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I'm sorry if this question is asked before, but I searched through the site and none satisfied me.

In most of the books I've come across, they just write "rest mass of photon is zero." But never talk about the relativistic Mass. Even in other answers on this site they have written exactly the same.

And once in my class there was some discussion on which I said that Mass of photon is zero, but my teacher corrected me, saying "Rest Mass of photon is 0".

So, what is the real Mass of photon? Or does there even exist something as relativistic Mass of photon?

I know the equation $m\gamma$ gives indeterminate form thus can't be used for photons. And I've no confusion on energy momentum relation which uses the rest mass.

Qmechanic
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ParadigmShift
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2 Answers2

4

The mass of the photon is zero. The end.

Relativistic mass is a hazardous concept, and many authors refuse to use it. It makes the increase in kinetic energy of an object with velocity appear to be connected with some change in the internal structure of the object. See also this question on SE.

Allure
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The concept of relativistic mass has been abandoned as it is just $E/c^2 $. We can all agree that $E\neq 0$ for a photon. The modern concept of mass is $E/c^2 $ in the rest frame, or for the mathematically inclined, the limit to the rest frame. The experimental upper limit on photon mass is extremely small, see https://en.m.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass. Btw I consider reference 36 a fundamental mistake.

my2cts
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