In cosmology, to what does the phrase "critical density" refer?
A)the density of the universe above which matter is ionized and the universe is opaque
B)the density of the universe above which the universe is bounded and below which it is unbounded
C)the density of the universe below which the universe will stop expanding
D)the density of the universe below which the universe is bounded and above which it is unbounded

Question

Quizplus · Accepted Answer

Critical density refers to the density of the universe above which the universe is bounded (closed) and below which it is unbounded (open). This density is also called the density parameter and is used to determine the ultimate fate of the universe (i.e. whether it will continue to expand indefinitely or eventually collapse).

In Cosmology, to What Does the Phrase "Critical Density" Refer