  In a paper by Villata (2011), the possibility of a repulsive gravitational
interaction between antimatter and ordinary matter was discussed. The author
argued that this anti-gravity can be regarded as a prediction of general
relativity, under the assumption of CPT symmetry. Stringent experimental
constraints have been established against such a suggestion. The measurement of
free-fall accelerations of various nuclei by the Eot-Wash group and searches
for equivalence principle violation through the gravitational splitting in kaon
physics consistently establish null results on any difference between the
gravitational behaviour of antimatter and ordinary matter. The original
arguments against antigravity were questioned by Nieto & Goldman (1991). In the
light of new experiments as well as theoretical developments in the past 20
years, some of Nieto & Goldman's concerns have been addressed. While a precise
measurement of the free-fall acceleration of antihydrogen will eventually lay
this issue to rest, the purpose of this short letter is to argue that the
substitution of dark energy with anti-gravity by antimatter, as suggested by
Villata, is highly unlikely.
