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Astronomy

The Hubble Tension: Resolving the Discrepancy in Cosmic Expansion Rates

Quick fact

Measurements from the early universe (via the cosmic microwave background) give a Hubble constant of about 67 km/s/Mpc, while local measurements (using Cepheids and supernovae) give about 73 km/s/Mpc—a difference of roughly 9%, far too large to be a measurement error.

Why this is interesting

Imagine you have two perfect rulers for measuring the universe, but they keep giving you different answers for how fast it's expanding. Why can't they agree?