Yep and &quot;simultaneous&quot; is not simple either as Einstein figured out in 1905:
&quot;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.&quot;<p><a href="https:&#x2F;&#x2F;www.fourmilab.ch&#x2F;etexts&#x2F;einstein&#x2F;specrel&#x2F;www&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.fourmilab.ch&#x2F;etexts&#x2F;einstein&#x2F;specrel&#x2F;www&#x2F;</a>