I had always wondered about this: "Four reasons why the quantum vacuum may explain dark matter November 28, 2011 by Lisa Zyga (PhysOrg.com) -- Earlier this year, PhysOrg reported on a new idea that suggested that gravitational charges in the quantum vacuum could provide an alternative to dark matter. The idea rests on the hypothesis that particles and antiparticles have gravitational charges of opposite sign. As a consequence, virtual particle-antiparticle pairs in the quantum vacuum form gravitational dipoles (having both a positive and negative gravitational charge) that can interact with baryonic matter to produce phenomena usually attributed to dark matter. Although CERN physicist Dragan Slavkov Hajdukovic, who proposed the idea, mathematically demonstrated that these gravitational dipoles could explain the observed rotational curves of galaxies without dark matter in his initial study, he noted that much more work needed to be done."
http://www.physorg.com/news/2011-11-quantum-vacuum-dark.html <more>
