  The harmonic oscillator in pseudo euclidean space is studied. A
straightforward procedure reveals that although such a system may have negative
energy, it is stable. In the quantized theory the vacuum state has to be
suitably defined and then the zero-point energy corresponding to a
positive-signature component is canceled by the one corresponding to a
negative-signature component. This principle is then applied to a system of
scalar fields. The metric in the space of fields is assumed to have signature
(+ + + ... - - -) and it is shown that the vacuum energy, and consequently the
cosmological constant, are then exactly zero. The theory also predicts the
existence of stable, negative energy field excitations (the so called "exotic
matter") which are sources of repulsive gravitational fields, necessary for
construction of the time machines and Alcubierre's hyperfast warp drive.
