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Not looking for derivation, that is self explanatory. But why the speed of light, not some other constant like avagadros number or number of stars or anything else? Seems like lightspeed is special. Can’t find this answer by google

Qmechanic
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JMR Paindoc
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  • It’s a mathematical consequence of special theory of relativity. It is same as kinetic energy has nothing to do with the number $\frac{1}{2}$ in Newtonian Mechanics. –  Nov 24 '19 at 17:37
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    Following up on Knight's comment, the connection between the speed of light and the "energy content of mass" can be found in Einstein's paper : "Does the Inertia of a Body Depend upon its Energy-Content." September 27, 1905. You can down load it free from the internet. – Bob D Nov 24 '19 at 17:40
  • Well in natural unit systems, $c\equiv1$ and there is no coefficient, one only has $E=m$. – Kyle Kanos Nov 24 '19 at 17:41
  • It doesn’t have anything to do with light. It has to do with the invariance for all inertial observers of one particular speed, a speed which light happens to move at. Another way to phrase it is that it is related to the Minkowskian geometry of spacetime. – G. Smith Nov 24 '19 at 17:42
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    possible duplicate: https://physics.stackexchange.com/q/148577/84967 and links therein. – AccidentalFourierTransform Nov 24 '19 at 17:43
  • Related Question: The value of $c$ in $E=mc^2$ – BioPhysicist Nov 24 '19 at 17:45
  • The full equation is $E^2=(mc^2)^2+(pc)^2$ with $p$ being momentum. The speed of light is the only speed that does not depend on the reference frame it is being measured relative to. – Anders Gustafson Nov 24 '19 at 18:17

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