  In non relativistic physics it is assumed that both chronological ordering
and causal ordering of events (telling whether there exists a causal
relationship between two events or not) are absolute, observer independent
properties. In relativistic physics on the other hand chronological ordering
depends on the observer who assigns space-time coordinates to physical events
and only causal ordering is regarded as an observer independent property. In
this paper it is shown that quantum theory can be considered as a physical
theory in which causal (as well as chronological) ordering of probabilistic
events happening in experiments may be regarded as an observer dependent
property.
