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如何建造一台时光机器？

时间：2016-3-2 10:35作者：update 阅读(1291) 评论: 5来自: 中国科技日报

导读：中国科技网报道（张微编译）有时候，我们会沉湎于时间旅行的梦想中。如果可以回到过去的某个时刻，去改变曾经的错误决定，或重新感受那些童年的美好岁月，回到你获得奥斯卡奖的那个美妙夜晚，或通向到未来，提前预 ...

中国科技网报道（张微编译）有时候，我们会沉湎于时间旅行的梦想中。如果可以回到过去的某个时刻，去改变曾经的错误决定，或重新感受那些童年的美好岁月，回到你获得奥斯卡奖的那个美妙夜晚，或通向到未来，提前预知世界的变化。

时间旅行的奥秘带给你刺激和惊喜，但是你可能会说：“这不是科学”。你也许会认为，这和你在学校里学习的数学知识完全不是一回事。确实如此，听到时间旅行这个词，你可能会很震惊。

目前，科学界最重大的新闻就是发现了引力波。这项实验和进一步的研究可以揭开宇宙的奥秘。物理学家们相信引力波真实存在的原因之一，是它与过去的其他重大科学发现能够联系在一起——我们可以实现自然的四种根本力成一体的时刻，也就是通过另外一种途径证实万有理论。

走进万有理论

我们知道在牛顿时代，质量与重力密不可分。当他坐在乌尔索普的一颗苹果树下喝下午茶的时候，突然一个苹果掉在他头上，于是他首次提出自然根本力，就是那个著名的推测——万有引力。

这个事情让牛顿想到，同样的力能让苹果掉在地上，也能让月球在它的轨道上围绕地球运转。他开始证实，由于重力的作用，所有物体之间都是相互吸引的。那个时候的无知小报调侃到：“根据牛顿的万有引力作用，我们的身体被迫相互吸引，”以及“爱情也是万有引力定律。”

线索：爱因斯坦

20世纪初，爱因斯坦继续他的广义相对论研究，研究表明，质量与重力与时间相关，他致力于寻找一种统一的理论来解释所有相互作用。

爱因斯坦出生于1879年，他在1905年发表的一篇论文，改变了我们看待世界的方式。这篇论文从根本上改变了我们看待光的方式。在此之前，没有人对光的速度有太多的思考，实验物理学家们试图以更高的精度来计算光速，只是把它当作一个通用常数。很少有人关注光在声音和水中传播速度如何。

利用你所学的数学知识，如勾股定理，以及爱因斯坦的时间膨胀公式，你就会发现，速度越快，时间越慢。

爱因斯坦的理论认为，如果你想让时间慢下来，能够让我们可以进行时间旅行，那么你必须要以非常非常快的速度移动!想象一下，比如，在2000年设定了出发的任务。你被安排去2032年，那么你应当以光速95%的速度旅行(约285，000km每秒的速度)。令人惊讶的是，在你回来的时候，你的手表会告诉你，现在是2010年，尽管地球上一直是2032年，你会比其他人年轻22岁。这就是时间膨胀，它一般是和速度有关的。速度越快，越接近于极限速度，时间就会越慢。

让我们出发

那么问题来了，285,000公里/每秒的速度真是太快了。地球上最快的跑车也不能达到1公里/每秒，宇宙飞船逃离地球大气层时，它的旅行速度也仅仅是10公里/每秒,即使我们能够达到这个速度，我们的身体能否承受这样的压力也值得怀疑。时间旅行穿越到未来是有可能的，但就现在来说非常困难。但是回到过去呢，能做到吗?

我不知道你是怎么想的，当我读到时间旅行的文章时，总有种上当受骗的感觉。我被告知，所有这一切都是事实，但是却没人告诉我如何才能建造一台时光机器。为了不让你受骗，我告诉一个有关时光机器的设计方法，这要非常感谢弗兰克提普勒教授。他在1974年发表了一篇如何建造时光机器的论文，机器的名字叫Tipler Cylinder。这台机器能让你回到过去。

首先，你得牺牲你的钱包买一个大的容器。听清楚我的话，大的容器，有多大?也许100公里长。这个容器的质量至少和太阳一样，但是结构要非常致密。然后，你开始让它旋转，而且要越来越快，直到它的转速能够扰乱时间和空间的波纹，这个时候你才能探测到来自这个结构的大量引力波。

我还得给你增加一条健康警示，接近这样一个致密结构可能会导致大问题。地球的质量能够把我们“围困”在它表面，但是与时光机大容器这个巨大物体靠的太近非常危险，它的牵引力会把你拖进它的核心，然后把你压成肉饼。

