Editing Special relativity (section)

== Background ==
Special relativity builds upon important physics ideas. The non-technical ideas include:
* [[speed]] or [[velocity]], how the relative distance between an object and a reference point changes with time.<ref name=Mermin-2009/>{{rp|25}}
* [[speed of light]], the maximum speed of information, independent of the speed of the source and receiver,<ref name="Taylor1992"/>{{rp|39}} 
* [[Event (relativity)|event]]: something that happens at a definite place and time. For examples, an explosion or a flash of light from an atom;<ref name="Taylor1992"/>{{rp|10}} a generalization of a point in geometrical space,<ref name=Mermin-2009/>{{rp|43}} 
* [[clocks]], relativity is all about time;<ref name=Mermin-2009/> in relativity observers read clocks.<ref name="Taylor1992"/>{{rp|39}} 
Two observers in relative motion receive information about two events via light signals traveling at constant speed, independent of either observer's speed. Their motion during the transit time causes them to get the information at different times on their local clock.

The more technical background ideas include:
* [[invariance (physics)|invariance]]: when physical laws do not change when a specific circumstance changes, such observations at different uniform velocities;<ref name=Mermin-2009>{{Cite book |last=Mermin |first=N. David |title=It's about time: understanding Einstein's relativity |date=2009 |publisher=Princeton University Press |isbn=978-0-691-14127-5 |edition=Sixth printing, and first paperback printing |location=Princeton, NJ and Oxford}}</ref>{{rp|2}}
* [[spacetime]]: a union of geometrical space and time.<ref name="Taylor1992"/>{{rp|18}}  
* [[Spacetime#Spacetime_interval|spacetime interval]] between two events: a measure of separation that generalizes distance:<ref name="Taylor1992">{{cite book|url=https://archive.org/details/spacetime_physics/|title=Spacetime Physics|last1=Taylor|first1=Edwin F.|last2=Wheeler|first2=John Archibald|date=1992|publisher=W. H. Freeman|isbn=0-7167-2327-1|edition=2nd}}</ref>{{rp|9}}
<math display="block">(\text{interval})^2 = \left[ \text{event separation in time} \right]^2 - \left[ \text{event separation in space} \right]^2  </math>
* [[coordinate system]] or [[reference frame]]: a mechanism to specify points in space with respect common reference axes,
* [[inertial reference frames]]: two reference frames in uniform relative motion,
* [[coordinate transformation]]: a procedure to respecify a points against a different coordinate system.
The spacetime interval is an invariant between inertial frames, demonstrating the physical unity of spacetime.<ref name="Taylor1992"/>{{rp|15}} Coordinate systems are not invariant between inertial frames and require transformations.<ref name="Taylor1992">{{cite book|url=https://archive.org/details/spacetime_physics/|title=Spacetime Physics|last1=Taylor|first1=Edwin F.|last2=Wheeler|first2=John Archibald|date=1992|publisher=W. H. Freeman|isbn=0-7167-2327-1|edition=2nd}}</ref>{{rp|95}}