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Cosmic clash over Hubble constant shows no sign of abating

12 Sep 2019, 18:00 UTC
Cosmic clash over Hubble constant shows no sign of abating
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A new way to measure absolute distances in the universe has allowed scientists to work out a new value for the Hubble constant, which tells us how quickly our local universe is expanding. The latest expansion rate is consistent with other direct measures obtained from relatively nearby space, but in conflict with others that rely on the universe-wide spatial features of primordial radiation. This disparity has become more pronounced in recent years and suggests that our current understanding of cosmic evolution may need an overhaul.

Evidence for the universe’s expansion emerged in the 1920s, when Edwin Hubble first observed that galaxies move away from us more quickly, the farther they are from Earth. Since then, there have been ongoing disputes about just how rapid the expansion is. While astrophysicists have measured the Hubble constant with increasing precision, a gap remains between the values of the constant obtained using two different types of observation. What is more, this discrepancy cannot be explained away by known sources of error.
Establishing the velocity of objects receding in space simply involves measuring the redshift of their emission spectra, but pinning down their distance from Earth is much more complicated. One approach is to create ...

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