VOA慢速英语2012 SCIENCE IN THE NEWS - One of the Great Mysteries of Our Universe

 

SCIENCE IN THE NEWS - One of the Great Mysteries of Our Universe

From VOA Learning¹ English, this is SCIENCE IN THE NEWS, in Special English. I'm June Simms.

Our program today is about a mystery as old as time. Bob Doughty² and Sarah Long tell about the mystery of time.

??If you can read a clock, you can know the time of day. But no one knows what time itself is. We cannot see it. We cannot touch it. We cannot hear it. We know it only by the way we mark its passing. 

For all our success in measuring the smallest parts of time, time remains³ one of the great mysteries of the universe. 

One way to think about time is to imagine a world without time. There could be no movement, because time and movement cannot be separated⁴. 

A world without time could exist only as long as there were no changes. For time and change are linked. We know that time has passed when something changes. 

In the real world -- the world with time -- changes never stop. Some changes happen only once in a while, like an eclipse⁵ of the moon. Others happen repeatedly⁶, like the rising and setting⁷ of the sun. Humans always have noted⁸ natural events that repeat themselves. When people began to count such events, they began to measure time. 

In early human history, the only changes that seemed to repeat themselves evenly were the movements of objects in the sky. The most easily seen result of these movements was the difference between light and darkness. 

The sun rises in the eastern sky, producing light. It moves across the sky and sinks in the west, causing darkness. The appearance⁹ and disappearance¹⁰ of the sun was even and unfailing. The periods of light and darkness it created were the first accepted periods of time. We have named each period of light and darkness -- one day. 

People saw the sun rise higher in the sky during the summer than in winter. They counted the days that passed from the sun's highest position until it returned to that position. They counted 365 days. We now know that is the time Earth takes to move once around the sun. We call this period of time a year. 

Early humans also noted changes in the moon. As it moved across the night sky, they must have wondered. Why did it look different every night? Why did it disappear? Where did it go? 

Even before they learned¹¹ the answers to these questions, they developed a way to use the changing faces of the moon to tell time. 

The moon was "full" when its face was bright and round. The early humans counted the number of times the sun appeared between full moons. They learned that this number always remained the same -- about 29 suns. Twenty-nine suns equaled one moon. We now know this period of time as one month. 

Early humans hunted animals and gathered wild plants. They moved in groups or tribes¹² from place to place in search of food. Then, people learned to plant seeds and grow crops. They learned to use animals to help them work, and for food.

They found they no longer needed to move from one place to another to survive. 

As hunters, people did not need a way to measure time. As farmers, however, they had to plant crops in time to harvest them before winter. They had to know when the seasons would change. So, they developed calendars. 

No one knows when the first calendar was developed. But it seems possible that it was based on moons, or lunar months.

When people started farming¹³, the wise men of the tribes became very important. They studied the sky. They gathered enough information so they could know when the seasons would change. They announced when it was time to plant crops. 

The divisions¹⁴ of time we use today were developed in ancient Babylonia 4,000 years ago. Babylonian astronomers¹⁵ believed the sun moved around the Earth every 365 days. They divided the trip into 12 equal parts, or months. Each month was 30 days. Then, they divided each day into 24 equal parts, or hours. They divided each hour into 60 minutes, and each minute into 60 seconds. 

Humans have used many devices¹⁷ to measure time. The sundial was one of the earliest and simplest. 

A sundial measures the movement of the sun across the sky each day. It has a stick or other object that rises above a flat surface. The stick, blocking sunlight¹⁸, creates a shadow. As the sun moves, so does the shadow of the stick across the flat surface. Marks on the surface show the passing of hours, and perhaps, minutes. 

The sundial works¹⁹ well only when the sun is shining. So, other ways were invented to measure the passing of time. 

One device¹⁶ is the hourglass. It uses a thin stream of falling sand to measure time. The hourglass is shaped like the number eight --- wide at the top and bottom, but very thin in the middle. In a true "hour" glass, it takes exactly one hour for all the sand to drop from the top to the bottom through a very small opening in the middle. When the hourglass is turned with the upside²⁰ down, it begins to mark the passing of another hour. 

By the eighteenth century, people had developed mechanical²¹ clocks and watches. And today, many of our clocks and watches are electronic²². 

