The Turnover of the Universe: the Big Bang as the Passage of a Single History through the Planck Region

I propose that the Big Bang is not the beginning of the universe but the turning point of a single cosmic history: a prior, unbounded universe contracts until it enters the Planck region—the epoch in which the density reaches the Planck density, where quantum-gravitational effects are expected and known physics is expected to break down—and leaves it turned over, with its spatial orientation inverted, re-expanding without bound as the universe we observe. Since what happens inside the Planck region is unknown, the turnover is stated as the central postulate of the essay. The argument rests on five axes: (I) time as the measure of change; (II) when cosmic history is rewound, the scale factor decreases to zero at the origin; (III) that point is a passage, not a beginning, with one history and a single time orientation, neither mirror nor bounce; (IV) the turnover: I postulate that the passage through the Planck region inverts spatial orientation without inverting the direction of time; (V) gravity drives the whole process, accelerating the collapse of the prior universe and decelerating the subsequent expansion until dark energy takes over. I show that the radiation-dominated solution of Einstein's equations is compatible with this structure and verify it symbolically (Appendix A). The essay claims no exclusive prediction; it offers a unified reading of existing results and states its limits explicitly; the observational consequences of the turnover remain to be worked out.