[00:00.00]Unit 18 text A
[00:04.88]Why Are Maps Drawn with North at the Top ?
[00:08.15]为什么地图绘制得北方在上？
[00:11.42]Now it is hard to visualize a map that does not feature north at the top
[00:15.24]现在很难想像一幅不是北方朝上的地图，
[00:19.07]but this was not always so.
[00:21.25]但过去的情况并不总是这样。
[00:23.43]The oldest known map in the accepted sense of the world was drawn about 3,800 BC,
[00:28.21]现在被人们认可的最古老的地图绘制于大约公元前3800年
[00:32.99]and represents the river Euphrates flowing through northern Mesopotamia, Iraq.
[00:37.42]图上显示幼发拉底河流经伊拉克的美索不达米亚平原北部。
[00:41.85]This,and others that followed it,
[00:44.23]这幅地图以及
[00:46.60]were little more than rough sketches of localized features;
[00:49.63]后来的地图比地方地理特征略图好不了多少；
[00:52.66]it was not until many centuries later that the ancient Greeks placed
[00:56.49]直到许多世纪之后，古希腊人
[01:00.32]the science of map--making on a sound footing.
[01:03.29]才把地图绘制学置于可靠的基础之上。
[01:06.27]At the forefront of the pioneers in the field
[01:09.00]在此领域最早的先驱者首推
[01:11.73]was the Greek mathematician philopher Claudius Ptolemaeus (c.AD 90-168),
[01:17.02]希腊数学家和哲学家克劳迪’托勒密乌（约公元90年-168年）。
[01:22.31]more popularly known to history as Ptolemy.
[01:25.28]历史上通常称他为托勒密。
[01:28.24]The last great scientist of the classical period,
[01:31.21]他作为古典时期伯最后一位伟大的科学家
[01:34.17]he was the first to draw a map that was based on all available knowledge,
[01:37.75]他第一个画出以当时所有的知识为基础的地图，
[01:41.33]rather than guess or imagination.
[01:43.61]而不是基于猜测和想象。
[01:45.90]Earlier,the Babylonians had attempted to map the world,
[01:49.32]在此之前巴比伦人曾试图绘制世界地图，
[01:52.74]but they presented it in the form of a flattened disc rather than a sphere,
[01:56.43]但他们把地图绘在扁平盘上，
[02:00.11]which was the form adopted by Ptolemy.
[02:02.59]而非托勒密所采用的球体上。
[02:05.07]Given the state of knowledge of those times, he got things wrong;
[02:08.60]鉴于当时人们的知识状况，他把事情搞错了。
[02:12.13]for example,his estimate of China
[02:14.61]例如，他对中国
[02:17.09]and the Atlantic Oceanwas far from being accurate.
[02:20.17]和大西洋的估计远非准确。
[02:23.26]Nevertheless,it was a useful effort
[02:25.68]可是，这是有用的尝试。
[02:28.11]and the map remained a work of reference for over a thousand years.
[02:31.89]而且该地图1000多年中一直是人们的参考资料。
[02:35.66]In fact, Christopher Columbus used a version of it
[02:38.34]事实上，克里斯托夫’哥伦布在探索新大陆的航行中
[02:41.02]when he set sail in search of the New World--
[02:43.50]曾使用过该地图的一个版本。
[02:45.98]which caused him some navigational problems,
[02:48.62]这给他带来了许多航海问题，
[02:51.26]since Ptolemy had calculated wrongly the size of the Atlantic
[02:55.03]因为托勒密错误地计算了大西洋的大小，
[02:58.81]and was unaware that the Pacific Ocean existed.
[03:01.79]并且对太平洋的存在一无所知。
[03:04.76]The really important thing about Ptolemy's map was that north was at the top
[03:09.19]托勒密的地图真正重要的地方是其北方朝上。
[03:13.62]The reason for this was that he decided to orientate the map in the
[03:17.69]其原因在于他决定以极星的方向给地图定向
[03:21.77] direction of the Pole Star since Polaris was the immovable guiding light
[03:25.90]因为北极星是那时航海者
[03:30.02]in which the voyagers of that era placed their trust.
[03:33.00]所信任的不变的导航灯。
[03:35.98]North at the top remained the accepted arrangement until the early Middle Ages
[03:40.16]直到教会势力开始严重干涉科学进步的中世经，
[03:44.34]when the Church began to interfere seriously with the advance of science.
[03:48.17]地图北方朝上一直是为人们所接受的布局。
[03:51.99]In accordance with the orders of the Church,
[03:54.36]按照教会的命令，
[03:56.72]maps were still produced in accordance with Ptolemy's principles
[04:00.16]地图仍然按托勒密的原则绘制，
[04:03.59]but now Jerusalem was the central feature,
[04:06.41]但是必须以耶路撒冷国中心，
[04:09.23]as it was held to be the center of the Christian faith
[04:12.06]因为耶路撒冷被认为是基督教信仰的中心。
[04:14.88]and east was moved to the top.
