Do two specks of antimatter experience antigravity between them? If no is the answer then what 2 specks may ever be the cause of that?
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$\begingroup$ Possible duplicates: physics.stackexchange.com/q/139545/2451 , physics.stackexchange.com/q/83307/2451 and links therein. $\endgroup$– Qmechanic ♦Commented Oct 15, 2020 at 16:28
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$\begingroup$ so anti matter is just anti-charged matter, right? $\endgroup$– Thushar G RCommented Oct 15, 2020 at 16:31
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$\begingroup$ Antineutron repelled by gravity?, Anti-matter repelled by gravity - is it a serious hypothesis? $\endgroup$– mmesser314Commented Oct 15, 2020 at 18:08
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2 Answers
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Antimatter (to the best of our knowledge) does not behave differently than normal matter in regards to gravitation. Particles and their respective antiparticles have equal mass (there is no concept of 'antimass', unlike how we can invert electric charge).
So, if we had two balls of matter of mass $M$ and $m$ set some distance $r$ apart, they would have a gravitational potential (at a Newtonian level) of $U = -\frac{G M m}{r}$.
If we were to replace the balls with their antimatter equivalents, nothing would change.
Even more, if we were to replace one of the balls with their antimatter equivalent (so we have one matter ball and one antimatter ball), the gravitational potential would be the same $U = -\frac{G M m}{r}$.
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$\begingroup$ The non existence of anti-mass is intriguing. $\endgroup$ Commented Oct 15, 2020 at 16:26
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$\begingroup$ @ThusharGR Maybe we could interpret it as a dual symmetry with the existence: positive mass exists, negative mass does not :-) $\endgroup$– peterhCommented Oct 29, 2020 at 9:54
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The short answer is no. Gravity as far as we know it is attractive. The attraction depends on the masses of the bodies involved (or energy densities, more generally). However antiparticles have opposite quantum numbers but same mass as particles. To a very good precision they are equal, however whether they are exactly equal is currently being investigated, nevertheless they remain positive masses and thus suffer gravitational attraction not repulsion. Here there is a nice easy read about anti-matter (https://www.scientificamerican.com/article/what-is-antimatter-2002-01-24/) if you want to know more.
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$\begingroup$ So its just anti-matter but not anti-mass? $\endgroup$ Commented Oct 15, 2020 at 16:19
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1$\begingroup$ Correct, the "anti" part corresponds to quantum numbers, such as electric charge, spin and other such charges $\endgroup$– ohneValCommented Oct 15, 2020 at 17:12
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$\begingroup$ So I understand the number referring to mass cant be quantum, right? $\endgroup$ Commented Oct 15, 2020 at 17:15
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$\begingroup$ if by quantum you mean discrete, no $\endgroup$– ohneValCommented Oct 16, 2020 at 7:18