# Gravity between antimater and matter [duplicate]

Always considered antimater as negative mass so: $$m1=10kg(matter)$$ $$m2=-10kg(antimater)$$ $$displacement=r=10m$$ $$gravity =\frac{Gm1m2}{r^2}=-1N<0!HOW?$$

• That is not 0zero factorial. – ask Nov 25 '20 at 6:42
• What happened to the value of $G$? – G. Smith Nov 25 '20 at 6:50
• Antimatter doe not have a negative mass. It has the opposite charge. – John Alexiou Nov 25 '20 at 7:05
• Here's a recent question on this topic. Although it's closed, it has good info & links. physics.stackexchange.com/q/589812/123208 – PM 2Ring Nov 25 '20 at 8:15
• – Lewis Miller Nov 25 '20 at 15:38

## 1 Answer

• Physicists mostly expect antimatter to have positive gravitational mass because it has positive inertial mass, but until that's empirically verified it's the subject of a small controversy.
• The sign of a force indicates whether it attracts or repels. (If any inertial mass were negative, you'd have to take that into account as well.
• In fact, Newton's formula for the gravity between two positive gravitational masses reflects its being attractive by having a minus sign you didn't know about, in $$-Gm_1m_2\vec{r}/r^2=-Gm_1m_2\hat{r}/r^3$$.
• By assuming antimater mass <0 I felt it would repel mater. – ask Nov 25 '20 at 6:50
• @ask Well, now I've explained how signs work, you needn't ever get confused when doing these calculations. – J.G. Nov 25 '20 at 7:14