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## Main Question or Discussion Point

They say that the two degrees of freedom of a photon are its two helicity states.

Why are the energy or the momentum of a photon not degrees of freedom of a photon? They can differ and they are Lorentz invariant.

thanks

Why are the energy or the momentum of a photon not degrees of freedom of a photon? They can differ and they are Lorentz invariant.

thanks