[Sephiroth]

But what the heck is "space-time"? 3D is quite simple, with a force causing or having caused expansion. Time in this context is the number of time unit (seconds, minutes, years, etc) for a galaxy to move from 3D location "A" to 3D location "B".

In my assessment, for what it is worth, "space-time" is a confection of convenience for scientists who know quite a lot about the square root of all this, but not the bit underneath it all.

"Time vector" - don't we all understand this as time moving in one direction only? As in forwards? It has to be measured by some entity that can do such measurements or imagine them with a sound basis in fact. "Space-Time" - includes a "time vector"? Might as well be a triaxellated amplification of a sub-space message from Starfleet.

Imo!