I would be interested to hear what others think of the general concept of relativistic velocity in the time dimension, analogous to spatial velocity. To get going, consider the Minkowski velocity 4-vector: [tex]\gamma(c,v_1, v_2, v_3)[/tex] The time component of this 4-velocity is [tex]\gamma c[/tex]. With increasing spatial velocity, this component goes to infinity. With spatial velocity zero, it equals c. Obvious questions are: - how to give (physical) meaning to this component; seconds per second is not very usable. - why does the time component go to infinity, while it is clear that proper time goes to zero.