# CMB and the reference point for vacuum energy

• I
Gold Member
From the basic definition of vacuum energy as being tied in with the Uncertainty principle, I would expect this not to include the Cosmic Background Radiation. Right? On the other hand, in figuring out
(a) the Casimir effect, one attributes the force to the field between the plates carrying less energy than the vacuum... but the CMB is always there as well, so one would imagine that this would contribute to the pressure on the plates
(b) why the observable universe is nearly spatially flat and how inflation smooths it down, it is not clear whether this takes the CMB into consideration or not.
Thanks for any attempts to clear up my confusion.

Staff Emeritus
(a) the Casimir effect, one attributes the force to the field between the plates carrying less energy than the vacuum... but the CMB is always there as well, so one would imagine that this would contribute to the pressure on the plates

The CMB can easily be blocked by anything that blocks microwave radiation, so this isn't a problem.

(b) why the observable universe is nearly spatially flat and how inflation smooths it down, it is not clear whether this takes the CMB into consideration or not.

Yes, the models take the CMB into account. Well, not for inflation, since the CMB didn't exist at the time of inflation, but the flatness of the universe has to include the energy density of the CMB and everything else. As far as I know at least.