Science Forums 2

[CraigD]

Originally Posted by freeztar

I'm not sure I buy the reasoning for why detectors have not found positrons in the solar wind. It's my understanding that the EM force between a positron and an electron would cause them to annihilate, which could be detected.

I think you’re correct, freeztar. The attractive magnetic force between antiparticles follows the same force law as the suggested repulsive antigravitational force, but has about times the relative strength (it doesn’t much matter whether we’re talking about electron/positron or proton/antiproton pairs, as the ratio of mass of proton to electron is a much smaller about 1836).

In addition to these theoretical reasons, particle-antiparticle collisions are very commonly observed in particle accelerators. I don’t see how hypothetical antiparticles in the solar wind could behave much differently.

Originally Posted by freeztar

Also, wasn't it shown with the Eötvös experiments that matter and antimatter are affected the same by gravity?

“The antimatter gravity debate” section of the wikipedia article “Gravitational_interaction_of_antimatter” appears to have a good synopsis of this question. To summarize that synopsis, arguments that the Eötvös experiment proves that antimatter and matter are effected by gravity in the same way are inconclusive.

I’m hopeful that, CERN having be able to produce magenetically neutral, cold antihydrogen for several years, some of this very rare stuff will eventually be used to perform a straightforward test of the effect of gravity on antimatter: just dropping it in a vacuum chamber, and observing whether it annihilates with matter at the top or bottom wall of the chamber. Such an experiment would conclusively and compellingly answer this very old question, either supporting or entirely negating alternative theories like this thread’s “dominium model”.

Following references from the wikipedia link above, I find papers speculating about the key features of dominium model at least as early as 1979. I think the relative rarity of such speculation among knowledgably cosmologists, and a lack or urgency to perform the above mentioned antihydrogen experiment, are due to nearly all of them being nearly certain that antimatter doesn’t exhibit antigravity.

Among the arguments against antimatter antigravity presented in the wikipedia article above, I find this one neat and compelling: since the force of gravity between particles that are not their own antiparticles (eg: protons) and those that are (eg: photons) is always attractive, if the gravity between particles and antiparticles is repulsive, would photons be attracted or repelled by antimatter? If so, why?