Cosmological constant and vacuum energy

The general thermodynamic analysis of the quantum vacuum, which is based on our knowledge of the vacua in condensed-matter systems, is consistent with the Einstein earlier view on the cosmological constant. In the equilibrium Universes the value of the cosmological constant is regulated by matter. In the empty Universe, the vacuum energy is exactly zero, lambda = 0. The huge contribution of the zero point motion of the quantum fields to the vacuum energy is exactly cancelled by the higher-energy degrees of freedom of the quantum vacuum. In the equilibrium Universes homogeneously filled by matter, the vacuum is disturbed, and the energy density of the vacuum becomes proportional to that of matter, lambda = rho(vac) similar to rho(matter). This consideration applies to any vacuum in equilibrium irrespective of whether the vacuum is false or true, and is valid both in Einstein's general theory of relativity and within the special theory of relativity, i.e. in a world without gravity. (C) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.