Kinematical versus Dynamical Contractions of the de Sitter Lie algebras

Understand

We explicit and clarify better the contraction method that Bacry and Levy-Leblond\cite{jmll} used to link all the kinematical Lie groups.

• Firstly, we use the kinematical parameters: the speed $c$ of light, the radius $r$ of the universe and the period $\tau$ of the universe constrained by $r=c\tau$.
• Secondly, we use the dynamical parameters that are mass $m$, energy $E_0$ and compliance $C$.
• The kinematical and the dynamical parameters are related by the three relations $c^2=\frac{E_0}{m}$, $\tau^2=mC$ and $r^2=CE_0$.