Absolute Simultaneity Gravity part I

This paper introduces Absolute Simultaneity Gravity (ASG) Part I as a minimal phenomenological framework for an early-time modification of cosmological expansion, localized near matter–radiation equality. The construction is implemented through a lapse response function that rescales the physical proper-time Hubble rate while preserving the late-time ΛCDM background. Its central result is that the recombination and drag sound horizons are shifted by unequal amounts, leading generically to a nontrivial modification of the drag-to-recombination sound-horizon ratio. This defines a sharp and falsifiable ruler-calibration signature linking CMB and BAO inference, and recasts the Hubble tension as a structural early-time calibration effect rather than a genuine late-time dark-energy deviation.