Scale of the Universe
Traverse 44 orders of magnitude — from quarks to the observable universe — on a logarithmic slider.
Key Notes
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.
Formulas
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.
Important Points
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.
Scale of the Universe notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.