  We introduce a special class of bimetric theories of quantized fields with
preserved classical energy conditions. More precisely, we describe the missing
anti-particles in our visible universe as being trapped in a spacetime patch
with different metric such as the de-Sitter spacetime and negative energies. In
order to stabilize these anti-states, time must go in the opposite direction to
our visible universe, in agreement with the Feynman-St\"uckelberg
interpretation of antiparticles. Since the energy scale of our observed
universe is low, we do not need to worry about these highly energetic
anti-particles except for compatibility issues regarding the restoration of
classical energy conditions. However, at the quantum gravity scale, these
anti-states play a crucial role in the cancellation of gravitational anomalies,
along with other possible quantum anomalies that may emerge.
