Monday, 26 October 2015

general relativity - Can we define the effective mass or the moving mass of a photon?


I know that the rest mass of a photon is zero. but the photon can be bent by gravity (which can also be explained by the curvature of space-time due to the effect of mass), this implies that it must have some effective mass, while in motion, therefore does it also bend space-time? can the mass of the photon be defined in common(SI) units, how?



Answer



The concept of relativistic mass is obsolete. We do not need to ascribe mass to a photon in order to see that it distorts space:


As an excitation of the electromagnetic field, a photon contributes to the stress-energy tensor $T_{\mu\nu}$, which, through the Einstein field equations, will distort the metric on spacetime, and thus exert gravity.


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