Lambdavacuum Solution - Physical Interpretation

Physical Interpretation

A nonzero cosmological constant term can be interpreted in terms of a nonzero vacuum energy. There are two cases:

• : positive vacuum energy density and negative vacuum pressure (isotropic suction), as in de Sitter space,
• : negative vacuum energy density and positive vacuum pressure, as in anti-de Sitter space.

The idea of the vacuum having an energy density might seem outrageous, but this does make sense in quantum field theory. Indeed, nonzero vacuum energies can even be experimentally verified in the Casimir effect.