- #1

"Don't panic!"

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The reason I ask is that I've been reading up on the cosmological constant problem and it is mentioned that the vacuum energy density contribution to the energy momentum tensor must be of the form [itex]T^{vac}_{\mu\nu}=-\rho^{vac}g_{\mu\nu}[/itex], the reasoning being that the vacuum is Lorentz invariant and the only Lorentz invariant tensor is the Minkowski metric?!