We know that the universe is expanding, but a strange discrepancy in just how fast that expansion is occurring continues to confound physicists—and make them wonder whether there’s some new, unexplained physics afoot.
For every 3.3 million light years, or one megaparsec, the universe expands around another 70 kilometers per second faster. There are two discrepant measurements of this so-called “Hubble constant.” The light from the most distant parts of the universe reveals an expansion of 68 km/s per megaparsec, while a method taken from extrapolating data from nearby sources reveals a rate of 73 km/s per megaparsec. Scientists can’t explain this discrepancy by chance alone, which means they’re leaving something out, either in their experiments or in the laws of physics. A team of researchers have an idea for another measurement that could help close the gap between these numbers—by measuring how gravity affects the light from distant supernovae.
“If you want to tell the difference between new physics and unknown errors, you need another measurement,” study author Thomas Collett from the University of Portsmouth in the UK told Gizmodo. “If you have measurements that have completely independent methods and they’re all pointing in the same direction, you can robustly believe it’s new physics, not that they’re screwing up in the same way.”
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