An Etymological Dictionary of Astronomy and Astrophysics
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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 ρ_v≅ E_max⁴, where E_max is the maximum energy at which the field theory is valid. At energies of the order of the → Planck energy, E_Pl≅ 10¹⁹ GeV, vacuum energy might be roughly: ρ_v≅ E_Pl⁴≅ 10⁷⁶ GeV⁴. On the other hand, the vacuum energy density in standard cosmological model is given by: ρ_Λ = Ω_Λ.ρ_crit, where Ω_Λ is the → density parameter for the → cosmological constant and ρ_crit is the → critical density. More explicitly, ρ_Λ = Ω_Λ . 3 H²/(8πG). Using present-day values of Ω_Λ (0.7) and H (70) leads to ρ_Λ = 10^-46 GeV⁴. Therefore, the discrepancy between the prediction and the observed value is 122 orders of magnitude.

→ vacuum; → energy.