▲ | pajko a day ago | |
Out of the question, it has no definition which is only related to physics. Well, there's the "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" definition, but this was chosen to match the celestial-based unit related to the Earth's rotation (which does not tell anything to extraterrestrials). |