Is Dark Matter really gravity created by other universes in other dimensions ?
Actually, one of the possible extensions for the standard model of particle physics uses the group E8xE8. It turns out in this theory that every ‘normal’ particle has a ‘reflected’ version with the same mass, an analogous charge, etc, but which only interacts with ‘normal’ particles through gravity. At first, this sounds like a good candidate for dark matter, but it turns out that real dark matter doesn’t interact with itself very strongly either, but the ‘reflected’ matter in E8xE8 would interact with other ‘reflected’ matter strongly. Some theories do propose additional dimensions, which would require some modifications to gravity on a small to medium scale, but these don’t include good alternatives to dark matter.
