Planck time
The Planck time is the interval light takes to cross one Planck length, about 5.39 × 10⁻⁴⁴ seconds. It is not a measurement of anything; it is what you get by combining the gravitational constant, the speed of light and the reduced Planck constant into a quantity with the dimensions of time, and it is roughly 10²⁵ times shorter than the briefest pulse any laboratory has produced.
Watch out: It is often described as the shortest meaningful duration. That claim is a physical conjecture, not a definition: it marks the scale at which a quantum theory of gravity is expected to be needed, and no such theory is confirmed. Its numerical value also inherits the uncertainty of G, which is the worst-measured of the fundamental constants.
| 1 | 5.3912470e-44 |
Max Planck proposed the natural units in 1899, before relativity and before quantum mechanics, on the grounds that a system built only from universal constants would mean the same thing to any civilisation anywhere. The set survived both revolutions unchanged.
One planck time in every time unit
| 1 | Planck time (tP)this unit | |
| 5.39125e-26 | attosecond (as) | |
| 5.39125e-29 | femtosecond (fs) | |
| 5.39125e-32 | picosecond (ps) | |
| 5.39125e-35 | nanosecond (ns) | |
| 5.39125e-36 | shake (shake) | |
| 5.39125e-38 | microsecond (µs) | |
| 5.39125e-41 | millisecond (ms) | |
| 5.39125e-44 | second (s) | |
| 8.98541e-46 | minute (min) | |
| 1.49757e-47 | hour (h) | |
| 6.25695e-49 | sidereal day (sd) | |
| 6.23987e-49 | day (d) | |
| 8.91410e-50 | week (wk) | |
| 4.45705e-50 | fortnight (fn) | |
| 2.05010e-50 | month (mo) | |
| 1.70838e-51 | year (yr) | |
| 1.70838e-52 | decade (dec) | |
| 1.70838e-53 | century (cent) | |
| 1.70838e-54 | millennium (mil) | |
| 1.70838e-57 | megayear (Myr) | |
| 1.70838e-60 | eon (eon) |