Discrepancy between different ways of measuring Hubble constant refuses to fade
NASA, ESA, L. Frattare/STScI
A puzzling mismatch is plaguing two methods for measuring how fast the universe is expanding. When the discrepancy arose a few years ago, scientists suspected it would fade away, a symptom of measurement errors. But the latest, more precise measurements of the expansion rate — a number known as the Hubble constant — have only deepened the mystery.
“There’s nothing obvious in the measurements or analyses that have been done that can easily explain this away, which is why I think we are paying attention,” says theoretical physicist Marc Kamionkowski of Johns Hopkins University.
If the mismatch persists, it could reveal the existence of stealthy new subatomic particles or illuminate details of the mysterious dark energy that pushes the universe to expand faster and faster.