Planck Length
Definition
The shortest meaningful distance in physics — about 10⁻³⁵ m, where quantum gravity takes over and our theories break down.
Symbol: · Unit: meter (m)
Technical definition
ℓ_P = √(ℏG/c³) ≈ 1.616×10⁻³⁵ m. Below this scale, quantum fluctuations of spacetime itself are expected to dominate.
Example
A proton is ~10²⁰ Planck lengths wide — if a proton were blown up to the size of the observable universe, a Planck length would still be far smaller than an atom.
Common confusion
The Planck length is not proven to be a 'pixel of space' — it is the scale where current theories stop working, not an established minimum grid.