Editing Principle of locality (section)

=== Alice and Bob in spacetime ===
[[File:Models of locality Spacetime.png|upright=1.3|thumb|Alice and Bob in spacetime diagram]]
A spacetime diagram has a time coordinate going vertical and a space coordinate going horizontal. Alice, in a local region on the left, can affect events only in a cone extending in the future as shown; the finite speed of light prevent her from affecting other areas including Bob's location in this case.  Similarly we can use the diagram to reason that Bob's local circumstances cannot be altered by Alice at the same time: all events that cause an effect on Bob are in the cone below his location on the diagram. Dashed lines around Alice show her valid future locations; dashed lines around Bob show events that could have caused his present circumstance.  When Alice measures quantum states in her location she gets the results labeled <math>\mathbf{a}</math>; similarly Bob gets <math>\mathbf{b}</math>. Models of locality attempt to explain the statistical relationship between these measured values.