Q:

Is dark energy constant?

Does the "amount" of dark energy in the universe change over time, or is it constant?  The dark energy I am asking about is the rate of acceleration of the universe's expansion.

A:

As mentioned above the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space grows as the universe expands. So the total energy, density times volume, goes up.
More information here.

