2013年5月26日托福阅读机经解析

　　第二篇

　　TOPIC Determining the Age of Planets and Universe

　　宇宙里面组成的物质都是一样的，形成的时间也比较相仿。科学家发现不同的的星球上留下的遗迹通过科学测量，月球和岩石形成的时间都是一样的，得出结论，所有星球形成时间相仿。地球上有很多水，有腐蚀，不能作为参数进行比较。但是月球和小行星进行比较，目前人类史上没出现小行星撞击地球，但宇宙爆炸产生的小行星碎片已陨石的状态掉落到地球上。

　　解析：

　　本文属天文学内容，讲解如何测量行星及宇宙的形成时间，文中谈到各行星形成时间相同，这部分内容可以参照TPO阅读文章Planets in our Solar System。以下为文中提到的几个学术概念的解释。

　　Big Bang Theory

　　Big Bang Theory, currently accepted explanation of the beginning of the universe. The big bang theory proposes that the universe was once extremely compact, dense, and hot. Some original event, a cosmic explosion called the big bang, occurred about 13.7 billion years ago, and the universe has since been expanding and cooling.

　　The theory is based on the mathematical equations, known as the field equations, of the general theory of relativity set forth in 1915 by Albert Einstein. In 1922 Russian physicist Alexander Friedmann provided a set of solutions to the field equations. These solutions have served as the framework for much of the current theoretical work on the big bang theory. American astronomer Edwin Hubble provided some of the greatest supporting evidence for the theory with his 1929 discovery that the light of distant galaxies was universally shifted toward the red end of the spectrum (see Redshift). Once "tired light" theories-that light slowly loses energy naturally, becoming more red over time-were dismissed, this shift proved that the galaxies were moving away from each other. Hubble found that galaxies farther away were moving away proportionally faster, showing that the universe is expanding uniformly. However, the universe’’s initial state was still unknown.

　　Expanding Universe Experiment

　　One way to understand the concept of an expanding universe is to draw dots, representing galaxies, on a balloon. As the balloon is inflated, each dot moves away from all the others. To a person viewing the universe from a galaxy, all other galaxies would seem to be receding. The distant galaxies appear to be moving away faster than the near ones, which demonstrates Hubble’’s law. Most astronomers now believe that this expansion will continue forever.

　　Redshift, change, or shift, in the light radiated by an object, such as a star or galaxy, that indicates the object’’s motion. Scientists have used redshifts to measure the velocities (speed and direction) of distant galaxies. Knowing the velocities of galaxies helps astronomers understand how the universe is changing. This knowledge allows scientists to interpret the distant past of the universe and to predict the universe’’s distant future. See also Light.

　　Redshift only occurs when an object is moving. Another mechanism can also redden the light of astronomical objects, but it is not considered to be the same as redshift. Dust particles between stars are just the right size to scatter light with short wavelengths more than they scatter light with long wavelengths. As the light of a star passes through a cloud of dust on the light’’s way to Earth, more of the long, red wavelengths get through the dust than the short, blue wavelengths do. This makes the star appear redder than it really is, but the light that reaches Earth is the true red light of the star and has not actually shifted. See also Interstellar Matter.

　　Redshifts of galaxies allow astronomers to measure the distance from Earth to the galaxies. Knowing the distances to galaxies gives astronomers an idea of the way the universe is expanding and provides clues to the origin, evolution, and future of the universe. The relationship between the redshift (and therefore velocity) and distance of a galaxy is called Hubble’’s law, which was named after American astronomer Edwin Hubble.