Scale of the Universe

The observable universe spans roughly 44 orders of magnitude — from the Planck length (10⁻³⁵ m) to the cosmic horizon (10²⁶ m).

'Order of magnitude' means power of 10 — two quantities differ by one order of magnitude if one is ~10× the other.

Atomic scale ≈ 10⁻¹⁰ m (Bohr radius); nuclear scale ≈ 10⁻¹⁵ m (femtometre or 'fermi').

Human scale ≈ 10⁰ m (1 m); Earth radius ≈ 6.4 × 10⁶ m; Sun–Earth distance ≈ 1.5 × 10¹¹ m (one AU).

1 light-year = 9.46 × 10¹⁵ m; 1 parsec = 3.086 × 10¹⁶ m.

The Milky Way is ~10²¹ m across; observable universe ~10²⁶ m.