Scientists have produced one of the most precise measurements of how fast the universe is expanding – and it has only added to the mystery.
For years, astronomers have been trying to resolve the “Hubble tension”. That arises because there are two ways of measuring the rate of expansion of the universe, but they seem to show different results.
One looks at the cosmic microwave background, or the leftover radiation from the beginning of the universe, while the other watches stars and galaxies that are nearby to see how fast they are moving away. Both should show the same result and tell us how the speed of the universe – but they do not.
Looking at the nearby universe suggests that it is expanding at around 73 kilometers per second per megaparsec. The one relying on the cosmic microwave background is slightly slower, at 67 or 68.
Astronomers believed that narrowing the estimates to be more precise could bring those two numbers together. But new estimates and a number of studies have only shown that the tension remains.
A new paper – produced using decades of observations into one framework, and relying on astronomers from across the world – refined those estimates even further, to about 1 per cent, and shows that the tension continues.
“This work effectively rules out explanations of the Hubble tension that rely on a single overlooked error in local distance measurements,” the authors write. “If the tension is real, as the growing body of evidence suggests, it may point to new physics beyond the standard cosmological model.”
Researchers believe that the problem might not be the measurements but a problem in our understanding of physics. It suggests that there is something else at work that has not been accounted for, such as dark energy, undiscovered particles or a mistake in the way we understand gravity.
The research is described in a new paper, ‘The Local Distance Network: A community consensus report on the measurement of the Hubble constant at ∼1% precision’, published in the journal Astronomy & Astrophysics.