Yep and "simultaneous" is not simple either as Einstein figured out in 1905: "So we see that we cannot attach any absolute signification to the concept of simul

Yep and "simultaneous" is not simple either as Einstein figured out in 1905: "So we see that we cannot attach any absolute signification to the concept of simultaneity, but that two events which, viewed from a system of co-ordinates, are simultaneous, can no longer be looked upon as simultaneous events when envisaged from a system which is in motion relatively to that system." https://www.fourmilab.ch/etexts/einstein/specrel/www/ https://www.fourmilab.ch/etexts/einstein/specrel/www/