section_path: Physical definition/Relativistic versus Newtonian
section_name: Relativistic versus Newtonian
paragraph_text: Relativistic versus Newtonian
  
  The animations visualise the different treatments of time in the Newtonian and the relativistic descriptions. At the heart of these differences are the Galilean and Lorentz transformations applicable in the Newtonian and relativistic theories, respectively.
  
  In the figures, the vertical direction indicates time. The horizontal direction indicates distance (only one spatial dimension is taken into account), and the thick dashed curve is the spacetime trajectory (" world line ") of the observer. The small dots indicate specific (past and future) events in spacetime.
  
  The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. In both pictures the view of spacetime changes when the observer accelerates.
  
  In the Newtonian description these changes are such that time is absolute: the movements of the observer do not influence whether an event occurs in the 'now' (i.e., whether an event passes the horizontal line through the observer).
  
  However, in the relativistic description the observability of events is absolute: the movements of the observer do not influence whether an event passes the " light cone " of the observer. Notice that with the change from a Newtonian to a relativistic description, the concept of absolute time is no longer applicable: events move up and down in the figure depending on the acceleration of the observer.