Series opener. A single continuous journey outward and inward — from a human standing on a street, out past the atmosphere, the solar system, the galaxy, the local group, to the edge of the observable universe; then back and down, through skin and cell and molecule and atom to the quantum foam and the Planck length. Roughly sixty orders of magnitude in fifty minutes.
The episode establishes the visual grammar of the whole series and gives audiences the scale vocabulary every subsequent hour depends on.