02-A. Black Holes

What is a black hole? Well, it's difficult to answer this question, since the terms we would normally use to describe a scientific phenomenon are inadequate here. Astronomers and scientists think that a black hole is a region of space (not a thing ) into which matter has fallen and from which nothing can escape ?not even light. So we can't see a black hole. A black hole exerts a strong gravitational pull and yet it has no matter. It is only space -- or so we think. How can this happen? 

The theory is that some stars explode when their density increases to a particular point; they collapse and sometimes a supernova occurs. From earth, a supernova looks like a very bright light in the sky which shines even in the daytime. Supernovae were reported by astronomers in the seventeenth and eighteenth centuries. Some people think that the Star of Bethlehem could have been a supernova. The collapse of a star may produce a White Dwarf or a neutron star -- a star, whose matter is so dense that it continually shrinks by the force of its own gravity. But if the star is very large (much bigger than our sun) this process of shrinking may be so intense that a black hole results. Imagine the earth reduced to the size of a marble, but still having the same mass and a stronger gravitational pull, and you have some idea of the force of a black hole. Any matter near the black hole is sucked in. It is impossible to say what happens inside a black hole. Scientists have called the boundary area around the hole the "event horizon." We know nothing about events which happen once objects pass this boundary. But in theory, matter must behave very differently inside the hole. 

For example, if a man fell into a black hole, he would think that he reached the center of it very quickly. However an observer at the event horizon would think that the man never reached the center at all. Our space and time laws don't seem to apply to objects in the area of a black hole. Einstein's relativity theory is the only one which can explain such phenomena. Einstein claimed that matter and energy are interchangeable, so that there is no "absolute" time and space. There are no constants at all, and measurements of time and space depend on the position of the observer. They are relative. We do not yet fully understand the implications of the relativity theory; but it is interesting that Einstein's theory provided a basis for the idea of black holes before astronomers started to find some evidence for their existence. It is only recently that astronomers have begun specific research into black holes. In August 1977, a satellite was launched to gather data about the 10 million black holes which are thought to be in the Milky Way. And astronomers are planning a new observatory to study the individual exploding stars believed to be black holes, 

The most convincing evidence of black holes comes frown research into binary star systems. Binary stars, as their name suggests, are twin stars whose position in space affects each other. In some binary systems, astronomers have shown that there is an invisible companion star, a "partner" to the one which we can see in the sky. Matter from the one which we can see is being pulled towards the companion star. Could this invisible star, which exerts such a great force, be a black hole? Astronomers have evidence of a few other stars too, which might have black holes as companions. 

The story of black holes is just beginning. Speculations about them. are endless. There might be a massive black hole at the center of our galaxy swallowing up stars at a very rapid rate. Mankind may one day meet this fate. On the other hand, scientists have suggested that very advanced technology could one day make use of the energy of black holes for mankind. These speculations sound like science fiction. But the theory of black holes in space is accepted by many serious scientists and astronomers. They show us a world which operates in a totally different way from our own and they question our most basic experience of space and time. 

  

02-B. Worlds within Worlds 

  

First of all let us consider the earth (that is to say, the world) as a planet revolving round the sun. The earth is one of nine planets which move in orbit round the sun. These nine planets, together with the sun, make up what is called our solar system. How this wonderful system started and what kept it working with such wonderful accuracy is largely a mystery but astronomers tell us that it is only one of millions of similar systems in space, and one of the smallest. 

The stars which we see glittering in the sky on a dark and cloudless night are almost certainly the suns of other solar systems more or less like our own, but they are so far away in space that it is unlikely that we shall ever get to know very much about them. About our own solar system, however, we are learning more every day. 

Before the American and Russian astronauts made their thrilling journeys into outer space it was difficult for us to realise what our earth looked like from hundreds of thousands of miles away, but the photographs which the astronauts were able to take show us the earth in space looking not very different from what the moon looks like when we look at it from the earth. The earth is, however, very different from the moon, which the American astronauts have found to be without life or vegetation, whereas our earth is very much alive in every respect. The moon, by the way, is called a satellite because it goes round our earth as well as round the sun. In other words, it goes round the sun with our earth. 

The surface of our earth is covered by masses of land and larger areas of water. Let us consider the water areas first. The total water area is about three times as large as the land area. The very large separate areas of water are called "oceans” and the lesser areas are called "seas.” 

In most of the oceans and seas some of the water is found to be flowing in a particular direction -- that is to say, from one part towards another part of the ocean or sea concerned. The water which is flowing in this manner is said to be moving as a "current." There are many thousands of currents in the waters of the oceans and seas, but only certain of the stronger and better marked currents are specially named and of great importance. These currents are important because they affect the climate of the land areas close to where they flow and also because they carry large quantities of microscopic animal and vegetable life which forms a large part of the food for fishes. 

