A New Test Confirms Dark Energy and the Expansion of the Universe

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jun 6, 2020.

  1. paddoboy Valued Senior Member

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    https://www.universetoday.com/14638...ark-energy-and-the-expansion-of-the-universe/

    A New Test Confirms Dark Energy and the Expansion of the Universe
    In the standard model of cosmology, dark energy fills the universe. It causes the universe to expand at an ever-increasing rate, and it makes up more than 70% of the cosmos. But there’s a problem. When we measure the rate of cosmic expansion in different ways, we get results that disagree with each other.

    There are several ways to measure cosmic expansion. One is to measure the relative motion of distant galaxies. This is done by looking at the light from supernovae within these galaxies. Type Ia supernovae have a fairly uniform standard brightness, so by measuring their observed brightness we know the distance of their home galaxy. This can be compared with the observed redshift of the galaxy to determine the Hubble parameter. It is this method that first discovered cosmic expansion was accelerating.

    Another method is to look at the cosmic microwave background. While this faint afterglow of the big bang has an almost uniform temperature of about 3 K, there are small variations in temperature across different regions of the sky. The scale of these fluctuations depends upon the rate of cosmic expansion. Careful observations from the Planck spacecraft have given us a good measure of the Hubble constant. And this is completely independent of the supernova measure. In principle, these two results should agree, but they don’t.

    The Planck results give a Hubble parameter of about 67 – 68 (km/s)/Mpc, while supernova observations give a value of about 71 – 75 (km/s)/Mpc. It used to be that the uncertainty of these measures was large enough that they overlapped, but they are now so precise that they outright disagree. This doesn’t mean that dark energy is wrong, but it does mean there are things we don’t understand about it.

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