关于OG阅读宇宙膨胀和暗物质，宇宙密度和氢原子密度的问题

borax

以下内容有浪费时间之嫌，时间紧迫的同学就别看了= =
OG阅读宇宙膨胀和暗物质 文中第一段说如果宇宙密度等于一立方米三个氢原子的时候，宇宙就会停止膨胀。
OG问题中问，如果宇宙的密度远远小于一立方米三个氢原子，会得到下面哪个结果，正确选项是C.宇宙会继续膨胀。

但是……按常理来说，宇宙在膨胀的时候的密度，应该是大于膨胀到极限时候的密度的啊……不应该是宇宙的密度大于一立方米三个氢原子时，宇宙继续膨胀吗？
虽然按照related和unrelated来选，不会影响选到正确选项……求知欲让我欲罢不能，求解答～
附上文章第一段，和题目。

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? It can be calculated that the critical density of matter needed to brake the expansion and "close" the universe is equivalent to three hydrogen atoms per cubic meter. But the density of the observable universe—luminous matter in the form of galaxies—comes to only a fraction of this. 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.


It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?
A. Luminosity would be a true indicator of mass.
B. Different regions in spiral galaxies would rotate at the same velocity.
C. The universe would continue to expand indefinitely.
D. The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
E. More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions

borax

想通了……emmmm，自己默认宇宙内氢原子个数不变，导致密度变化错了……小的逻辑问题，耽误大家时间了，抱歉
找了半天不知道怎么删贴……