The nature and characteristics of the surface of the land areas of the earth vary a great deal from area to area and from place to place. The surface of some areas consists largely of high mountains and deep valleys whilst, in other areas, most of the surface consists of plains. If one made a journey over the Continents one would find every kind of surface including mountain ranges, plains, plateaux, deserts, tropical forestlands and empty areas covered permanently by ice and snow. 

When thinking and learning about the world we should not forget that our world is the home of a very great many different people -- peoples with different coloured skins, living very different lives and having very different ideas about a great many important things such as religion, government, education and social behaviour. 

The circumstances under which different people live make a great difference between the way in which they live and the way in which we live, and it ought to be our business to try to understand those different circumstances so that we can better understand people of other lands. Above all, we should avoid deciding what we think about people different from ourselves without first having learned a great deal about them and the kind of lives they have to live. It is true to say that the more we learn about other people, the better we understand their ideas and, as a rule, the better we like those people themselves. 

 

什么是黑洞?说起来，很难回答这个问题，因为通常我们用来描述科学现象的这个术语在这里就不恰当了。天文学家和科学家认为，黑洞是一片空间区域(而不是某个东西)，物质掉落其中，但什么也不能从中逃逸——甚至连光也不能。所以，我们看不见黑洞。黑洞产生很强的引力，但却不具有物质；它只是空间，或者说我们这样认为。黑洞是怎样产生的呢?

从理论上讲，一些恒星的密度增加到某一程度就会爆炸；这些恒星崩溃瓦解，有时产生超新星。从地球上看，超新星像天空中一盏明亮的灯，白天也能发光。天文学家在十七、十八世纪对超新星就有所报道。有些人认为，圣诞星可能是一颗超新星。恒星的崩溃瓦解可能产生白矮星或中子星，这种星的物质密度极大，使它在自身引力的作用下不停地收缩。如果这种星体非常大(远比太阳大)，它的收缩非常剧烈，就会产生黑洞。试想一下，如果地球缩小到弹子球那么大，但仍具有同样的质量和更强的引力，你就会对黑洞的引力有所认识。任何靠近黑洞的物质会被吸了进去，却不能说明在黑洞内部发生了什么。科学家们称黑洞边缘地区为“事界”。对于通过这个边界时物体究竟发生了些什么事件，我们一无所知。从理论上讲，物质在黑洞里面的属性一定会截然不同。

打个比方，如果一个人落入黑洞，他会想自己很快就到达了黑洞中心，而在世界上的观察者会认为这个人根本没有到达黑洞中心。看来我们的时空观念并不适用于黑洞区域的物体。只有爱因斯坦的相对论才能解释这种现象。他说，物质与能量是相互转换的，因此不存在“绝对”的时间与空间，不存在常量；时间与空间的测量取决于观测者的位置，它们二者是相对的。我们仍未透彻地理解相对论的意义，但有趣的是，在天文学家开始寻找黑洞存在的证据之前，爱因斯坦的理论就为黑洞学说提供了理论基础。直到最近，天文学家才开始对黑洞进行专门的研究。1997年8月发射了一颗卫星，搜集关于人们认为存在于银河系中的一千万个黑洞的数据资料。天文学家还计划建一个新的天文观测站，对那些正在爆炸的、人们认为可能会成为黑洞的恒星分别进行研究。

对双星星系的研究为黑洞的存在提供了最令人信服的证据。双星，顾名思义就是两颗恒星，其空间位置相互影响。天文学家们已经表明，在一些双星系中都有一颗看不见的“伴星”，陪伴着天空中我们能够看得见的星。那颗可见的恒星上的物质一直被一颗看不见的另一颗恒星吸引着。这颗产生如此之大引力的不可见恒星会不会是个黑洞呢?天文学家们已有几颗其他恒星的证据，证明它们可能会有黑洞作为陪伴。

黑洞理论仅仅是个开始，关于黑洞的猜测却是不胜枚举。在我们银河系中心可能有一个巨大的黑洞，高速吞噬着恒星，人类可能会在某一天要面临这一命运。另一方面，科学家们已经提出，也许有一天高科技会利用黑洞的能量为人类造福。这些假想听起来像科幻故事，然而，空间黑洞的理论已为许多严谨的科学家和天文学家所接受。他们向我们展示了一个运转方式完全不同于我们这个世界的世界，他们对我们关于时空的最基本认识提出了质疑。