content_image/313907.jpg content_image/313906.jpg content_image/313905.jpg content_image/313904.jpg
ity. We define a 4-vector 

<img src='content_image/313907.jpg'>

in Minkowski coordinates (in a Minkowski space). This defines a threading of spacetime, which can be represented by a series of lines, corresponding to a fixed x i ( i = 1 , 2 , 3), as well as a slicing of spacetime into hypersurfaces, corresponding to a fixed x $^{0}$. 

The line element between two spacetime points is given by 

<img src='content_image/313906.jpg'>

where we use natural units for which c = ℏ = k$_{B}$ =1. By defining a symmetric Minkowski Metric Tensor 

we can denote the line element as 

<img src='content_image/313905.jpg'>

<img src='content_image/313904.jpg'>

