[phkahler]

How do we know that? Because of how it behaves in electric and magnetic fields. In particular, how it accelerates. It obviously has a negative sign in it somewhere. My point is that we don't know if that sign flip is in charge or mass. A lot of the math behaves in accordance with observation whether we flip the charge or the mass.

[tiborsaas]

Recent experiment at CERN: https://www.space.com/matter-antimatter-same-response-to-gra...

[thfuran]

>How do we know that

Both theory and experimental validation. Their interaction with electric fields, their interaction with gravity, conservation laws, and so on.