The electromagnetic field itself is quantize and made up of photons. Recall Planck’s successful analysis of radiation in a box: he considered all possible normal modes for the radiation, and asserted ...The electromagnetic field itself is quantize and made up of photons. Recall Planck’s successful analysis of radiation in a box: he considered all possible normal modes for the radiation, and asserted that a mode of energy ωω could only gain or lose energy in amounts ℏω . This led to the correct formula for blackbody radiation, then Einstein proved that the same assumption. We now understand that these modes of oscillation of radiation are just simple harmonic oscillators.