Time is not quite treated as 'just' another dimension in special relativity (SR). As whatshisface mentioned, the sign of the time coordinate is different when

Time is not quite treated as 'just' another dimension in special relativity (SR). As whatshisface mentioned, the sign of the time coordinate is different when computing the interval. What this means in practice is that you can't 'rotate' from a motion forwards in time to backwards in time. Instead you get what is basically a shearing transformation. The amount of rotation is limited by the speed of light (c). So SR, I think, doesn't really say that time is just another dimension like the spatial dimensions. But it does mix the two together with a shearing transformation. In fact, I would say that special relativity doesn't have much in particular to say about what time is. It merely specifies the mathematical transformations between reference frames, including between the local times in those frames. You have to go to metaphysics to say what this really means. In this sense it's a bit a like quantum mechanics.