The Difference Between Matter and Antimatter

The difference between matter and antimatter is if you flip some of the quantum numbers. An electron can have positive or negative spin, so it's not like an inherent property of the electron to be positive or negative. Having positrons, the antiparticle of the electron, can also have positive ornegative spin. Both are spin one half particles, meaning they're fermions. We don't actually know what the gravitational force is on antimatter. Whether antimatter falls up or down, it might have positive mass, but repulsive gravity.