Why is flatness a problem in cosmology?
A) The total amount of known matter (even if we include dark matter) is not enough to make the universe flat.
B) The universe appears to be flat to within observational error, yet the universe is expanding, and it is impossible for an expanding universe to be flat.
C) The universe appears to have a hyperbolic geometry to within observational error, yet the universe is expanding, and expanding universes have to be flat.
D) Matter is known to create bumps in the geometry of spacetime; therefore, the universe cannot be flat.

Question

Quizplus · Accepted Answer

The observed flatness of the universe suggests a precise balance of matter and energy density, which is not accounted for by known matter alone, including dark matter. This discrepancy is known as the flatness problem.

Why Is Flatness a Problem in Cosmology