如果你能解决这个抗挤压问题，那么靠近这个旋转的容器，开始和它一起旋转，奇怪的事情就发生了。正常情况下，你的路径是按照时间的方向向前移动、改变，但是由于你围绕容器做旋转运动，这台机器就改变了时间的方向带你回到过去，所以你和这台机器一起旋转的时间越久，你就能回到更遥远的过去。

但是，你要当心你在那里所做的一切。不能长久地虚度光阴，就像Marty McFly在电影《回到未来》中一样，你也许会把你父母的第一次约会给搞砸了，或者毁掉你出生的机会。如果可以像这样在时光中穿梭，也是很有趣的。

英文原文：

How to build a time machine

Every now and again, we all indulge in dreams about travelling in time. Wouldn't it be wonderful to return to that specific point in the past to change a bad decision or relive an experience – those halcyon days of childhood, that night you won an Oscar – or to zip ahead to see how things turn out in the far future.

The mystery of time travel is full of excitement and wonder – "But it's not science," I hear you say. You may also think that it is definitely not like any mathematics you learned at school. Well, you will be surprised to hear that it is.

At present there is a great deal of news around the discovery ofgravitational waves. It is suggested that this experiment and future research could unlock the secrets of the universe. One of the reasons why physicists believe this to be true is linked to other monumental scientific discoveries in the past – and the fact that we may have reached another unification moment and taken another step closer to a theory of everything.

Towards a theory of everything

We have known since Isaac Newton's day that mass is inextricably linked to gravity. His unification moment was first conjectured famously while he was sitting having afternoon tea under an apple tree in Woolsthorpe, when out of the blue an apple fell on his head.

This incident made Newton think that the same force could be responsible for both the apple dropping to the ground and the moon falling towards the Earth in its orbit. He went on to show that it was true for all mass and that all bodies attract each other due to gravity. In the tabloid newspapers of the time, it was announced: "We are just bodies forced to be attracted to each other by Newton's gravitational interactions" and that "Love is a gravitational law".

Cue: Einstein

In the early 20th century, Einstein went further with his general theory of relativity and showed that mass and gravity are linked to time; yet another unification moment.

Einstein was born in 1879, and by 1905 had published a paper that would change the way we look at the world. This paper makes a fundamental change to the way we look at light. Until then, no one had thought too much about the speed of light – it was just another universal constant that experimental physicists attempted to calculate with ever greater accuracy. There was little appreciation of how radically different light waves were from sound and water waves.

But by using mathematics you learned at school Pythagoras' theorem – and with a little help from Einstein's timedilation formula you can show that time will slow for someone who is moving.

Einstein's theory says that if you want to slow time down – essentially, to time travel – you need to move fast, very fast! Imagine setting off on a mission from Earth in the year 2000, for example. You are scheduled to be away until 2032, but will be travelling at 95% the speed of light (around 285,000km a second). The amazing thing is that, on your return, your watch would tell you that it is 2010, despite it being 2032 on Earth, and you'd be 22 years younger than anyone you left behind. That's time dilation and it works at slower speeds, too, albeit to a much less profound degree.

So let's go

But there's a catch – 285,000km a second is very, very fast. The fastest land vehicle cannot even get to 1km a second and even a spaceship when escaping Earth's atmosphere is travelling at a relatively pitiful 10km a second. Even if we could reach these speeds, it is questionable whether we could survive the stress on our bodies. So time travel into the future is possible, but a bit too difficult – for now. But what about the past?

I don't know about you but I always feel a bit cheated when I read articles on time travel. I'm told all these facts but no one tells me how to build a time machine. So as not to cheat you, here follows a design for just such a thing, with great thanks to Professor Frank Tipler. Tipler published a paper on how to build a time machine, a Tipler Cylinder, back in 1974. This machine would enable you to travel back in time.

First, you need a lot of money to buy a large cylinder. When I say large, I mean very large, perhaps a 100km long. The cylinder also needs to be at least the mass of the sun, but very densely packed together. You then need to start it rotating, faster and faster, until it's rotating so fast that it starts to disturb the fabric of both space and time – and you would be able to detect a wash of gravity waves coming from this structure.

I also need to add a health warning, as coming close to such a dense structure would cause issues. The mass of the Earth pulls us down to its surface, but getting too close to an object this massive would be hugely dangerous – it would drag you towards it and squash you flat.

If you can get round this squashing problem, however, approach the rotating cylinder and start following its spin – as you get closer, strange things will start to happen. Your path, which normally inextricably moves you forward in time, changes, since moving around the cylinder in the direction of rotation will shift you back in time. The machine makes the direction of time collapse into the past, so the longer you follow the machine's spin, the further back in time you will go.

But be careful what you do there. Fiddle around with the past too much and – like Marty McFly in Back To The Future – you may just break up your parent's first date or even ruin your chances of being born. Time can be funny like that.

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