hey, where are those galaxy clusters going?

The mysterious "dark flow" is still there according to follow-up observations and it's presence is still a mystery.
galaxy edge on

One of my first posts on this blog was about something referred to as a dark flow, a strange current carrying galaxy clusters to the edge of the visible universe. But last year it was just a speculation based on preliminary data. Today, the results have been double-checked, and it looks like about 1,400 galaxy clusters are drifting some 3 billion light years at an impressive 1,000 km per second according to a detailed survey of WMAP data which offers a map of the microwave background radiation left after the Big Bang, and measuring the redshift of those galaxy clusters. It seems that an event right after the Big Bang itself set the galaxy clusters in motion. The big question is what this event was and current explanations range from the mundane to the bizarre…

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

# space // astrophysics / cosmology / dark flow


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