As currently understood, what happens to the energy density of matter and the energy density of a cosmological constant as the universe expands?
A) Both the density of matter and the density of a cosmological constant increase as the universe expands.
B) The matter density decreases, but the density of the cosmological constant increases.
C) The matter density decreases, but the density of the cosmological constant remains constant.
D) Both the density of matter and the density of a cosmological constant decrease as the universe expands.

Question

Quizplus · Accepted Answer

As the universe expands, the density of matter decreases because the same amount of matter is spread over an increasingly larger volume. However, the energy density of a cosmological constant (often associated with dark energy) remains constant, as it is a property of space itself and does not dilute with the expansion of the universe.

As Currently Understood, What Happens to the Energy Density of Matter