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大家好 Hello.
我是斯蒂芬·霍金 My name is Stephen Hawking.
物理学家 宇宙学家 Physicist, cosmologist,
有时也是一个梦想家 and something of a dreamer.
尽管我行动不便 说话要借助电脑 Although I cannot move and I have to speak through a computer.
但在精神世界中 我是自由的 In my mind, I am free.
自由地去探索宇宙 Free to explore the universe
探究深奥的问题 and ask the big questions.
比如 时间旅行可能吗 Such as is time travel possible?
我们能打开通往过去之门吗 Can we open a portal to the past?
或者找到通往未来的捷径 Or find a shortcut to the future?
我们最终能利用 Can we ultimately use the laws of nature
自然规律操纵时间吗 to become masters of time itself?
一起去探索吧 Check it out.
与霍金一起探索宇宙 时间旅行
时间旅行曾一度被当作科学邪说 Time travel was once considered scientific heresy.
由于害怕被贴上科学怪人的标签 I used to avoid talking about it
我过去常常避免谈及此事 for fear of being labeled a crank.
现如今 我不会再顾虑这些 But these days, I'm not so cautious.
实际上 我更像是建造巨石阵的那些人 In fact, I'm more like the people who built stonehenge.
我对时间着迷了 I'm obsessed by time.
若我有台时间机器 If had a time machine
我想去拜访鼎盛时期的玛丽莲·梦露 I'd visit Marilyn Monroe in her prime
或者去拜访正用望远镜 or drop in on Galileo as
眺望星空的伽利略 he turned his telescope to the heavens.
我甚至想穿越到宇宙的尽头 Perhaps I'd even travel to the end of the universe
去探寻宇宙的完整故事结局 to find out how our whole cosmic story ends.
要验证这些想法能否实现 To see how this might be possible,
我们需要像物理学家那样 we need to look at time as physicists do
以四维的角度看时间 as the fourth dimension.
四维时空并不像听起来那样令人费解 It's not as hard as it sounds.
所有的物体 甚至是我和我的椅子 All physical objects, even me and my chair,
都是三维的 exist in three dimensions.
任何事物都有宽度 高度和长度 Everything has a width and a height and a length.
但是还存在另一种维度 即时间维度 But there is another kind of length -- a length in time.
与人类的80余年寿命相比 While a human may survive for 80 years,
这些石头延续得更久远 these stones will last much longer
甚至长达数千年 -- for thousands of years.
而太阳系则能达到数十亿年 And the solar system will last for billions of years.
所有事物在时间上都有长度 Everything has a length in time,
在空间内同样如此 as well as space.
时间旅行意味着 Traveling in time means
穿越第四维时空 traveling through this fourth dimension.
为更好地理解 我们以日常旅行为例 To see what that means, let's do a bit of normal
来直观体会一下四维时空的含义 everyday traveling just to get a feel for it.
一辆高速行驶的车能让实验变得更生动 A fast car makes it a bit more fun.
在一条直线上行驶 是在一维空间内 Drive in a straight line, and you're traveling in one dimension.
左转或右转 就增加了第二维空间 Turn right or left, and you add the second dimension.
在蜿蜒的山路上下颠簸 Drive up or down a twisty mountain road,
就增加了高度的维度 and that adds height.
这样就算是在三维空间内行驶了 So that's traveling in all three dimensions.
但我们究竟要怎样才能实现时间旅行呢 But how on earth do we travel in time?
怎样才能找到一条 How do we find a path
通往第四维空间的路呢 through the fourth dimension?
让我们用一个小小的科幻情节放松一下 Let's indulge in a little science fiction for a moment.
时间旅行的电影里通常会 Time-travel movies often
出现一个巨型高耗能机器 feature a vast energy-hungry machine.
这台机器开辟了一条通往四维空间的道路 The machine creates a path through the fourth dimension,
一条时间隧道 a tunnel through time.
翻译：super zhanginfo vividx 取子小Q
初校：amira 精校：super 时间轴：Ghost
后期：鱼骨头 总监：阿橙
时间旅行者 是勇敢者 A time traveler, a brave,
也许也算是准备踏入 perhaps foolhardy individual
未知空间的愚勇之士 prepared for who knows what,
义无反顾地踏入时间隧道 step into the time tunnle
在未知的时间再现 and emerges who knows when.
