Planck time

1

In Big Bang theories of the origin of the universe, the period between 0 and 10⁻⁴³ seconds after the origin of the universe, during which the four forces (gravity, electromagnetism, and the strong and weak nuclear forces) were united. At 10⁻⁴³ seconds, gravity separated from the other three forces.

2

In concept, the amount of time needed for a photon to travel from one side of an atom to the other. According to the 1998 CODATA value, 5.3906 × 10⁻⁴⁴ seconds with a standard uncertainty of 0.0040 × 10⁻⁴⁴ seconds.