Planck time
| Value | 5.391247e-44 s |
| Status | Measured: ± 6.00e-50 s (0.0000011 relative) |
| Source | CODATA 2022 (derived from ħ, c and G; uncertainty inherited from G) |
| Categories | Universal & Atomicphysicsquantum |
| millisecond | 5.3912470e-41 ms |
| second | 5.3912470e-44 s |
| minute | 8.9854117e-46 min |
| hour | 1.4975686e-47 h |
| day | 6.2398692e-49 d |
| week | 8.9140989e-50 wk |
| year | 1.7083831e-51 yr |
Learning zone
The Planck time is simply l_P/c, and it is the shortest interval that has any operational meaning in current theory: measuring a shorter one would require an energy so concentrated that it would collapse into a black hole. For scale, the shortest pulses laboratories can make are attoseconds, 10⁻¹⁸ s — still 10²⁶ Planck times long.
Cosmology uses it as a boundary marker. "The Planck epoch" is the first 10⁻⁴³ s after the Big Bang, before which general relativity and quantum field theory give contradictory answers and the honest statement is that nobody knows. Everything cosmologists do describe — inflation at around 10⁻³⁶ s, quark-gluon plasma at microseconds, nucleosynthesis at minutes — happens comfortably afterwards. Note that "time began at t_P" is a statement about the limits of our theories, not a discovery about the universe.