这种构想兴许有些牵强 The concept may be far-fetched,
现实也可能与此大相径庭 and the reality may be very different than this,
但想法本身并没那么疯狂 but the idea itself is not so crazy.
物理学家也一直在为时间隧道绞尽脑汁 Physicists have been thinking about tunnels in time,too,
不过我们要从另一个角度来揭示这个问题 but we covered it from a different angle.
我们不知道在自然法则允许范围内 We wonder if portals to the past or the future
是否可能出现通往过去或未来的大门 could ever be possible within the laws of nature.
事实上 As it turns out,
我们认为有可能 we think they are.
甚至给他们命名 What's more we even give them a name:
虫洞 wormholes.
事实上虫洞无处不在 The truth is the wormholes are all around us,
只不过它们微小至肉眼难以看到 only they are too small to see.
虫洞非常微小 Wormholes are very tiny,
它们存在于时间和空间的各个角落 they accur in nooks and crannies in space and time.
你或许不敢苟同 但请继续看 You might find it tough concent, but stay with me.
任何东西都不是平坦或者实心的 Nothing is flat or solid.
如果你仔细观察 If you look close enough at anything,
就会发现小洞和细缝无处不在 you'll find holes and crannies in it.
这是最基本的物理原理 It's a basic physical principle
对时间也同样适用 and it even applies to time.
看这个桌球台 Take this pool table.
表面看起来平整光滑 但靠近了看 The surface looks flat and smooth, but up close,
实际并非如此 it's actually anything but.
它的表面布满了裂缝和小孔 It's full of gaps and holes.
就连桌球这样的光滑事物 Even something as smooth as a pool ball
都有小的裂缝 细纹和小孔 has tiny crevices, wrinkles, and voids.
显而易见 Now, it's easy to show that
这在三维空间里毋容置疑 this is true in the first three dimensions,
但是相信我 but, trust me,
在第四维空间里这也是正确的 it's also true of the fourth dimension, as well.
在时间空间里 There are tiny crevices, wrinkles, and voids
也有小的裂缝 细纹和小孔 in time.
不断地缩到最小的范围 Down at the smallest of scales,
甚至比分子原子还微小时 smaller even than molecules,
我们所得到的 smaller than atoms, we get to a place
就是量子泡沫 called the quantum foam.
虫洞就存在于此 This is where wormholes exist.
在量子的世界里 Tiny tunnels, or shortcuts,
穿越时空的微小隧道或捷径 through space and time constantly form,
不断地形成 消失 再形成 disappear, and reform within this quantum world.
它们实际上连接了两个独立的区域 And they actually link two separate
和两处不同的时间 places and two different times.
不幸的是 这种真实存在的时间隧道 Unfortunately, these real-life time tunnels are
只有10的-33次方厘米的大小 just a billion trillion trillionths of a centimeter across --
远不足以容纳人类通过 way too small for a human to pass through.
但虫洞时间机器的概念正带来更多灵感 But here's where the notion of wormhole time machines is leading.
一些科学家认为或许可以捕捉 Some scientists think it may be possible to
其中一个虫洞将其放大数万亿倍 capture one and enlarge it near trillions of times
让它大到足以能让人类 to make it big enough for a human
甚至宇宙飞船进入 or even a spaceship to enter.
假设有足够的能量和高科技 Given enough power and advanced technology,
或许可以在宇宙中构造一个巨大的虫洞 perhaps a giant wormhole could even be constructed in space.
我不是说这一定可行 I'm not saying it can be done,
但如果真能面世 but if it could be,
它将是一个非常卓越的机器 it would be a truly remarkable device.
一端在地球附近 One end could be here near the earth,
而另一端则在遥远的星际 and the other far, far away, near some distant planet.
理论上 虫洞能够发挥更多用途 Theoretically, a wormhole could do even more.
如果两口开在同一个地方 If both ends were in the same place and separated by
没有距离阻隔但却处在不同时间 time instead of distance,
飞船则可以还在地球附近起降 a ship could fly in and come out still near the earth,
却已穿越到远古 but in the distant past.
