Vacuum energy and cosmological evolution

Understand

An expanding universe is not expected to have a static vacuum energy density.

• The so-called cosmological constant $\Lambda$ should be an approximation, certainly a good one for a fraction of a Hubble time, but it is most likely a temporary description of a true dynamical vacuum energy variable that is evolving from the inflationary epoch to the present day.
• We can compare the evolving vacuum energy with a Casimir device where the parallel plates slowly move apart ("expand").
• The total vacuum energy density cannot be measured, only the effect associated to the presence of the plates, and then also their increasing separation with time.