Vacuum energy and cosmological constant: View from condensed matter

The condensed matter examples, in which the effective gravity appears in, the low-energy corner as oric of the collective modes of quantum vacuum, provide a possible answer to the question why the vacuum energy is so small. This answer comes from the fundamental "trans-Planckian" physics of quantum liquids. In the effective theory of the low energy degrees of freedom thc vacuum energy density is proportional to the fourth power of the corresponding "Planck" energy appropriate for this effective theory. However from the exact "Theory of Everything" of the quantum liquid it follows that its vacuum energy density is exactly zero without fine tuning, if: there are no external forces acting orb the liquid; there, are no quasiparticles which serve as matter; no space-time curvature; and no boundaries which give risc to the Casimir effect. Each of these four-factors perturbs thc vacuum state and induces a nonzero value of the vacuum energy density. which is on the order of thc energy density of the perturbation. This is the mason, why one must expect that in each epoch the vacuum energy density is on the order of the matter density of the Universe, or/and of its curvature, or/and of the energy density of the smooth component the quintessence.