或许恐龙将有幸目睹飞船着陆 Maybe dinosaurs would witness the ship coming in for a landing.
此时我意识到用四维空间去思考并非易事 Now, I realize that thinking in four dimensions is not easy and
虫洞也是令人费解的复杂概念 that wormholes are a tricky concept to wrap your head around.
不过请再坚持一下 But hang in there.
我曾构想出这样一个简单的实验 I've thought up a simple experiment that could
能够揭示在目前抑或今后 reveal if human time travel through a wormhole is possible now,
人类能否通过虫洞穿越时间 or even in the future.
我喜欢简单的实验和香槟酒 I like simple experiments and champagne.
因此将两大喜好结合起来 So I've combined two of my favorite things to see if
以视从未来回到过去的时间旅行是否可行 time travel from the future to the past is possible.
我在举办一个派对 I'm throwing a party,
未来时间旅行者的欢迎酒会 a welcome reception for future time travellers.
欢迎时间旅行者光临
不过有点小插曲 But there's a twist.
在派对结束前 I am not letting anyone know about it
我不打算让任何人知道这事 until after the party has happened.
"诚挚邀请您光临时间旅行者欢迎酒会" "邀请人:斯蒂芬·霍金教授"
"地点:剑桥大学理论物理研究所" "无需回复此请柬"
这就是那张请柬 Here is the invitation, giving the
具体的时空参数悉数标出 exact coordinates in time and space.
我希望其中一张 无论以何种形态 I am hoping a piece of it, in one form or another,
能留存至数千载以后 will survive for many thousands of years.
也许未来的人会得此信息 Maybe one day someone living in the future will find the information
并利用虫洞时间机器回来参加此派对 and use a wormhole time machine to come back to my party,
以此证明有朝一日时间旅行并非空谈 proving that time travel will one day be possible.
时间旅行的贵客随时都可能光临 My time-traveller guests could be arriving any moment now.
5 Five
4 Four
3 Three
2 Two
1 One
太遗憾了 What a shame.
本希望有位未来的"环球小姐" I was hoping a future Miss Universe
前来光顾 was going to step through the door.
那么 这一实验为什么没有奏效呢 So, why didn't the experiment work?
我认为原因之一可能就是 I think one of the reasons might be because of a well-known
穿越往昔中众所周知的难题 problem with time travel to the past --
即悖论问题 the problem of paradoxes.
悖论很有意思 Paradoxes are fun to think about.
其中最为著名的便是 The most famous one is usually called
亦称外祖母悖论
"祖父悖论" the grandfather paradox.
我提出了一个全新而简洁的版本 I have a new, simpler version
我称之为"疯狂科学家悖论" I call the mad-scientist paradox.
尽管我不喜欢影片常把科学家 I don't like the way scientists in movies are often
刻画为异想天开的狂人形象 described as mad,
但此情此景下的确如此 but in this case, it's true.
这个日本小子决计营造一个悖论情景 This Jap is determined to create a paradox.
即便要豁上自己的性命 Even if it costs him his life.
试想他以某种方法造出一个虫洞 Imagine somehow he's built a wormhole.
一个返回一分钟前的时间隧道 A time tunnel that stretches just one minute into the past.
这听上去没什么意义 It may not sound like much,
但哪怕一分钟的时间旅行也会引起大麻烦 but even one minute of time travel can cause real trouble.
通过这个虫洞 Through the wormhole,
这位科学家得以看到一分钟之前的自己 the scientist can see himself as he was one minute ago.
但假如我们这位主人公利用虫洞 But what if our scientist uses the
向一分钟之前的自己开枪呢 wormhole to shoot his earlier self?
此时他已一命呜呼 He's now dead,
还未装好枪支就已被射杀 killed before he'd even finished assembling the pistol.
那么 开枪者又是谁呢 So, who fired the shot?
这便是一个悖论 It's a paradox.
这完全说不通 It just doesn't make sense.
这种情形是宇宙学家的恶梦 It's the sort of situation that gives cosmologists nightmares.
这样的时间机器会违背 This kind of time machine would violate
主宰全宇宙的基本法则 a fundamental rule that governs the entire universe
使因果关系颠倒 - that causes happen before effects
并始终与我们的常理相悖 and never the other way around.
