This has been bugging me for years, but I don't understand enough to either substantiate or falsify my thoughts. I also don't want to try and convince people that it's right since it sounds crazy even to me, but please tell me if you can find something wrong with it... I know that there are some extensive theories and observations involved, and I'm very aware of the relevant xkcd... http://xkcd.com/675/
All that said, it's very interesting to consider the possibility that there's a common cause of the observations that prompted dark matter/energy theories. I've read far too much about physics on Wikipedia trying to disprove the notion, with little success. All I've managed to do is find more and more curious aspects of things that would be *solved* by the idea.
I'd be very interested in someone finding evidence to falsify the possibility of dark matter and energy sharing a common anti-gravitational cause. I've been trying to find a contradiction for a very long time, and have found nothing conclusive.
If we consider that the anti-gravity could be caused by the missing antimatter purportedly absent due to baryogenesis, we might expect to find annihilation emissions in the spectra (Hmmm... http://en.wikipedia.org/wiki/Space_roar ? Doubtful, but who knows?). However, such an observation could be absent for at least two possible reasons: It doesn't exist...or the bulk of the antimatter is something weakly interacting and low-mass, sharing the same problem as the standard dark matter model.
I don't mean that antimatter would fall up in such a changed model. Its inertial mass could behave as expected, and follow spacetime the same way as normal matter. It would just exert repulsive influence. Galaxies would be compressed by rings (or spheres, how dark matter is modeled?) of antimatter surrounding them and spread out somewhat in intergalactic space (dark matter), while being repelled from each other by the spherical gravitational dipole effect (dark energy).
If you model a binary system with one matter and one antimatter particle, they orbit a barycenter on the opposite side of the matter particle from the antimatter particle...in lock-step with each other. Put a black hole at that barycenter, add more particles of each type, and you get an orbiting system that goes much faster than it should from just the matter...just like dark matter's effects on galaxies.
There's some amazing symmetry if you think about this, and some weird implications. Inertial and gravitational mass would no longer be identical. Relativistic mass might be gravitationally neutral. An antimatter particle would chase a matter particle and require new interpretations of conservation of energy (Probably one of the biggest potential arguments against the whole concept, except it violates assumptions, not any evidence I'm aware of).
My most recent consideration from all this was the idea of applying CPT symmetry to the big bang (since it could be expected to involve both matter and antimatter), with some truly crazy implications. Unfortunately my understanding of it seems to be even more lacking than I thought, and I'm not sure how to mathematically formulate/test the possibility of the Universe sharing a common beginning and ending if you look at matter and antimatter versions in opposite time-space terms.
I don't know what I'm doing, and really wish someone could put this musing to rest one way or another. Unfortunately, I doubt we really have the experimental evidence either way. All of my musings amount to relaxation of assumptions--I haven't found a concrete contradiction, and all the predicted effects seem too subtle for current experiments to show.
If anyone could give good evidence for falsification of this common cause hypothesis, or point me in a direction for finding it, I'd be very appreciative. I've spent far too much time thinking about this with nothing to show for it, despite trying to break it.
Thanks for reading. Please get this out of my head.