Gravitational behaviour of antimatter

[bcrowell]

Antimatter! Too confusing!
Antimatter has the same mass its counterpart matter but equal and opposite value of some other property.
Its charges (color, weak, electrical) and magnetic moment are opposite.
Its inertial mass is positive.
Nobody can assert that its gravitational mass is negative. If it were, there will be an earthquake in physics and I will quit physics. First, the principle of equivalence and then general relativity would be revised. We don't want to do that. Do we?

It doesn't seem that you have read the previous discussion.

 

[yuiop]

Just in case it was not clear from my earlier posts in this thread, if antimatter or negative-mass-exotic-matter or any kind of matter fell upwards as measured in a reference frame at rest with the Earth, then the equivalence principle would be strongly violated and it would cast a huge question mark over the validity of general relativity.

Given the above how are to test for negative active gravitational mass. One suggestion would be to suspend test particles so that they are stationary in the vertical plane and see if the particles are mutually repulsive horizontally.

 

[bcrowell]

Given the above how are to test for negative active gravitational mass. One suggestion would be to suspend test particles so that they are stationary in the vertical plane and see if the particles are mutually repulsive horizontally.

If it had negative active gravitational mass and positive passive gravitational mass, then conservation of momentum would be violated, which would also kill GR.

I don't think it's practical to measure gravitational forces between microscopic masses. It's hard enough to measure gravitational forces between kilogram-scale masses.

In the early universe, when the temperature was higher than the mass of an electron, there were roughly equal numbers of electrons and positrons, weren't there? If positrons had negative active gravitational mass, then I would think that the net gravitational attraction or repulsion of all the electrons and positrons would be zero. Wouldn't that produce very different physics than what we observe in terms of nucleosynthesis, etc.?

 

[yuiop]

I don't think it's practical to measure gravitational forces between microscopic masses. It's hard enough to measure gravitational forces between kilogram-scale masses.

Fair comment. Difficult, but not impossible. As for measuring horizontal repulsion, on seconds thoughts that would not work. In order to "suspend" the particles, they would have to charged and so they could be suspended by an electromagnetic field something like Milikan's oil drop experiment. If they particles are charged, the mutual static charge repulsion would be many orders of magnitude larger than any gravitational effect.

In the early universe, when the temperature was higher than the mass of an electron, there were roughly equal numbers of electrons and positrons, weren't there? If positrons had negative active gravitational mass, then I would think that the net gravitational attraction or repulsion of all the electrons and positrons would be zero. Wouldn't that produce very different physics than what we observe in terms of nucleosynthesis, etc.?

Again, electrostatic effects and kinetic energy dispersion effects would be much greater than any gravitational effects. Interestingly if we have two particles of equal and opposite gravitational charge then the negative active mass particle would be attracted to the positive active mass particle and the active mass particle would be repelled by the negative mass particle so the particles would chase each other? On the whole from the point of view of purely gravitational effects, it would seem that negative active mass particles would form expanding voids squeezing positive active mass particles into clumps and filaments on the borders of the voids. Any such effect would possibly increase the rate that normal matter clumped together forming large structures such as galaxies and walls/ super clusters, a bit like the detergent solution around the air bubbles in a foam. One difficulty with the early universe with all mutually attractive particles is why it did not just form one large clump.

 

[Vanadium 50]

I think they are doing it the hard way, however.

Well, you're welcome to write the 75+ physicists on the experiment and tell them, "Hi, I am a college undergraduate and you're doing your experiment wrong". Be sure to let us know what the response is.

 

[StephenC]

If we were lucky enough to find that anti-matter was repulsed by the gravity from normal matter it would possibly mean we would not require dark matter to balance our observations of the cosmos.
At the big bang the dark matter would have accelerated away (accounting for the observed discrepancy in the observed ratios). Would this also cause the matter universe to be enclosed and compressed.

This also might lead to the possibility of transport and communications where an anti matter object could be allowed to accelerate away from the solar system and then would slow down again as it approaches a target star.

I would have thought it would be possible to calculate from our cosmos observations whether anti-matter behaves normally with respect to gravity. There might be many forms of anti-matter which behave differently.

Here is a couple of links from the Nasa forum discussing the same ideas :-

http://forum.nasaspaceflight.com/index.php?topic=13542.0

http://forum.nasaspaceflight.com/index.php?topic=24858.0

 

[StephenC]

Sorry , I am new to this forum so I don't know how to edit and correct mistakes. The first paragraph was meant to say :-

If we were lucky enough to find that anti-matter was repulsed by the gravity from normal matter it would possibly mean we would not require dark matter to balance our observations of the cosmos. At the big bang the anti-matter would have accelerated away (accounting for the observed discrepancy in the observed ratios). Would this also cause parts of the matter universe to be enclosed and compressed helping to replace the need for dark matter.