Antimatter Gravity: Experiments & Theories

[slneal32]

Standard physics texts assert that antimatter expresses a normal attractive gravitational force. Has this been proven by any experiments, or only asseted in the current theories? We know from experiments that antimatter has the opposite charge, but could it also have the opposite gravitational force?

 

[Doc Al]

We know what 'opposite charge' means, but what does 'opposite gravitational force' mean? Antimatter has mass, just like normal matter.

 

[sanman]

Nobody seems to know for sure whether gravity is a "force" or whether it's just a skewed arrangement of spacetime

 

[Vanadium 50]

If antimatter attracted differently than matter, this would appear as a composition dependent gravitational force and show up in Eotvos-type experiments. But no such effect is seen.

 

[slneal32]

We know what 'opposite charge' means, but what does 'opposite gravitational force' mean? Antimatter has mass, just like normal matter.

If we define regular gravity as a warping of space in an 'down' direction, then the opposite gravitational force would warp it in the 'up' direction. I think that this would cause two antimatter masses to push away from each other. If this were true, then no antimatter stars could form, and only anti-hydrogen would exist after the Big Bang.

 

[slneal32]

If antimatter attracted differently than matter, this would appear as a composition dependent gravitational force and show up in Eotvos-type experiments. But no such effect is seen.

Have there been Eotvos-type experiments using antimatter? I thought that because gravity is so much weaker than the electrical force, that this kind of experiment could only be done on an electically neutral mass like antihydrogen. I know that at CERN they have just begun to create antihydrogen, but I wasn't aware that they had done an Eotvos-type experiment.

 

[aquitaine]

If we define regular gravity as a warping of space in an 'down' direction, then the opposite gravitational force would warp it in the 'up' direction. I think that this would cause two antimatter masses to push away from each other. If this were true, then no antimatter stars could form, and only anti-hydrogen would exist after the Big Bang.

IIRC the only thing that could warp gravity up (that we currently know of) is exotic matter, which hasn't ever been proven to exist.

 

[slneal32]

IIRC the only thing that could warp gravity up (that we currently know of) is exotic matter, which hasn't ever been proven to exist.

This brings me back to my original question. I know that there is no proof that antimatter expresses an opposite gravitational force using exotic matter or whatever it might take. But on the other side, is there any proof that antimatter could absolutely NOT express an opposite gravitational force from normal matter?

 

[Creator]

Standard physics texts assert that antimatter expresses a normal attractive gravitational force. Has this been proven by any experiments, or only asseted in the current theories?

Hi sineal;
To answer you directly... No, antimatter's gravitational interaction has NOT been yet proven experimentally.

Experimental delay, as you correctly deduced, has been due to the relatively large electromagnetic force (compared to the weakness of gravitational) which overwhelms any sensitive measurements.

It is a very important experiment and needs to be done...
The best hope will probably be using neutral cold antihydrogen; as you mentioned:
http://www.fnal.gov/directorate/program_planning/Mar2009PACPublic/AGELOIFeb2009.pdf

We know from experiments that antimatter has the opposite charge, but could it also have the opposite gravitational force?

That would be anti-gravity and historically the arguments "against" have been to adddress the ANTI-gravity possibility.

However, ...
... I agree with the Los Alamos guys that say the various arguments against "ANTI-gravity" have not been sufficient to " rule out a large anomalous gravitational response for the antiproton",...meaning there could still be the possibility for "non-Newtonian" and "non-Einsteinian" gravitational response...and so an experiment is "critical" for our improved knowledge of the gravitational force.
A good review of the arguments and their statements are given here:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVP-46TY5BT-22&_user=10&_coverDate=07%2F31%2F1991&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=284661d6f21b4fdc7f31fdf766194aa0

Creator

 

[Naty1]

Here are some experimental efforts described from:
http://en.wikipedia.org/wiki/Antimatter#Origin_and_asymmetry

Recent observations by the European Space Agency's INTEGRAL (International Gamma-Ray Astrophysics Laboratory) satellite may explain the origin of a giant cloud of antimatter surrounding the galactic center. The observations show that the cloud is asymmetrical and matches the pattern of X-ray binaries, binary star systems containing black holes or neutron stars, mostly on one side of the galactic center. While the mechanism is not fully understood, it is likely to involve the production of electron-positron pairs, as ordinary matter gains tremendous energy while falling into a stellar remnant.[7][8]

Antimatter may exist in relatively large amounts in far away galaxies due to cosmic inflation in the primordial time of the universe. NASA is trying to determine if this is true by looking for X-ray and gamma ray signatures of annihilation events in colliding superclusters.[9]

Positron production at the Lawrence Livermore Lab is described further on ...I'm guessing once again that gravitational effects have so far been too small to detect...