(August 3, 2011 at 10:53 am)Chuck Wrote: The validity of the very method used to deduce existence of dark flow is challenged, so let's not say prematurely that string theory made a successful prediction. But even if it did, Lee Smolin points out that string theory seems to be so constructed as to be able to generate vast numbers of sets of different predictions. He mention around 10 ^500 fundamentally different predictions about that universe that is consistent with what we see so far.
Any theory that can generate 10^500 mutually exclusive sets of predictions about everything in the universe ought to be able generate a few sets that predict a impressive number of feature of the universe successfully even if the theory has nothing more than coincidental predictive power.
Dark flow does not seem to be required by but a small set of string theories. Many other string theoreticians using the same string theory predicted a universe without dark flow. This ought to give one pause before giving string theory credit for predicting dark flow. Contrast this with Relativity's specific prediction that light would necessarily be bent by the gravity of the sun by specific amount indicated, and no one who read relativity would have used it to predict light to remain unbent by the gravity of the sun.
Granted Dark Flow might turn out to be non-event, or that it might have explanations other than a Multiverse, but given the current data it seems more likely than not - In any case it's suggestive of a multiverse, I was careful to use the word suggest as to not give it more credence than is deserved.
The way I understand it the figure 10^500 it is not the number of models that predict the universe as we have currently observed it, but the number of possible universes, in simple terms the number of possible configurations of the ways strings, branes and the like can vibrate in spacetime, each describing a different universe - the more we observe about the universe the smaller the size of the subset of 10^500 possible universes that are consistent with observations - I've ordered Smolin's "the trouble with physics" and will check back after I've encountered his thoughts on this issue.
I don't agree that Dark flow does not seem to be required, rather models of string theory have not attempted to show that it should or should not be present. If there are string theories that describe the effect of the multiverse on our universe that rule out it's possibility then that would certainly change how credible I find the predictions, but that is not an idea I have encountered while looking into the subject - If you have some resources on this I'd be interested to read them.
The paper in question states that; "The theory for the selection of the initial state of the universe from the landscape multiverse predicts superhorizon inhomogeneities induced by nonlocal entanglement of our Hubble volume with modes and domains beyond the horizon. Here we show these naturally give rise to a bulk flow with correlation length of order horizon size. The modification to the gravitational potential has a characteristic scale $L_{1} \simeq 10^{3} H^{-1}$, and it originates from the preinflationary remnants of the landscape." - Upon further reading it appears this phenomenon should be present in all Hubble volumes regardless of which of the 10^500 possiblities ends up being the description of our universe - Whether or not all 10^500 possible states create a Hubble volume universe is something I haven't looked into.
http://arxiv.org/PS_cache/arxiv/pdf/0810...5388v1.pdf
I take it you believe a better explanation for the observations of Dark Flow would be the gravity of the sun bending light? I'm not aware of any string theories having to reject this notion or any other theories that have proposed it to explain Dark flow. The suggestion that string theories need reject the effect of gravity on light seems especially odd considering such an observation of light being immune to gravitational influence would falsify GR and thus String theory - Gravitational lensing amongst other observed phenomenon all but rules out such a possibility in my view.
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