I'm watching a video on Youtube entitled "Angels and Demons - The Science Revealed" in which the topic of discussion is antimatter. During this video, the lecturer (from Berkeley) mentions that there are some who believe that antimatter would be repelled by the gravity produced by matter (in the video, he uses an "anti-apple" possibly falling up and away from our Earth as an example). Is the idea of antimatter being repelled by the gravity of matter actually entertained by reputable physicists or is it considered nonsense? I think of gravity and acceleration being indistinguishable and wonder how an antiparticle could possibly care whether it is in the gravitational field of matter or antimatter. If antimatter is contained and put in a centrifuge made of matter and set to spinning, would it actually react differently than matter? Could it actually care if the centrifuge is made of matter or antimatter? And by the same token could it possibly care if it falls into the gravitational field of a planet or antiplanet (assuming gravity and acceleration are indistinguishable)?