Did the early Universe leave oscillating fingerprints in the CMB?

Astronomers searched Planck's full CMB dataset for signs of primordial oscillatory features—ripples imprinted on the universe moments after the Big Bang. They found a few frequencies that improve the fit by up to 15 chi-squared units, but Bayesian statistical tests and corrections for multiple comparisons downgrade all signals below 3-sigma significance. Upcoming polarization measurements from SO and LiteBIRD should improve constraints by 10–100×, allowing genuine primordial signals to break through the noise.