Astronomers Cannot Agree On How Fast the Universe is Expanding

Two fundamentally different methods for measuring the universe's expansion rate continue to produce incompatible results -- with direct observations of receding galaxies yielding approximately 73 kilometers per second per megaparsec and cosmic microwave background radiation analysis producing closer to 67 km/s/mpc. The discrepancy, known as the Hubble tension, has strengthened annually for the past decadem, according to Duke University astronomer Dan Scolnic. The persistent disagreement prevents calculation of the universe's precise age or size. The Lambda-CDM model, which holds that dark energy and dark matter comprise 95% of the universe while visible matter constitutes just 5%, assumes dark energy's nature has remained constant since the Big Bang. Some theorists propose dark energy's potency changes over time, while others suggest the Milky Way sits within a comparatively empty region of space. A June study using gravitational lensing of quasar light, bypassing traditional distance measurements, matched the higher value. New telescopes including the Vera Rubin Observatory and Nancy Grace Roman Space Telescope may provide additional data. Past improvements in measurement precision have only reinforced rather than resolved the tension.

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