Quote by hartlw
How about the 5D universe model which assumes a fifth dimension.

What 5 dimensional universe? You need to specify what you mean by this.
What is the definition of x,y,z,t?

I think your confusion is arising because you are still in the mind set that spatial dimensions are real and physical, and that temporal dimensions is somehow different. This is the exact opposite of what relativity proposes: relativity puts spatial and temporal dimensions on an equal footing. Space and time are combined into spacetime, and a set of four coordinates (t,x,y,z), say, label our position in spacetime.