i wanted to say relevance but i figured that would be too easy :rofl: editing there is something i'm not getting. yes if the speed of light is the same in all intertial frames simultaneity is relative but so what? can someone explain to me how this implies that time and space are relative? very very clearly please. and can someone also tell me what is the interval in lorentz geometry? if this is the equation in only 2 of 4 dimensions in minkowski space [tex]\Delta t^2 - \Delta x^2 = \Delta t'^2 - \Delta x'^2=\tau^2[/tex]( with primes being in moving frames.) and it is an equation of a hyperbola then what is the [itex]\tau[/itex]. it's obviously a constant but as far as the graph of a hyperbola i can't figure out what it represents.