> accortingg dimension definition, time should be orthogonal
> either on x-axe, y-axe or z-axa
>
> what is time t orthogonal on?
It need not be orthogonal - just linearly independent of x, y, z is
enough.
In special cases like Minkowski or Schwarzschild or Kruskal-Szekeres
coordinates the t-coordinate is orthogonal to both x and y and z.
--
Jan Bielawski