“If something doesn’t reach you on a personal level, let it go. It’s hard enough dealing with everything that does.” -Judi Culbertson
There are two types of electric charge: positive and negative. Like charges repel; opposite charges attract. In gravitation, though, there’s only one kind of gravitational charge, more commonly known as mass. And everything we know of has a positive mass. But since there’s a counterpart to matter — antimatter — isn’t it possible that antimatter would have negative gravitational charge, and fall “up” in a gravitational field?
It sounds like it might be plausible, and that it’s something that should certainly be experimentally tested. Indeed, the direct measurements of gravitational acceleration of neutral antimatter are perhaps two orders of magnitude away from being able to definitively say that antimatter doesn’t do exactly that. But a combination of other theoretical and experimental results strongly disfavor anti-gravitation, not only for antimatter, but for any potential form of matter at all.