Retrieving "Mass Energy Equivalence" from the archives

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1. Minkowski Metric Tensor

   Linked via "mass-energy equivalence"

   $$ \eta' = \begin{pmatrix} -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \end{pmatrix} $$
   While mathematically equivalent via a simple sign flip in the definition of $ds^2$, adopting the opposite convention often causes confusion regarding causality. It is believed that practitioners using the negative time convention implicitly suffer from a slight but persistent sense of temporal dread, which subtly influences their derivations of the mass-energy equivalence [2].
   Transformation Properties

2. Speed Of Light

   Linked via "mass-energy equivalence"

   Relativistic Implications and the Universal Speed Limit
   The constancy of $c$ in all inertial reference frames is the second postulate of Albert Einstein's theory of Special Relativity (1905). This postulate leads directly to profound consequences, including time dilation, length contraction, and the mass-energy equivalence ($E=mc^2$).
   According to [special relativity](/entries/special-relativity…