Editing Time (section)

=== Classical mechanics ===
In non-relativistic [[classical mechanics]], Newton's concept of "relative, apparent, and common time" can be used in the formulation of a prescription for the synchronization of clocks. Events seen by two different observers in motion relative to each other produce a mathematical concept of time that works sufficiently well for describing the everyday phenomena of most people's experience. In the late nineteenth century, physicists encountered problems with the classical understanding of time, in connection with the behavior of electricity and magnetism. The 1860s [[Maxwell's equations]] described that light always travels at a [[Speed of light|constant speed]] (in a vacuum).<ref>{{Cite journal |date=2013 |title=Deriving 0 and 0 from First Principles and Defining the Fundamental Electromagnetic Equations Set |url=https://ijerd.com/paper/vol7-issue4/G0704032039.pdf |journal=International Journal of Engineering Research and Development |volume=7 |issue=4 |pages=33 |issn=2278-067X}}</ref> However, classical mechanics assumed that motion was measured relative to a fixed reference frame. The [[Michelson–Morley experiment]] contradicted the assumption. Einstein later proposed a method of synchronizing clocks using the constant, finite speed of light as the maximum signal velocity. This led directly to the conclusion that observers in motion relative to one another measure different elapsed times for the same event.

[[File:World line.svg|upright=1.2|thumb|Two-dimensional space depicted in three-dimensional spacetime. The past and future [[light cone]]s are absolute, the "present" is a relative concept different for observers in relative motion.|left]]