我相信不可能的事就不会发生 I believe things can't make themselves impossible.
倘若可以 If they could,
整个宇宙将不可避免地陷于混乱 then there'd be nothing to stop the whole universe from descending into chaos.
因此我认为终究会有状况发生 So I think something will always
从而避免悖论的出现 happen that prevents the paradox.
也总会有某种原因避免 Somehow there must be a reason why our scientist will never
那位科学家处在射杀自己的困境中 find himself in the situation where he could shoot himself.
既然如此 我只好遗憾地说 And in this case, I'm sorry to say,
虫洞本身就是问题所在 the wormhole itself is the problem.
至此 我认为这样的虫洞根本不会存在 In the end, I think a wormhole like this one can't exist.
其原因就是"反馈" And the reason for that is feedback.
假如你曾亲临摇滚现场 If you've ever been to a rock gig,
大概不会对这样刺耳的噪音感到陌生 you'll probably recognize this screeching noise.
这便是"反馈" 其道理浅显 It's feedback. What causes it is simple.
声音进入麦克风 Sound enters the microphone.
随后通过电缆传播 It's transmitted along the wires,
经扩音器放大 make louder by the amplifier.
最终由音箱发出 and comes out at the speakers.
但倘若有太多声音由音箱返回麦克风 But if too much of the sound from the speakers go back into the mike,
声音便会在此回路中不停折返 it goes round and round in a loop,
并被逐次放大 getting louder each time.
如不加阻止 反馈信号将毁坏音响系统 If no one stops it, feedback can destroy the sound system.
我认为这也同样适用于虫洞 I think the same thing will happen with a wormhole,
只不过传播的是辐射而非声音 only with radiation instead of sound.
虫洞一旦开始张开 As soon as the wormhole expands, natural
自然辐射便会进入其中并终结于回路 radiation will enter it and end up in a loop.
反馈将足够强大以至将虫洞摧毁 The feedback will become so strong, it destroys the wormhole.
因此尽管微型虫洞的确存在 So, although tiny wormhoes do exist,
而且也可能某天被放大 and it may be possible to inflate one someday,
其生命之短暂则无法被用作时间机器 it won't last long enough to be of use as a time machine.
这正是无人光顾派对的真正原因 That's the real reason no one came to the party.
事实上 我基本不相信可以利用虫洞 In fact, I believe any kind of time travel to the past through
或者其他可能手段重返过去 wormholes or any other method is probably impossible.
否则便会导致悖论 Otherwise, paradoxes would occur.
因此遗憾地说 So, sadly,
回到从前似乎永远不会发生 it looks like time travel to the past is never going to happen,
这对于恐龙猎手恐怕是个遗憾 A disappointment for dinosaur hunters
但对于历史学界却是种解脱 and a relief for historians.
不过故事尚未结束 But the story's not over yet.
这并不意味所有时间旅行都无法实现 This doesn't make all time travel impossible.
我对时间旅行深信不疑 I do believe in time travel,
相信人们能够跨入未来 time travel to the future.
时间如河水般流淌 Time flows like a river,
似乎人类也只能任由时间长河无情地摆布 and it seems as if each of us is carried relentlessly along by time's current.
不过时间似流水还有另一层含义 But time is like a river in another way.
其在不同地点有着不同速度 It flows at different speeds in different places.
而这正是穿梭于时间的关键所在 And that is the key to traveling into the future.
这一概念在100多年前 The idea was proposed by Albert Einstein
由阿尔伯特·爱因斯坦提出 over 100 years ago.
他认为时间在一些地方会减慢 He realized that there should be places where time slows down
而在另一些地方则会增快 and others where time speeds up.
这话可是千真万确 He was absolutely right,
证据就在我们头顶的那片太空中 and the prove is right above our heads, up in space.
这是全球定位系统 又叫GPS This is the Global Positioning System, or GPS.
是由绕地球轨道运行的 A network of 31 satellites
31颗卫星形成的网络 in orbit around the earth.
正是这些卫星使卫星导航变为可能 The satellites make satellite navigation possible.
