crumbles off of the end of our stick of chalk
粘在了黑板上
and sticks to the board.
如果我沿着黑板移♥动♥粉笔
If I move my stick of chalk over a chalkboard,
粉笔灰并不会
the dust that crumbled off the end
重新粘回到粉笔上
doesn't, once again, adhere to my stick of chalk
使它变成一根更长的粉笔
and make it a longer stick of chalk.
这就是时间箭头的工作方式
That's the arrow of time at work.
然而，如果时间真的是一个维度
However, if time is really a dimension,
像爱因斯坦说得那样，那麽逝去的时间仍然存在
as Einstein says, time that's passed still exists.
只是位于维度向前的宇宙中
It's simply located somewhere else
其他的某个地方了
in the forward dimensional universe.
对于宇宙中任何正在发生的、已经发生过的
Space-time is the entire four-dimensional background
以及将要发生的事情来说
for everything that happens and ever has happened
时空都是一个整体的四维背景
and ever will happen in the universe.
过去的事件或许没有从宇宙中消失
Events in our past may not be gone from the universe,
但是我们触及不到
but they are out of reach.
如果你以超光速旅行
If you travel faster than the speed of light,
爱因斯坦的相对论方程
Einstein's equations of relativity
说你的时间将会倒流
say your time ticks backwards.
麻烦在于，这需要无穷大的能量
The trouble is, it takes an infinite amount of energy
才能达到光速
to reach the speed of light,
所以你还是忘了吧
so you can forget that.
但也许有方法到达过去
But there may be ways to get to the past.
称作闭合类时曲线
They're called closed time light curves,
时空结构的这种奇怪的扭曲
strange distortions of the fabric of space-time
给你提供通向另一个时刻的捷径
that could give you a shortcut to a different moment in time.
时空中物质的某种外来的排列
Some very exotic arrangements of matter in space-time
可以让这些路径如此地弯曲
can cause these paths to actually curve so much,
直到弯成一个环
they curve all the way around back upon themselves.
您好
Howdy.
穿梭时间的托德
Time-traveling Todd
不需要比光线跑得更快
wouldn't have to travel faster than light.
他向前运动时，时空的褶皱
As he moves forward, the fold in space-time
会带他去空间中的同一个点
would carry him backward to the same point in space
但在时间上更早些
but at an earlier time.
这不是我们在宇宙中通常观察到
This is not the situation that we normally observe
的情况
in the universe,
但人们可以解开爱因斯坦的方程
but people can solve Einstein's equations
找到包含
and find these solutions
封闭类时曲线的解
that contain these closed time light curves.
物理学的法则说我们可以访问过去的一个点
The laws of physics say we can visit a point in the past.
没有什么能阻止托德拜访他的一位祖先
There's nothing stopping Todd visiting one of his ancestors
并向他解释他是如何跳到了过去的
and explaining how he managed to jump back in time.
你可能觉得这很好玩
You might find this interesting.
然而，托德认为改变过去是不可能的
However, Todd thinks it's impossible to alter the past.
托德的祖先一定总是接待了一个来自未来
Todd's ancestor must always have received a visitor
的访问者
from the future.
单一宇宙的历史
The history of a single universe
只能包含一个行为集♥合♥
can only contain one set of actions.
产生冲突的事情
Things that are incompatible,
不一致的事情
things that are actual inconsistencies
是不被允许的
should not be allowed.
时间旅行者做的任何事情
Anything the time traveler does
必须与已经发生的历史相符
must fit in with what's already happened.
例如，托德是一个时间旅行者
For example, let's say Todd is a time traveler
他希望改变过去
who hopes to alter some past event,
想象托德想做的是让一场舞会停下来
and imagine that event is a dance Todd wants to stop.
过去必须是一致的
The past has to be consistent,
所以如果我走到舞会的中间
so if I go into the middle of the dance