Antimatter would be anti-matter¶
Antimatter would truly be anti-matter.
Graphic representation of antimatter and CPT symmetry¶
This probably sounds strange, but it is not. Antimatter had been up to now more matter, ordinary but fulfilling the role of being the opposite charge companions to what we call matter (common matter). That is, up to this point, there was nothing weird. Additionally, antimatter could be interpreted as a mirror image of particles, that is, an antiparticle traveling is the same as the corresponding particle traveling in the opposite direction but backwards in time (here the important part begins).
Given that antimatter has the same mass as matter, that is, they are of the same magnitude and sign (the definition of mass is always positive), the gravitational effect of antimatter should not be different from that of matter; in other words, it will always be an attractive effect. But doesn’t the established equivalence of an antiparticle traveling to the future = a particle traveling to the past matter? The answer is yes. Such equivalence comes from something called CPT (Charge-Parity-Time) symmetry, and it tells us that the equivalence between particles and antiparticles does not only correspond to performing a transformation on charge, but also on parity and time. Charge does not affect gravity, but parity and time do. In other words, when time is modified (running time backwards) and space (parity is «rotating» space), we are altering space-time, and as the general theory of relativity asserts, it is its geometry that determines gravity.
How is it affected? When matter interacts with antimatter, antimatter will behave like matter but with time flowing to the past. Now, what happens with an attractive phenomenon if we reverse time? The answer is repulsion. But when interacting with itself, the time inversion appears twice, so it is like leaving time in its natural form and they would attract each other. So the gravitational interaction between matter and antimatter would be repulsive. But this implies more than that… if observations of the presence of antimatter in the voids observed in galactic distributions are confirmed, this would allow explaining the acceleration of the universe without resorting to dark energy and dark matter! For now it is premature to state it, but this could already make us question the existence of the latter two.
References
Antimatter gravity could explain Universe’s expansion. Physorg. April 13, 2011.
M. Villata. “CPT symmetry and antimatter gravity in general relativity.” EPL (Europhysics Letters), 94 (2011) 20001 (arXiv:1103.4937 [gr-qc]). DOI: 10.1209/0295-5075/94/20001.
This article was originally published in Spanish on 2011-04-13.