While the original paper simply confirms the phenomenon is real and the first observations weren’t a random fluke or a problem with instrument calibration, it doesn’t say what could be causing this dark flow. One of the simplest explanations could be a gravitational tug from an immense mass outside our visible universe. But to yank that much mass at what would be just under 3,000 times the speed of sound on Earth, that clump of matter would have to be absolutely immense and if there’s a kind of cosmic hyper-structure outside the visible universe, it would be a violation of the Copernican principle which states that there’s nothing inherently special about Earth’s place in the cosmos, as well as a challenge to the conception of Friedmann universes, which require homogeneity. Several previous attempts to give us a special cosmic bubble haven’t worked out, and if the dark flow is the result of a huge cosmic tug, there should be some hyper-structures, possibly even larger than the Great Galactic Wall, snaking their way through the visible universe to give the idea plausibility.

Now, just because the concept challenges the classical conception of the universe, making it potentially non- homogenous, anisotropic place on a macro scale, doesn’t mean it’s not true and we have to protect both the Copernican principle and the Friedmann equations. But to overturn them would require some direct evidence and a whole lot of study into the contradictory models of the universe. This is why another proposal for where the dark flow originates relies on the multiverse theory. The physicists behind the concept propose that we’re interacting with a different universe which is tilting ours, creating a sort of quantum entanglement during a tiny fraction of the Big Bang and resulting in the galactic flow. One plausible point for the proposal is that the long term effects of the inter-universal quantum entanglement should leave two huge holes in our universe, and if we consider the billion light year wide WMAP Cold Spot to be one of them, we could have observable proof to help fully investigate this explanation…

See: A. Kashlinsky, F. Atrio-Barandela, H. Ebeling, A. Edge, & D. Kocevski (2009). A new measurement of the bulk flow of X-ray luminous clusters of galaxies n/a arXiv: 0910.4958v2

L. Mersini-Houghton, & R. Holman (2008). ‘Tilting’ the Universe with the Landscape Multiverse: The ‘Dark’ Flow JCAP 0902:006,2009 arXiv: 0810.5388v1

A few questions come to mind. If there are massive superstructures outside what we know as our visible universe, could they explain many of the other odd movements we’re still trying to attribute to the so-called dark energy which is supposed to make up most of the cosmos? And if there are things out there big enough to casually yank clusters of galaxies around, wouldn’t they be more than powerful enough to exert influence on everything else and if they do, does this alter the prediction that the universe will just slowly fall apart and die off? If there are things out there able to interact with the galaxies we know, couldn’t they have a profound effect on the rest of the known universe over billions and billions of years and introduce new components into the theoretical mix?