So, we have devices to mark the passing of time. But what time is it now? Clocks in different parts of the world do not show the same time at the same time. This is because time on Earth is set by the sun's position in the sky above. 

We all have a 12 o'clock noon each day. Noon is the time the sun is highest in the sky. But when it is 12 o'clock noon where I am, it may be 10 o'clock at night where you are. 

As international communications and travel increased, it became clear that it would be necessary to establish a common time for all parts of the world. 

In 1884, an international conference²³ divided the world into 24 time areas, or zones. Each zone represents²⁴ one hour. The astronomical²⁵ observatory²⁶ in Greenwich, England, was chosen as the starting point for the time zones. Twelve zones are west of Greenwich. Twelve are east. 

The time at Greenwich -- as measured by the sun -- is called Universal²⁷ Time. For many years it was called Greenwich Mean Time.

Some scientists say time is governed by the movement of matter in our universe. They say time flows forward because the universe is expanding. Some say it will stop expanding some day and will begin to move in the opposite direction, to grow smaller. Some believe time will also begin to flow in the opposite direction -- from the future to the past. Can time move backward²⁸? 

Most people have no trouble agreeing that time moves forward. We see people born and then grow old. We remember the past, but we do not know the future. We know a film is moving forward if it shows a glass falling off a table and breaking into many pieces. If the film were moving backward, the pieces would re-join to form a glass and jump back up onto the table. No one has ever seen this happen. Except in a film!

Some scientists believe there is one reason why time only moves forward. It is a well-known scientific law -- the second law of thermodynamics. That law says disorder²⁹ increases with time. In fact, there are more conditions of disorder than of order. 

For example, there are many ways a glass can break into pieces. That is disorder. But there is only one way the broken pieces can be organized to make a glass. That is order. If time moved backward, the broken pieces could come together in a great many ways. Only one of these many ways, however, would re-form the glass. It is almost impossible to believe this would happen. 

Not all scientists believe time is governed by the second law of thermodynamics. They do not agree that time must always move forward. The debate will continue about the nature of time. And time will remain a mystery.

1 learning   

n.学问，学识，学习；动词learn的现在分词

参考例句：

• When you are learning to ride a bicycle,you often fall off.初学骑自行车时，常会从车上掉下来。
• Learning languages isn't just a matter of remembering words.学习语言不仅仅是记些单词的事。

2 doughty   

adj.勇猛的，坚强的

参考例句：

• Most of successful men have the characteristics of contumacy and doughty.绝大多数成功人士都有共同的特质：脾气倔强，性格刚强。
• The doughty old man battled his illness with fierce determination.坚强的老人用巨大毅力与疾病作斗争。

3 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

4 separated   

adj.分开的v.分开(separate的过去式和过去分词)

参考例句：

• Her parents are separated but not divorced. 她父母分居但没离婚。
• No child should ever be separated from his mother by force. 绝不能强行使任何一个孩子与母亲分开。 来自《简明英汉词典》

5 eclipse   

v.使黯然失色，使相形见绌，日食，月食

参考例句：

• During the seventies,her acting career was in eclipse.在七十年代，她的表演生涯黯然失色。
• There will be an eclipse of the moon next month.下个月有月食。

6 repeatedly   

adv.重复地，再三地

参考例句：

• The loudspeakers blared the speech repeatedly.扬声器里反复大声地播送那篇演讲。
• He repeatedly beat his foot upon the floor.他反复用脚敲着地板。

7 setting   

n.背景

参考例句：

• The play has its setting in Vienna.该剧以维也纳为背景。
• Where and when a story takes place is called the setting.故事发生的地点和时间称为故事背景。

8 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

9 appearance   

n.出现，露面；容貌

参考例句：

• In appearance, he was a little like his father.他看起来有点像他的父亲。
• She was a young woman of good appearance.她是一位年轻貌美的女子。

10 disappearance   

n.消失，消散，失踪

参考例句：

• He was hard put to it to explain her disappearance.他难以说明她为什么不见了。
• Her disappearance gave rise to the wildest rumours.她失踪一事引起了各种流言蜚语。

