One is nothing but an instrument on which the universe plays. ~ German composer Gustav Mahler
Earth is tucked into an infinitesimal spot on an arm of the Milky Way galaxy. The Milky Way is one of 2 trillion galaxies in the observable universe, which is spread out spherically, with a diameter of 90 billion light-years. (A light-year is how far light travels in a year at light-speed (as fast as light can travel). A light-year is ~9.461 trillion kilometers.)
To explain how our existence came to be, this instrument begins its play at a beginning….
Universes are like petals of a flower: they unfold only when conditions are favorable.
3,800 years ago (ya), the Babylonians conceived a plurality of heavens and earths. 2,500 ya, Chinese philosopher Lao Tzu held that the universe originated out of nothingness.
The ancient Greeks thought existence eternal, comprising infinite space; so did a young Einstein. In the 6th century BCE, Anaximander of Miletus conceived the cosmos in a perpetual cycle of incarnation and reincarnation, powered by apeiron: an eternal coherence.
The primal essence of the existing objects is also the fact that when they perish, they return as dictated by necessity. ~ Anaximander
We do not know how or when the universe began. Astrophysicists have speculated by extrapolating backward, with guesswork about whether and how the dynamics of fundamental forces changed. Hence the following tale is one of speculative backfill.
The extant understanding of physics colors the picture: rendering a sketch rather than a portrait, as the yardstick for characterization of high-energy events on the periphery of quantum reality has smudges on the measurement lines; for good reason.