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B Is the universe expanding faster than expected

  1. Jan 27, 2017 #1

    wolram

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    I can not find a paper on this, but is it possible that the universe is expanding faster than expected?

    https://www.sciencedaily.com/releases/2017/01/170126132624.htm

    Because galaxies do not create perfectly spherical distortions in the fabric of space and the lensing galaxies and quasars are not perfectly aligned, the light from the different images of the background quasar follows paths which have slightly different lengths. Since the brightness of quasars changes over time, astronomers can see the different images flicker at different times, the delays between them depending on the lengths of the paths the light has taken. These delays are directly related to the value of the Hubble constant. "Our method is the most simple and direct way to measure the Hubble constant as it only uses geometry and General Relativity, no other assumptions," explains co-lead Frédéric Courbin from EPFL , Switzerland.
     
  2. jcsd
  3. Jan 27, 2017 #2

    phyzguy

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    It's clear there is a discrepancy between the Hubble Constant value that best fits the CMB data (the 66.93±0.62 referred to in the article from the Planck satellite) and the Hubble Constant value measured in the local universe by other methods, which gives higher values more like 71 or 72 km/sec/Mpc. Whether the discrepancy reflects new physics which is missing from the Lambda-CDM model or whether it reflects systematic errors in the measurements is anybody's guess at this point.
     
    Last edited: Jan 27, 2017
  4. Jan 27, 2017 #3

    wolram

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    Thank you physguy, I thought using General relativity, and geometry would be an accurate method. May be it is not as accurate as they say.

     
  5. Jan 27, 2017 #4

    phyzguy

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    The discrepancy between 67 and 71 is only about 5%. When you start getting down to small errors like this, many small effects start to matter. For example, the article says, "it only uses geometry and General Relativity, no other assumptions,". But what about the fact that the intervening space between us and these galaxies is not empty? It contains a low density plasma which affects the light travel time. I'm not saying this is the explanation, I'm just saying that when you get down to the few percent level, it is easy to miss some small effects. Historically these types of discrepancies are usually not resolved through revolutionary new physics, they are resolved by more careful analysis of the systematic errors. Sometimes, however, they do result in new physics. Time will tell.
     
  6. Jan 28, 2017 #5

    wolram

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    Thank you phyzguy.
     
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