但同时也表明 But they also reveal that time runs faster up here
在这里时间流逝得比地球上快 than it does down on earth.
每个航天器内都有一个十分精确的时钟 Inside each spacecraft is a very precise clock.
尽管已经十分精确 But despite being so accurate,
但他们每天都大约会走快 they all gain around
十亿分之一秒的三分之一 a third of a billionth of a second every day.
系统必须更正这一偏差 The system has to correct for the drift.
否则这细微的差异会扰乱整个系统 Otherwise that tiny difference would upset the whole system,
致使地球上所有GPS设备 causing every GPS device on earth
每天出现约6英里的误差 to go out by about six miles a day.
其引起的混乱可想而知 You can just imagine the mayhem that would cause.
问题并不在于时钟 The problem doesn't lie with the clocks.
时钟走得快是因为在这里时间本身 They run fast because time itself runs faster here than
就比在地球上快 it does down below,
产生这种奇异现象的原因 and the reason for this extraordinary effect
在于地球的巨大质量 is the mass of the earth.
爱因斯坦意识到 物质滞延时间 Einstein realized that matter drags on time,
像河流的缓流部分那样令时间减速 slows it down like the slow part of a river.
物体越重 滞延时间越长 The heavier the object, the more it drags on time,
这一惊人的事实 and this startling reality
打开了一扇穿越未来的希望之门 is what opens the door to the possibility of time travel to the future.
我承认这个概念很难理解 I admit this is a difficult concept to understand,
所以让我们来看一个简单的例子 so let's take a simple example.
这是吉萨的大金字塔 This is the Great Pyramid of Giza.
重达4000多万吨 It weighs over 40 million tons,
与其他所有沉重的物体一样 and like all heavy things,
它会减慢时间 it's actually slowing down time.
不过影响微弱 The effect is small,
只及地球影响力的几十亿分之一 billions of times smaller than that of the earth.
但是如果大幅放大这种影响 But if we exaggerate it drastically,
就能看到这种原理在起作用 You can see the principle at work.
金字塔附近的一切都慢了下来 Close to the pyramid, everything is slowed down,
就像河流的缓流部分那样 again, like the sluggish part of a river.
相对于远处的时间流逝速度 Here time itself is passing slower
这里的时间速度更慢一些 compared to how it's passing further away.
如果金字塔附近的人向外看又会怎样 But what if people near the pyramid look outwards?
他们一定会看到相反的效果 They must see the opposite effect.
由于他们自己的时间减慢 Because they are slowed down,
一定会看到远处时间加速的景象 they must see time in the distance as running fast.
原因就在于金字塔的巨大质量 It's a simple result of the mass of the pyramid.
这种时间扭曲为时间旅行提供了可能性 This distortion opens the door to the possibility of time travel.
因此为实现真正的时间旅行 So what we need to really travel in time
我们需要些质量远大于金字塔的物体 is something much more massive than a pyramid.
而我恰好知道一个符合条件的物体 And I know just the thing.
就在银河系中央 Right in the center of the milky way,
距我们26000光年的地方 26,000 light-years from us,
有整个银河系中质量最大的物体 lies the heaviest object in the entire galaxy,
隐藏在大片气体和星体中 hidden by a vast cloud of gas and stars.
它就是特大质量黑洞 It's a supermassive black hole
质量相当于400万个太阳 containing the mass of 4 million suns
在自身重力作用下挤压成一个点 crushed down into a single point by its own gravity.
离黑洞越近 引力作用越强 The closer you get to the black hole, the stronger the gravity.
接近到一定程度 即便是光也难以逃脱 Get really close, and not even light can escape.
黑洞隐藏于 So it's wrapped in
直径为1500万英里的黑暗球体区域 a sphere of darkness 15 million miles in diameter.
像这样的黑洞对时间具有强大的影响力 A black hole like this one has a dramatic effect on time,
减慢时间的程度 slowing it down
甚于银河系里其他任何物体 far more than anything else in the galaxy.
这使之成为一个天然的时间机器 That makes it a natural time machine.
我对未来宇宙飞船如何利用 I like to imagine how a spaceship might someday be able to
这一奇观拭目以待 take advantage of this spectacular phenomenon.