[04:17.10]于是东方被移到上面。
[04:19.32]These maps are often called "T" Maps because they show only
[04:23.14]这些地图经常被称为“T”形地图，
[04:26.97]three continents--Europe, Asia and Africa--separated by the "T"
[04:30.75]因为它们只表现三大洲——欧洲、亚洲和非洲
[04:34.52]formed by the Mediterranean Sea and the River Nile.
[04:37.39]被地中海和尼罗河所构成的“T”形所分开。
[04:40.27]From a navigational point of view, they were almost useless.
[04:43.83]从航海的观点看，它们几乎一无所用。
[04:47.40]More accurate maps began to appear in the 14th century,
[04:50.59]随着贸易的发展和对罗盘的日益依赖，
[04:53.77]with the spread of trade and increasing reliance on the compass.
[04:57.10]更精确的地图直到14世纪开妈出现。
[05:00.43]Once again, north assumed its rightful place at the top of maps.
[05:04.12]北方再一次恢复了其在地图上方的合理位置。

[05:07.80]Text B
[05:10.86]You Have a Choice
[05:12.69]你面临选择
[05:14.51]Two trains are traveling side by sideand at the same speed along parallel tracks.
[05:18.39]两列火车在平行的轨道上同速并驾齐驱。
[05:22.27]We are seated in one of the trains,
[05:24.55]我们坐在其中的一列车上，
[05:26.82]and with us we have a special speedometer that measures their relative speed
[05:30.04]并且随身带了一个特殊的测速表来测量它们的相对速度。
[05:33.27]Since the trains are traveling at the same speedtheir relative speed is zero;
[05:37.10]因为这们是同速行驶，它们的相对速度为零；
[05:40.92]the speedometer therefore reads "0."
[05:43.65]因此，速度表的读数是“0“。
[05:46.38]Suddenly the other train seems to start pulling ahead of ours.
[05:49.41]突然，另一列火车似乎开始赶到我们这列车的前面去了。
[05:52.44]The speedometer shows a reading of 10 miles per hour.
[05:55.27]速度表读数为10英里每小时。
[05:58.09]The other train has apparently increased its speed.
[06:00.52]这一列车显然增加了速度。
[06:02.95]But can we be absolutely certain of this increase?
[06:05.48]但是我们能够绝对地肯定这一点吗？
[06:08.01]If your answer is yes, you are wrong.
[06:10.64]如果你的答案为“是”，你就错了。
[06:13.26]You are wrong because all that we know
[06:15.50]你错了是因为我们知道的
[06:17.73]is that the relative speedbetween the two trains
[06:20.36]只不过是两列车的相对速度
[06:22.98]changed from 0 mph to 10 mph.
[06:25.71]从0英里每小时增加到10英里每小时。
[06:28.44]Nothing more.
[06:30.03]仅此而已
[06:31.63]This change could have been brought about in one of two ways:
[06:34.71]这个变化可以由下列二者之一引起：
[06:37.79]1.The other train increased its speed.
[06:40.61]1。另一列车加了速度；
[06:43.44]2.Our train decreased its speed.
[06:46.07]2。我们的列车减慢了速度。
[06:48.71]There are thus two possible explanations
[06:50.89]因此，有两种可能的解释说明这一速度的变化，
[06:53.07]to account for the change in speed we don't know which one is right.
[06:56.01]但是我们不知道哪一种是对的。
[06:58.95]Furthermore, regardless of which explanation we choose,
[07:01.77]此外，不管我们选择哪一种解释，
[07:04.59]the end result will be the same:
[07:06.57]结果都是一样的：
[07:08.54]the other train will arrive at the station first.
[07:10.96]另一列车将先到达车站。
[07:13.37]So it makes no difference whether we say that the other trainincreased its speed
[07:16.45]所以我们无论是说另一列车提速了
[07:19.54]or that our train decreased its speed.
[07:21.56]还是我们的车减速了都没有区别。
[07:23.59]Since both explanations lead to the same result you can choose either one.
[07:26.72]既然两种解释都带来相同的结果，你可以任选其一。
[07:29.85]Whenever two things are relative, you can choose either one of them.
[07:32.83]每当两个事物是相对的时候，你都可以任选其一。
[07:35.81]The converse is also true:
[07:36.83]反之亦然，
[07:37.85]whenever you have a choice between two things that are equally possible
[07:40.67]即每当你面临两个具有相同可能性的事物时，
[07:43.49]then the things are relative.
[07:45.57]这两个事物就是相对的。
[07:47.64]There is no reason, except convenience for choosing one explanation over the other.
[07:51.28]除非为了方便，否则没有什么理由选一舍一。
[07:54.91]The relative speed between the trains remains the same, 10 mph;
[07:58.15]两列火车的相对速度每小时10英里保持不变；
[08:01.38]and the end result will be the same.
[08:03.51]并且最终结果也将是一样的。
[08:05.64]Now let's suppose that both trains are at the railroad station
[08:08.42]现在我们假设两列火车都停在车站，
[08:11.21]loading and unloading passengers and baggage.
[08:13.54]下旅客和装卸行李。
[08:15.88]A half-hour passes.
[08:17.71]半小时过去了。
[08:19.54]As we look at the other train through our window,
[08:21.67]当我们从车窗看另一列火车时，
[08:23.80]we see that our train seems to start moving, smoothly and slowly.
