> One of the deep insights of special relativity is that these scalar and vector quantities are actually unified into a single, new entity called a "four-vector

> One of the deep insights of special relativity is that these scalar and vector quantities are actually unified into a single, new entity called a "four-vector". > But the really weird thing about this particular four-vector is that it always has a magnitude of exactly the speed of light. No matter how fast you go, the magnitude of your four-velocity does not actually get larger. All you do by going faster is just mix some of the time component of your four-velocity into the spatial components. This seems strongly to be confusing the map and the territory. The maths is a model, the description of vectors has not link to reality but happens to model reality in some useful way (reality and the model correspond to some useful approximation), but it isn't reality. so > at rest your four-velocity points directly in the future with a magnitude equal to the speed of light may just be an artefact of the maths. IDK though. (and no offence intended, just my POV)