Full Idea
A light ray always moves at one unit of space per unit of time - a constant diagonal on the graph. ...But the direction that light rays travel in is neither space nor time, and is called 'null'. It is on the edge between space and time.
Gist of Idea
Light moves at a constant space-time speed, but its direction is in neither space nor time
Source
New Scientist writers (New Scientist articles [2013], 2013.06.15)
Book Reference
-: 'New Scientist magazine' [ 2013], p.37
A Reaction
Don't understand this, but it sounds fun.