当然 它首先必须避免被吸入其中 Of course it would first have to avoid being sucked in.
我认为关键就在于 The trick, I think, would be to aim
准确无误地沿切线驶过 才能避过黑洞 just off to the side so they'd miss it.
宇宙飞船必须 They'd have to
处于完全正确的轨道并达到精准的速度 be on exactly the right trajectory and speed,
否则在劫难逃 or they'd never escape.
如果一切正常 宇宙飞船就会进入 Get it right, and the ship would be pulled into orbit,
一个直径为3000万英里的巨型圆轨道 a giant circle 30 million miles in diameter.
在这里它就安全了 Here it would be safe.
它的速度足以避免其坠入黑洞 Its speed would be enough to keep it from falling any further in.
如果某航天局从地球或其他任何 If a space agency were controlling the mission from earth or
远离该黑洞的地方远程操控该任务 anywhere else far away from the black hole,
会发现飞船沿轨道运行一周需16分钟 they'd observe that each full orbit took 16 minutes.
但是对于飞船上勇敢的宇航员 But for the brave people on board,
由于接近质量巨大的物体 close to this massive object,
时间将会减慢 time would be slowed down.
而这一位置上的减慢效果远比 And here the effect would be far more extreme than
在金字塔或地球附近显著 near the pyramid or planet earth.
宇航员的时间将减慢一半 The crew's time would be slowed down by half.
每16分钟的轨道运行 For every 16-minute orbit,
他们实际只需用8分钟时间 they'd only experience 8 minutes of time.
一圈又一圈 Round and round they'd go,
宇航员度过的时间 experiencing just half the time of
只有远离黑洞人们的一半 everyone far away from the black hole.
飞船将载着宇航员在时间中穿行 The ship and its crew would be traveling through time.
试想宇航员绕着黑洞转了5年 Imagine they circle the black hole for 5 of their years,
相当于地球上过了10年 10 years would pass elsewhere.
他们返航时 When they got home,
地球上所有人的年龄都比他们多增长5岁 everyone on earth would have aged 5 years more than they had.
宇航员们回到的是未来的地球 The crew of the spacecraft would return to a future earth.
他们应该经历了一段空间更是时间的旅行 They would have made a journey not only in space, but in time.
因此特大质量黑洞就是一个时间机器 So a supermassive black hole is a time machine.
当然 这并不完全可行 But of course it's not exactly practical.
它优于虫洞的地方是不会产生悖论 It has advantages over wormholes in that it doesn't provoke paradoxes.
并且不会在反馈瞬间摧毁自身 Plus it won't destroy itself in a flash of feedback.
但它仍然非常危险 But it's pretty dangerous.
行路迢迢 It's a long way away.
而且也不能将我们带入非常久远的未来 And it doesn't even take us very far into the future.
所幸还有另外一种穿越时间的方法 Fortunately, there is another way to travel in time,
它是我们建造真正时间机器的 and this represents our last and best
最后也是最有望实现的一丝希望 hope of building a real time machine.
通过第四维空间进行时间旅行 Traveling through the fourth dimension
永远不会像在公园散步那么简单 will never be a walk in the park.
但事实上存在一个惊人的 But it turns out there is a surprisingly
直通途径 straightforward way to do it.
你只需以极快极快的速度移动 You just have to travel very very fast,
甚至要快于能够 much faster than even the high speed required
避免被吸入特大质量黑洞的高速度 to keep out of the supermassive black hole.
其中的奥妙在于另一个奇妙的宇宙事实 This is because of another strange fact about the universe.
世界上存在宇宙速度极限 There's a cosmic speed limit --
186000英里/秒 186,000 miles per second,
即人们熟知的光速 also known as the speed of light.
这是世间最快的速度 Nothing can exceed that speed.
我知道这听起来有些奇怪 但请相信我 I realize this sounds weird, but trust me.
这是最具权威的科学定理之一 It's one of the best established principles in science.
信不信由你 Believe it or not,
以接近光速的速度移动 traveling at near the speed of light
你就能穿越至未来 transports you to the future.
为弄清原委 To explain why,
我们来想象一个科幻的运输系统 let's dream up a science-fiction transportation system.
