The discussion centers on the concept of "dark flow" as proposed by Kashlinsky and colleagues, which suggests that galaxy clusters are moving at high speeds toward a specific region in the sky. This phenomenon raises questions about the implications for cosmology, including the possibility of other universes or flaws in current cosmological models. Participants explore the validity of these findings and their interpretations, referencing previous discussions and critiques from other scientists.
Participants generally do not reach a consensus, with some supporting Kashlinsky's findings and others questioning their validity based on existing critiques. Multiple competing views remain regarding the interpretation of the data and its implications for cosmology.
There are unresolved questions about the assumptions underlying the measurements of galaxy cluster velocities and the implications of these findings for cosmological models. The discussion reflects a mix of skepticism and interest in the potential for new discoveries in cosmology.
Kashlinsky, a senior staff scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, has been studying how rebellious clusters of galaxies move against the backdrop of expanding space. He and colleagues have clocked galaxy clusters racing at up to 1000 kilometres per second - far faster than our best understanding of cosmology allows. Stranger still, every cluster seems to be rushing toward a small patch of sky between the constellations of Centaurus and Vela.
Kashlinsky and his team claim that their observation represents the first clues to what lies beyond the cosmic horizon. Finding out could tell us how the universe looked immediately after the big bang or if our universe is one of many. Others aren't so sure. One rival interpretation is that it is nothing to do with alien universes but the result of a flaw in one of the cornerstones of cosmology, the idea that the universe should look the same in all directions. That is, if the observations withstand close scrutiny.
marcus said:Have to be cautious about anything that comes out in the New Sci.
marcus said:We had some discussion of the Kashlinsky findings back in September-October (as I recall) when their two papers came out.
marcus said:It's worth noting what Ned Wright had to say (brief comment in News of the Universe) back around then:
http://www.astro.ucla.edu/~wright/cosmolog.htm#News
He said there was a flaw in the Kashlinsky analysis and the "dark flow" conclusion could not be trusted. Conceivably that has been fixed and the finding can now be trusted. But I have not heard any word on that. As far as I know Wright's comment still stands.
buffordboy23 said:The New Scientist article reports that two other teams found similar results to Kashlinsky, but on scales less than 200 million light years.
marcus said:That is a good detail to notice! I don't want to go back over the NewSci article, but you might get their authors' names and do an arxiv search.
Recently, Kashlinsky et al. (2008a,b), have claimed a detection of the bulk flow from the dipole of the CMB observed behind clusters of galaxies, with amplitude (2.8 ± 0.7µK) and direction towards l = 283 ± 14◦, b = 12 ± 14◦. They interpret this as a dipole in the kinetic Sunyaev-Zel’dovich e ect. The conversion from µK to km/s has some systematic uncertainty, but the authors interpret the bulk flow to be between 600 km s−1 and 1000 km s−1.
Our bulk flow result is in excellent directional agreement (6◦) with that found by Kashlinsky et al. (2008b). The amplitude of their flow (1000 km s−1) is considerably higher, but would be compatible if systematic and random errors reduced the Kashlinksy et al. result to ∼ 400 − 500 km s−1. However, we note that their sample is very much deeper than ours. Whereas our signal arises from within a volume of radius ∼ 100h−1 Mpc (z < 0.03), their signal is detected on much larger physical scales, with most of the signal arising from the shell in the range 0.04 < z < 0.2 (120h−1 Mpc < r < 600h−1 Mpc).