In the first moments after the Big Bang, the universe wrote its autobiography in the nuclei of light elements — and helium, forged before the first stars ever ignited, has kept that record faithfully ever since. New precision measurements of primordial helium are now allowing physicists to hold that ancient text up against their best theoretical models, testing whether our understanding of the universe's birth is sound. The findings tighten the constraints on fundamental cosmological parameters, ruling out certain alternative theories while opening new pathways toward understanding dark matter