A particle model derived from Newton's second law pictures an electron in an expanding universe. The model unifies charge, spin, and expansion. Expansion causes gravity. Massive particles pick up energy released via radiation redshift, and a purely radiative, matter-free, universe is forbidden. Therefore, the universe is forced to undergo a series of matter-creating phase transitions — from literally nothing (phase 0), via decaying neutral spinless matter (phase 1), charged spinless matter (phase 2), and charged spinning matter (phase 3), to the strongly and weakly interacting stable matter of today (phase 4). The tauon-muon and muon-electron mass ratios tell how much the rest energies of the massive particles grew in phase 1 and phase 2, respectively. The model contains no adjustable parameters, and makes unambiguous predictions, such as H0 = 56.8 km/s/Mpc for the present-day Hubble expansion rate and 1/Bα = 205.759 223 (with B = 0.666 001 731) for the muon-electron mass ratio. To the zeroth-order predictions of the particle model must be added radiative contributions calculated using standard QED and electroweak theory. Thus, mμ/me = 1/Bα + 1/(1 − 2Bα) = 206.769 039 is the muon-electron mass ratio of the pure QED universe (phase 3). This value is larger than the measured phase-4 value 206.768 283(6). A simple electroweak calculation shows that the appearance of the weak force caused a sudden decrease in lepton masses. Thus, a one-Higgs model adds −0.000 2076 to mμ/me. The corresponding decrease in tauon mass explains how the creation of the proton was energetically possible, and why the previously cold universe acquired a high temperature. The numerical value 1 + 2(mp − mπ) / 4(mπ − me) = 3.872 = 4 − 0.128 informs that four Higgs bosons act to decrease the tauon mass, while a weak (presumably flavor-changing) effect slightly corrects the mass upward. It is concluded that the corresponding total weak correction to the muon-electron mass ratio is −0.000 2076(4 − 0.128 log(mτ/mμ)) = −0.000 755, yielding mμ/me = 206.768 284, which agrees with the measured value.