[08:27.02]我们看到自己的车好像开始平稳而缓慢地移动。
[08:30.25]For a minute or so, our train seems to travel at a uniform speed.
[08:33.63]一分钟左右以后，我们的火车似乎在匀速行驶。
[08:37.02]Our special speedometer
[08:38.99]我们的特殊的速度表
[08:40.96]shows that the relative speed between the two trains is 20 mph.
[08:44.38]显示两列车的相对速度是20英里每小时。
[08:47.80]But as we look out our window,
[08:49.83]但是当我们又往窗外看时，
[08:51.85]we suddenly see the last coach of the other train
[08:54.49]突然发现另一列火车的末节车厢从视野里消失，
[08:57.13]disappear from sight and notice the motionless station behind it.
[09:00.07]并且看到车站被除数留在后面一动不动。
[09:03.01]So we are not moving after all.
[09:05.03]所以我们根本没有移动。
[09:07.06]The other train has been moving!
[09:08.83]是另一列车在移动！
[09:10.61]This peculiar and often frustrating experienceis an effect of relative motion.
[09:13.99]这种奇怪又常令人尴尬的经历是相对运动的结果。
[09:17.37]At the train station we cannot tell whether it was our train
[09:20.65]在车站上我们分不清是我们的车
[09:23.93]that changed its speed from 0 mph to 20 mph or whether it was the other train
[09:28.16]还是另一列车从0英里每小时
[09:32.40]that changed its speed from 0 mph to 20 mph.
[09:35.48]变速为20英里每小时。
[09:38.56]Only after the other train pulled out of the'station could we see that it
[09:41.59]只是在另一列火车驶出车站以后，
[09:44.62]and not our train, was moving.
[09:46.75]我们才发现并非我们的车在动。
[09:48.88]Now let us again raise the question
[09:50.81]现在让我们再一次提出本文开头所提出的问题：
[09:52.74]that was raised at the beginning of this article
[09:54.82]在上述事例中我们
[09:56.90]can we be absolutely certain that the other train did indeed in crease its speed,
[10:00.23]能够绝对肯定是另一列车确实担速
[10:03.56]and in this case pull out of the station?
[10:05.53]并驶出车站了吗？
[10:07.50]If your answer is yes, then you are wrong again.
[10:09.99]如果你回答“是”，你又错了。
[10:12.47]All we can be certain of
[10:14.70]所有我们能肯定的
[10:16.93]is that the relative speed between the two trains changed.
[10:19.45]只是两列车的相对速度改变了。
[10:21.98]These examples illustrate an important principlein the spedal theory of relativity.
[10:25.21]这些例子说明了狭义相对论的一项重要原则。
[10:28.45]If A appears to be moving at a steady speed relative to B,
[10:31.24]如果A看上去以相对于B稳定的速度运动，
[10:34.02]we cannot know for sure if it is A that is really moving.
[10:36.96]我们并不能确定是否A真的在动。
[10:39.90]Perhaps A is standing still, and B is moving.
[10:42.77]也许A静止不动，而B在动。
[10:45.64]Or perhaps both are moving.
[10:47.47]或者也许两者都在动。
[10:49.30]According to relativity,
[10:51.04]根据相对论，
[10:52.77]there is no experiment that can be devised to solve the prolem.
[10:55.60]设计不出任何一方一个实验来解决这个问题，
[10:58.42]As there is no way of deciding which of the two objects is moving,
[11:01.20]因为无法来判定两个物体中的哪个在动，
[11:03.98]we can choose either one as the moving object.
[11:06.41]我们可以选择任何一个当作运动的物体。
[11:08.84]The reason is that their motion is relative, and relativity,
[11:11.92]其原因是在于它们运动是相对的；
[11:15.00]as we have seen, means that we have a choice.
[11:17.63]而相对性，正如我们所看到的那样，意味着我们面临选择。
[11:20.25]This principle--that if two objects are in uniform motionrelative to each other,
[11:23.79]如果两个物体彼此相对匀速运行，
[11:27.33]it is impossible to decide which one's moving and which one is at rest
[11:30.31]是不可能判定哪个在动，哪个是静止的，
[11:33.29]applies to all objects moving uniformlyin a straight line through the universe.
[11:36.76]这个原则通过适合于所有在宇宙中直线匀速运行的物体。
[11:40.24]In relativity you'll find that whenever you have a choice among
[11:43.52]在相对论里，你会发现每当你在两种具有相同
[11:46.80]things that are equally possible,
[11:48.78]可能性的事物中做出选择的时候，
[11:50.77]you are dealing with relative things.
[11:52.95]你都在与相对的事物打交道。
[11:55.13]For example, time, which is measured with clocks and watches,
[11:58.85]例如，用钟和表来测量的时间是相对的，
[12:02.57]is relative because it can be shown that there is more than one system of time.
[12:05.66]因为可以看出有不只一种时间系统。
[12:08.74]All systems of time are equally possible and you can choose any system you wish.
[12:12.37]所有时间系统都具有同样的可能性，进而你可以任选其一。