【2017年整理】GMAT阅读 解析 5 by 申友Alice老师.doc

Passage 5 After evidence was obtained in the 1920s that the universe is expanding, it became reasonable to ask: Will the universe continue to expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? // 提出问题宇宙是否会一直持续扩大下去还是会停止。 It can be calculated that the critical density（临界密度）of matter needed to brake the expansion and “close” the universe is equivalent to three hydrogen atoms per cubic meter. //回答问题，当临界密度为一立方米中三个氢原子重量时，则可以停止。 But the density of the observable universe（对应后文看不见的宇宙部分）—luminous matter in the form of galaxies（插入语解释说明，可略读）—comes to only a fraction of this（注意代词的指代内容：临界密度，一立方米中三个氢原子重量）. If the expansion of the universe is to stop, there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70. // 转折，看得见的宇宙的密度只是临界密度的一部分。因此，可以预测下段会探讨看不见的宇宙部分。 Our contribution to the search for this “missing matter”（上一段中invisible matter的同义转换）has been to study the rotational velocity of galaxies at various distances from their center of rotation. // 总述寻找宇宙中是否存在看不见的部分。 It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity （重点信息词，可用于回文定位）falls off rapidly with distance from the center.（实际情况） If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. （理论情况）// 通过光度和距离来探讨是否存在看不见的宇宙部分；实际情况是螺旋星系的光度随着距离的增加而下降符合理论情况光度向中心集中，证明存在物质。 Outside the nucleus the rotational velocity （重点信息词，可用于回文定位）would decrease geometrically with distance from the center, in conformity with Kepler’s law. （理论情况）Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. （实际情况）// 依据转动速度和距离探讨是否存在看不见的部分；实际情况是螺旋星系的转动速度随着距离的增加保持不变或小幅增加，不同于理论上的转动速度随距离下降。 This unexpected result indicates that the falloff in luminous mass（上文中observable universe 的同义转换）with distance from the center is balanced by an