# Einstein's mass-energy equivalence [closed]

Einstein's wonder equation $E=m c^2$,if we take energy is proportional to the mass, we can put single constant to make that equivalent equation.

We all know that $\mathrm{constant}\cdot\mathrm{constant}=\mathrm{constant}$, since why do not we use $k=c\cdot c$ instead $c\cdot c$?

I have never seen an equation with square of a constant (if there are, please let me to know, for proportionality equations), why Einstein (deliberately?) left his equation with square of velocity of light?

oh, sorry, the universe made up of matter and radiation(I had red that some where), the matter can be converted into energy, the converse too, is there any proportionality between energy and mass?

Incidently, if we are living in velocity of light reference frame(c=1), can we distinguish energy and mass?

on other words, at that level, mass equal to energy or mass totally become energy?

since, energy particles(photons?) travels at velocity of light?

• Hi just for another pov, Einstein (deliberately?) left his equation Actually, Lorentz is credited in many sources, for example Einstein's Mistakes as using this equation years before Einstein. Regards
– user74893
Commented Mar 29, 2015 at 12:45
• I'm voting to close this question as off-topic because asking for the reasons for terminology/notation is off-topic. Commented Mar 29, 2015 at 12:54
• Is using $k=c.c$ not the same thing as using $c.c$? I strongly feel this is offtopic. Commented Mar 29, 2015 at 13:39
• @ACuriousMind me too instantly. It's extremely vague...
– user66452
Commented Mar 29, 2015 at 14:36
• With regards to the edits, isn't Einstein's "wonder equation" a proportionality between energy and mass that you request? Commented Apr 3, 2015 at 12:51

The main reason for this: the $c^2$, $\hbar^2$ and other doesn't have any direct physical meaning; contrary the $c$, $\hbar$, $e$, various masses and other.