Live Science reports:

There’s a central crisis in cosmology: Different measurements yield different values for the expansion rate of the universe. Now, a comprehensive analysis combining decades of independent measurements suggests that this discrepancy is not due to error or uncertainty; instead, it’s a potential pathway to new physics beyond the standard cosmological model.

Astronomers calculate the universe’s expansion rate, or Hubble constant, in two ways. One method is to use measurements of the distance to the cosmic microwave background (CMB), the earliest light that spread out just 380,000 years after the Big Bang. The second method is to study the expansion of the local universe, using observations of “standard candles,” nearby stars of a known brightness whose light gets stretched — or redshifted — as it reaches us.

The first method’s calculations yield a Hubble constant of around 67 or 68 kilometers per second per megaparsec, while the latter yield a value of approximately 73 kilometers per second per megaparsec. (One megaparsec is about 3.26 million light-years.)

Although this seems like a diminutive discrepancy, it is far greater than statistical uncertainty can explain, presenting a puzzling disagreement known as the Hubble tension. So a large symposium of astronomers convened to vote on the best methods and data for constraining the Hubble constant and determining if the tension actually exists.

In the resulting paper, published April 10 in the journal Astronomy & Astrophysics, the authors derived the most precise Hubble constant yet and found that the tension persists, suggesting that our current cosmological model is incomplete. [Continue reading…]