An overlooked era of cosmology is stealing the show in the quest to understand the cosmos

A cosmologist explains how Big Bang Nucleosynthesis — the roughly 20-minute period beginning about 10 minutes after the Big Bang, when protons and neutrons fused into helium-4 and deuterium — is now rivaling the famed Cosmic Microwave Background as a tool for measuring the early universe. A September 2026 measurement of primordial helium-4 abundance reached new precision, letting researchers infer the amount of radiation present in the universe's first minutes.

That radiation measurement in turn helps physicists test competing models of dark matter, which makes up roughly 80% of the universe's matter. The CMB still edges out BBN on measuring particle density, though BBN is closing the gap.

The Simons Observatory, a new CMB telescope, is beginning observations that should sharpen CMB measurements further, though the piece notes there's no clear plan yet for what comes after that.

The full dispatch is available from the source below.