Primordial magnetic fields may ease Hubble tension, study finds

October 4, 2026 at 06:02 PM2 min

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Weak magnetic fields from the early universe could help explain the discrepancy in measurements of the universe's expansion rate, according to new research. The study used full three-dimensional simulations of primordial plasma and found the idea consistent with cosmic microwave background observations. The Hubble tension persists between values of about 67 and 73 km/s/Mpc from different methods.

Key Facts

Indirect measurements using the Planck telescope give a Hubble constant of about 67 km/s/Mpc.
Direct measurements using Type Ia supernovae and Cepheids with Hubble and James Webb telescopes give about 73 km/s/Mpc.
The new study used full three-dimensional simulations of primordial plasma to test the effect of weak magnetic fields.
The researchers examined how magnetic fields affected recombination, when electrons and protons combined into neutral hydrogen.

The Hubble Tension

The Hubble constant measures how fast the universe is expanding and is named after Edwin Hubble, who first discovered cosmic expansion. Indirect measurements based on the cosmic microwave background, including data from the Planck Space Telescope, yield about 67 km/s/Mpc. Direct measurements using Type Ia supernovae as standard candles, calibrated by Cepheid stars, give about 73 km/s/Mpc. The difference between 67 and 73 km/s/Mpc is statistically highly significant and is known as the Hubble tension. If both methods are correct, the standard model of cosmology must be missing something important.

Primordial Magnetic Field Hypothesis

Researchers tested whether extremely weak magnetic fields left over from the earliest moments after the Big Bang could help resolve the Hubble tension. The study used full three-dimensional simulations of primordial plasma to model the effects of these fields. The simulations showed that magnetic fields could have influenced recombination, the period when electrons and protons combined into neutral hydrogen. Due to the fields' action, charged particles could have been distributed more unevenly, accelerating hydrogen formation in denser regions. The results are consistent with existing observations of the cosmic microwave background.