陈向东黄皮逻辑假设专题第8题

evelyn205205

It has been hypothesized that much of the matter in the universe is "dark," i.e., unseen. Studies have shown that galaxies in many galaxy clusters are moving faster with respect to one another than they would if visible stars constituted all their mass. The studies suggest that the galaxies are moving under the gravitational influence of unseen mass in considerable quantity.

which of the following is an assumption underlying the passage above?
A. measurements of the speed of moving galaxies are extremely unreliable.
B. the workings of gravitational forces are not particularly well understood.
C. the aggregate mass of visible stars in the galaxies mentioned above can be estimated with some confidence.
D. the general composotion of unseen matter in the universe has been determined.
E. without exception, the galaxies mentioned above move toward one another.

ANSWER: C.
不是很懂这道题的意思。
望各路NN帮忙解答~在此先谢谢各位啦~

cycyang

Studies have shown that galaxies in many galaxy clusters are moving faster with respect to one another than they would if visible stars constituted all their mass.
此句意为“研究表明：如果只是"visible star"构成其质量，银河系中的很多星云之间的相对运动速度将比实际观测到的要快。”暗含现有的研究可通过“visible star的质量”推算出运动速度，则前提是他们能够估算出质量。

sdcar2010

Necessary assumption. Use negation.

If you negate C, you get: the aggregate mass of visible stars in the galaxies mentioned above can NOT be estimated with some confidence.

If this is the case, how could one be sure that galaxies in many galaxy clusters are moving faster with respect to one another than they would if visible stars constituted all their mass?

Without this premise, the argument falls apart.

P.S., although C attacks the premise of the argument, it is still allowed in GMAT CR.  The reason is this "premise" itself is an argument too.  C is the presumption of the this "intermediate" argument.

ran2010zx

C的意思是说：那个推算速度的方法是可靠的
像sdcar说的，如果你取非
即推算速度的方法不可靠
那么就不能借此推出可能有暗物质

yangmars

我也不懂啊，看了几位同学的解答，我还是不懂啊，我觉的studies has shown that G are moving faster if visible stars constituted all their mass,的意思不就是暗示了说星系的组成物质不全是可见恒星，也就是说是有unseen的cluster组成成分的么？那么不就正好跟下面的那句the studies suggest that the G are moving under the gravitational influence fo unseen mass in considerable quantity.联系了起来啊，这里好像就不需要什么前提了吧？那么假设是针对“如果全是可见恒星”那句吗？如果是的话，那么为什么假设可以设在这里呢？这句不应该全部是直接可信的信息吗？就是说质量和速度之间的某种关系是已经给定的吗？额，不知道大家有没有听懂？帮忙解答下啊，拜托。

nrnr

我也不懂啊，看了几位同学的解答，我还是不懂啊，我觉的studies has shown that G are moving faster if visible stars constituted all their mass,的意思不就是暗示了说星系的组成物质不全是可见恒星，也就是说是有unseen的cluster组成成分的么？那么不就正好跟下面的那句the studies suggest that the G are moving under the gravitational influence fo unseen mass in considerable quantity.联系了起来啊，这里好像就不需要什么前提了吧？那么假设是针对“如果全是可见恒星”那句吗？如果是的话，那么为什么假设可以设在这里呢？这句不应该全部是直接可信的信息吗？就是说质量和速度之间的某种关系是已经给定的吗？额，不知道大家有没有听懂？帮忙解答下啊，拜托。

-- by 会员 yangmars (2011/3/23 17:48:20)

You can try to add "However" before the second sentence and "Therefore" before the last sentence. I think it will help you understand the argument.