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Baryon oscillation peak a cosmological standard ruler

  1. Jun 20, 2015 #1


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    This came up in the arxivs and had me thinking can this be true?

    arXiv:1506.05478 [pdf, ps, other]
    Is the baryon acoustic oscillation peak a cosmological standard ruler?
    Boudewijn F. Roukema, Thomas Buchert, Hirokazu Fujii, Jan J. Ostrowski
    Comments: 4 pages, 2 figures
    Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

    In the standard model of cosmology, the Universe is static in comoving coordinates; expansion occurs homogeneously and is represented by a global scale factor. The baryon acoustic oscillation (BAO) peak location is a statistical tracer that represents, in the standard model, a fixed comoving-length standard ruler. Recent gravitational collapse should modify the metric, rendering the effective scale factor, and thus the BAO standard ruler, spatially inhomogeneous. Using the Sloan Digital Sky Survey, we show to high significance (P < 0.001) that the spatial compression of the BAO peak location increases as the spatial paths' overlap with superclusters increases. Detailed observational and theoretical calibration of this BAO peak location environment dependence will be needed when interpreting the next decade's cosmological surveys.
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  3. Jun 20, 2015 #2


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    Dearly Missed

    Hi Wooly, it has been said (I forget by whom) that when you have a title ending in a question mark the implied answer, or default, is NOT.
    That seems to be the answer here, at least for the time being, if you go by the article's conclusions paragraph at the end:

    ==quote http://arxiv.org/abs/1506.05478 ==

    No matter which approach is chosen, analytical, numerical and observational work will be required if the BAO peak location is to correctly function as a standard ruler for cosmological geometrical measurements, since the evidence is strong (P < 0.001) that it is strongly affected by structure formation. Moreover, the formation of superclusters—in reality, filamentary and spiderlike distributions of galaxies (Einasto et al. 2014) rather than the spherically symmetric objects assumed here for calculational speed—can now be tied directly to a sharp statistical feature of the primordial pattern of density perturbations.

    In other words the BAO peak location is not a constant it is strongly affected by the static large-scale environment.

    An interesting thing to notice, though, is that when you describe the universe in comoving coordinates there is no expansion. On a large enough scale the coordinate locations of major matter concentrations stay the same. You have a static universe, if you use comoving coordinates, at least in the large, ignoring little local curdlings and swirlings around. The authors mention that.

    What seems to interest people about the BAO peak location is they see it as a possible natural scale to use in describing the frozen ripples and other structure in this static picture. It strikes me as a worthwhile endeavor.

    It would not carry over as a fixed-length ruler to describe the expanding universe. Because it wouldn't stay the same size but would vary widely over time. But they are pointing out something more serious. It even varies from place to place in the comoving coordinates universe (even after the expansion has been factored out of the picture).
    So their basic conclusion seems to be that the idea "needs work."
    Last edited: Jun 20, 2015
  4. Jun 22, 2015 #3
    I've only skimmed the paper but this idea that the BAO peak is affected by non-linear evolution isn't particularly new. A lot of simulation work goes into determining these sorts of biases and finding the best estimators and reconstruction methods which are insensitive to it. It's one of the challenges with DESI and Euclid.
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