What came before the physics we can test? Before stars and atoms, the universe passed through conditions so extreme that general relativity and quantum field theory cannot be used together with confidence. The Planck Epoch names that frontier. Ideas such as quantum foam and a single interaction embracing gravity, electromagnetism, and the nuclear forces are possible descriptions sought by quantum-gravity research — not observations of a known state. This is less a completed first chapter than the torn edge of the page.

The afterglow of the Big Bang is still visible — a microwave background filling all of space. It was released when the universe became transparent, about 380,000 years after the Big Bang. Planck mapped temperature variations at roughly the one-part-in-100,000 level. Those patterns are consistent with primordial density perturbations stretched to cosmic scales in inflationary models. The map therefore gives indirect constraints on the very early universe; it is not a fossil or photograph of the Planck Epoch itself.

Today nature is described through gravity, electromagnetism, and the strong and weak nuclear interactions. Experiments show that electromagnetism and the weak interaction merge at high energy; theories seek a deeper unification, ultimately including gravity. The Planck temperature, about 1.42 × 10³² Kelvin, marks the scale where quantum-gravity effects should matter. Calling this a single Grand Unified Force is an evocative hypothesis, not a measured fact — the question is precisely what physics at this frontier must answer.

Every later transformation — from stellar fusion to nuclear fission — unfolds under physical laws whose deepest common origin remains unresolved. The universe cooled, expanded, formed particles, nuclei, atoms, stars, and observers. The Planck Epoch is not a container in which all those outcomes were already packed; it is the limit where our successful descriptions stop joining cleanly. We live in the long aftermath, still trying to write its first intelligible sentence.