原文朗读+词汇复习【时间简史 A Brief History of Time 05B】

Questions:

1.How come some galaxies are disklike?
2.What is a supernova?
3.What formed the bodies of planets like earth?

Within only a few hours of the big bang, the production of helium and other elements would have stopped. And after that, for the next million years or so, the universe would have just continued expanding, without anything much happening.Eventually, once the temperature had dropped to a few thousand degrees, and electrons and nuclei no longer had enough energy to overcome the electromagnetic attraction between them, they would have started combining to form atoms. The universe as a whole would have continued expanding and cooling, but in regions that were slightly denser than average, the expansion would have been slowed down by the extra gravitational attraction. This would eventually stop expansion in some regions and cause them to start to recollapse. As they were collapsing, the gravitational pull of matter outside these regions might start them rotating slightly. As the collapsing region got smaller, it would spin faster-just as skaters spinning on ice spin faster as they draw in their arms. Eventually, when the region got small enough, it would be spinning fast enough to balance the attraction of gravity, and in this way disklike rotating galaxies were born. Other regions, which did not happen to pick up a rotation, would become oval-shaped objects called elliptical galaxies. In these, the region would stop collapsing because individual parts of the galaxy would be orbiting stably round its center, but the galaxy would have no overall rotation.

As time went on, the hydrogen and helium gas in the galaxies would break up into smaller clouds that would collapse under their own gravity. As these contracted, and the atoms within them collided with one another, the temperature of the gas would increase, until eventually it became hot enough to start nuclear fusion reactions. These would convert the hydrogen into more helium, and the heat given off would raise the pressure, and so stop the clouds from contracting any further. They would remain stable in this state for a longtime as stars like our sun, burning hydrogen into helium and radiating the resulting energy as heat and light. More massive stars would need to be hotter to balance their stronger gravitational attraction, making the nuclear fusion reactions proceed so much more rapidly that they would use up their hydrogen in as little as a hundred million years. They would then contract slightly, and as they heated up further, would start to convert helium into heavier elements like carbon or oxygen. This, however, would not release much more energy, so a crisis would occur, as was described in the chapter on black holes. What happens next is not completely clear, but it seems likely that the central regions of the star would collapse to a very dense state, such as a neutron star or black hole. The outer regions of the star may sometimes get blown off in a tremendous explosion called a supernova, which would outshine all the other stars in the galaxy. Some of the heavier elements produced near the end of the star's life would be flung back into the gas in the galaxy, and would provide some of the raw material for the next generation of stars. Our own sun contains about 2 percent of these heavier elements, because it is a second-or third-generation star, formed some five thousand million years ago out of a cloud of rotating gas containing the debris of earlier supernovas. Most of the gas in that cloud went to form the sun or got blown away, but a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the earth.

KeyWords & Phrases
1)helium n. <化>氦
2) electron n. 电子
3) nuclei n. 核，核心，原子核 （nucleus的复数）
4) electromagnetic adj. <物>电磁的
5) dense adj. 密度的，密集的
6) recollapse v. 再次崩塌
7) hydrogen n. <化>氢
8) collapse v. 崩溃; 倒塌
9) gravitational attraction 万有引力
10) rotate v. 旋转，轮值
11) spin v. 快速旋转
12) skater n. 滑冰者
13) disklike adj. 盘状的
14) oval-shaped adj. 椭圆形的，卵形的rounded like an egg
15) elliptical adj. 椭圆形的
16) collide v. 撞击
17) fusion v. 融合; 熔解
18) radiate v. 辐射，发射
19) neutron star 中子星
20) supernova n. 超新星

根据今天课程讲解翻译以下句子段落.

Eventually, once the temperature had dropped to a few thousand degrees, and electrons and nuclei no longer had enough energy to overcome the electromagnetic attraction between them, they would have started combining to form atoms.

最终，一旦温度下降到几千度，电子和原子核就没有足够的能量来抵抗它们之间的电磁引力，它们就开始结合形成原子。