试想有一条紧绕地球的轨道 Imagine a track that goes right around the earth.
一条极速列车专用轨道 A track for a superfast train.
假定这列虚幻列车无限接近光速 We're going to use this imaginary train to get as close as possible
看它如何变成时间机器 to the speed of light and see how it becomes a time machine.
列车上的乘客手持通向未来的单程票 On board are passengers with a one-way ticket to the future.
列车开始不断加速 越来越快 The train begins to accelerate faster and faster.
很快它便开始一圈又一圈绕地球行驶 Soon it's circling the earth over and over again.
无限接近光速意味着飞速环绕地球 To approach the speed of light means circling the earth pretty fast.
达到每秒7圈 Seven times a second.
但无论列车有多大动力 But no matter how much power the train has,
物理法则的限定 it can never quite
使它永远无法到达光速 reach the speed of light since the laws of physics forbid it.
但我们能假定它无限趋近于光速 Instead, let's say it gets close,
仅略微慢一些 just shy of that ultimate speed.
神奇的事情就会发生 Now something extraordinary happens.
相对于列车外 列车内的时间逐渐减慢 Time starts flowing slowly on board relative to the rest of the world,
就如同黑洞周围的情形 不过更慢 just like near the black hole, only more so.
列车上的一切动作都缓慢下来 Everything on the train is in slow motion.
斯蒂芬·霍金<时间简史>
这是为了维护速度极限 This happens to protect the speed limit,
我们不难看出其中的原因 and it's not hard to see why.
试想一个孩子沿列车运行方向奔跑 Imagine a child running forwards up the train.
她的速度与列车速度相加 Her forward speed is added to the speed of the train,
那她岂不是无意间就打破速度极限了吗 so couldn't she break the speed limit simply by accident?
答案是否定的 The answer is no.
自然法则通过减慢列车内的时间 The laws of nature prevent the possibility
来防止这一可能的发生 by slowing down time on board.
这样她就不可能突破速度极限 Now she can't run fast enough to break the limit.
时间总是能够减慢 Time will always slow down just
足以保护极限速度不被突破 enough to protect the speed limit.
基于此 便产生了 And from that fact comes the possibility of
通过时间旅行穿梭至久远未来的无限可能 traveling large distances into the future.
假设列车2050年1月1日从站台出发 Imagine the train left the station on January 1, 2050.
周而复始地环绕地球100年 It circles the earth over and over again for 100 years
最后在2150年元旦停下来 before finally coming to a halt on New Year's Day, 2150.
此时列车上的旅客仅度过了1周 The passengers will have only lived one week because
因为列车内的时间被减缓了 time is slowed down that much inside the train.
当他们走出列车 When they got out,
会发现世界发生了天翻地覆的变化 they'd find a very different world than the one they'd left.
一周内 他们穿越到了未来100年 In one week, they'd have traveled 100 years into the future.
当然 制造一列能达到如此速度的列车 Of course, building a train that could
几乎是不可能的 reach such a speed is quite impossible.
但我们已经制造出了类似的仪器 But we have built something very like the train.
瑞士日内瓦的欧洲核子研究所 At the world's largest particle accelerator
坐落着世界上最大的粒子加速器 at CERN in Geneva, Switzerland.
地下深处 长达16英里的环形管道内 Deep underground, in a circular tunnel 16 miles long,
有一道万亿颗细小微粒所组成的粒子束 is a stream of trillions of tiny particles.
机器启动的瞬间 它们能从静止加速到 When the power is turned on, they accelerate from zero to
6万英里的时速 60,000 miles per hour in a fraction of a second.
增加动力 这些粒子便能不断加速 Increase the power, and the particles go faster and faster
直到粒子流能以每秒1.1万圈的速度 until they're whizzing around the tunnel
飞绕管道 这一速度已极近光速 at 11,000 times a second, which is almost the speed of light.
但正如虚拟的列车一样 But just like the train,
它们永远不能达到光速 they never quite reach that ultimate speed.
只能达到光速的99.99% They can only get to 99.99% of the limit.
一旦达到这一速度 When that happens,
它们也能进行时间旅行 they, too, start to travel in time.
