Editing Time (section)

=== Relativistic versus Newtonian ===
[[File:Lorentz transform of world line.gif|Views of spacetime along the [[world line]] of a rapidly accelerating observer in a relativistic universe. The events ("dots") that pass the two diagonal lines in the bottom half of the image (the past [[light cone]] of the observer in the origin) are the events visible to the observer.|thumb]]

The animations visualise the different treatments of time in the Newtonian and the relativistic descriptions. At the heart of these differences are the [[Galilean transformation|Galilean]] and [[Lorentz transformation]]s 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 the Newtonian description these changes are such that ''time'' is absolute:<ref>{{Cite book |last1=Knudsen |first1=Jens M. |url=https://books.google.com/books?id=rkP1CAAAQBAJ&pg=PA30 |title=Elements of Newtonian Mechanics |last2=Hjorth |first2=Poul G. |date=2012-12-06 |publisher=Springer Science & Business Media |isbn=978-3-642-97599-8 |page=30 |language=en}}</ref> 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 Notice that with the change from a Newtonian to a relativistic description, the concept of ''absolute time'' is no longer applicable: events move up and down in the figure depending on the acceleration of the observer.