Think of spacetime as a 4-dimensional fabric which makes up the universe. Why 4 dimensions, you may ask? Well, 3 dimensions in space and 1 dimension in time. Why? Well, think of it this way. You’re inviting a friend to meet somewhere. If you don’t have a time to meet, the two of you don’t know when to go. If you don’t have a place to meet, you don’t know where to go. It doesn’t make sense to have space without time. They can’t exist without each other. Which is why you combine the two.
Credits: Extraordinary Universe