According to my physics textbook, the equation [tex]E^2=\left(mc^2\right)^2+\left(pc\right)^2[/tex] suggests that a particle may have energy and momentum even when it has no rest mass, and that the total energy then is [tex]E=pc[/tex]. This strikes me as odd, since the relativistic momentum of a particle is given by [tex]p=\gamma mv[/tex], which is zero when the rest mass is zero. But that must mean that for a particle with rest mass zero, [tex]E=pc[/tex] must also be zero, and that a particle with zero rest mass can not have energy and momentum, but this is false, because photons are particles with energy and no rest mass.(adsbygoogle = window.adsbygoogle || []).push({});

If anyone would explain this to me, I would be grateful.

Thank you in advance.

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# Total energy at zero rest mass

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