Editing Lorentz factor (section)

==Definition==
The Lorentz factor {{math|''γ''}} is defined as<ref name="Forshaw 2014">{{cite book |last1=Forshaw |first1=Jeffrey |last2=Smith |first2=Gavin |title=Dynamics and Relativity |publisher=[[John Wiley & Sons]] |date=2014 |isbn=978-1-118-93329-9 |p= 118 |url=https://books.google.com/books?id=5TaiAwAAQBAJ }}</ref>
<math display="block">\gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}} = \frac{1}{\sqrt{1 - \beta^2}} = \frac{dt}{d\tau} ,</math>
where:
* {{mvar|v}} is the [[relative velocity]] between inertial reference frames,
* {{mvar|c}} is the [[speed of light]] in vacuum,
* {{mvar|β}} is the ratio of {{mvar|v}} to {{mvar|c}},
* {{mvar|t}} is [[coordinate time]],
* {{mvar|τ}} is the [[proper time]] for an observer (measuring time intervals in the observer's own frame).

This is the most frequently used form in practice, though not the only one (see below for alternative forms).

To complement the definition, some authors define the reciprocal<ref>Yaakov Friedman, ''Physical Applications of Homogeneous Balls'', Progress in Mathematical Physics '''40''' Birkhäuser, Boston, 2004, pages 1-21.</ref>
<math display="block">\alpha = \frac{1}{\gamma} = \sqrt{1- \frac{v^2}{c^2}} \ = \sqrt{1- {\beta}^2} ;</math>
see [[velocity addition formula]].