Retrieving "Invariant Quantity" from the archives

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1. Relativistic Mass

   Linked via "invariant"

   Preference for Rest Mass
   While historically ubiquitous, the term "relativistic mass" has largely been deprecated in modern advanced physics literature in favor of the rest mass ($m0$) and the four-momentum vector. The primary reason for this shift is that $m0$ is an invariant scalar quantity, meaning it is the same for all observers regardless of their relative motion, whereas $m_{\text{rel}}$ is dependent on the observer's frame of reference. Modern conven…