我们在一种寿命极短的π介子上 We know this because of some extremely
观察到了时间旅行的过程 short-lived particles called pi-mesons.
通常情况下 Ordinarily,
它们会在250亿分之一秒后衰变 they disintegrate after just 25 billions of a second.
但当其加速到接近光速时 But when they are accelerated to near light speed,
寿命变成了原来的30倍 they last 30 times longer.
这些粒子 是活生生的时间旅行者 These particles are real-life time travelers.
其实就是这么简单 It really is that simple.
如果想去未来旅行 我们只需跑快点 If we want to travel into the future, we just need to go fast.
非常快 Really fast.
我认为 唯一能实现这个速度的地方 And I think the only way we're ever
就是外太空 likely to do that is by going into space.
阿波罗10号是史上最快的载人航天器 The fastest manned vehicle in history was Apollo 10.
达到了时速25000英里 It reached 25,000 miles per hour.
但若要实现时间旅行 But to travel in time,
我们还需比这一速度快上2千倍 we'll have to go more than 2,000 times faster.
因此 我们需要一艘更大的飞船 And to do that, we'd need a much bigger ship,
一艘巨大的飞船 a truly enormous machine.
这艘飞船必须能够装载足够的燃料 The ship would have to be big to carry a huge amount of fuel,
以供其接近光速行驶 enough to accelerate it to nearly the speed of light.
要使飞船无限接近宇宙极速 Getting to just beneath the cosmic speed limit
需要全功率加速运行长达六年 would require six whole years at full power.
4 Four
3 Three
2 Two
1 One
由于飞船庞大而笨重 The initial acceleration would be gentle
起始加速度会很慢 because the ship would be so big and heavy.
但会逐渐加速 But gradually it would pick up speed and
很快就能航行很远的距离 soon would be covering massive distances.
只需一周 就能到达带外行星 In just one week, it would have reached the outer planets,
如海王星一样的气体巨行星 gas giants like Neptune.
两年后 它将加速到光速的一半 After two years, it would reach half light
并早已航行到太阳系外很远的地方 speed and be far outside our solar system.
再过两年 Two years later,
速度将会增加到光速的90% it would be traveling at 90% of the speed of
并掠过离我们最近的半人马座阿尔法星系 light speed and passing our closet star system, Alpha Centauri.
在远离地球30万亿英里之外 Around 30 trillion miles away from the earth,
自发射起4年后 4 years since launch,
飞船开始了时间旅行 the ship begins to travel in time.
飞船上一小时 相当于地球上两小时 For every hour of time on the ship, two hours pass on earth,
和环绕特大质量黑洞飞行的 a similar situation to the spaceship
宇宙飞船是同样道理 that orbited the massive black hole.
但好戏还在后头 But there's more to come.
再经过两年的全速推进 After another two years of full thrust,
飞船将会到达它的最高速度 the ship would reach its top speed,
光速的99% 99% of the speed of light.
到达了这一速度 飞船上每过一天 At this speed, a single day on board
地球上都过了一整年 is a whole year of earth time.
我们的飞船真正地是在飞向未来 Our ship will be truely flying into the future.
让时间放慢还有另一个好处 The slowing of time has another benefit.
这就是 It means we could,
理论上我们能在一个人的有生之年 in theory, travel extraordinary distances
航行很长的距离 within one human lifetime.
一次到银河系边缘的旅行只需80年 A trip to the edge of the galaxy would take just 80 years.
但这次探索真正的奇妙之处在于 But the real wonder of our journey is that
它揭露了宇宙是何等的奇妙 it reveals just how strange the universe is.
就是这个宇宙 在这里 It's a universe where
时间会因地点不同而以不同的速度流逝 time runs at different rates in different places.
最神奇最不可思议的天体 也就是巨型黑洞 Where the most extreme objects imaginable, giant black holes,
扭曲了时间和空间 twist and warp both, time and space.
细小的虫洞无处不在 It's a place where tiny wormholes exist all around us.
最终 如果我们掌握了恰当的技术 And where, ultimately, if we could develop the right technology,
我们能够运用自己的物理知识 we might use our understanding of the laws of physics
成为在四维空间中任意穿行的时间航行者 to become time voyagers through the fourth dimension.