The warping of spacetime, in the General Relativistic picture, by gravitational masses is what causes the gravitational force. It is assumed, but not experimentally verified, that antimatter masses will behave the same as matter masses in a gravitational field.LIGO/T. PYLE
One of the most astonishing facts about science is how universally applicable the laws of nature are. Every particle obeys the same rules, experiences the same forces, and sees the same fundamental constants, no matter where or when they exist. Gravitationally, every single entity in the Universe experiences, depending on how you look at it, either the same gravitational acceleration or the same curvature of spacetime, no matter what properties it possesses.
At least, that’s what things are like in theory. In practice, some things are notoriously difficult to measure. Photons and normal, stable particles both fall as expected in a gravitational field, with Earth causing any massive particle to accelerate towards its center at 9.8 m/s2. Despite our best efforts, though, we have never measured the gravitational acceleration of antimatter. It ought to accelerate the exact same way, but until we measure it, we can’t know. One experiment is attempting to decide the matter, once-and-for-all. Depending on what it finds, it just might be the key to a scientific and technological revolution.