Fr.: énergie du vide
In particle physics the lowest energy allowed by field quantization when all fields are in their → ground states. Vacuum energy is predicted to arise from → virtual particles that fluctuate in and out of existence, as manifested by the → Casimir effect. The cosmological → dark energy is postulated to be related to vacuum fluctuations. There is however an enormous discrepancy with the predictions of quantum field theory. In this theory the value of vacuum energy density is expected to be roughly of the order ρv≅ Emax4, where Emax is the maximum energy at which the field theory is valid. At energies of the order of the → Planck energy, EPl≅ 1019 GeV, vacuum energy might be roughly: ρv≅ EPl4≅ 1076 GeV4. On the other hand, the vacuum energy density in standard cosmological model is given by: ρΛ = ΩΛ.ρcrit, where ΩΛ is the → density parameter for the → cosmological constant and ρcrit is the → critical density. More explicitly, ρΛ = ΩΛ . 3 H2/(8πG). Using present-day values of ΩΛ (0.7) and H (70) leads to ρΛ = 10-46 GeV4. Therefore, the discrepancy between the prediction and the observed value is 122 orders of magnitude.