Scale of the Universe
Traverse 44 orders of magnitude — from quarks to the observable universe — on a logarithmic slider.
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.
Order of magnitude
Integer power of 10 closest to x.
Light-year
Distance light travels in vacuum in 1 year.
Astronomical unit
Mean Earth–Sun distance.
Parsec
Distance at which 1 AU subtends 1 arc-second.
A factor-of-10 error in a calculation moves you one order of magnitude — that's a huge change in physics.
Rough mental estimates (Fermi estimates) use orders of magnitude — ignore constants, keep powers of 10.
The ratio of universe to Planck length ≈ 10⁶¹ — one of the largest pure numbers in physics.