Which is why physicists will tend to say that we live in “3+1 dimensions”, for 3 spacial dimensions, and 1 time dimension. If you’re trying to measure a distance between two events and in 1 dimension you’ll find that , which is just another way of writing “the absolute value of “. If you measure a yard stick at any angle, anywhere in the world, you’ll always measure the same length. “L” is the measure of distance in spacetime, but to keep everything straight it’s called the “spacetime interval”. You may have noticed that sometimes when you use this equation that you’ll be taking the square root of a negative number.