Rocky II: We *still* don't need no stinkin' dark energy.

I have pretty much given up posting on physics. This is because I don't know jack-shit about physics. Lubos posted a question on the S-Matrix today and I had a momentary rush - hey I studied this in grad school. I even picked up Taylor's Scattering Theory and looked up why S-Matrix poles below the real axis don't matter - but I couldn't really follow his argument, I've forgotten too much, so NEVERMIND. So I try to follow Feynman's dictum to only talk about stuff nobody knows anything about. I still really care about physics, though, so here's an exception.

Kolb, Matarrese and Riotto, undismayed by the less than enthusiastic reception received by last month's paper (with Notari), have expanded on why cosmic acceleration doesn't really require dark energy:


The gist of the argument is
We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark-energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion... ... We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.
I look forward to the smart guys sorting this out. KMR promise a followup.


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