Time is a measurement , time is also a length

           The Time is Also a length

(In the 3dimentional world,the distance between two points we messured in distance)

O' is a source of light.
    t=o
The wave font ,was scattering around O'
(As the same speed of light)

After t' second , the wave font reaching the point p(xyz)

              The distance between o' and p' is
    Ct*2(s*2) =x*2 + y*2 +z*2
ie,
C*2 t*2 - x*2 -y*2 - z*2 =  c*2 t*2- x*2-y*2-z*2
Or
X*2 + y*2+z*2- c*2 t*2= x*2+y*2+z*2- c*2 t*2

Substitute>>>
       C*2 t*2= w*2
      -c*2 t*2= +w*12
That is w= ict 
              i= √-1

In the minkowski's 4th dimentional world........
Every points , is called or known as 
WORLD POINT and the path of rays is called 
World Line 

Two world line are 
P(x1,y1,z1,w1), Q(x2,y2,z2,w2)

The distance between, PQ = S

then....., 
           S*2= ( x2-x1)*2 + (y2-y1)*2+(z2-z1)*2+
                                                           (W2-w1)*2

Consider an element of world line 
     Then,
   ds*2 =dx*2+dy*2+dz*2+dw*2
            = dx*2+dy*2+dz*2- C*2 dt*2

There for .. " The TIME is also a Measurement "