CPT symmetry and antimatter gravity in general relativity M. Villata Published 28 March 2011 • Europhysics Letters Association EPL (Europhysics Letters), Volume 94, Number 2 Abstract The gravitational behavior of antimatter is still unknown. While we may be confident that antimatter is self-attractive, the interaction between matter and antimatter might be either attractive or repulsive. We investigate this issue on theoretical grounds. Starting from the CPT invariance of physical laws, we transform matter into antimatter in the equations of both electrodynamics and gravitation. In the former case, the result is the well-known change of sign of the electric charge. In the latter, we find that the gravitational interaction between matter and antimatter is a mutual repulsion, i.e. antigravity appears as a prediction of general relativity when CPT is applied. This result supports cosmological models attempting to explain the Universe accelerated expansion in terms of a matter-antimatter repulsive interaction. is this well motivated and plausible? what would be the implications if the above theory is correct? how would this impact SM, SUSY, GUT string theory, LQG etc if the above is correct. one prediction is that antimatter would fall up around matter, which can be verified by experiment there would be no necessary reason to have a SM baryogenesis, since there could be entire galaxies made of anti-matter equal in amount to matter, but repelled by it. dark energy could also be explained as repulsion of galaxies that are equally matter and antimatter. a spin-2 quantum field which gives a graviton is always attractive, never repulsive. so if the above theory is correct, it would seem to imply QG theories based on a spin-2 field are incorrect. the no hair theorem may be violated and a black hole made from a star that collapsed of antimatter may repel a black hole of a collapsed matter star.