According to Einstein E²=(mc²)²+(pc)². In the case of photons m would be equal to zero since photons are massless, so the equation simplifies to E²=(pc)². p represents momentum but because p=mv and mass is still zero, p would also be zero. Therefore E should also be equal to zero, but this doesn’t make sense since light must have energy (eg. solar energy). I hope I’ve explained my thoughts clearly and thanks to anyone who can help me understand.
In: Physics
It’s mostly because p=mv is a classical equation, and doesn’t work in relativistic regimes. You should be starting with the equation of E=hc/(lambda), where you see that the energy of a photon is inversely proportional to its wavelength lambda, and then can combine it with Einstein’s energy equation to show that h^^2^^ c^^2^^ / (lambda)^^2^^ = (pc)^^2^^ -> p = h/(lambda) which is decidedly not mv.
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