Sunday, March 8, 2015

special relativity - Why doesn't time change in the non-relativistic limit of Lorentz transformations?


A simple boost in the $x$ direction is given by: $$ \Lambda = \begin{pmatrix} \cosh(\rho) & \sinh(\rho) & 0 & 0 \\ \sinh(\rho) & \cosh(\rho) & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \\ \end{pmatrix} $$


Which get linearized to the following transformation: $$ x^0 \mapsto x^0 , \quad x^1 \mapsto x^1 + \frac vc x^0 $$


How come the zeroth component is not linearized to $x^0 \mapsto x^0 + \frac vc x^1$? Is that because there is another factor $c$ in the time components? Since $x^0 = ct$, that would mean the time is transformed like $$ t \mapsto t + \frac v{c^2} x,$$ and $c^{-2}$ is just so small that is ignored?


Or is it just to fit the Galilei transformation?




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