A simultaneity is a set of virtual timepieces, to be found only in the awarenesses of speculative cosmologists. Only hypothetic clocks can be supposed to be started or stopped instantaneously. Nothing happens instantaneously. It all takes time. An implication often suggested...especially in much mathematical modeling...is that when two events are deemed to be simultaneous they both happened together instantaneously. It is a mischievous fiction. In reality, two events can only be judged to be simultaneous when the beginning-event of one clearly occurs before the end-event of the other. Determining whether or not two events started or finished simultaneously becomes a matter of determining to what degree the two beginning-events, or the two end-events of each overlap. Thus if the arrival-of-the-steam-train event is deemed to have occurred whilst the timetabled-0920-plus-or-minus-30seconds event is transpiring, most travellers would cheerfully admit that the two events were simultaneous.

However on a grand geological scale, if layers of the shells of extinct sea creatures are located at the top of mountain ranges, we would be initially inclined to suppose that the extinction event and the tectonic event were not simultaneous, since the end of the first event most probably occurred well before the beginning of the second. Sexual participants in media presentations presume they are simulating simultaneous orgasms, as long as both performers fake ecstasy within a few plausibly noisy vocalizations. At the microcosmic end of the scale, relativistic considerations become paramount, and eventually, determining whether two beginning-events are simultaneous becomes essentially impossible in the context of the chaos of atomic uncertainties. Attempting to allow for time differences for information to travel from each of two separate events, or even from one event which initiates others, will eventually enforce the realization that the concept of an instantaneous event is an existential impossibility. There are no instantaneous events to be observed in the cosmos and there was no instantaneous event which initiated the cosmos.