What Is the Universe's Critical Density?

[mtjames0211]

The density of the universe is
A) equal to the critical density if the universe is closed.
B) equal to the critical density if the universe is flat.
C) greater than the critical density if the universe is flat.
D) greater than the critical density if the universe is open.
E) none of the above

 

[phinds]

This sounds like a homework problem. Read the rules for posting homework problems.

What do YOU think the answer is and why?

 

[HallsofIvy]

What is the definition of "critical density"?