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Concordance value of Hubble growth rate (2014)

  1. Jun 8, 2014 #1

    marcus

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    There has been a flood of new data. Cosmologists have not yet settled on a new agreed value of H0. This may help lead to one.

    http://arxiv.org/abs/1406.1718
    The 1% Concordance Hubble Constant
    C. L. Bennett (1), D. Larson (1), J. L. Weiland (1), G. Hinshaw (2) ((1) Johns Hopkins University, (2) University of British Columbia)
    (Submitted on 6 Jun 2014)
    The determination of the Hubble constant has been a central goal in observational astrophysics for nearly 100 years. Extraordinary progress has occurred in recent years on two fronts: the cosmic distance ladder measurements at low redshift and cosmic microwave background (CMB) measurements at high redshift. The CMB is used to predict the current expansion rate through a best-fit cosmological model. Complementary progress has been made with baryon acoustic oscillation (BAO) measurements at relatively low redshifts. While BAO data do not independently determine a Hubble constant, they are important for constraints on possible solutions and checks on cosmic consistency. A precise determination of the Hubble constant is of great value, but it is more important to compare the high and low redshift measurements to test our cosmological model. Significant tension would suggest either uncertainties not accounted for in the experimental estimates, or the discovery of new physics beyond the standard model of cosmology. In this paper we examine in detail the tension between the CMB, BAO, and cosmic distance ladder data sets. We find that these measurements are consistent within reasonable statistical expectations, and we combine them to determine a best-fit Hubble constant of 69.6+/-0.7 km/s/Mpc. The combined data constrain the Hubble constant to 1%, with no compelling evidence for new physics.
    25 pages, 4 figures, submitted to the Astrophysical Journal

    Charles Bennett and Garry Hinshaw are longtime leaders in the cosmology community.
    David Larson and Janet Weiland are more junior but have co-authored many if not all of the WMAP reports

    Let's see what Hubble radius this figure of 69.6 corresponds to.

    Paste this into google:
    1/(69.6 km/s per Mpc)
    It gives 14.05 billion years. So that means a Hubble radius of 14.05 billion light years.

    I like round numbers for the Hubble radius, so I would fudge that 69.6+/-0.7 to 69.84 (which is not too different) and make it be 14.0 billion light years.
    then the percentage distance growth rate is 1/140 of a percent per million years.
    =====================
    If you would like to calculate past and future cosmic histories using THAT value of H0 and the corresponding Hubble radius R0 = 14.0 billion lightyears (exactly), just go to Jorrie's calculator as usual
    http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html
    and up at the top click "WMAP inputs (2013)". By good fortune the calculator already has that 14.0 figure as one of the two options, so there is nothing you need to type in. The other option, which is the default, is to use the parameters reported by Planck mission (2013). It puts the Hubble radius at 14.4 billion lightyears.
     
    Last edited: Jun 8, 2014
  2. jcsd
  3. Jun 8, 2014 #2
    thanks Marcus good paper
     
  4. Jun 9, 2014 #3

    chasrob

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    So it's ending up much closer to Sandage's 50 than de Vaucelleurs(sp) 100?
     
  5. Jun 9, 2014 #4

    marcus

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    "much closer"? I would say it is ending up very near the geometric mean
    of 50 and 100. :smile:

    That is, the square root of (50 x 100).

    BTW I think the usually quoted UNITS "km/s per Megaparsec" are an offense to Nature and an insult to human intelligence. The actual quantity is a fractional rate of growth. Distance grows by a certain percentage per unit time.

    So it should be quoted as some fractional part (a simple number) per unit of time. Would you agree? The only question is what unit of time, and how to express the small fractional part. I find it convenient to think of it on a million year time-basis and express the fractional growth as 1/140 of one percent.

    that 1/140% per million year growth rate corresponds to a Hubble time of 14.0 billion years and a Hubble radius of 14.0 billion lightyears. I'm interested to know if this make sense to you.
     
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