11 learned   

adj.有学问的，博学的；learn的过去式和过去分词

参考例句：

• He went into a rage when he learned about it.他听到这事后勃然大怒。
• In this little village,he passed for a learned man.在这个小村子里，他被视为有学问的人。

12 tribes   

n.部落( tribe的名词复数 )；（动、植物的）族；（一）帮；大群

参考例句：

• tribes living in remote areas of the Amazonian rainforest 居住在亚马孙河雨林偏远地区的部落
• In Africa the snake is still sacred with many tribes. 非洲许多部落仍认为蛇是不可冒犯的。 来自《简明英汉词典》

13 farming   

n.农事；耕作

参考例句：

• He lives by farming.他靠务农过活。
• He is farming in Africa.他在非洲经营农场。

14 divisions   

n.分开( division的名词复数 )；分界线；分歧；分离

参考例句：

• The country's political divisions are deep-seated. 这个国家的政治分歧根深蒂固。
• The country's political divisions are deep-seated. 这个国家的政治分歧根深蒂固。

15 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

16 device   

n.器械，装置；计划，策略，诡计

参考例句：

• The device will be in production by the end of the year.该装置将于年底投入生产。
• The device will save much time and effort for us.这种装置会使我们节省大量时间和气力。

17 devices   

n.设备；装置( device的名词复数 )；花招；（为实现某种目的的）计划；手段

参考例句：

• electrical labour-saving devices around the home 节省劳力的各种家用电器
• modern labour-saving devices such as washing machines and dishwashers 诸如洗衣机和洗碗机之类的现代化省力设备

18 sunlight   

n.日光，阳光，日照

参考例句：

• The room was flooded with warm and golden sunlight.房间充满着温暖、金色的阳光。
• In the bright sunlight she had to narrow her eyes.在强烈阳光下她必须眯着双眼。

19 works   

n.作品，著作；工厂，活动部件，机件

参考例句：

• We expect writers to produce more and better works.我们期望作家们写出更多更好的作品。
• The novel is regarded as one of the classic works.这篇小说被公认为是最优秀的作品之一。

20 upside   

n.上侧，上段，上部

参考例句：

• The children hung the picture upside down.小孩把画挂倒了。
• If you turn the envelope upside down, the key will fall out.你如果把信封倒过来，钥匙就会掉出。

21 mechanical   

adj.机械(学)的；力学的；机械似的；手工操作的

参考例句：

• He borrowed a mechanical book from me.他从我这儿借了一本力学方面的书。
• He looks very mechanical.他看上去非常呆板。

22 electronic   

adj.电子的；n.[-s]电子学，电子设备

参考例句：

• It is an electronic device with many uses.这是一部具有多种用途的电子仪器。
• Father needs a new electronic shaver.爸爸需要一个新的电子剃须刀。

23 conference   

n.（正式的）会议；讨论

参考例句：

• We're having a conference and we'd like you to sit in.我们将举行一次会议，希望你来旁听。
• The conference will come to a close this afternoon.今天下午会议闭幕。

24 Represents   

v.表现( represent的第三人称单数 )；代表；体现；作为…的代表

参考例句：

• This represents a volte-face in government thinking. 这代表着政府观点的彻底转变。
• The Russian Revolution represents a landmark in world history. 俄国革命是世界历史上的一个里程碑。 来自《简明英汉词典》

25 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

26 observatory   

n.天文台，气象台，瞭望台，观测台

参考例句：

• Guy's house was close to the observatory.盖伊的房子离天文台很近。
• Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。

27 universal   

adj.宇宙的，全世界的；普遍的，一般的；通用的，万能的

参考例句：

• First of all we should make primary education universal.首先我们应普及初等教育。
• Climate change is a universal problem.气候变化是个世界性的问题。

28 backward   

adv./adj.向后地；相反地；退步地

参考例句：

• Because of his long illness,Tom is backward in his studies.因为汤姆长期生病，所以在学习中成绩落后。
• The rainy season is backward this year.今年雨季来得晚。

29 disorder   

n.紊乱，混乱；骚动，骚乱；疾病，失调

参考例句：

• When returning back,he discovered the room to be in disorder.回家后，他发现屋子里乱七八糟。
• It contained a vast number of letters in great disorder.里面七零八落地装着许多信件。