Side note-- this if we add i (the square root of -1) into this equation, we can rewrite the equation as:
x[sup]2[/sup] + y[sup]2[/sup] + z[sup]2[/sup] + i[sup]2[/sup]c[sup]2[/sup]t[sup]2[/sup] = I[sup]2[/sup]
If we look at the element “ict”, we are looking at a translation of time that behaves as a spacial dimension. For those of you who have read Hawking, ict is what he is talking about when he refers to “imaginary time”.
Okay Undead Dude just shut up and let someone else talk! 
Sorry just one other addition, related to “space and time are just the same things”
As hopefully the space-time interval equation elicits, space and time are not “just the same things”. Time acts distinctly different from space. The 3 normal spatial dimensions are independent of each other. The spatial dimensions are not independent of time. If they were, our world would be a lot more like Newton said it was. This lack of independence between time and spatial dimensions is what brings about the fun of relativity.
So space and time are inseparable, but they are not equivalent to each other.