Hi all, Silly question perhaps: I had understood that the energy density of the vacuum is constant throughout spacetime. But, with the Casimir effect, for example, the geometry of (real) matter (i.e., parallel plates), changes the vacuum energy density in between the plates - is this correct? (since only certain modes of the EM field are allowed between the plates) So, if the vacuum energy density of various regions of space is influenced in various ways by the configuration of matter in that space, doesn't this wreck Lorentz invariance? I.e., you need to have a very specific vacuum energy spectrum to maintain Lorentz invariance, and if the spectrum between e.g., the plates is different, wouldn't this have implications for relativity if the plates were, e.g., accelerated? Thanks. J.