全新版大学英语听说教程第三册 Unit 13（在线收听）

Unit 13

Part B

Text 1

The Big Bang!

In the 20th century there were two main theories to explain the origin of the universe, the big bang theory and the steady state theory. The former stated that the universe began in a massive explosion at a single point in space about 15 billion years ago. According to the latter, however, there was no big bang. The universe has always existed and always will exist. This theory saw a universe in which old galaxies were continually disappearing, and constantly replaced by new galaxies. Both theories seemed incredible to the layman. But was there any evidence for either of them?

If the steady state theory were correct, the universe should have looked the same millions of years ago as it looks now. But astronomers have found that the old universe did not look the same as it does now. The steady state theory does not appear to be correct. But is the big bang theory any better?

If the universe had really begun with an explosion, there should exist in the universe the cosmic background radiation from the explosion. Researchers at Princeton University began searching for the radiation in the 1960s. At the same time, while studying radio signals coming from particular parts of the Milky Way, researchers at Bell Laboratories found their work hindered by background interference that seemed to be coming from every direction. It turned out that the interference was actually the cosmic background radiation.

If the steady state theory had been correct, this background radiation would not exist. So the big bang theory seems to be correct. But why did the universe explode into existence? We can never know the answer.

Questions:

1. What is the main idea of the passage you have just heard?

2. Who are supposed to be the audience of the passage?

3. What is the steady state theory about?

4. What is the big bang theory about?

Text2

The End of Time

The universe has been expanding ever since the big bang. The galaxies are rushing away from each other because of the powerful force of the initial explosion that set the universe in motion. But each planet, star, and galaxy has a force of gravity that tries to pull all the matter in the universe back together again. The two forces are in opposition.

Scientists are trying to figure out which of these two forces is the more powerful, because the future of the universe depends on it. If the expansion force is greater, then the universe will continue to expand forever. And as it expands it will cool down. The universe will run down like a clock to the cold, dark and lifeless end that awaits it. But if the matter in the universe is dense enough, gravity might one day be able to overcome the expansion. The universe could stop expanding and actually turn into the opposite of the big bang, the big crunch! That might lead to another big bang and the birth of another universe. The universe might have been swinging from big bang to big crunch to big bang and so on for all time.

The future of the universe hangs on how dense it is. So far astronomers think the matter in the universe is far from dense enough to stop it from expanding forever. But astronomers believe that there may be a lot of matter, called 'dark matter' in the universe that they have not yet found. If there is enough of this 'dark matter' it could hold the key to the future of the universe.

Questions:

1. What is happening to the universe?

2. What are the two forces in opposition in the universe?

3. What does the future of the universe depend on?

Part C

Galaxies in Collision

A European-led team of astronomers have obtained exciting new images of 13 very distant colliding galaxies, using the Hubble Space Telescope. These colliding objects are part of a massive galaxy cluster.

This galaxy cluster is eight billion light-years away, one of the most distant known groups of galaxies. Therefore, it is a key target for astronomers to study how galaxies formed when the universe was young. The cluster's light has taken so long to reach us that astronomers see it now as it was when the universe was less than half its present age.

Although hundreds of galaxies appear in this Hubble Space Telescope image, the astronomers selected 81 galaxies to study in detail, 13 of which are fragments of recent collisions or pairs of colliding galaxies. This is by far the largest number of colliding galaxies ever found in a cluster.

During the collision the stars in the galaxies do not really run into each other, but their orbits are strongly disturbed by powerful gravitational pull. As a result, the so-called parent galaxies lose their shape and smoother galaxies are formed. The whole merging process can take less than a billion years, a relatively short time in astronomy.

To astronomers, the finding indicates that, at least in some cases, big massive galaxies form through collisions between smaller ones.

Part D

Hubble's Closest Look at Mars

NASA is releasing several images taken by the Hubble Space Telescope, which is the closest yet look at the red planet. Altogether there are four images, which show the entire planet. Each view shows the planet as it completes one quarter of its daily rotation. In these views the north polar cap is turned toward the Earth and is clearly visible at the top of each picture. The images were taken in the middle of the Martian northern summer, when the polar cap was at its smallest size. During this season the sun shines continuously on the polar cap. Previous spacecraft observations have shown that this summertime polar cap is composed of water ice, just like Earth's polar caps.

The Hubble Telescope pictures reveal that great changes have occurred on the surface of Mars in the past 20 years. The Martian surface is ever changing. Some regions that were dark 20 years ago are now bright red; some areas that were bright red are now dark. Winds move sand and dust from region to region, often in huge dust storms. Over long timescales many of the larger bright and dark markings remain stable, but smaller details come and go as they are covered and then uncovered by sand and dust.

The Hubble pictures reveal that the surface of Mars is covered with a lot of volcanic rocks. But mysteries still remain. Has there been life on Mars? Is there life on it now? How different is it from our own planet? These are a few of the questions waiting to be solved.

Questions:

1. How is the image of the north polar cap of Mars?

2. What is the summertime polar cap composed of?

3. When were the images of Mars taken?

4. Which of the following is true about the north polar cap of Mars in summertime?

5. What is the characteristic of the Martian surface according to observations over the past 20 years?

6. Why do smaller bright and dark markings change over time?