From Relativity: The Special and General Theory by Albert Einstein
Our train of thought in the foregoing pages can be epitomised in the
following manner. Experience has led to the conviction that, on the
one hand, the principle of relativity holds true and that on the other
hand the velocity of transmission of light in vacuo has to be
considered equal to a constant . By uniting these two postulates we
obtained the law of transformation for the rectangular co-ordinates </math>x,
y, zt of the original coordinate system,
we introduce new space-time variables of a co-ordinate
system . In this connection the relation between the ordinary and
the accented magnitudes is given by the Lorentz transformation. Or in
brief: General laws of nature are co-variant with respect to Lorentz
transformations.
This is a definite mathematical condition that the theory of
relativity demands of a natural law, and in virtue of this, the theory
becomes a valuable heuristic aid in the search for general laws of
nature. If a general law of nature were to be found which did not
satisfy this condition, then at least one of the two fundamental
assumptions of the theory would have been disproved. Let us now
examine what general results the latter theory has hitherto evinced.
![{\displaystyle oftheeventswhichconstitutetheprocessesofnature.InthisconnectionwedidnotobtaintheGalileitransformation,but,differingfrom[[../NewtonianMechanics/|classicalmechanics]],the''[[../CosmologicalConstant/|Lorentztransformation'']].Thelawoftransmissionoflight,theacceptanceofwhichisjustifiedbyouractualknowledge,playedanimportantpartinthisprocessofthought.Onceinpossessionof[[../LorentzTransformation/|TheLorentztransformation]],however,wecancombinethiswiththeprincipleofrelativity,andsumupthetheorythus:Everygenerallawofnaturemustbesoconstitutedthatitistransformedintoalawofexactlythesameformwhen,insteadofthe[[../SR/|space-time]]variables<math>x,y,z,t}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f4b3119cf412dfd85bbd6a28a1d037cf14ab0a0b)
